CALH'ORI:\IIA S'l'ATE UNIVERSITY 1 NORI'HIUDGE
'l'IIE HIS'l'ORY 0'"' CONCRB1'E FROH ROI-.!AN 'I'JJ,!E.S H TO 'l'HE EIGH'l.'BEl\!TH CEl\'l'URY
A t·.hesis EUbn:Lt.t:ed L:1 ra:r:i:·.J..al sat:i.sfacti..on of the :t··f~(Jnix·enlC~!·~:.s fer t.£~·2 d.E:g~~c;e of X1la.st.er oE A.rt.s i~1
1\Tt
hy
Jum:>. 1979 The 'l'hes:i.s of Janet Irene Atkinson is approved:
-;.=:----~-~r------:.--r---:::_-.--.-~- -- -~ ~-'r. Rpqer [,_t,Jul_~.o •"
Dr. Jean-LtlC Bordeaux.
------~~·---· Dr. Donald S. Strong, Chairman -~~-----·
California State University, Northrid I wish to thank my Father from whom I heard my first stories regarding concrete construction; Dr. Strong for his tireless patience; Charlotte Oyer, Librarian, loTho was able to locate many rare references; and Linda Hartman for t.yping this paper. iii TABLE OF' CONTENTS Page J~IST OF' ILLUSTRATIONS • v GLOSSARY viii ABSTRAC'r xvii INTRODUCTION . . . . •...... " . . . . . 1 Chapter I. THE :LEGl~CY OF' ROME 9 II. THE \1\JA:'NING OF' CONCRETE AECHITECTURE 46 III. THE REVIVAL OF CONCRE'rE IN EUROPEAN AECHITEC'lUHI~ 83 136 BIBLIOGRhPHY 146 iv LIST OF ILLUSTRATIONS Figure Page 1. Map . . • . 6 .2. Specimen of Mortars from Egypt:, Greece, Italy and Cyprus, 18 65 . . • . . ~ • • • • 13 3. Map of Italy 18 4. "Example of Poured Concrete 24 5. Use of Iron in Antiquity 27 6. ~l'emple of Castor 30 7. 'I'emple of 117 B.C. 31 8. Trajan' s Market .. 9. The Sanctuary of Fortune at Palestr.Ln21, 35 .10. 'l'he Pantheon Showing the Arch Construction 38 11. '!'he Baths of Caracal1a 40 12. 'i'he Baths of Diocletian, Rome, 298-305 A.D. 41 1.3. 'I'he Basilica of Constantine ...... 4.2 14. Late Pagan Architecture in Rome, 'l'emple of !4inerva Medica, Lie in ian Gardens, Fourth Century A.D. . . . • . . . • • . ... 52 15. The E>:t.erior ~vall of t.he Imperial Basilica ~rrier, 310 A.D. . .•. • • "'! 0 • 55 16. Mausoleum of Galla P1acidia, Ravenna, 440 A.D. 57 17. Ravenna, San Vitale, 526--547 A.D·. 59 .18. Ccnst.anU.nople, St. Sophia, 532-537 A.D. 61 l Q -~· .... Medieval 'l'ic11ber Structures: Winchester Czt:hsdx:al, 1093 A.D. 67 List of Illustrations (continued) F.igure Page 20. Vio1let-le-Duc 1 s Drawing of the Fill in the Lo'V'Jer Portion of the Vaul tin9 Conoid, Amien's Cathedral (Notre Dame, 1220-·1270) • • 68 21. Scaffolding for a Stone Building (about 1460) 70 22. Ogmore Castle Showing Lime Kiln, Court House and :tvloat 72 81 23. Cellular "Crystalline'' Vaults . . ~ ...... 24. Proposals for the Cross Section of Milan Cathedral 86 25, Francesco di Giorgio, Elevation of an Ideal Church 87 26. Leonardo 1 s Diagram of How to Dete:r.-mine t.he Breaking Strength of an Arch . . • . 91 27. Galileo Galilei's Drawings 93 28. B:r:unelleschi 1 s Dome of s. Maria del Fiore 97 .29 •. Stress Configurations for Brunelleschi's Dome 99 30. The Donie of St. Pet.er' s, Rome ...... 101 31. Plans for St. Peter's . . • . . . 103 32. The Catenary Chain for a Dome of Uniforr·l Weig"!l.t and for the Dome of St. :Pe:t.er' s ...... 1.06 33. The Fa.rallelogram of Forces from Memorie· istor iche della Gran CUpola del Tempio Vatic.:mo by Giovanni Poleni, Padua, 1748 107 34. Reinforcement in St. Genevieve, Paris llO 35. Dome of the Pantheon, Paris .. 111 36. Emile Gauthey's Testing Machine 112 37, Rondelet's Testing Machine 113 .38.. Machine for 'I'esting Small Tension Specimens, from Phys:Lca.e experimentales ei: geomet.ricae dissertationes :!Jy Petrus van t:tJ.usschenbroek, 1729 115 vi List of Illustrations (continued) Figure Page 39. John Smeaton, Civil Engineer . 129 40. Edystone Lighthouse 131 vii GLOSSlL~Y Aggregate lonse; s.t.ones, pebbles, gravel or sand of various sizes. Agrimensorial RP.....fers to Roman land surveying. It is mentioned in Villard De Hnn~•ecourt ,. s notel:ook. Air Mortar Li:t Alumina Arnphorae Jar or vase characterized by oval or egg shape·, usually made from c.1rry. lh~gillaceous Lime Hyil:t:au1ic lime from Holland 1 al:x.Nl.mdingc ir:t clay. Asphalt A bituminous substance. I·t is SlliiXJth, hard:, brittle 1 black or brO':\'!lT:ish black, and is a resinous 1tli1'rJ.C'ral consisting of different. h}'tirocarbons.. A. con,position con- sisting of~ b±t.umen pitch and sand or R\anufactured from nat.ural hi'h:mrinous lime stone. Batten St:>fips of wood used for attaching {nad&Iing}.. acroc,s oi.:.her pieces. U:'>et:f for stiffening. Bending (moment.) The moment: tending to bend a beam. 'l'he moments of re si st.ance. Bitlillten Sf.;~imenta:ry rock, sue h as shale 1 sax;ilstone or limestone t:bat is na.ihilrally impregnated with bitumen. Cc11:cposed o'f' hydrocarbons. vii5k Brick-relieving Arch An arch used for structural purpose of concentrating and directing the weight of t.hrust, and/or to con tain the concrete core when it dried out. It may have been used to facilitate construction as well. Buttress A mass of masonry or brick~urk projecting from or built against a wall to give additional stress. Caementa, Caernentum Broken stones, aggregate. Calcinate To reduce to a powder by heat. Calcium Carbonate A compound CAC02 which occurs in limesi:one, marble and aragonite. Also found in plant ashes, bones and in many shells. Calx Small stones, or the process of making lime itself. Cas·t Concrete Concret:e poured into a mould. AlEC• :ref.er s to poured concrete. Catenary The shape assumed by a perfectly flexible inextensible infinitely fine c.ord in equilibrium under given forces. Exemplified by a chain or be Cellular Pertaining to cell-like, having the top and bottom of a large l:ox beam divided into cells or com partments. Cement Fossiliferous, clayey limest.one that contains alu..mina, silica, and lizii!e. Centering A s.t.ruct.ure on which a masonry arch or vault is built.. Removed when mortar has set. ix Chaff Tl1e. glumes. or husks of grains and grasses separated from seed by thrashing. Straw or hay cut up finely. Chalk 1\brd comes from the Latin, calx. Means a soft limestone of earthy texture and is of marine origin. May be pure white to gray limestone and consists almost wholly of calcite. Clamp, Cramp A metal device that holds, binds masonry together, usuaLly at the corners. Clay Pure clay io:: a hydrated alumina silicate, technically knov.;n as kaolin, and is pure white. J:t is produced by the weaJchcring of fe:u:=: spars, a group of minc'ral sub stances, consisting of the sili cates of alumina, potash, soda, and lime. Common clays are formed by the weathering of igneous rocks, shales and clayey limestones. Jren oxide is present in most clays and small quantities of lime, magnesia, and alkal i.e s. Clinker Stony material fused together. Compression External stress applied uniformly to an object. Concre·te Cement mixed with coarse or fine agg.regate, e.g., pebbles, crushed stone, brick. Sand and wa·ter in SIJecific proport.ions are added to form a thick mass. Eggs Substances such as molasses, resin, eggs, and Y-'RX, were used in con crete·-l.ike mixt.ure s, due in part to their ability to coagulate. Elas·ticity The property of a body with the ability to escape original shape. Co-efficient elasticity is the ratio of internal stress to the strain giving rise to it. Feeble Refers to limestone containing little hydraulicity. Ferro-Concrete Reinforced concrete. Flint Chalcedony, usually black, pulver ized quartz. Formacean Ancient pise construction. Graphic Statics Branch of statics, in which magni tJ.lde, direction and position of :forces are represented by straight lines and unknown quantii:ies found by mechanical measurement. Grit Sand, gravel, rough hard particles, especially sand. Grout A thin mortar used to fill chinks or cracks. G:y-psum A hydrated sulfate of calcium, occurring naturally in sedi1nentary rocks and used for making plaster of paris and in treating soilo Haunches Either of the parts of an arch at: U1e sides of the crown between the crown and the springings. Hoop Stresses, Hoop Tension 'rhe circumferential tension in a shell or in any thin concentric el eNent of a thick-vva ll.ed solid of .revolution subjected to pressure .. Hydraulic Refers to substances which harden under water and are hence imper vious to it. Hydraulic L:Lmes C'.onstituted almost excJ G;;ivel.y of silica and calcium carlxmate. C.ontains less clay than cement mixtures" rr'hey set more slowly and attain less hardness than cements. xi Laconicum Laconicus, or sweating room in the mth.. Lava Fluid rock ejected from a volcano ar~ classified as basaltic. Lime Calcium Oxide. Specifically quick lime and hydraulic lime. The term is used: loo·sely for calcium hydroxide and incorrectly for calcium carbonate. Limestone Ci?<1cium carlxmate, yielding lime wlrem burned . Maltha An:y of var:ious cements, some bi:Lcrminous, others resembling IROJcta:rr. A. black-vissid substance r~tween petroleum and asphalt. Marl EaTt:hy deposits consisting chiefly o.f clay with calcium carlxmate in varying, proportions. Honolithic Fo:naed. of. a single piece or block. Mortar May· refer to a container. Hay be a plastic ma.terial which can be llyd'raulic or non-hydraulic, made by mixing lime cement or gypsum with sand, water or other materials such as clay. It is a binder which ce'tire:nts materials, substances tDS)•E!ther. Mud Mixture of silt and clay, and may CL"fltain particles of other materials. Natural Cemt:n t A product obtained by finely pul-· vexizing calcined argillaceous li11\8Stone. The temperature of ca;leination is no higher than is necessary to drive off carbonic acid gas. Non-hydraulic :Re·fers to tho::."'-~ substances that axe water salub.le. xii Opus Caementicum Cement mixtures. Opus Incertum Roman walling of concrete faced with irregularly shaped stones. Opus Latericium Facings of sun-dried brick. Opus ListattJm Walling with alternate courses of hrick and small blocks of stone. Opus Mixtum Applied combinations of brick, stone, and tufa in alternate courses. Opus Reliculatum, Roman walling faced with squared Quasi-Reliculatum stones, arranged diagonally like meshed net. Opus Sectile Technique o£ surface ornament. Opus Signimum Cement mixture associated wit~h pavements or surface exposed to water. Opus 'l'est.acium Facings of fired bricks. Parallelogram, The rnethod of compounding two Parallelogram Law accelerations, forces or the like by t~he parallelogram law. Paral lelogram lav.r: the law that the resultant of two vect~or quant.it~ies represented in magrd.t:ude, d in;c t:. ion and sense,. by two adjac0nt sides of a parallelogram, both directed to\\Brds or away from their point of intersection, is the diagonal of the parallelogram thxough that point. Tiny, or small dressing, covering. Pise De :!-'errc:_, rammed earth construction. A walling of damp earth, that is rammed or cast in wooden forms. Pitch Black or dark-colored viscous substance obtained from ~tar, 'M)Od, bone oil, and occurring naturalJ~y in asphalt. xiii Plaster Pasty composition made by mixing sand and \vater with gypsum, quick lime or hydrated lime. Hair or fiber may be added to act as a binder. Pumice Light colored vesticular, glassy rock, having a composition like rhyolite, from volcanic eruptions, having a spongy frothy appearance. Putty A cement consisting of lump lime slaked with water to the consis tency of cream. In ancient times, linseed oil was sometimes added to mixture. Puzzo lana Siliceous tuff, ash or other material. Named after Leveite Tuff near Puzzoli, Italy. Also called Possolan, Pozzolana, Puzzolan, puzzolana, puzzuolane. Quick Lime Calcinated limestone (CaO) . It has a definite affinity for vldter with which it unites with a g-reat release of heat to form calcium hydroxide (CaOH2) . Radical Crackjng Distinguished from longitudinal, at right angles to a curved part. Resin See definition of eggs. Rich Lime ~Jre lime, containing little or no silica or alumina. Sometimes known as feeble limes. Lean or impure limes are difficult. to slack. Rubble, Mortared Ru:bble Refuse. May attain the quality of a hydraulic mortar in lLmestone, contains proper amoun·ts of alumina and silica, or it may consist of mud, rocks, refuse, unhewn stones laid in irregular courses. Santorium Earth Puzzolana, a rhyolite ruff from the Island of Santorin, Italy. xiv Scaffolding 'Temporary framework of platforms and poles construc-ted to provide accommodations for workmen and their materials during erection, repairing, and decoration of a lmilding. Selce Porous rock of volcanic origin. Selenite Variety of. gypsum occurring in transparent crystals. Shoring Act. of propping up or supporting. Shuttering Fonnwork, temporary that "wet" concrete is poured into, of timber or metal, and is removed when concrete nas set and retains te'.Lture of formwork. -Silica Silicon dioxide or silicic anhy drite. Occurs naturally in crystalline form as quartz. Sand is impure silica. Slag Product of" smelting, containing silicates. The substance not sought to be produced as metal. illlso, the scoriaceous lava from a volcano. Slake 'l'o cause lime to heat and crumble by treatment with water; to hydrate by exposure to air. Soft, moist earth or clay, viscous mud. Sod Stratum of soil filled with roots of grass, herbs, tu:r.f, or peat. Static Noment. 'il'he product of a force into its lever ann. Stress Force per unit area. s-tucco A fine plaster used for covering surfaces of buildings composed of lime or gypsUtll with sand and pounded marble. Tarras, Terras, Light colored volcanic tuff resemb Ta:r.rice, Trass ling puzzolana in composition, occurs on lower Rhine. Trasses of Eifel, Moselle, Netle and Brohl valley played important part in yaterworks of Gaul erected during reign of Trajan (98-117 A.D.) and Hadrian (117-138 A.D.). Tas-de-charqe The lowest course of a vault or arch laid horizontally and bonded int.o the wall, Tension l''orce causing· extension, measured usually per unit area of cross seetion. Converse of pressure. Thrust Force or pressure of one part of a construction against another. Truss p,n assembly of strajght tension and compression members which performs the same function as a deep bsam. Tufa, Tuff Porous rock formed as a deposit from springs. Usually applies to calcareous deposits. 'Is more or less stratified and in various states of consolidation. Virtual Displacement Such an infinitesimal displacement o:f any point of a mechanical system as is at any instant, compatible with the cons·t.raints of the system. Virtual Work The work associated with a virtual displacement. Voussoir A brick or wecge-shaped stone forming one of t_he units of an arch. Contains some hydrocarlxms. xvi ABSTRACT THE HISTORY OF CONCRETE FROM ROivlAN TL'1ES 'l'O 'l'HE EIGHTEENTH CENTURY by Janet Irene Atkinson Master of Arts in Art History The st~bject of t:his paper is the historical account of t"he development of concrete and its use in architecture from early Roman ·t.imes to its "re-discove:r:y" by Jolm &!aeaton in t.he eighteenth cen·tury. vi·truvius had 'W:ritt.en do'ND the precep·ts for concrete by the beg-inning of t.he first century B.C. Due to the special qualities of 122!!2'-:.?J-a~_, Roman mortar contained a tenacity Hhich made it last for The basic structural princ.iple de:r:·i,··ed by deductions .based on ,~:v,;:perience and observat.ion, was that the st~abilit.y of a vaulted ;:;t"ruct:ure did not depend upon friction or preso::ure as in vaults con struc·ted of cu·t stone, but upon the co he sian and hornogenei ty of the Roman conc:t:·ete mass. In Che centuries following t11e fall of Rome' r:; Wes·tern Empire, brick and ~;-tone supplanted concrete. The wanr.i.ng of concrete archi- tec·ture in Msclieval Europe was due in part to a general lack of xvii knowledge regarding the calcination and slacking of limestone. It was also due to a lack of understanding statical theory. With the Renaissance, dome construction required a new application of the knowledge of statics and its relevance to the strength of arches. The scientific revolution of the seventeenth century inspired the investigation of ancient Roman cement. John Smeaton' s Edystone_ ~ighthouse in the eighteenth century provided a basis upon which all future concrete construction could proceed. Not until the twentieth century, however, were engineers and architects capable of creating an architecture applicable to concrete which expressed statically t.ested data of the material in aesthetically new ways. xviii INTRODUCTION The subject of this thesis is the historical account of t.:he development of concrete and its use in architecture from early Roman times to its "re-discovery" by John Smeaton in the eighteent:h cen- 1 tury. While a complete account of t.he use of concrete up to the eighteenth century is not possible, important developments in the history of concrete can be pointed out. An historical approach has been used in dealing with this subject in order to avoid the kind of isolated treatment of concrete that occurs in technical literat.ure writ·ten for engineers and scientists, and to broaden the base of information on concrete architecture, often treated narrowly by art 2 and architectural historians. Much lit.erature exists on concrete 1 Lengt.h preven'ced me from incorporating nineteenth and twen- tieth cent.ury material wi t:hin the text. I have briefly noted some of these developmEmts within the conclusion. 2 Henr:}r-Russell Hitchcock and Siegfried Giedion include chap ters on concrete in thei:c architectural s·tudies. The import:ant relationship between concrete design and scientific developmen·ts relevant to concrete has not always been sufficiently emphasized. Fox example, monolithic construction, i.e., the pouring of slab, beam and girder at one time, was not possible until sufficient data was available for correct mathematical analysis. 'l'he history of concrete design is the result of both aesthe·tic considerat:ions and technical investigations. See Henry-Russell Hitchcock, _?\rchitec-ture: Nine .!::~~~!2!:..~ ~n~ Twent~£th _s:enturies, 2nd edition (Baltimore: Penguin Books, 1968). See aJ. so Siegfried Giedion, Space, !_~:::._ and Architecture, the Growth ·:..~:t ,3 1\ev Tradition (Cambridge: Harvard University Press, 1967). 1 2 ,, . \\>ritten by engineers with slight reference to its historical or 3 aesthetic role in architecture. Other wri·ters have concentrated on the period following John Smeaton witl1 little reference t.o earlier 4 investigations. An historical and scientific account of concrete from Rome's contribution to the present has not yet been written in 5 English. The modern terms concrete and cement differ from those used to describe ancient lime or rubbled mortar, beton, puzzolana, and 6 the numerous other terms by which concrete has been known. The 3 Charles Spachaan and Gilbert R. Redgrave, Calcareous Cement~: Their Nat:-u~E.:J Manufacture and Use_ (London: Charles Griffin and Co., 1905) . Frederick Mea sham Lea, The Chemistry of_ S:.~!flent ~nd Concrete (London! Edward Arnold, 1970). 4 Peter Collins writes about concrete architecture beginning with the eighteenth century. It is the most thorough architectural study of the material to date. Peter Collins, Concrete: Visio~ ~fa ~ew ~chj~tecture (London: Faber & Faber, 1959). Alyahmed Raafat begins his work on reinforced concrete with the twentieth century. See Alyalu~ed Raafat, Reinforced ~oncre~~jn P~chitecture (New York: Reinhold Co., 1958). Pier Nervi has contributed an engineer's insight into the subject of structural form during the Medieval period. How ever, references to the role of concrete in this development are scant. Pier Nervi, The Works of Pier Luigi Nervi, translated by Ernst Prie:fert, introduction byErnstPriefert (New York: Frederick Praeger, 1957). 5 nr. Gustav Haegennann' s y~m ~~aementum ~urn Zemerrt covers both the technical and architec-tural history of concrete from F.orne to the t:wentieth century. Dr. Gustav Haegermann, Vom Caementum zum Zernent (Wiesbauen, Berlin: Bauverlag GmbH, 1964}. 6 Ivloder·n cement has no connection in meaning with the Latin word caementum. rrhe modern builder employs the tenn lime morJcar to designate non-hydraulic mortar, and cement for hydraulic material. Cement today refers to a fine po-.;vder obtained by burning alumina silicate (clay) wi·th calcium carbonate (limestor.e). This process was unknown in ancient times. Marion Blake, A:nc;:ie!1t Ro~an Const:r:~c t~on in ~~~~ly .:f~·om the_ Prehistor~£ Period t~ l',ug~stus (Washington, 3 7 word cement- occurred in Medieval documents. The term concret.e did 8 not. appear unt:il the nineteenth century. The only source for such technical terminology in ancient times \vas Vitruvius, and his defini- tion of lime and puzzola~~ cannot be related to precise definitions 9 of modern-day concrete and/or cement. In addition, Vi·truvius lived prior to the period when concrete was most fully explored in Roman architecture. There is virtually no documentation on tho use of concrete in architecture subsequent to the time of Vitnwius so t.bat~ knowledge of this development rests on contemporary descriptions of ancient extan·t architectural remains. Before the scientific revolu- tion of the seventeenth century, no accurate descriptions on the D.C.: Carnegie Institute of Washington, 1947), pp. 308-309. Concrete is a r,tixture COi1t:aining cement, sand, ;.vater and aggregate. Beto~1- is a French word sb2nuning originally from the Latin word bib:I_~~-12_, or rnineral pitch. Originally mineral pitch referred to asphalt. See .!ieb~!_eot:~_s ~~~~ _!__n!:ernatior:al pictiol2_~I.":Z ~.!__!he English !nng~~g~, ?nd edition, m:abridged (Nassachusetts: G. C. Merriam Company, 1948), pp. 259, 2T7. _?uzzolana refers to volcanic ash of cementitim;:s quality found in Italy. See Glossary for definitions of these terms. 7 ~£!~c:_ 9~ford ~ng_li~- !?_~_9_!i_on_~!Y, eds. James A. H. Murray et al., Vol. IT (Oxford: at the Clarendon Press, 1970), p. 216. n 0 IDlCL,'-·. - p. 7.76 . 9 vi·tru.vius' word ~ar~_I1a, meaning sand, is misleading. He speaks of t:hree: kinds of har-=:E~- used in Rome, namely harena from pits, the -~.!::£!:1_":_ frr)m rive:t·s, and the ~rena from the seashore. He refers in the first: class ·to the pits of puz_:;:olana which are seen everywhere m.:::tside the gates, hence re£erring to both puzzolan':l and sand as the same. Vitruv:i.us, On A~· chi tecture, translated by Frank Granger, Vol. 1 (Cambridge: Harvard University Press, 1955), 11.4, 2 and 11.6, 5. Also the word materia and its collateral materies were terms as :indef:Lnitc, as tl{;{r Englif;h equivalent and~ere ~ometimes used to c1efinc,; concrct:E:!-like mixtures. Blake, Ancien>c Construction, p. 308. 4 mixing of mortars were available, nor were there any writt.cn documents that described how arch or vault construction could be accomplished 10 using these mortars. Huch of this information, therefore, must be based on conjecture extrapolated from what is known about construction procedures today. When the French and other Europeans began experi- menting with cement.s in the seventeenth century, t~hey did not clearly understand the meaning of ·hydraulic cemen-t. The chemical properties of cement and its relationship to the utilization of the material was unclear as WE;ll. Not until the nineteenth century when microscopic chemical analysis of cementitious properties -v;ras begun, were clearer definitions possible. Only in the twentieth century, when governme1t t.esting of cement and concrete was established by law, was it possible to arrive at conclusive definitions concerning the strength of cementitious materials and, in '.::urn, to determine the limitations of its use. · One of t.he purposes in researching the subject of concret.e vJas t.o try t.o find out why and how the knowledge of a hydraulic mortar disappeared from the \.Vest after the fall of the Roman Empire when it is knovm that H.ome ha.d transmitted this technology to provinces in Englar.d, Gaul and ·the Near East. 'I'here is evidence that some form of cement; was used as late as the sixth century in the Eastern 1 °For example, knowledge of the centering· or falsev..urk employed in an arch can often reveal whether the mortar used was quick-drying and possibly hydraulic, or was lime mortar and therefore non-hydraulic. 5 11 Roman \vorld. Knowledge of concrete in some form must have been 12 re·tained throughout. Medieval times. There is a question as t:o why concrete was not used in the thin-shell vaults of Got.hic cathedrals. Although little is known about the engineering techniques of !-ledieval master-builde:r·s, this writer suggest.s that concret:e was not utilized in the Middle Ages in part because of the absence of a theory of statics. J).1any of the rules of building were de,:ived from numbers . . 13 and proportlons. Without structural analysis based on the mathe- m.at.icaJ. determination of the composition of forces, the use of concrete wou1d have been impossible. 11 \v. :E:rnerson and R. L. Van Nice, "Hagia Sophia: 'rhe Collapse of the First Dcme and the Construction of the Second Dome and its Later Repairs," .Archaeology 4, 1951, pp. 101-102. 12 . . To my knowledge there are no specifJ.c wrltten documents per·· tai:1ing to t:he early use of trass in Germany or Holland during t.he early Medieval period. •rrass was a light-colored volcanic tuff (':Jlossa:ry) rese.mbling puzzolana in composition and occurred on t.he lower Rhine. However, hydrauli~ mortars were a-vailable in cert:ain geographic areas throughout Europe, recause trade was established with some of these more remote areas by late Medieval times (see Chapter II). (See Figure 1.) Faujas de Saint--Fond (1741-·1819) showed that the tra~ of Andernach was a true p_~Z_!:?lar.a. See Friedrich Qnietmeye:r:, -~::':E. ~eschich!e der Erfindung des !'ortl_~?dzelnen tes (Berlin: 'l'onindustrie-Zeit.ung, 1915). 13 . Jacques HP.}'Inan 1 "'l'he Stone Skel.e-ton," Inter_E_at.J.ona!_ _g.9.urna~ of .§'.<:::~~~~ !3:!2:2: _Q!_~uct~::-.·e s, Vol. 2, No. 2 (April 1966) , p. 24 9. This ~>ns known as Scientia Geometriae which required that the main lines and forms of a st.ructure, such as the heights of vaults and the pro po:ct:ions of piers and buttresses, conform to a certain predetermined geometric grid. See Paul Frankl, "The Secret of the Mediaeval am;ons," Th':: _ _Ar-t:_ Bu~_le!j.n, Vol. XXVII, No. I (March 1945), pp, 46-- GO. 6 Figure l. Mapa aDr. Gustav Haegemann, Vom Caementum Zum Zeme_Et (Wiesbaden, Berlin: Bauverlag, 1964), p. 38. During the Renaissance, problems encountered in the construe- tion of domes such as that of Brunelleschi's Florence Cathedral and Michelangelo's St. Peter's in Rome raised questions concerning the resisting forces necessary to counteract thrust and of the strength of materials. The problem was how to turn a statically indeterminate arch into a stat.ically determinate structure, a condition crucial for its stability. In spite of the addition of iron rings by Fontana and della Porta when building the dome of St. Peter's, the dome 14 nevertheless cracked badly. Renaissance architectural theory which attributed both the beauty and the st.ructural strength of a building to proper proportions was difficult to translate into larger domical shapes. The relationship between structural form and structural stabiliLy had worked fairly well in Medieval architecture. The arcrd:tectural developments of the following centuries was a con·tinuous 15 attempt to resolve artistic fonn and structural theory. During Lhe Medieval and Renaissance periods treatises on mineraology were written which laid the foundation for nevl scient.ific interest in minerals and metals. This scientific zeal resulted in ·the fonna·tion of cornmunit.ies of scholars, organizations and schools dedicated ·to experimen·tal investigations in a variety of fields. With ·the scientific :r:e.Yolution of the seventeenth century, work which 14 Howa:rd Saalman, "Early Renaissance Architectural Theory and Pract·ice in Antonio F'ilarete' s Trattato di Architettura," Art .~_E_l.:!:_~~~-:i_:!.!.r Vol. XVI, No. I (March 1959), p. 101. 15 He-y·man, "The Stone Skeleton," p. 268. 8 had begun earlier in statics would revolutionize the new field of engineering. The pioneering treatises on mineraology turned men's attent.ion to alchemy in the eleventh and twelfth centuries, and eventually to chemistry in the sixteenth and seventeenth centuries. •rhe result of investigations in both chemistry and engineering laid a foundation for research relevant to concrete. 16 In 1756, when the engineer John Smeaton was asked to build a lighthouse that could withstand the onslaught of high winds and pounding sea, he began a search into the properties of cement, overthrowing two-thousand years of prejudice, based largely on the vrritings of Vitruvius and others. It was the climax of one historical journey, and proved to be a beacon that would light the vm.y into a far more t:echnical, specialized area of concre'ce archii.:ec Lure and engineering in ·the nineteenth and twentieth centuries. 16 h h f . . . , Jo m S'meaton was t e ounder of the ClVll englneeru~g pro-- fession in Britain. This was significant, for as an engineer, Smcat.on laid the ground:;.vork for the schism that: would occur in the historic role that concrete would subsequently assume in the field of archi· tecture and engineering. Chapter I THE LEGACY OF ROME 1 Concrete is one of the oldest building materials known. Many people in the ancient world discovered that mud (glossary) or clay (glossary) mixed with lime made a stronger mortar than lime alone and could be used as a binding agent. The more clay that was included, the better the mortar (glossary), and a soil containing lime was bet:·ter yet. Some soils produced a better adhesive than others, yet no one was quite certain why. None of these combinations produced a strong enough mixture to bind the whole into a monolithic mass (glossary). Both Vitruvius and Pliny suggest t.hat asphalt 1 Genesis 11:3, "And they used brick for stone, and they used tar for mortar." --New American -----Standard Bible (California: The Lock-- mah Foundation, 1973), p. 14. Exact definitions of concrete, cement, and mortar are difficult to establish in ancient times and therefore their individual origins are often impossible to trace with certainty. Mor-tar mean::; a substance which cements something together and this may account for some of the resulting confusion in the terminology. Mortar used in .?-'mcient Egypt before Graeco-Roman times was of two kinds, depending upon the nature of its constitution. Clay was principally used with sun-dried bricks; gypsum with stone. "No ins·t.ance of the use of lime-mortar in Egypt, or of lime in any form is known, as occurring before the t.ime of Ptolemy I (323-285 B.C.)." A. Lucas, Anci~nt Egyptian !'::laterial~ _;:tnd I~9__llSt_£i-~, translated by J. R. Harris (London: Edward Arnold, 1962), p. 74. Lime burning however was practiced in Mesopotamia at least. as early as 2450 B.C. See F. M. Lea, 'r0e Chemistry of Cement and Concrete (London: Edward Arnold, 1970), p. 2. 9 ·10 2 . (glossary) or bitumen (glossary) may be used as mortar. L~ne came to be used as a binding agent like mud or clay between courses of stone walls. It was sometimes mixed with water or combined with oil, 3 or used as a covering for the joints betv~en earthware water pipes. Lime mixed with caementa (glossary) was another way to strengthen 4 lime mortar. The Latin word calx (glossary), meaning small stone, became interchangeable with the word lime, suggesting that the word lime and the process of its making were one and the same. The word mortar, meaning a binder to join stones and bricks, is derived from the Latin mortarium, which refers to either a recep-tacle where sub- stances from which colors were obtained were ground, or the trough where lime was slaked (glossary) and mixed with different ingredients 5 to form stucco (glossary), plaster (glossary), or mortar. The Romans used the word materia much as we do, to define an indefinite 2 Vitruvius, On Architecture, edited and translated by Frank Granger, Vol. I (Cambridge: Harvard University Press, 1955). "For whereas at Babylon, where they have plenty of liquid pitch instead of lime and sand, they can have their walls built of burnt brick." Ibid. , Book I, V, 8, p. 53. "Calc is quoque usum praebui t ita feruminatis Babylonis muris." (It has also been used as a· substitute for lime, the walls of Babylon being cemented with it.) Secundus C. Pliny, Nat~~~]~ History, translated by H. Rackham (London: Harvard University Press, 1961), Book 35, 182, pp. 394-395. 3 vitruvius, _On Architecture, Book 8, Chapter 6, pp. 181-189. 4 This process may have been inherited from Mycenaean. Marion E. Blake, '"rhe Pavements of the Roman Buildings of the Republic and Early Empire," Memoirs of!:~~ American Academy 2:.!: Rome, Vol. 8 (1930), pp. 68-70. 5 vitruvius, On Archi·tecture, Book 7, Chapter X, 3, p. 123; Chapt:er 13, 3, p. 127. 11 6 mixture. These early non-hydraulic {glossary) mortars, made of lime, mud, clay~ small stones, sand, water or·oil, were used for pavements, lining of aqueducts, and cisterns. Hore importantly, in terms of the historical significance of concrete, they came to be associated 7 with brick and tile construction. Cements (glossary) are different than limes, and are capable of solidifying when brought into contact with water. Gypsum (glossary) 8 plaster may have been the earliest deliberately manufactured cement. It was preferred to lime due to the scarcity of fuel. Lime required much higher temperatures for burning and hence more fuel than 9 gypsum. Today we call it plaster of paris. Some gypsum contains limestone (glossary), and if burned at a high enough temperature, produces qualities of limestone. Plasters and mortars were used to consolida·te stone or brick structures from time immemorial. Plasters 6 Calx et _llare12_~, calx harenat.<'!-_, or harenatum were all used as indefinite t.erms for mortar, binder or matrix. Vitruvius, On Architecture, 7, 3, 5 and 2; 4, 3; Pliny, Natural Hist~ry, 31, 49; 36, 176, 177; and Harcus Porcius Cato, ~-Agriculture, translated by William D. Hooper (London: William Heinemann, 1960). "Pavimenta ad hunc modum facito: ubi libraveris, de glarea et calce harenato primum corium facjto." (Construct the pavement as follows: after leveling spread the first layer of gravel and sanded l.hae, and tramp do"ll'm.) Ca·i.:.o, On Agriculture, 18, 4-9, pp. 34, 35. 7 Harion E. Blake, ~nc_~~nt ~nan_ Cons·t~~ctio~ in Ita~y_ from the Prehistoric Period_ to ~ugustus {Washington, D.C.: Carnegie Institute of Washington, 1947), p. 311. 8 ·Both gypsum and alabaster are found in large quantities in the vicinity of Giza, Egypt. "7illiam Wallace, "On Ancient Mortars," The Che~lical News and Jol!.E_nal of Physical Science, edited by William Crookes, Vol. XI (1865), pp. 185-186, 12 have been used to finish walls, conceal irregularities in pre-pottery levels of Jericho (7000 B.C.) where floors and walls were covered 10 with a lime plaster. Theophrastus noted that both in Phoenica and 11 Syria gypsum was made· by being burned in a furnace. When the material was baked (calcinated), it was broken up like lime. "Its nature is such that it seems in some v.ays to combine the qualities 12 of lime and of earth." The English \.zord cement is derived from the Latin word caementurn. The latter refers to broken stones which serve 13 as the aggregate for concrete. Modern cement, however, has no such ------10 Andre Rosenfeld, The Inorganic Ra~Materials of Antiquity (New York: Frederick A. Praeger, 1965), p. 190. I-1r. Wallace secured specimens of mortars from Egypt, Greece, Italy and Cyprus in 1865, and subrnit·ted them to chemical analysis. He judged the mortars to range in age from sixteen hundred to three thousand years. He ascertained that tv.u specimens examined from both the interior and exterior pyramid of Cheops contained gypsum. These specimens did not appear to contain any-sand; the silica acid evidently in combination with alumina as clay. Part of the selenite (glossary) was burnt, and the result mixed with burnt lime, ground chalk (glossary) or marl (gloE; sary), and coarsely-ground selenite. {See Figure 2.) The most ancient mortar was found in Cyprus. Samples included cement used for joining pipes ten feet below the surface of the ground. 'rhey contained red clay, connected by a spigot and fawcet joints, filled between with cement and bitumen. (See Figure 2.) Ancient Roman mortars differed from the others in that they were prepared by mixing with burnt lime, not sand but puzzolana or improperly known as volcanic ash. These were taken from Hadrian's Villa at Tivoli, Herculanemn and Tombs near --- Rome. The fourth specimen was a cement or mortar taken from the floor of the Baths of Caracalla, Rome. (See Chart 4, Figure 2.) See William Wallace, The Chemical News, pp. 185-186. 11 . Theophrastus was born in 372 or 370 B.C. 1n Ereasos, on the Island of I,esbos and was a member of Aristotle's circle. 12 Theophrastus, De Lapidi_!::us, edited and translated by D. E. Eichholz (Oxfore: at the Clarendon Press, 1965), Books 68-69, Chapter 9, p. 85. 13 The adjective caementicia is used by Vitruvius to make his meaning clear. On Architecture, II, 8, 16, p. 125. 13 Chart 1. Egypt Interior Exterior Sulphate of lime, hydrated 81.50 82.89 Carbonate of lime (C02 calculated) 9.47 9.80 Carbonate of Magnesia (do, do.) .59 .79 Oxide of iron .25 .21 Alumina 2,41 3.00 Silicic Acid 5.30 4.30 99.52 100.99 Chart 2. Phoenicia Temple Cement Lime 26.40 51.58 Magnesia • 97 .70 Sulphuric Acid . 21 .82 Carbonic Acid 20.23 40.60 Sesquioxide of iron .99 Alumina 2.16 • 40 Silicic acid and fine sand 16.20 • 96 Coarse sand 3.37 Small stones 28.63 Organic rna t.ter .56 . 24 Water . 54 3.09 100.26 98.39 Chart 3. Greece Pnyx ~emple at Pentelicus Lirne 45.70 49.65 Magnesia 1.00 1.09 Sulphuric actd l. 04 Carlxmic a.cid 37.00 38.33 Sesquioxide of iron • 92 .82 Alumina 2.64 . 98 Silicic acid and sand 12.06 3.90 \'later .36 3.07 99.68 98.88 Chart 4. F.ome Hadrian's Villa Herculaneum Temple Mosaic Lime 15.30 29.88 19.71 25.19 Magnesia . 90 .30 .25 .71 __ b Potash l. 01 3.40 Soda 2.12 3.49 Car:J:xmic acid 11.80 23.80 13.61 17.97 Peroxide of iron 4. 92 2.32 l. 23 3.67 Aluinina 14.70 2.86 16.39 10.64 Silicic acid and sand 41.10 33.36 36.26 30.24 Organic matter 2.28 1. 50 2.48 Water 5.20 l. 00 ----8.20 5.50 98.73 101.86 --b Figure 2. Specimen of Mortars from Egypt, Greece, Italy and Cyprus, 1865a a Wallace, The Chemical News, pp. 85-86. b . Not est1.mated. 14 connection in meaning with the word caementa, and this leads to confusion in the terminology as well. Concrete (glossary), on the other hand, refers to a monolithic mass which consists of broken stones bound t.ogether with a hydraulic mortar, water and sand. The excellence of the mixture depends upon the quality of the mortar. The first literary source to mention concrete in Republican Rome was Cato (232-147 B.C.). Calce et caementis referred to small stones and calx was mortar made of burnt lime and sand. The mortar des- cribed by Cato consisted of stone, lime, sand, water, chaff (glossary) 14 and clay. This calc~ et caementis recommended by Cato for the walls of a farmhouse, consisted of stone and mortar, an early form of pseudo-concrete. Vitruvius speaks of "prirnumque_ incipiarn de ruderatione" in . 15 ref erence to concrete fl. oor 1.ng. Marion Blake maintains that the word ruderatio seems to have had a more general application, since it was used by Vitruvius for both flooring and the filling between 16 walls. Both the word rudus or ruderation refers to a mixture of 14 "Cetera lex uti villae et caJ.ce caementis." (The rest of --- the specifications as for the house of rough stone set in mortar.) Cato, On !:\_<;;ric~lt~, 14, 4. "Macerias ex calce caementis silice." (Construct the enclosure walls of mortar, rough s·tone and rubble.) Ibid., 15, l, pp. 30-31. In Cicero, "1\Iurn hoc in lateri aut in ~aemen!:_~ ex quiluis urbs effecta et.s, potuit valere?" (Does it also follow that the stone could have had any influence over the bricks and cemen·t of which the city was buil·t?) See Cicero, De Senectute, De Amuitia, De Divinat~on~, translated by William Armistead Falconer (Cambridge: Hassachusetts: Harvard University Press, 1971) , XD, p. 482. 15 v 1-rUVlUS,· t · On Arc h lLecture,·..... Book 7 r c ha pert I, p. -.l (First, I shall begin with concrete flooring.) 16 Blake, Ancient Construction, p. 324. 15 broken stone and mud, clay or lime. The English word rubbl~(glossary) 17 as applled. to anclent. constructlon. h as t h e same am b'lgulty. . Fre- quently the word rubble is used to suggest concrete, i.e., the aggregate used in filling or for course masonry. Mortar, on the other hand, set in rough, irregular stones, may refer to a variety of binders or adhesives, such as clay, mud, lime or gypsum. Concrete, however, contains distinct characteristics which set it apart from these earlier cementing· agents. First, concrete implies a specific formula for mixing contingent on specific ratios between the propor- tions of sand, water, aggregate and mortar. Second,it contains hydraulicity. Third, it is structurally load-bearing. And fourth, 18 lt. possesses mono 1'lt h' lC qua1' ltles. . In modern terminology, mortar and concrete are the same except that mortar can pass through a sieve with a 3/16 inch square opening, whereas aggregates with coarser textures are classified as concrete. Stucco is a coating applied to external or int:ernal wall surfaces and contains 19 various degrees of lime, gypsum and/or concrete. The development 17 . 'Norman Davey, A History of Building Materials (London: Phoenix House, 1961), p. 122. Rubble: (of obscure origin; applied in some way to Rubbish.) Waste fragments of stone, especially as constituting the rubbish of decayed or demolished buildings. The OXford English Dictionary, eds. James A. H. Murray et al., Vol. VIII (Oxford: at the Clarendon Press, 1970), p. 857. 18 concrete is often used to describe aggregates with mortar. However, its historical importance resides in the search for a hydraulic mortar and these definitions have been provided to under line this important difference. 19 Davey, Materials, p. 122. 16 of concrete depended upon the quality of the mortar used. In one sense, concrete is of recent origin, due to the scientific develop- ments of the nineteenth and twentieth centuries which clearly defined concrete's chemical properties. While the first written indications of concrete may be the caementia et calce harenato of Cato, and later, quod commixtum cum 5::alce et caementis of Vitruvius, the English word cement has come to have another meaning entirely. Today, it refers to a powder, separate from the aggregate. There is evidence that crushed potsherds were added to lime mortar to give it hydraulicity in the Middle Minoan civilization of 20 Crete, circa 1500 B.C. Later, the Greeks themselves were aware that certain sands yielded a mortar which was strong and capable of 21 resisting the action of water. Greece, however, preferred cut-stone construction for public buildings and sun-dried bricks for humble 22 dwellings, neither requiring mortar for a binder. 20 Lea, Chemistry, p. 4. 21 rbid., p. 4. Strabo, the geographer (b63 B.C.),men·tions the city of Puteoli in his Geography as having a foul smell and "the city has b2come a very great emporirun, since it has havens that have been made by the hand of man--a thing made possible by the natural qualities of the sand, for it is in proper proportion to the lime, and takes a firm set, and solidity." The_ Geography of Stra_bo, translated by H. L. J·ones (Cambridge: Harvard University Press, 1960), 5, 4, 6, pp. 447-448. 22 The Greek system of combining ashlar work with dry rubble led to Roman masonry faced with squared stone and a filling of earth, rubble, or concrete. With the use of concrete all other ingredients were combined into one mixture. Blake, Ancient Construction, p. 190- 191. The Greek use of mortar was largely restricted to surfaces exposed to the action of water. In Sicily, lime mortar may have been 17 The Greeks' use of mortar was generally not structural, yet its introduction into Italy by the third century B.C. was revolu 24 tionary.23 Until Puzzolana (glossary), Italy, a country with PC?Or introduced by the Phoenicians. "Thanks to the then recent discovery of the uses to which plaster with slaked lime could be put, the Phoenicians were able to dig cisterns everywhere and to line them with true lime plaster impervious to water." w. Leland, ?tudies _:!-E._ the Histor: aGisela M. A. Richter, ~Handbook of Greek Art (London and New York: Phaidon, 1974), p. 392. 19 building stone, could add little to the knowledge of mortar which she inherited from Greece. It was the hydraulic character of the red puzzolana, though Rome was a-t first unaware of it, which gave mortar the hydraulic power to weld different materials into a compact mass capable of bearing fantastic weight. This durable mortar made from the local volcanic sand led to the evolution of a concrete construe- tion which was one of Rome's great contributions to Western Civiliza- . 25 tJ..on. Roman concrete was neither a mixture which contained a separate powder with aggregate and sand like modern day concrete; nor did it consist of plain lime mortar, nor was it mixed with a filling 26 beforehand. The Romans first burned limestone or chalk at 900° value, or hydraulicity. The designation Puzzolana has been extended to the whole class of mineral matters of which it is but one type. See Lea, Che~~try, pp. 3-4. The Italian puzzolanas, e.g., from Puzzoli, are natural. •rhe artificial ones are made from sherds and certain slags (glossary). See Davey, f centigrade (1625° F.), in order to convert it to quicklime (glossary). When burned and exposed to air, it rapidly attracted moisture from the atmosphere, and when combined with water, formed calcium hydroxide or slaked lime (glossary). "The freshly burned quicklime "'as slaked with an excess of water in an upper basin and allowed to flow in a creamy state into a lower basin where the remainder could evaporate, 27 leaving lime putty [glossary] . " To prevent lumps or unburnt material from passing through, a grating was placed between the two basins. The lime was then made into a mortar by the addition of sand. Vitruvius suggested that with regard to lime, we must be careful tha.t it is burned from a. stone which, whether soft or hard, is in any case white. He believed that lime made of close~grained stone of the harder sort WD!Jld be good in structural parts; lime of porous stone, in stucco. He suggested that after slaking it, the mortar should be mixed, if using pit sand, in the proportions of three parts of sand t.o one of lime; if using river or sea-sand, mix two parts of sand with one of lime. Further, in using river or sea-sand, the addition of a century B.C., medium-sized caement~_ appear in the walls of the Theat~!:_ of _!'ompex_, Rome. Blake, Construction, p. 350. Vitruvius recommended that caemen~~ in cella walls be as small as possible. Vitruvius, On Architecture, translated by Morgan, IV, IV, p. 116. 27 Davey, Mater1.a. 1 s, p. 102. . BurnJ_ng. 1'1mestone to prod uce quicklime requires higher temperatures than that required for burning gypsum. Hence lime burning generally was a later development. Timber was the fuel used for the kiln in ancient times and charcoal in Roman times. "If you cannot sell your fire1t.-ood and faggots, and have no stone to burn for lime, make charcoal of the firewood and burn in the field the faggots and brush you do not need." Cato, On ~griculture, 38, 4. Coal was not used until the end of the thirteent:h or early fourteenth centuries. Though lime was more abundant, gypsum was often used due to the scarcity of fuel. Lea, Chemistry, pp. 2-3. 21 ·third part composed of burnt brick, pounded up and sifted make mortar of a better composition to use. Vitruvius argued that if limestone was merely pounded up into small pieces and mixed with sand, the mass would not solidify or hold together. But if the limestone was first placed into the kiln, it lost its former property of solidity and strength by exposure to the heat of the fire. With the strength of the stone liberated, the stone should then be immersed in water. 28 After it cooled, heat was released from the lime. The Romans were fortunate in that much of the "sand" of Italy 29 wa:s puzzol_9-na wlt. h h ydrau.l" lC qua l"ltles. . 28 vitruvius, On Architecture, translated by Morgan, II, V, pp. 45-46. For floors, Vitruvius suggested: "after the planking is finished, lay upon this the bedding, composed of stones not smaller than can fill the hand. After the bedding is laid, mix the broken stone in the proportions, if it is new, of three parts to one of lime; if it is old material used again, five parts may answer to two in the mixture. Next, lay the mixture of broken stone, bring on your gangs, and beat it again and again with wooden stamps into a solid mass, and let it be not less than nine inches in thickness when the beating is finished. On this lay the nucleus, consisting of powdered pottery mixed with lime in the proportions of three parts to one, and forming a layer not less than six inches thick. Book 7, l, 3, p. 203. Vitruvius emphasizes the quality of materials used. "When it is taken not thoroughly slaked but fresh, it has little crude bits con cealed in it,. and so, when applied, it blisters.·" Book 7, ll, l, p. 204. 29 Puzzolana was not, at the time Vitruvius wrote, the aston- ishing building material later builders carne to realize. Vitruvius describes it as a substance "when mixed with lime and rubble not only lends strength to buildings of other 1dnds, but even when piers of it are constructed in the sea, they set hard under water." Vitru.vius, On Archite~_:!:ur~_, translated by Morgan, 11, 6, 1, p. 46. Puzzolana alone did not account for the durability of Roman concrete at t.he time that Vitruvius wrote. It was rather, the fact that the mixtures bad to be properly selected, the caementa graded and the materials for common aggregate be correctly chosen, properly sifted and well supervised. The quality of puzzolana_ varied from one locale to another. It also 22 The ancients could convert non-hydraulic lime into hydraulic li.TUe by adding suitable materials. These additions, called puzzolanas, consisted of silica and alumina which combined with-the non-hydraulic or semi-hydraulic limes at ordinary temperature in the presence of moisture to form stable insoluble compounds of cementiticms value, such as calcium silicates and aluminates. When mixed with lime mortar in addition to or in partial substitution for sand, they imparted hydraulic properties and g-reater strength.30 The method used for constructing walls was to lay courses of 31 broken stones, or broken brick and fill the interstices when laid. Al·though the main bulk of the concrete was in a semi-fluid mass {judging from the regularity at which the larger pieces of stone appear) , these larger stones were placed separately by hand, not 32 poured :tn. at rand om as was t h e rest o f the m1xture. . The concrete was poured into a long wooden box, containing an "upright post ten to fifteen feet high stuck in the ground along the line of roth faces of the future wall at intervals of about three feet, and against these posts w:>oden boards ten or eleven inches wide were varied in appearance. Ashy gray, dark gray, brown, reddish brown, and red are some of the colors one finds. Mixtures of black and white may be seen as well. Blake, Ancient Construction, p. 313. 30 Davey, Mate;r:ials, p. 102. Sometime around the third century B.C., the dusky red puzzolana was added to the mixture of lime and mortar, thus beginning the his-tory of hydraulic concrete in Rome. -~1 - D. S, Robertson, !!._ _!:Iand:too~ of Greek ~nd Rom~~- A.rchitecture (London: Cambridge University Press, 1969), p. 233. No external pressure v.ras appJ.ied during construction, judging from the lack of compactness and size and frequencies of the voids in the mass. Earlier, the weight of the stones held the whole together far more ·than t.he a.dh-::;sive power of the mortar. 32 J. Henry M1'ddl e t on, "On t h e c·h'~ 1er ~ Me tho d s o f c onst rue t'.1on Used in Ancient Rome," Archaeologia, Vol. LI (February 24, 1877), pp. 41-60. 23 33 nailed horizontally, overlapping each other. " To keep t.he lx>ards in place until the concrete had set, cross-timbers were fixed as ties. When the concrete hardened, the framework was removed, and a second quantity of concrete was poured in. The hydraulic pressure against the wooden framework must have been very heavy. While Middleton (see Figure 4) believes that cross timbers were fixed as ties, Davey suggests: Sometimes flints were placed in layers in timber formwork and mortar was spread on each layer before the next was placed. Mortar was of stiffer consistency and did not penetrate far into the interstices between the stone. By building in this way, rather than by grouting,34 pressure on timber formwork during building of the wall was greatly reduced, and work could proceed faster. It was usual to carry up concrete in "lifts" about three feet in height and then to lay on a bonding course of two or three inches thickness of tile. Apart from the fact that these string courses or bonding courses strengthened work and helped insure stability, they also provided a level base on which to place ·the next lift of concrete. 35 3' ~Ibid., p. 49. 34 See glossary. 35 Davey, Mater1a. 1 ~, p. 123 • In actua1 construct1on,. a wa 1"~ of cemented rubble was corrunonly built between boards. The boarding w~s supported by external upright battens (glossary) , but occasionally it was held in position against the wood by post placed inside the boarding, Le., against the rising structure. The matrices of these internal upright.s, toget.her with ·the imprint of the horizontal boarding, were recorded on a Roman wall found in and before 1906 in Friday Street, London. The walls of the Roman vaulted structure under Colchester Castle, England, show, at intervals of about five feet, the sockets of posts upwards of ten feet high, which were in position when the walls were built; their heads were enveloped in the masonry, leaving a socket sometimes as IT~ch as nine inches deep. See R. E. M. Wheeler, "Notes on Building Construction in Roman Brit ain," Journal of Roman Studies, Vol. XXII, 1932, p. 122. 24 ..0 ;:: v 0 ~ ;! "' 0:: ...~ ~ li ~ !!: ::3 ~ ~ "e ..~ i'! .."' i ci iii: ~ ! D D-----" 0 tl ,!! a Figure 4. Example of Poured Concrete aMiddleton, Archaeologia, p. 50. 25 The bonding courses also prevented settlement and the spread of con- crete before it had set. The difficulties of centering (glo$Sary), shuttering (glossary), shoring (glossary}, and scaffolding (glossary) were in some part eliminated by the use of heavy mortar. Later brick rel1ev:t.ng. . arches were set 1nto. t h e concrete. 36 This made concrete construction more efficient, economical, and reduced long setting periods. Masonry was fastened with iron clamps (glossary), when mortar was not used. Iron and bronze were also used in the form of clamps (or cramps) and plugs to insure a permanent bond between 37 marble fac1ng. and the sett1ng. beds o f cement 1n. wa l ls an d p1ers. . Thin sheets of lead were inserted horizontally to support the vaulting and arches in Christian churches thus substantiating the fact that a metal tradition in conjunction with concrete had evolved from Roma.n t1mes. or ear 1"1er. 38 36 By the time of Claudius (41-54 A.D.) well-planned use of brick with reticulate (glossary} in bands to help bind the facing to the core and perhaps prevent cracking, was seen. Blake, Roman_ ~on_ struction f:E~~ :!:iberius Through the Flavi~ (Washington, D.C.: Carnegia Institute of washington, 1968), p. 161. The only ~Dodwork required for brick-faced walls was scaffolding. Once the mortar had hardened, shuttering was unnecessary because the speed of erection and accuracy of construction were performed by the drying rate of the mortar. The brick skins and concrete core went up together. ·william MacDonald, The Architecture of the _Roman Empire (New Haven & London: Yale University Press, 1965), p. 156. Lethaby suggests: "These layers not only bound the external and internal skins together, but they locked up the moisture in the concrete stage by stage. For if it were too quickly absorbed into the part already built, or dried out by the hot sun, the mass would not set properly." William R. Let.haby, Architecture (London: OXford University Press, 1955}, p. 91. 37 MacDonald, The Architecture o~ the ~om~~ Empire, p. 145. 38 "welding had become an established part of the Greek black smith's art: by the middle of the fifth century B.C., for examples from 26 With foundations, once the roa left unfaced. If stucco was appliedr the use of iron nails wedged or driven into the concrete was the method used for roughing the concrete surface or br1ck. 1n . order to make the stucco a d here. 39 The concrete core was then faced with brick or stone blocks. In the first and second century B.C., stone block ~acing was replaced by smaller stone facing called ~pus incertum (glossar-.t}. Later opus quasi-ret:i.:::ulatum 40 (glossary) was used and lasted until t:he second century A.D. Then concrete walls were faced \>;ith brick, opus testaceum (glossary) , ------the Parthenon at Athens have been recovered in the form of clamps built: up by welding together iron flats about 4 inches wide and 3/8 it1ches thick, or less." See S. B. Hoonilton, "The Structural Use of Iron in Antiquity," Tran_?ac_:tions of t:l~~ Newcomen Society, XXXI, 1957- 1959, p. 31. (See Figure 5.) Kirby suggests that "they used con cealed \\Tought iron bars to reinforce their masonry; they knew some thing of the problems of stress under tension as well as compression and that they found iron useful in ss.:1lving them." R. S. Kirby, S. ~Ht.hington, A. B. Darling, F. G. Kilgour, E'ngineering in History (New York: McGraw, 1956), pp. 46-47. Vitruvius notes: "Iron bars or arches are to be made and hung on the timber close together with iron hooks. And these rods or arches are to be placed so far apart that the titles without raised edges may rest upon,. and be carried by them; thus the whole vaulting is finished resting upon iron." Vitruvius, On !\rchitect.m:e, translated by Morga.>t., V, X, 3, p. 158. Some authors believe that the Romans' knowledge of iron was not used in terms of modern reinforcement, in the s..:mse t.s1at metal offsets stress. How ever, other authors disagree. Cowan notes that the clamps, usually of iron, but sometimes of bronze, were used as metal reinforcement like that of modern concrete reinforcement. The ------Pons Cestius ove:r the Tiber in Rome is an example, where every stone is fixed to every other by two metal clamps. See Henry J .. Cowan, The Master Builders (New York: John Wiley & Sons, 1977), p. 72~ 39 Middleton, Arc::haeologia, P~ 50. 40 The. d eve 1 opment f rom t h e use o f opu~ !ncertum . to t h at o f ~pus quasi-_ret.iculatum in facings of the first century B.C., marks an increase in the use of concrete :for fillings. Blake, Ancient Constr~tion, p. 330. 27 -·-..--··------~------· ------··-THE STRUCTURAL USE OF IRON IN ANTIQUITY Fig. 2. Cr.MU'S AND DOWELS IN nm MASONRY OP Tffil PARTHl!NON, ATilEWl Mi .r--~~--··-----.~.,.--~~ ... - l~ ,..I (~ .. \~ .. ----....~-:.- --=-i~----- / 2 Figure 5. Use of Iron in Antiquitya aHamilton, Transactions of th~ Newcomen Society, p. 32. 28 lasting until the fourth century. From the third century A.D. 1 brick 1 stone and tufa {glossary) were combined to produce w:n:k called opus 41 mixtum. The principle function of the facing was t:o simplify the process of cons·truction by providing a quasi-independent framework, so that the main body of the wall could be laid with as little . . . . 1 42 s h utter1ng, or superv1s1on, as poss1b e. The method of building walls in Pompeii during the third and fourth centuries B.C., involved the use of cores held together by ·43 mud or clay. By the time lime mortar replaced clay and mud in the third century, Rome was constructing an early form of opus incertum. Vitruvius called this an ancient style and that "lying course above course and b~·eaking joints 1 furnishes walling which is not pleasing 44 but is stronger than the reticulatum." In addition, Vitruvius describes a wall known as emplekton which had a cavity behind the 45 facing, filled with mortar. Forerunners of these types of walls 41 Davey, ~ate~ials, p. 122. C?us. Carmenticium referred to broken tile called s:armenta, wherein each layer was grouted with lime mortar. 0]21..1~ _!Uix-t:~..lm.:. had been used earlier and was reintroduced during this time. 42 .. . .Alex Boe·thJ_us and J. B. Ward-Perkins, ------Etruscan and Roman Architecture, Pelican History of Art, edited by Nicholas Pevsner {Baltimore:- Penguin Books~l970) ~- 24.7. 43 George Hanfmann, review of Roman Construction in_ Italx_ from Tiberius Through the Flavians by Marion E. Blake, in the Society of Archit.ectural Histori~~ol. 7, No. 3-4 (July-December,l948), - pp. 33-36. 44 . . . V1truv1us, On Archltecture, translated by Morgan, Book II, 8, 1, p. 51. 45The Italians generally fill the central spaces of their walls by throwing in alternate layers o-f broken rubble and mortar. '}'he Greeks, on the o-ther hand, filled the center with stones not 29 were found in Africa and Spain and made of moulded earth and gravel, . ) . 46 or pJ.se (glossary constructJ.on. 47 The earliest structures made of concrete were road beds. 48 Next came foundations, such as the podia of the Temple of Concord, rubble, carefully placed and balanced in position, and laid in alter~ nating courses. The carefully constructed fill is bonded t.o the faces of worked stone by means of the headers of the faces, called emplekton_. Vitruvius was referring to a Greek walL Emplekton referred to a solid core of unbroken stones not rubble, arranged in courses and set in mortar. See R. A. Tomlinson, "Emplekton Masonry and Greek Struc ture," Journal of Hellenic Studies, Vol. LXXXI, 1961, p. 134. 46 Varro speaks of the type of fence made of earth and gravel in a mold, found in Spain around Tarentum: "quod ex terra et lapilJ is compositis in fonnis" (and that fonued earth and gravel in moulds such as occur in Spain and the district of 'l'arentum}. Marcus Terentius Varro, On Agriculture, with an English translation by William Davis Hooper, Book I, 14 (Cambridge: Harvard University Press, 1960), p. 219. Varro's earthen wall at Carinae at Rome could have been built this way. Varro, On the Latin Languag.e, translated by Roland G. Kent (Cambridge: Harvard University Press, }958), V, 48, p. 45. Pliny referred to these as !_~rmacean {glossary) w"all s, because they were moulded between parallel wooden frames. "Moreover, are there not in Africa and Spain walls made of earth that are called framed walls, because they are made by packing in a frame enclosed between two boards, one 0'-1 each side, and so are stuffed in rather than built." pliny, Natura! History, Book 35, Chapter 47, 167. 47 rt is possible that road-building of the third century B.C. contributed to the development of concrete construction. By the second century B.C., :road building had become an art. Blake, Ancient Constructio~, p. 328. 48 Templ~ of Concord, originally constructed in 367 B.C., rebuilt by Opimuis in 1212 B.C. and by Tiberius in 7 B.C. From a review by R. Gardner of "Roman Buildings of the Republic: An Attempt to Date Them From Their Ha-terials," by Tenny Frank, from Journal of Roman ~t~dies, Vol. 15 (London: 1924), p. 121. (See Figures 6 and 7.) 30 A.., Fig. IV. A ~ Augustan concrete. M ~ Metellan concrete. P ~ Peperino plinth. X ~ Oldest platform., Figure 6. Temple of Castora a Tenny Frank, "The First and Second Temples of Castor at Rome," Me!Uoirs_ of the American Academy in Rome, Vol. 5, 1925, p. 54. 31 i '' -= a Homer F. Rebert and Henri l'iarceau, "Temple of Concord in the Roman Forum," Me~ 49 erected by Opimius in 121 B.C., and tl1e Temple of Castor, 117 B.C. Only gradually did concrete replace ashlar. The use of mor-tar to hold stone blocks together for masonry did not become common un·til 50 after the Augustan era. In foundations below ground, it was left without protection; where it was used in substructures above the ground or in free-standing walls, it TNaS faced with stone o:r: brick; where it served as vaulting it often stood alone except for a protec- tive coat of plaster. That the Romans did not entirely trust their new material is proven by the fact tt6t they, employed stone for the 1 parts which had to bear the greater weight of the superstructure. 5 49 Davey, Materials, p. 122. '"These earliest extant examples of opu~ caementicum were already so perfect that the material must have been in use for some time." Euqenie Strong, Art in Ancien!_ Rom~, Vol. 1 (New York: Charles Schribner & Sons, 1928), p. 53. "Cato knew fifty years before how it [concrete] was made. What restricted its wide use was apparently the high cost of good sand at Rome and the failure to discover that the voleanic ash near Rome was an excel lent substitute. In the podium of the Concord Temple it is used with such conviction of its •~rth that there must have been a period of experimentation before that." Tenny Prank, "Roman Buildings of the Republic, an Attempt to Date Them from Their Materials," Papers and Monographs of the American Acad~my in ~ome, Vol. III, 1924, p. 38. 50 Blake, Ancient Construction, p. 188. 51 Blake, Construction, p. 342. Vitruvius protested regularly to Augustus against buildings with concrete due to the resulting accidents and deaths in a number of apartment houses. Unscrupulous builders had hurridly constructed structures without proper super vision or had removed the form work :Defore the concrete had set. "The city was filled with the noise of buildings collapsing or being torn down to prevent it." Jerome Carcopino, Daily Life in Ancient_ Rome, translated by E. 0. Lorimer (London~ Yale University Press, 1973), p. 31. "But here we inhabit a city supported for the most part by slender props: for that is how the h~iliff holds up the tottering house, patches up gaping cracks in the old wall, bidding the inmat:es sleep at ease under a roof ready to t-umble. about their ears." Juvenal ~nd Persius, translat:ed by G. G. Ramsay (Cambridge: Harvard Univer sity Press, 1957), III, p. 47. 33 "A limit was placed to [the] height of houses; open spaces were left 52 and colonnades added to protect the fronts of tenements." 'l'he fact that in the Augustan era the barrel vault of stone still served as a permanent centering in all bridge construction, proves that the value of- concrete was not f u 11 y apprec l.attti. ~-"· at t ha t tlllle.. 53 Few realized that concrete might be anything more tllan a cheap, efficient substi- 54 tute for wood or stone. The real innovations in concrete occurred more fully in Imperial times with curvilinear and multilinear forms. "Walls and vaults of concrete buildings were not separate entities but were par·ts 52 The Annal:=: of Cornelius Taci_tus, English translation by George Gilbert Ramsay (London: J. Murray, 1904-1909), Book XV, Chapters 43-43, p. 279. 53 Blake, Ancient Construction, p. 344. Practically all Claudian bridges were of cut-stone masonry because engineers did not trust concrete, p. 80. 54 Sulla's epoch (82-79 B.C.} marks a new direction in the use of concrete in Republican Rome. In the Tabularium_ concrete was used only for the substructure, the pavements and vaults, and the walls were of masonry. Experimentation in the use of concrete was beginning which would find its climax in the Imperial period. Blake, Ancient Construction, p. 331. The _Sanctuary ~! Fortuna at Palestrina was perhaps the most splendid monument in Italy o.f the Republic. The use of eoncre.te amounts to an architectural revolution in taste, combined wii.:h mat.erials and methods (see Figures 8 and 9). Paul MacKendrick, 'l'h::_ ~ute .s·tones Speak {New York: New American Library, 1960), p. 129. Statics, a.nd the distribution of stress, were worked out here with remarkable scientific precision.. While the Colosseum was built in 80 lLD., and was simplified and cheapened by concrete, there is little in the struc·ture that could not have been built in stone. Ward-Perkins, "Roman Concret.e and Roman Palaces, u The Listener, Vol. LVI, No. 1440 (November 1, 1956), pp. 701-703. 34 i)· TraJatJI. • Market!, tsom. etric drau1ng. · of lhe remains aMacDonald, 35 ''\ . [ .~-·-·· !. Figure 9. The Sanctuary of Fortune at Palestrinaa a 1-1acDonald, The Architecture .?f the Roman Empir~, Figure 8. 36 of a single rigid envelope enclosing a certain tract of space and 55 this enclosed space could be any shape that the architect chose." Once this idea was accepted, interior space could be dealt with in a way that demanded solutions from the inside out, rather than from trad1tional. Gree k concepts o f exter1or, . rect1'1' 1near masses. 56 For the first time new possibilities in the shape of a room outweighed 57 quest1ons. of construct1onal. conven1ence. an d f unct1ona . 1 1 og1.c. . Concrete was the key that unlocked the door to a whole new architec- . 'd 58 tural wor ld , and once opened , progress ~tJas rap1 . 55 Ward-Per kin s, _The ~i stene~, p. 7 02. 56 Giedion describes these concep-ts of architecture in terms of space conceptions. The first was that of Egyptian and Greek temples which stood as volumes in space. In Rome, interior space was hollowed out as well as opened up by means of windows and the use o:L concrete. See Siegfried Giedion, ~pace, Time and Architec~ure, The ~~ird Space ~onc~ption (Cambridge: Harvard University Press, 1967), passim. 57 ward-Perkins, ThE.:_ List:ener, p. 703. 58 Numerous reasons were responsible for the growth of con crete. Before Sulla's time the recognition of the core as a distinct structural factor was actually a detriment to the understanding of concrete. So long as the core and facing remained separate, concrete had not gained any structural advanta.ge over its forerunners. The differentiation of aggregate size led to lighter and larger vaults. The impulse toward curvilinear struct:ure was not possible until mastery of the principles involved in making brick-faced concrete were firmly .~stablished. The difficulty of laying aggregate on cente.ring led. to more effec·tive methods of butt1:essing. The form of the vault depended upon the wooden framework. The science of vaulting followed closely the mastery of concrete. A greater understanding of carpentry by Nero's time, as well as mass production of materials was also responsible for a fuller application of concrete. Reduction of forrnwork, and its resulting simplication made concrete far more manipulative. 'I'he Pax Romana was a stimulus to building and Roman order and organization in administrative functions led to the ulti mate freedoms necessary to explore concrete. The fires of 64 A.D. 37 The fiJ::st umnistakable monuments of the new architecture in concrete date from Nero's time, between 60 and 70 A.D. By 130 A.D. this revolution in concrete was a fact. By reducing problems to essentials, such as decreasing the weight of the walls '\lith pumice (glossary), the vaulting and ancillary supports allowed new liberation 59 1n. p 1 ann1ng . wh' 1c h .1.n . turn l e d to an emp h as1s . on spac1a. l d e f.1n1t1.on. . . Concrete cro~s-vaulting enabled the Romans to take up the thrust of their vaults by the walls or by the massive thickness of the con- 60 crete. The Pantheon remains one of the greatest achievemen-ts in concre·te architecture of the ancient world. Built around 126-128 A.D. 61 b y an un k nown arc h1tect,. 1ts. f1ve- . ·th ousan d --o dd tons o-f concrete stand as witness to the engineering and aesthetic brilliance of its builders. •rhe Pantheon was built on an immensely deep ring foundation of concrete. As the dome was poured upon a temporary wooden hemi-- sphere its outer surfaces were determined at first by the circular brick dams that formed the step-ring buttresses. The intermediate block, the ro·tunda, and the dome are made almost entirely of concrete. and 80 iLD. may also have contributed to the search for a safer type of.· construction. Blake, Ancie~t:_ Construction, p. 349. so -'Hollow clay pots were used to light:en the vaults as well. Richard Brilliant, Roman Art (London: Phaidon Press Ltd., 1974), pp. 26-·29. GO . ] . . . WL.l1am L. MacDonald, The Pantheon, De s1gn, ~ean1ng an Figure 10. The :Pantheon Showing the Arch Constructiona H. B. Armytage 1 !2_ so.::: ial_ Hi st Faber & Faber, 1961) 1 p. 49. 39 The bricks of the cylinder are a mere skin over the concre'ce structure and the dome is of poured concrete. There are st-ructural elements of stone and there are powerful thick vaults of tile-shaped bricks radiating out through the rotunda cylinder over the interior niches at ground level and the enclosed chambers above. These vaults carry t.he load of the superstructure downward, distributing it onto eight 62 great piers. The fact that architects managed these innovative solutions without metal reinforcement, has lead Wl:·iters to ascertain that the brick relieving arches {glossary) were structural devices. In both the ~at~s of Caracalla (215 A.D.) (see Figure ll) and the Basili_r::_~ .?J.:.. 5::onE;·ta~t~ne_ (Haxentius, 310-320 A.D.), brick arches were embedded in the concrete vaults (see Figure 13). These arches were superficial however, and penetrate only inches into the mass of 63 concrete which is often six feet thick. Brick is purely superficial skin. Its principle purpose was t.o provide an even surface and to contain the concrete core Hhen it dried out. Ano·ther fallacy was t·hat brickwork often incorpora"Ced VJhat appeared to be structural devices, like relieving arches over doors and windows. This has led 62 'I'"l 11c . l<:ness o f the domes decreases in order to lighten the ~,.;eight of the concre·te roof, a process known since the Temple of Fortuna in Palestrina. Kidle de fine Licht, The R~tu~~~ in Rome ------·· (,Jutland 1\rchaeological Socie~y Publications, VIII, 1966), p. 206. 63 War d ·-Per k'1ns, .'!:__~h L1ste~_, . p. 702 . The roofs of the Baths -of ------Caracalla were constructed of lime concrete reinforced with bronze rods, and so the dome of the Pant.heon may be similarly reinforced in part.s, but: it: is difficult to discover this in a structure completely int.act. Jl.rnold Whittick, ~~!opea!:!: Ar£hitect~rr:_ in the !_wen_-t:_iet~ Centur~, Vol. I, Part I, "Historical Background and the Early Years of the Century" (London: Crosby LockvJOod & Son, Ltd., 1950), p. 80. 40 Figure 11. The Bat.hs of Caraca11a a a . . . G1ed1on, Space, Tlllle ~nd Architecture_, p, 171, 41 F;Lgure 12, The Baths of Diocletian, Rome, 298-305 A.D.a 42 -.-,y ..... ~\~~q·::; <,.·. . . •• ·.· "i"if& ..... -~· .~ -~~~--~-\~·-: ''t?~.-:; '. ~'~~>71 ·_.·.;~--'-"~:··_··.,,)...·_·._·. ·. ___,,/J'~"":.·.•._· -~-/"'' "· ~%::~)~;:··-~= J ; ' i ; M • ~·'' ' ' f;, J I , I f · ·.·. l .: ... --~-,.·.· f__.-_._.~;·.-_· .. --~. t r J .. ··-· • · \~.;~~·-·i?:/~;;~,-.. :rJJ t :'l ~- -;: ~ ~- . ~ ;-r~<. ";·:;· ~ . -· :'. ;:: ~yl • H • -~~J I. • ;; •. 1 J .A f. is:-\: f} ,·, ~~~;1,!;!~~~·-~~T~~S... t :;:~=~··:~ lt!~ ., ' ,. ., .,,, ,,_..J;,.,~""v~ . ~ ~ ·" TT !'II / 'l{· '!!: ~ •,·~·.• .~_t:·-::.,.~ ., .i ~-" -xr'.,i ·-&·., ,.·,; ~,.;~~·:..,~...... ··~:,..: ·/ i ·r·-tt~-~ F--:::--.~~-fa;:(';:~ -,-:"~~ -,.:___ ~-- :~r~· .Y::_ ~~-:.-~ ~-~)"'";_- ~ )-: > v - 1 -~:\'!~,, l ·,· ,_' ' t 1 "}}'".,.. ·~~··.··' Figure 13. The Basilica of Constantinea a . . . . G~ed1.on, Space, :r1.me and !'-rchJ.tecture, p. 175. 43 people to talk about Roman vaults in terms of collection and transmission of thrust., as if Roman concrete building was a Gothic Cathedral. The truth is that once Roman concrete dried out, it was almost completely inert. Relieving arches played an important part in the construction, but once the building was finished, it stood by virtue of the immensely tough monolithic qualities of the concrete itself.64 The requirements of larger vaults led to technical problems regarding statics q.nd the strength of materials, no·t solved or com- pletely understood until the nineteenth century. From the beginning, Roman builders made use of engaged columns and pilasters to strengthen walls supporting vaults, but not until the Augustan era did they progress beyond this rudiment.ary buttressing. Removing stress by the use of architraves became a feature of Roman architecture. The concept of the springing cross-vault meant that the burden vTcl.s no longer carried by the thickness of the v.B.ll,. but by secondc..ry 65 .supports. Lightening walls with smaller aggregate, amphorae 64 ward-Perkins, Th~ ~J.:sten~_E_, p. 702. "The brick or flatst.one courses usually run completely through the wall and so tie it together, but they are sometimes used only for superficial leveling. Thus, at the base of the wall of London, on the inner side, super ficial brick courses-are used merely to level the facing, and corres pond for this purpose with an external plinth of sandstone." See R. E. M. v/h2eler' "Notes, II p. 123. Rivoira states that the brick relieving arches, reduce gravity of injuries due to external cau:ses.: Fissur·es and n'.onts found in structures never extend vertically for·l:he whole height of building as they are diverted or stopped by relieving arches. G. T. Rivoira, ~oman Architecture ~nd_ -~ts :!?E.:!:_nciples_ of S::52~1st:c~_<::_:l:._ion 9nde~ the Empire, translated by G. HeN. Rushforth (New York: Hacker Books, 1972), p. 130. 65 R1vo1ra,. . ~omar~ Arc h'J.tecture_, p. 117 . 44 66 (glossary), and coffered ceilin0s >vere all devices to divert stress. Stability of structure was not based upon voussoir (glossary) action, Le., pressure or friction transmi·tted along stone, but upon cohesion and homogenity of the concrete mass. Once the concrete dried, it acted as a monolithic mass, and there was no addi·tional transmission of forces. From the demise of Roman architecturM.principles to the end of the nineteenth century, architects and engineers were unable to reproduce with any material except iron, the same dimensions of the Pant.heon or the Imperial baths. 'l'he Romans did not use anti- tension devices such as tie-rods for their vaults or metal rings around the haunches of their free-standing domes. They converted. all t.ension forces into compression. In general, walls were thickened and strengthened by relieving arches to carry the weight of the va.ul t.ing, but no effective method of buttressing was developed. By Hadxian's (117-138 A.D.) time, many of the domical vaults at.tempted 67 by Dorcdtian (81-96 A.D.) had to be bolstered. The legacy that Rome left would not have been possible with- out o. qu:ick drying CPJ!l.ent. The speed with which a structure reached sufficient bearing strength was a key factor in concrete, differing fxom all build:i.ng materials used prior to that time. The stability 66 In the ?~nti:eon the weight of the kinds of aggregate used decreases regularly in layered, clearly differentiated zones as the height. of the building increases. 'l'he heaviest was used in founda tions, ·the next in the lower walls, and so forth to the upper dome, where pumice was used. See MacDonald, :r'h~ Pantheon, p. 43. 67 rv1arion Blake, Roman ~onst~~ction_ in Italy, p. 164. 45 of a structure which had traditionally depended on pressure or friction as in an arch or vault of cut stone, now depended on the 68 cohesion and homogeneity of the cured concrete mass. Not: until the nineteenth century, wi t.h the discovery of Portland cement, \vould a mortar be found that matched the quality of Roman cemen·t and not until the twentieth century, with the freedom brought. to architecture by reinforced concrete, would a reduction in the mass of the support 69 ing structure at ground level be achieved. 68 NcDonald, ~h~ Architecture of the_ Roman Empir~, p. 161. 69 Reyner Ban ham, Guid~- to Modern Architecture (London: The Architectural Press, 1962), p. 41. The first ribless dome to exceed the span of the _?a!!_theon (1421, feet) was the Market Hall, circa. 1930's, Algecira, Spain, which had a span of 156 feet. Like the !_>E:?theor:. it. has a. central light wi·th a diameter of 33 feet, the thickness of the shell is 3~ inches. A. Whittick, "The Era of Functiona.lism," European Archit.ecture, Vol. II, Part III, p. 163. _ce_~!.~D-.<3:~~ _!!<:::_11 in Rreslau had the first ribbed concrete dome to exceed the span of the !'~ntheoE._ (213 feet), built by Max Berg in 1913. Henry Co•,.Jdn, E!E_~::_~_ce_ ~-nd _!3u~}-_..?in'I_ (New York: Wiley & Sons, 1978), pp. 149- 151. Chapter II THE WAN,:ING OF CONCRETE ARCHITECTURE The most important development in concre-te occurred during the centuries following Vitruvius. Vitruvius held an official posit.ion in the rebuilding of Rome under Augustus. His treatise, however, never mentions Oc·tavian Caesar's official name "Augustus," and therefore it was preswnably written before 27 B.C., when the 1 title was conferred. It appears that the Vitruvian tradition lasted as late as the fifth century, and his influence upon the Roman colonies founded in the early Empire was extraordinary. The conquest of the Western Empire in the sixth century by Justinian tended to replace the authority of Vitruvius by the Byzant~ine tradition. Vitruvius' work was, however, represented in the manuscriptsofFlavius M. Aurelin Cassiodorus (487-583) at Squillace, Southern Italy, and of 2 the Benedict:ines at Monte Cassino. A version of Vitruvius' treatise may have been ·taken to the scriptorium at Jarrow by Coelfrid. There, It:alian ~3c:r ibes wrote the Codex Amiatinus and possibly the Harleian 1 secundus C. Pliny, Natural !"li:::tory, with an English transla tion by D. E. Eichholz, XXXI, 36 (Cambridge: Harvard University Press, 1962) r p. 29. 2 ,Saint Benedict of Nursia (c. 480-c. 547) was an abbot of Monte Cassion.. Encyclopaedia Britannica, s.v. "Benedict, Saint, of Nursia," Vol. 3 (l\Jew-York;-william Benton, 1972), p. 462. 46 47 +- • f . . 3 as we ll 1 t h e o ldest extan._ manuscr1pt o V1truv1us. 'l'he origin and dat.e of this work is not known. As early as Carolingian times 4 (eighth century) 1 fragments of Vitruvius were known to have existed. In the eleven·th century copies of: these fragments were available in Hedieval libraries. In the twelfth century he was known at Rauen, Cluny, and Montecassino. By the mid-fifteenth century,.his entire treatise was available not only in Italy, but also in England, Spain and Poland. \>Jhile no printed edition was available in Italy until 1486, it was not difficult to obtain access to Vitruvius at this time. A considerable number of ideas attributed to Vitruvius were 5 preserved in agrimensorial (glossary) manuscripts of the Middle Ages. Conan·t states that Vitruvius was not only read in Medieval t.imes, but that his ideas were incorporated into structural expres·- sion. "The ~arthex of Cluny III was proportioned like a Vitruvian atrium of the third class which has the length of the sides equal 6 to the length of the diagonal of a square erected on the end." 3 -Otto Von Simpson, ~he_ s;othi~ cathedral, Origins of Gothic A~:=:_hite'::!::':l-2~ an~ the Hedie_yal _s:oncept:_ of Order, Bollingen Series, XLIII (Pantheon Books, 1962), p. 30. 4 'l'he oldest extant M. S. Harle ian, once belonged to Goder amnu s of Coloqne, Abbo·t of Hildensheim (1022-1030). Sir John Edwin Sandys, A Hist:o_Ey 9f Classical._ Scholarship from ~he §_ixth Century_ ~.c._ to th~ _E:!_~. 9_!_ :the Middl~ Ages (New York: Hafner Publishing Co., 1958), p. 481. 5 carol H. Krinsky, "78 Vit.ruvian Hanuscripts 1 " _gou:£nal of the y~arburg _ _(:ln~ Court.auld Institutes, VoL 30 (Y.7arburg Institute of london, 1967), pp. 37-40. 6 K. J. Conant, "The After Life of Vitruvius in the Middle ,t:\.ges," ,Journal of the Society of Architectural Historians, Vol. 37 (March, --1968)-; p:-· 3~ ------48 Vitruvius knew Greek literat.ure and was acquainted with Greek architectural sources firsthand. His affinity for Greek architecture is deeply rooted in his ~Drk. "Ne putet. me erravi sse si credam 7 rationem" ("Let no one think I have erred if I believe in the logos"). Vi t:ruvius "'n~ote about Classical Greek architecture, not the technology of concrete construction of +,ate Roman times. Concrete construction was not fully explored until the centuries following Vitruvius. Hence the revival of Vitruvius' work in t.he Renaissance may explain in part why the knowledge of concrete proficip_.ncy was not also revived. Unfortunat.ely there is no spokesman for the architectural t:radition 8 of late Rome. This architecture was a prelude to our own time and .,Vii:ruvius, On Architecture, translated l:;y Morgan, II, l, 8. 8 Bot.h M. Cetius Faventinus and Palladius Rutilius 'I'aurus Aeroilianus w.r:ote ·works on architecture in the late Roman Imperial period. Scholars disagree on the relat.ionship between these writers and their work. 'l'he Compendium is now believed to be the work of Faventinus, and !i_~ R~ Ru-~_ica_,-the work. of Palladius, whose fifteen books were derived from Faventinus. Faventinus is thought to have lived and written in the third century A.D., and possibly as late as the fourth. Plornmer maintains ·that Faventinus wrote with extensive addit.ional knowledge of vaul·ting techniques, gained by builders under t~he Empire in the great age of concrete. See Hugh Plommer 1 Vitruvius ~l_~'! I~at:~.E. ~~?E•an_ Building ~annals (Cambridge: a.t the University Pressr 1973), pp. 15·-25. Architects Severus and Celer designed ·the Domu~ Aurea of l'!ero. _'l'he_ ~:t:l~-:.'?-ls of ~ornel]:_as _!~citus, English translation by George Gil bert Ramsay (London: John Murray, 1904-1909) , Book XV, p. 278. Rebix-ius built the mansions of the Palatjne in Trajan' s reign, \\'hen the real emergence of the dynamic style of concrete vaulted architect:ure ~vas exemplified in such v.urk as DoE_L_itia~ Palac~. Marcus Vale:c.ius Martialis, Epigrams_~_::_ :Spectac_ulus, English transla tion by Walter Ker (Cili-nbridge: Harvard University Press, 1968), VII, LVI, p. 463. In addition, Apollodorous, the great master-builder who built the Danu?~ Dridg~ and worked in Hadrian's time, must have had a great deal of influence on succeeding generations of architects. Pro copj:us of Caesa, On Building, English translation by H. B. Dewing with collaboration of Glanville Downey in seven volumes (Cambridge: 49 the transition more direct than that from Imperial Rome to the Middle 9 Ages. Later Roman development in concrete led to the perforation of 10 walls, resulting in the admission of greater light. This desire for height and the technical prerequisites necessary to pierce the structure to provide more lighting at clerestory levels, opened the way for the most daring and innovative concepts of early Christian 11 architecture in brick and masonry. •rhe functional advantage of brick-faced concrete introduced from Neronian times, was translated into bricks by Christian architects of the fourth century. Expres- sion of this new architectural austerity can be seen in the series Harvard University Press, 1954), IV, vi, p. 13. According t_o Tzetes (!'llegorial, -~liadiaE, V, 17}, Apollodorous wr.ote several ·teclmical works as well as a treatise on construction of engines for assaults. Isidorus, who de signed and built Haqj.a Sophia_, seerns to have been a professor of geometry or mechanics and wrote a conunentary on the los·t treaU.se, "On Vaulting," of Heron; while Anthemius also appears to have been a teacher and wrote treatises on mathematics and mechani cal devices. G. Downey, "Byzantine Architects: Their Training and Me·thods," B~_zantio~, XVIII (1948), pp. 99-118. 9 sie9fried Giedion, Arch.itec!ure_ an<'!_ the Phenomena of Transi .£.~011_:__ The ·~-~E~_c_:_ Space Co_nception in Architecture (Boston: Harvard University Press, 1971), p. 179. 10 rbid., p. 160. The outstanding feature in work of this period is that it points forward to the Middle Ages rather than back ward to antiquity in the formal symmetry of its layout and its avoid ance of fanciful spacial effects. J. B. Ward-Perkins, "The Italian Element in Ia.-te Roman and Early Medieval Architecture, 11 Proceeding~ ~!.the Brit:L;E_ Academy (November, 1947), pp. 170-172. 11 William MacDonald, "Some Implications of Later Roman Con struction, 11 Jc~rna~_ 9f the_ Society of llxchitec_!ural Hist:orians, Vol. XVII, No. 4 (Winter, 1958), p. 2. 50 12 o:f Imper1a. 1 Bat h s, be g1nn1.ng. . w1t . h Nero 1n . 62 A.D. The construction of the central hall of the -----Thermae of Diocletian (305 A.D.) with its cross-vaulted bays, ribs (glossary), massive angle piers and buttressing, resulted in a system of thrust and counter thrust which 13 had not been achieved previously. The Temple of Minerva (fourth century). in the Licinian Gardens (253-254 A.D.) was constructed of 14 light weight materials around a framework of brick ribs. The ribs were constructed of small bricks, laid upon one another in vertical bands linked together horizontally. The ribs rise together with the concrete envelope, resulting in a partitioning of the dome into independent compartments. The Licinian rotunda was a daring archi-· tectural feat. in that it solved for the first time, the problem of piercing a high drum with large windows, even though its vJalls were 15 five feet thick and strengthened by angle buttresses. Since the PC1_J]-theon, the stability of Roman vaults became a problem. 'I'he 12 verticality and the technical mastery required to pierce the drum so as to provide lighting at the clerestory level without impairing th.e stability of the dome was achieved in the Temple of Venus at Batne and the Baths of Caraca1la. Axel Boethius and J-:-B. Ward-l?erkins, ~:_!:E._~scan and Roman 1\rchi_!_::~~ture, Pelican History of l\r·t (Baltimore: Penguin Books, 1970), p. 513. 13 G. T. Rivoira, Roman ~rchitec~~yr~ and_ its Princ_~E_~es_ of Construct:_ion Un~_!_ _!:_he _:Empir~, translated by G. MeN. Rushforth (New York: Hacker Art Books, 1972), p. 207. 14 Compartmen·ta 1'1ze d or box r1bs. were f1rst. seen ln.. the caldarium or 1::he Thern:t~e of Agrippa, as rebuilt by Severns, to which the ruins in the ~i~ Dell 'Arco De~la Ciambella belong. Ibid., p. 128. 15 Ib1'd., p. 18'::>. 51 settlement and shrinkage of concrete produced cracks which needed constant repair. Buttressing was added from the time of the Flavians 16 to remedy t.hese structural defects. The use of brick ribs in the Temple of ~inerva Medica (see Figure 14) simplified construction and localized settlement_ while the concrete was drying out. The Basilica of Constantin~ (312 .A.D.) was an example of the technical virtuosity . 17 concrete achieved in the closing years of Pagan Rome. In the Circus of Romulus (310 A.D.) the raking vaults -vmre packed with inverted jars which saved time and money and were lighter to construct. v~alls were three feet thick and built with 18 ou·t buttressing . Such vaulting techniques used clay vessels set end-to-end, t.hus avoiding the need for outer scaffolding durinq construction. After the death of Maxentius (312 A.D.), there was a change in tbe use of concrete. While construction of public buildings continued in Constantine's time, the steady advance in concrete vaulted and domed structures ends. Post-Haxentian vaulted 16 Axel Boethius, Etruscan and Roman Architecture, p. 511. 17 The oblong hall is two hundred and seventy feet by two hundred and five feet, with a central span of over sevent.y feet, and is one hundred and twenty feet from t~he ground to the crown of the concrete vault (begun by Maxentius, finished by Constantine). A .. Minoprio, "A Rest.orat~ion of the Basilica of Constantine, Rome 1 " I:_apers _of_ .!:X'5': _!3ritish_ ~chool at Rome, Vol. XII (1932) 1 pp. 1-25. Perkins gives the dlinensions as 260 x 80, 115 feet from the floor to the crov.1fl. ~truscan and Ron~ Arc~itec!_~re 1 p. 503. Rivoira lists them as 270 x 205 (includes the nave and aisles) and 120 feet from floor to the crown. Rivoira, Roman_ A.rchitect.u:r·e, p. 213. 18 Iblc.,'1 p. 2 19 . Po·ttery jars were used in the haunches of the vault. 52 Figure 14 .. Late Pagan Archi·tecture in Rome, Temple of Minerva Medica, Licinian Gardens, Fourth Century, A.D.a a,, . . Boeth~.us, Et_E_2:!Scan and RoE_~~n ~chi tecture, Figure 194, p. ~)10. 53 buildings are constructed of brick and stone together in the facing {opus mixtum or opus list~tum (glossary)), with the wider mortar joints seen earlier in Republican times. Concrete gives way to brick as a structural material. The dome of S. Costanza (350 A.D.) incor- porated eight ribs of solid brick. By the sixth century stone aggregate has disappeared almost completely, and buildings cor:.sisted 19 of only brick and mortar. Concrete technology came to an end in the West soon thereafter, while the active centers of archit.ectural experiment moved to the East. Rome experienced a revival of classi- cal architecture in the fifth century, when S. Stefano Rotondo (468- 483 A.D.) was built. The sack of Rome in 410, the increasing weakness ·of the West and alienation from the East, forced the Papacy to 20 absorb Rome's cultural legacy. Much of concrete's success had been due to the Pax Romana. A system based on order and efficient. admin-· istration was necessary .for concrete construction. With the increase of barbarian invasions in the fifth and sixth centuries, little time and capital was left for repairs or building in the \>Jest. Homan fire-fighting, water-supply, and sewage-disposal systems decayed, and because of a lack of raw materials, Roman structures were pillaged for their metal, stone, and brick. An ample supply of labor ear·lier in Rome's hist.ory enabled builders to use a very dry 19 MacDonald, "Some Implications," p. 2. 20 Rlc. h arc." Kraut l 1enner,. Ear 1 y C }rr_~_"t:_lan . . and Byzan·t.lne. Arc h"l- tecture (Bali~imore: Penguin Books r 1965) I p. 65. 21 Il.,p.6.b"d 5 54 concrete mix and t.o compact it thoroughly. Therefore the shortage of labor, as well as the lack of timber necessary for formwork, may also have contributed to the increased use of brick in late Roman times. As masonry structures became more modest in size, they 22 reverted to more prJ.In1t1ve. . . met h o d s o f construct1on.. There was not just a break with the ancient building tradi- 23 tions, there was a shift in values as well. Replacing concrete with brick architecture was in part inspired by a new Christian aesthetic. There was a transition from the organically articulated wall, to one of greater simplication. The greater expanse of wall surfaces conveyed ideas of spatial unity at variance with the dif- . . . . l 24 ferent1ated surfaces 1n arclntecture seen prev1ous y. (See Figure 15.) Christian architecture began to develop within a frawework where practical needs were interwoven with ideological elements" The church became the image of heaven. Accordin9 to Plotinus, the 22 Henry J. Cowan, The ~1a ste_E_ Builder~. (New York: John Wiley & Sons, 1977), p. 96. MacDonald suggests that what changes is not the use of puz~~l~l~_, but the use of aggregate; that is, the change from pieces of s·tone to pieces of fired clay, and later to brick. The use of puzzolana_ was limited to central Italy, and "it is difficult to believe in it:s indispensability in later vaulted buildings because of the preservation and stability of so many provincial examples." MacDonald, "Some Implications," pp. 2-7. 23 Henr:L Focillon, The ~rt ~!_ th.e::_ West in !:.he Middle 1\ges, edited and in·troduced by. Jean Bony, translated by Donald King. Vol. I, "Romanesque Art" (London: Phaidon Publishers Inc., 1963), p. 18. 24 H. P. L I Orange, Art Porras ana'I C1v1c• • L1'f e 1n• t h e Late Roman Empir~ (Princeton: Princeton University Press~965),~~ 55 Figure 15. The Exterior Wall of the Imperial Basilica Trier, 310 A.D.a___ _ 56 1 25 body was beautiful only when it was illuminated by the sou_._. There was a turning inward in terms of values and thought; a turning away from the dialetical attitude toward the dogmatic. In the author's opinion, brick, rather than concrete was able to exemplify this new austerity better. In the struggle to keep the ancient building traditions alive, however, concrete survived as part of Rome's 26 legacy. The political, social, and artistic institutions of Merovingian, Visigoth, lombard, Anglo-Saxon peoples represented 27 conscious at-tempts to preserve the still living Roman traditions. In Ravenna (see Figure 16), the Mausoleum of Galla Placidia (440 A.D.) was erected with a cupola of bricks in which the extrados 28 cons1ste. d o f amp h orae set 1nto. a bed o f 1.1me mortar. St. Ma~y- at Ephesus (450 A.D.) was constructed of concrete masonry, anchored by 25 Plotinus (20S-·270 A.D.) the Neoplatonist, believed t.hat unification with God '-''aS not possible through thought, but attained only when the soul, in an ecstatic state, liberates itself from the physical restraints of the body. Plotinus, The Enneads_, translated by S. HacKenna (New York: Pantheon Books, 1957), p. 258. 26 • h h I • • • It lS t e aut or s bel1ef that wh1le concrete arch1tecture disappeared aft.er the sixth century, the ability to make a strong mortar continued in some areas throughout Europe and the East. In addition, while the knowledge of how to make this mortar declined, the presence of earlier Roman architecture was a reminder that a superior concrete consisting of puzzolana had existed in ancient times. It is my belief that a few ~en retained the knowledge that ruzzolana, or pm,.Uered brick, added to the lime mortar was necessary for making hydraulic concrete. 27 ] d. 1 "k. • H. Saa .man, Jvle ~eva ArC!lltecture, EuLopean Arch1tecture, 600-1200 (New York: George Braziller, 1962), p. 11. 28 G. 'r. Rivoira, Lombardic Architecture, Its Origin, Develop- t_n_e_n_t.:. ~~_n_d _12__er_~vatives, translated by G. HeN. Rushforth, Vol. I_I____ _ (London: \/Jilliam Heinemann, 1910), p. 28. 57 .. Figure 16. Mausoleum of Galla Placidia, Ravenna, 440 A.D.a aRivoira, _Ro~~~ !'rchitecture, p. 31, figure 41. 58 large vertical blocks and faced with alternating bands of bricks and 29 small stones. San Vitale (see Figure 17) in Ravenna (526-547 A.D.) was constructed entirely of brick. The walls, which have a thickness of three feet at their base, were formed of courses of large bricks separated by layers of mortar of varying thickness, and finished . 30 at t h e top b y a saw-toot h cornice. In Asia Minor, a_ substitute for puz~li:ma was found. Wit.hout. pu~_zolan~ the mortar lacked the strength needed for t.he creation of vaulting in the Roman manner. The vaults stood, not by the inherent strength of the mortar, but by the disposition of the material. Whereas in Roman architecture the structural stability of a vaulted building depended on the rigid monolithic quality of the concrete, in Byzantine buildings the entire inner surface of any vaul-t: was brick and it stood by virtue of the dynamic properties of the brick frame·· 31 wurk alone.. As a result, increasingly less concre·te building was done, and brick, rather than dressed stone or mor·tared rubble, was 32 used. By the time of Justinian (483-565 A.D.}, the art of concrete 29 K.rautheimer, Christian Architectur!:., p. 80. 3 0 RlVOJ_ra,. . Lom ba r d 1c . !trc h 1·tecture,. p. 58 . In a d d1t1on,- . . war d ·· Perkins asserts "there is nothing in San Vitale that could not equa.J.ly be explained as the culmination of a long tradition of concrete vaul·ted architecture, established first in Rome and later centered in Northern Italy." Ward-Perkins, Proceedings of :t;:he ~1.·itish Academy 1 p. 176. 31 J. B. Ward-Perkins, "The Archi·tecture of Rome and Constan tinople,'1 ~~ L~~ener, Vol. LVI, No. 1551 (November 8, 1956), p. 748. 32 . l . . . . Concrete, because of 1ts ack of elast1c1ty and lts stony nonfunctional nat.ure was gradually eliminated from F.oman building practice durin(J the fourth and fifth centuries. Its role was assumed 59 Figure 17. Ravenna, San Vitale, 526-547 A.D.a aRivoira, lDmbardic Architecture, p. 58, figure 83. 60 had been lost. or neglected, and the vaults of Hagia Soph_:!:<::. were of 33 brick and mortar. (See Figure 18.) Justinian's archi-tecture introduced a different language of constructional materials which featured vaulted shells of thin brick that were more flexible than earlier and able to cover wider areas. Generally they were composed of rubble cores faced with masonry and alternating bands of brick and 34 ashlar. Hagi~ _§ophia was both a culmination of the double-shell domical form seen at San Vitale, Ravenna, and secondly, it was a by a functional brick framework. This brick, combined with a concrete core con·tinued unbroken from late Republican Rome through the Imperial period, to the sixth century at Ravenna, where at St. Vi~ale it was used entirely in the Roman tradition. Emerson H. Swift, Roma12_ §9u:=-c~~ of Christian Art (New York: Columbia University Press, 1951), pp. 23, 71-72. 33 The master builder Anthemius and Isidorus made the plans for St. Sof>hia. The great piers were held together, not by lime, nor asphalt, but by lead poured into the interstices which flo\-7ed every· where in the spaces between the stones and hardened in the joints, binding them to each other. See Procopius, translated by H. B. Dewing, ~~J..ldings (Cambridge: Harvard University Press, 1954), I, i, 48-53. Host joints were of mortar, bu·t sheets of lead were substi tuted where it has been possible to inspect, at the springings of arches and vaults. See Rowland Jvlainstone, "'rhe Structure of the Church of _St:.. __So£1:::~.":.' Istanbul," Newcomen Soci~ty:rrans~cti_ons, V, 38,1965- 1966, p. 28. Specimens of the mortar analyzed by F. K. Norris have all been lime mortars to which were added various amounts of crushed brick. See W. Emerson and R. L. Van Nice, "Hagia Sophia_: The Col lapse of tb.':"! First. Dome and the Construction of t.he Second Dome and its Later Repairs," _?~}chae~~~2X..r 4., 1951, pp. 101-102. J4 Kr·au·theimer maintains that t.his rubbl.z; work las·ted from the fourth to t:he t:enth century. Krautheimer, Ea.E_~¥. S::.~EL::>!:_ _:i:_9-__r?_ !.::r:-chi_~- t~-<:~t=~~re_, p .. 258. 'falbot Rice maintains that rubblework was obsolete by the sixth cent.ury, and while seen occasionally in repairs later on, it was no longer a part: of everyday building practice. David 'I'a.ll:lOt Rice, ed., ~~~!~~- Gre_~~- !:~L:.::-~~ .£~.. the !'.Y::~~nti~ Emperors (Edinburgh: '!'he University Pre~;s, 19:'i8), p .. 77. 61 Figm~e 18. Constantinople, St. Sophia, 532-537 A.D.a aRivoira, Lombardic Architecture, p. 80. 62 transposition of Roman techniques v1hich included large-scale vaulting . . 35 in concrete with less massive brlck and mortar construct1on. The Romans carried their knowledge of the preparation of hydraulic mortars with them to the more remote parts of their empire. When the knowledge of mixing p_uzzolanas and preparing concrete was lost, ground t.iles and brick, already used in the provinces, contin- 36 ued. Excellent concrete was found in early Anglo-Saxon England. Faced wit.h fine plaster and mixed with red-pounded tile, it was 37 brought up to a fine polished surface. This work may have been due 35 In terms of the structural action of Hagia ~ophi~~ com- pleted dome, the difference between it and the Pantheon, was the later•s thickness up to ah"Jut half its height, giving it a shallow, stepped external profile. !lagi~- SoJ?hia_, on the other hand, was of uniform thickness and punctuated all round the base by windows. The substitution of bricks and mortar for t.he concrete of the Pantheon dome was unlikely, however, once the mortar had matured, to have made any difference in the characteristic strengths. See Rowland Hainstone, '"l'he Structure of the Church of St.. _ Sophia, Ist.anbul," ~_:::~ in part to the influenC.!e of St. Augustine (354-430 A.D.) who des 38 cribed the formulae for burning quicklime in The City of God. Later monks, such as St. Augustine of Canterbury (d607) were familiar wi·th that literature, and may have used St. Augus·tine' s method of mixing 39 lime when building the early churches in England. The v.10rk.ers for these churches were often imported masons from Gaul or Italy and were 40 trained in Italy. In Gaul, dressed stone and a version of Roman concrete, called "petit apparel" (glossary), continued to be used. This consisted of coursed and mortared rubble similar in composition and consistency to concrete of the late Republican period in Italy. "In a few districts deposits bearing some resemblance to ·the natural 12:-:zzolanas of the Bay of Naples were found. The use of Rhenish volcanic tuffs (glossary) was probably introduced at this time, and .1l this material, like puzzolana._, is still employed at the present day."-- Bede (673-·"/35 A.D.) recalled tha·t at the beginning of the fifth centu:cy Britons had to send for help to Rome in order to 38 st:.. Augustine, The City ~-!_Go~ Against the Pag<_::ns, trans lated by William \v. Green (Cambridge: Harvard Universit.y Press, 1972), p. 19. 39 St ..August.ine of Canterbury was the founder of the Christ.ian church in SouLhe:::.n England, and the first archbishop of Canterbury. He was a monl;: in t.he monastery of St. Andrew in Rome when Gregory I chose him to be the leader of a mission to England. He arrived in 'l'hanet with his monks early in S97 A.D. See F. Jvl. Stenton, Anglo :saxon EnglO.:.l!.~ (Oxford: at the Clarendon Press, 1967), p. 110. The plans of his churches, surviving only in fragments, are derived from It.aly and show a technical skill in the use of Roman brick which proves they are the w·:>.rk of Italian influences. Ibid., p. 111. 40 E. A. Fisher, An Introductio~ !_~ Anc;Jlo-Saxon Architecture 0nd: _s._~ulp1;:ure (London: Faber & Faber, 1959), p. 24. 41 Lea, .S:'E.~~:. st:r.· y, p. 4 . 64 construct their buildings. "Even so, the islanders raised the .~to~~ne Wal~, not of stone, having no artist capable of such work, 42 but of sods [glossary]." Good cutting tools were unavailable, therefore grit (glossary), which could be carved with sticks, was used by pre-Norman masons for cutting limestone. As a result of t.he general decline in skill, much Medieval stone work was bonded with mortars which were in a dangerously powdery condition. Lime or quicklime is a more or less impure oxide of calcium obtained by burning limestone, chalk, shells, coral, or any other substance composed of calcium carbonate (glossary) . When water is added, it slakes, i.e., it. absorbs the water with effervescence, srLving out heat and tumbles to a fine powder. Pure slaked lime I known as rich lime, has very little strength. Much of the mortar 43 made in Medieval times consisted of this mixture. It was water sol.nble and hence easily washed out by water. Roman cemen·t, on the other hand, owed its strength and permanence to a low water--cement 42 Ch ar_es1 SJ.nger, . Th e Me d.1terr_anean C1vl_~at1ons,. '1. . p. 3 2 . Bede also relates that St. Benedict of Wearmouth crossed into Gaul in 680 A.D. and brought back masons to build a church. Th~- Ve11erable _!?edes Ec:._<;.!_.::~t::~.? stical _!Iis·tory o~ Eng~_?nd, edited by J. A. Giles (London: Henry G. Bohn, 1849), p. 202. 43 G. A. T. 1'-iiddleton, Bu_ilding_ Mater_:!:_als {London: B. T. Bats- ford, 1905), pp, 105·-108. There is much evidence that many buildings were constructed by masons who used such bubbling hot lime. "The groins and principle ribs are of Chilmark stone; but the shell, or vaulting is laid with a coat of mortar and rubble of a consistance which was probably ground together and poured on bot, by this the \vhole is so cemented together, as to become all of one entire sub stance." Francis Price, !2_ Description_ of_ that AdmiE._9-~le Structure, the Cathedra~- of_ _§alisb~~.Z. {London: printed for R. Baldwin, 1774), p, 4. 65 ratio. Much poured Roman concrete contained tufa, selce (glossary), 44 and other rocks of volcanic origin which absorb water. Vicat, in the nineteenth century, observed that often very good mortars were 45 found in foundations and massive walls of Medieval structures. Vicat indicates that the lime used for these mortars was distinguished by the particles of lime not mixed with the sand. He continued to explain that~ We have generally found it to be either r:i_ch, or very feebly ·hydraulic.46 It results from this, that after a maceration of six or seven-hundred years, favoured by the constant humidity of the soil under which they are buried, the mortars of rich lime at last harden.47 Many Medieval foundations were defective due to the mortar used, 48 unlike surviving buildings of ancient Rome, Greece, and Egypt. Winchester ~~!E~dral (1093), the longest of the Medieval cathedrals in England (556 feet), has massive walls eighty feet high. The 44'cowan, Master Builders, p. 56. 45 t . 1 d . f . . 1 r... ,J... v.1ca'c, I:~ Prac 1ca__ an Sc1en t.1 1c Treat1se o~ Ca __ ·- careou~ Mor_!:~~ ~nd_ C~~ents !lrtificial and Natural, translated by J. T •. Smith (Loadon: John Vveale, 1837), p. 209. 46 Feeble (glossary) . 48 In the building account of an octagonal .!_~_!.err~. of -~ly, under the direction of Alan of VVakingham, workmen were directed ·to dig until they found solid ground for a foundation for the eight pillars needed. This was dug out and firmly founded with stones and sand, and where such firm ground was not available, the soil was reinforced with wooden piles, such as beech, granted to the Friars of Winchester for the foundation of their church in 1239. L. F. Salzman, Eng}:._j.:..sh Industr~_es of the Jvliddl~ Ages (Oxford: at t~he Clarendon Press, 1923), pp. 122-123. 66 foundat.ions, however, were only ten feet below ground level and con- 49 sisted of whole beech logs overlaid by a weak concrete. (See Figure 19.) ~iens Cathedral (1220-1270) had a bed of artificially compacted clay about fifteen inches thick, a bed of concrete, also fifteen inches thick; fourteen courses of medium quality stone, and three more courses of hard sandstone. This foundation was surrounded 50 by large blocks of rubble. (See Figure 20.) Perhaps the earliest description of the preparation of a foundation by the Anglo-Saxons is that of the Monastery of Croyland 51 in Lincolnshire, begun in the early eighth cent.ury. The walls of Aldboroug_l;_ ~hurch, Yorkshire, the tower of Earls Bc:!ton Church, and that of St. Peter's Church at Barton upon Humber, Lincolnshire, are of Anglo-Saxon construction and o:re composed of round pebble stones united by mortar, while others consist of rubble stone and flints vJGl l -groute. d ... 52 Sir Christopher Wren, when excavating for St. Paul's _s::_athedral (1675-1710), discovered building remains which had previously occupied the site. These remains were originally 49 There was no significan·t enlargement of the width to spread the load of the walls. The subsoil contained a thick layer of peat. Surprisingly, ·these foundations gave little trouble until 1905. Sir Francis Fox, consulting engineer, was engaged to rectify the condi 'cion, and in 1906 he excavc.ted the foundation in order to replace it ~Jith one of concrete. The inflow of \1uter vli.lS so great that it was necessary to employ a diver. Cowan, !:i~ster_ Builders, p. 110. 50 ·I:L.,p b" d ...110 51 George Godwin, "Prize Essay upon the Nature and Properties of Concre·te, and its Application to Construction up to t.he Present Period," The Builde.E_ (January, 1836), pp. 7-9. 52Ib'.l d •r p. a-'• 67 GRAVES I Figure 19. Medieval Timber Structures: Winchester Cathedral, 1093 A.D.a aCowan, ~'laster Bui1de~, p. 113, £igure 5.12. 68 Figure 20. Viollet-le-Duc' s Drawing of the Fill in the Lower Portion of the Vaulting Conoid, Amien's Cathedral (Notre Dame, 1220-1270)a 69 constructed upon the foundation of the old. Anglo-Saxon building \'lhich preceded it. 'l'his foundation was composed of a mass of Kentish 53 rubble stone cemented with extremely hard mortar. The purchases of lime and sand are among the commonest entries in building accounts in England during .this time. In an account of a Winchester Castle of 1258 (see Fi911re 21), an entry reads, "for 54 the purchase of 30 sesters of lime, 20s, at 8d. a sester." While the actual making of the mortar was unskilled, the burning of the lime was comparatively skilled >-JOrk, entailing night operations, 55 since the furnaces had to be kept burning. Burning chalk or li1ne- stone to produce quicklime was one of the processes essential to Medieval building. With the exception of piaster of Paris, there \vas 53 -As ..hl ax_· \vas very se ldom used 111.. t h e 1nter1ors . . o f v.Ja ] ..l s, and in all the Romanesque and in most Gothic churches the core of the walls consisted of local rubble. Ashlar was expensive due to tbe cost of transporta.tion and was used principally for facings. Where good building stone was available close .by, masonry would be well con structed. In many cases there is no·thing left of a Norman wall by -..vay of support but the thin external and internal facings of ashlar owing to the use of inferior mortar. Ail cohesive power disappeared in the thick core of the wall. If a block was extracted, "the inside wall will often run out like the savx:lust from a doll." Francis Bond, An Introductior~. !~ Early Church Arc.hi·tecture, From the Eleventh to the Sixteent.h Century, Vol. I (London: Oxford University Press, 1913), p. 419. Viollet-le-Duc complained that from an examination of Frenc;::h buildings in the ninth, t.ent:h, and eleventh centud_es, it was clear t.hat the art of making good mortar was almost completely lost. E. E. Vio.llet-le-Duc, Dictiormaire Raisonne deL' Architecture Frans:_aise (Paris: B. Bance, editeur, 1859), Vol. 4, pp. l-17. 54 H. H. Colvin, ed., Building Account.s of King Henry III (Oxford: c-J.Jc ·the Clarendon Press, 19"71~---p. lS-9-.-. -- 55E. F. Salzman, Building inEr~gland, Down to l54C?_, ~.!2ocu mentary !-IiS"!:_C?_!Y {Oxford: at the Clarendon Press, 1952), p. 153. '70 FIGURE 34'J-Scaffoldingfor a stone buiiding. The poles are ]a.llmi tugether at the dingonals with toumiqueiS lo tighten the binding. The masur-mason greets a party ofdignitt1fies led by Charlemagne. Stones are squared 1:rith mallet aurl chisel. Water for tlze mortf!r comes from a nen>ly dug wdl'(thc village pump was adoptedfrottl a type only then being developed for miue-drainage, see figure 11). Note the stone-layer's trotvel. From a French marmscript, 146a. Figure 21. Scaffolding for a Stone Building (about 1460)a a Charles Joseph Singer, The !:J_istory of_ ~~'?J:':!1ology (Oxford: at the Clarendon Press, 1954-1958) , p. 3H6. 71 no other available matrix for making mortar. Limehouses were the 56 equivalent to the modern cement business. These "limeoasts" or kilns had been the main center of supply since the fourteenth 57 century. From the twelfth century onward, the quality of lime making . 58 . 1mproved. The foundation upon wh1ch the north transept of Wes·t- 59 minster l\bbey is built, dating from 1245, is composed of flin·ts, 60 irregular stones, rubble and mortar. In England, the quality of Norman stone masonry is generally better than Anglo-Saxon and in the twelfth century, there was further improvement. 56 . ·In 1949, a c1rcular stone s·tructure was uncovered at. Ogmore _Castle, Glamorgan (see Figure 22). It was a Medieval limekiln. The abundant supply of limestone and coal close at hand, combined with its position near the river, made it a convenient place from which to ship lime to other places on the ~'Velsh coast. The Ogmore example was typical for limekilns in the thirteenth and fourteenth centuries. The limekiln continued to be used to the end of the sixteeni:h cen tury. 0. E. Craster, "A I'iedieval Limekiln at Ogmore Castle, Gla morgan," !U'chaeologia Cambrensis, Vol. 101 (1951), pp. 72-67. 57 John Harvey, _The Medieval Craftsmen (New York: Drake Publishers, Inc., 1975), pp. 113-114. 58 Abelard (1079-1142) reprimanded a group of masons for not building wii::h the proper cement. "When, therefore, he returned and found the walls bound not with cement but with slime [glossary] , and thus not only defiled but weakened, then he rebuked the Brethren and soon bJ:-ought the v-x:>rk back to its first model in matter and in form." See G. G. Coulton, A Medi~;!al Gar12..er, Human pocuments from the ~our S::~nt.ur~~-~- Pr~e<2ing !~~Reformation (London: Constable & Co., 1910), p. 88. 59 "The walls were usually faced with ashlar and filled wit.h rubble, flints, lompstones, broken tiles, and mortar." W. R. Lethaby, 1\Testminster Abbey, The Kings' Craftsmen, A Study of Medieval Building (New York: BenTa:-min Blom, Inc., 1971), p-:- 365. ~------ 60 , .. . 1 • ld 9 10 (,ooci vnn, ~-':2.<::.. B~~- er, pp. - . 72 Fig. 1. Figure 22. Ogmore Ca.stle Showing Lime Kiln, Court House and Moata aO. E. Craster, .Archaeologia _Cambrensis . , p. 7 3, figure l. 73 At Wallingford in 1365, tar is mentioned in conjunction with burning lime. When repairs were made to Pevensey Castle in 1288, old mortar wa.s reused from one structure to another, either by re-burning . d . . . . 61 or by poun d lng an mlxlng lt agaln. The expression "mortar earth" (morJcarherthe) is seen in written accounts in 1367 relating to repairs t.o a _!::odge of Beaumont in the Forest of Rutland. When lime 62 was not available, ordinary soil was used • Where masonry was exposed to water, a mixture of wax {glossary), pitch (glossary) or resin (glossary) was applied in a molten condition to the structure. 'rhe earliest account of the use of these ingredients was in 1258, when nineteen pounds of pitch and five pounds of wax and charcoal were 63 used at the King's Court at Westminster. In 1340 repairs to ~es·t- ~inster Palace included sixty pounds of pitch for cement sy!nen·t~- and ten flemish tiles for making dust. The addition of tiles would have greatly increased the strength of the mortar. Eggs (glossary) as well were added to cement mixtures. These various "recipes" accounted for the discrepancies in quality of rubble fill during this time. If the limestone contained more clay (silica·tes of alumina) then the limes became hydraulic. 1'-ledieval builders did not understand why some soils 64 and st:ones seemed to produce better results than others. ------~----- 61 salzman, ~uilding in England, pp. 151-152. (,2 . Ibld., p. 152. 63 I b"dJ. .• 64_, !!or a discussion of the published writings concerning lime and concrete, see Part III. 74 In early Medieval construction walls were very thick. In later Gothic architect.ure, buttresses consisted of cores of rubble in lime mortar, resembling Roman opus caementi tum, and stone masonry was usually superbly finished on the exterior. The rubble core, however, was probably laid in the modern manner, i.e., the mortar was placed in layers with the stones on top, not cast over the s·t.ones. While Medieval lime mortar ~us weak in comparison with Roman cement mortar, the strength of the wall depended more on the dressed stone 65 outside than on the rubble core. In 1215 Villard de Honnecourt' s notebook suggests: 'I'ake lime and pounded pagan tile in equal quantities unt.il its color predominates; moisten this with oil and with it you can make a tank hold water.66 After the fourteenth century mortar of excellent quality was to be found throughout Europe. The lime was well burned, well sift.ed., and the precau·tion taken of washing the sand free from adhering dirt. 67 or clay. In the seventeenth century documents refer to "tarrice" or "tarras" (glossary) indicating that the use of puzzolanas in 65 Cowan, The !4a ster Builde:r:_~, p. 12 2 . · 66 "on prent kaus (e·t) tyeule mulue de paiens, (et) feres kume, autrei:.ant de L'tme cu(m) de L'autre, (et) un poi pJus del tyeule de paiens taunt come ses color vainke les autres; destemprez ce ciment d' oile de lirmse: s' en poez fa ire un vassel pur euge tenir. " See Hans R. Hahnloser, Villard De Honnecou.rt, ~.:!:!:j.sche Gesamtausgabe des Bauhut:t<:mbuches (Austria: Akademische Druck, 1972), p. 129. 67 Lea, Cement, p. 4. 75 68 mortar must have been established by then in England. Imported puzzolana~ {Dutch tarras 1 trass, or terras) and lime mixtures were used. The usual mixtures for VIOrks exposed to the action of water was a composition of one volume of trass to tVIO volumes of slaked lime. The tarras were dug at Andernach 1 Bockenheim, and Frankfurt-on- }lain in Germany and transported down the Rhine to Holland wher€ t:fley tvere ground for mixing with lime mortars. In Holland the material wa.s mixed with a. hydraulic lime (blue argillaceous lime {glossary)) 1 made on the ban~s of t:he River Scheldt. The cement produced was the famous "t.arras mortar" used in Holland for the construction of sea 69 defences and for aquatic work. During the Medieval period the VIOrd "cemen!:." began to appear in writt.en documents. Beginning in 1300, Alisaunder King w-rote, "A ,,70 1 clay so strong so yren, ston, or syment. · In 320 Seuyn Sag 71 wrote, "the fir falsed the sement, and the stone." In ·the De "Lyme . is a 68 Ibid. 1 p. 4. Additional information may be obtained in J. c. Rogers, Transactions_ of §."!:-_:_ ~E_~ns and Hert~~_rdshire Architec !::~?.:ral_ and l-\t~chaeological Soc~et.x_, 70, 99 (1933), which the author was unable to obtain. 69 ·Davey, :r;uilding_ ~1-~!:_~_i.als, p. 103. 70 o.. dord English pj_ctionary, eds. James A. H. Murray et al., Vol. II (Oxford: at the Clarendon Press, 1970), p. 216. The word cement, cementum or cyment (syrr.ent} exist:ed in Saxon times, and was later used for special moJ:·tars which contained substances other than lime and sand. Wax, pit.ch, resin, eggs 1 et:.c. 1 were all used according to diffex-ent. fo:nnulaes, and povrlered tile, purchased in 1333, for making "cyment" was used for S-t:..:_ Stephens ~hape~. See Harvey, Crafts-· me~_, p. 114. 71 _Cr,..-forc1_ !-!.1:9...:"!:~~_!:!- !2Jctionary_~ p. 216, 76 stan brente; by medlynge per off with sonde and wa·ter .sement is 72 made." The word mortar was used as early as 1290 in written 73 documents. Developments in building which would influence the subsequent 74 history of concrete took place in Northern Europe. Gothic met.hods of construction provided the inspiration for iron skeleton and reinforced concrete of the late nineteenth and early twentieth cen- 75 turies. Supporting piers were reduced to extreme slenderness and vaults raised to greater heights as light assumed new importance. Gothic methods of construct:ion evolved a system of thin-shelled vaults (glossary). Like modern thin shells whose curvature is the source of their stiffness, Gothic vaults act like a stiff crust in v1hich the curvature of the surface accounts for t_he rigidity and s·tability of its shape. It is the cohesion of ·the mortar, after its final set, which makes the shell act as a whole, without voussoir action. Curvature, rather than thickness, accounts 72 I1n"d . ' P. 216 . (English translation by John 'l'revisa, 1397.) 73 A .. Ch 01sey,• .!:o__Ar_!_I -~d Batl£_~ • Cnez' ~1 Roma1ns,• No. 1 ( Pan.s:• Duchere, 1873j, p. 2. According to the Oxford Dictionary, the word cono:ete, meaning "a composition of stone chippings, sand, gravel, pebble;s, etc., formed into a mass with cement or lime," was not employed until 1834. OXford ~ng_}.ish Dictionary, Vol. II, p. 776. c/4 ·rn the South, small-stone rubble construction contrasted with the timber-framed structures of the richly forested North. As the shift in influence from the Hediterranean ·to the North occurred (after 476 A.D.) so did the basic change to vvood become apparent. The ability of wood ·to carry huge compressive loads on high slender: up rights was an architectural tradition more familiar to the Goths than \vas stOIH~. Walter Horn, The Barns_ of A~bey of Beaulieu at its Gra_pges of ~rea-t:_ Coxwe~.l:.. a~C!- _Beal!-_lieu, St._ LeonaJ~d (Los Angeles: University of California Press, 1965), p. l. 75 Giedion, _§pac~_, rrime and Archit.ecture, p. 255. 77 I • 'd • 76 f or t h e s h e~ll s r1g1 1ty. In spite of the fact that Medieval mortar was weak and slow setting and contributed little to the strength of shell during its construction, so long as the arc of the structure was maintained throughout, the structure was stiff enough to span a consider: able distance and strong enough to support a large load. Bore than minimum thickness was a detriment rather than an assurance of 77 any additional margin of safety. "Domes built by the Romans were limited in shape since these structures could only resist very small tensile stresses and had to be subjected essentially to compres- . 78 . Slon." The Roman system of vault cohesion cons1sted of a thick mass of rubble concrete, brick reinforced, with an overlay of addi- tional concrete and contained small spans in relation to thickness. This single unit of strength depended on the complete rigidity of the whole. With Gothic vaults, once the mortar in the joints had set, "the flat layers created an impervious dam which prevent.ed the liquicl ingredients of the subsequent concrete from leaking out. 'l'hus ·the function of .holding the liquid concrete in place until it had set 76 Jolm Fitchen, The Construction of Got~.::_ Cathedrals, ~ .Study of Medieva!_ Vaul!_ Erect.ion (Oxford: at the Clarendon Press, 1961) 1 P• 65. 77 "'I'he ambient stress in the she.ll is so low ·that the strength of the masonry is again irrelevant. The weakness of tufa, as at Canterbury, is of no consequence." At intersections or where curva tu.re is changed, reinforcement is necessary, and often concrete was used i.n the conoid-shaped section aJ.xJVe the pillars. Jacques Heyman, "0::1 the Rubber Vaults of the Middle Ages, and Other Matters," Gazette Qes Beau~~rts, Tome, LXXI (May 22, 1968), pp. 177-188. 78 . tv1ar1o G. Salvador, "Thin Shells," Architectural Engineering, Vol. 116, No. 1 (July 1954), pp. 174-179. 78 was taken over by the finished vault, rather than by planking of the 79 false,.oJOrk." Second, the brickwork created a st.iff shell which substituted for the supporting function of the planking. The survival of the dome of Hagia _Sophia from the sixth century, and of numerous thin Gothic vaults from the twelfth century onwards, indicates that 80 the masonry shell is a particularly stable form of structure. 'I'he Romans did not exploit this system, for they were interested in 81 masslveness,. not 1'lg h tness Ol.c cons t ·ructlon. . · The half-cylinder form of Pier Nervi's corrugated shells in the twentieth century stem from 82 the same evolutionary line which began with Gothic ribbed vaults. This progressive development of Medieval vaulting was working ·toward S3 a structural system which focused forces instead of dispersing them. The association of concrete with Roman massiveness did not allow for 79Fltcnen, . ' Cathedrals, p. 66. 80 Jacques Heyman, "On Shell Solutions for Masonry Domes," International ,Journal of Solids and St~esses, VoL 3, No. 2 (March 1967), pp. 229-230. 81 Greater thickness does not reduce the tensile stress to be resisted for ideal dome action. This is because, for a proportionate increase in thickness, the weight, and thus the total hoop tension, is increased to t:he same extent as the cross-sectional area available to resist the tension. Rowland Mainstone, Developments in Structural Form (London: Allen Lane, 1975), p. 118. 82 Pler. Nervl, . Structures, trans1 ated b y G. an d M. Sa l va d orl . (New York: F. W. Dodge, 1956), p. 15. 83 "G0thic architecture replaced the equilibrium of heavy masses with the equilibrium of forces created by the interplay of thrust and counter thrust of slender ribs buil·t with good materials." Pier Luigi Nervi, Aesthet.ic s and Techn::>logy i:~ Building, The Charles Eliot Norton Lectures, 1961-1962, translated by Robert Einaudi (Cambridge: Harvard University Press, 1965), p. 5. 79 beh d :ynanusm. or movement o:t- t h e Got h'1c. 84 Just as Roman concrete had liberated architecture from the restraints of traditional classical styles, so did the limitations of brick vaulting impose fresh res- traints on its builders. While the distribution of stress (glossary) in the Near East was on massive piers, in the West it was focused on the successful shaping of arches, vaults and ribs to a redis·tribution of these same forces. The use of brick relieving arches and concrete in the Roman Pantheon, deliberately concealed its structural system by using elaborate devices for distributing the weight of the dome wit.hin the walls of the drum. In Medieval times, architecture became a more logical and candid expression of structural facts. As Gothic architects pared down the size of their structural members 85 to achieve skeletal form, concrete generally disappeared. As masons became more confident of their thin shells, the art of utilizing 86 concrete all but vanished. The English continued to experiment with the vaulted form which subsequently became highly decorative. The influence of the English vault spread throughout Europe in the fourteenth century. 84 G ied ion, -~pace, Ti~~ ~~d Arc~i tecture, p. 17 2. gr.: -'wa)~d-Perkins, The Listener, p. 748. The thick Roman walls of the South were transmit·tedNorth-by christian monasteries in the eleventh cen·tury. This Romanesque style features a massive barrel vault of rubble and mortar, some eighteen inches thick. Gothic masons on the otb8r hand, evolved a stone fabric no more than four inches thick, formed into folding curving survaces that connected the ribs . .J. H. Acland, "Architectural,Vaulting," Sci::_~~!_ific::_~erica, Vol. 205, No. 5 (November, 1961), pp. 144-154~ 86 , F.l.i:.chcn, CatrJedrals, p. 220. 80 At length there came a complete turning away from the framing system of rib and panel. In the late fifteenth century, Arnold of West- phalia devised a new "crystalline," or cellular, vaulting system of f o ld e d p 1 anes wlt. h out rl'b s. 87 (See Figure 23.) In the first half of the sixteen·th century the style sp-read from Saxony into Poland and what are now the Baltic States and Czechoslovakia. Built of brick shells and covered with dead-white plaster, these vaults rival in teclmical virtuosity the most advanced ferro-concrete work of the twentieth century. While building in the Hiddle Ages was unscien- tific, and no exact rules of mechanics and statics were applied to the disciplines of construction, t!1ere was a progressive development 88 in theoretical stress analysis. Principles of vaulting resulted in important ·technical solutions di.st.inc-tly applicable to t.he unique character of reinforced concrete. Before the structural concepts of Gothic vaults could, however, be trans}.ated into the ferro-concrete shell architecture of the twentieth century, the scientific laws 87 Curvature of the fan vaults changes smoothly and the ribs are purely decorative. However, if t.he shell is given additional loads (tensile forces are not admissible in an unreinforced masonry shell) the hoop forces (glossary) become compressive throughout and a !as-d~_-charge (glossary) is needed to provide stability for the shell. Mainstone, For~, p. 130. 88 Acland, "Vaulting," Sci~'mtific_ Ame1.:ica, pp. 151-153. 81 Figure 23. Cellular "Crystalline" Vaultsa · aJ. Acland, Scientific America_, Vol. 205, "Architectural Vaulting," No. 5 (November 1961), p. 147. 82 that apply to statics and the strength of materials had to be 89 understood. ------89There is no evidence to support the contention that the Gothic master builders had secret knowledge of statics, now lost. The knowledge of mechanics at their disposal was less than that of ancient Greece when the :rarthenon was built, ancient Rome when the Pan-t:heon was built, or of Byzantium when Hagia_ Sophia was built. It may also be that the rules, if they did exist, were regarded as ars (craftsmanship) and not as scientia {theory) and therefore unworthy of a wTitten record. Perhaps t.he masters preferred not to commit them to parchment or mention them in discussion of de~ign. Another possible explanation is ·that the master mason was sworn to secrecy by his lodge. He may have been given these rules when he became a master and was not permit.ted to divulge them except to a new master at a special ceremony. Rosenberg states that the Bishop of Utrecht in Holland was k_illed by a master mason in 1099 because the bishop had induced the mason's son to divulge ·the method of laying out the foundation of a church. C. Rosenbe:r:g, "The Functional Aspect of .t.he Go1:hic Style," ~Journal o~. th~ Royal Ir!.:~itut~ ~!British Arcl1i!:_o::_cts, Vol. 43 (1936}, pp. 273-290. The opinion that a proper structural analysis was carried out for certain Gothic and perhaps Byzantine vaults was also noted by Professor A. Hertwig ( "Geschichte der Gewolbe," Tecru1ikgeschicllte, Vol. 23, 1934, p. 86.) See Hans Straub, !2 History o~-!-::.:fv-il Engineering, translated by Erwin Rockwell (Cam bridge: the M.I.T. Press, 1964), p. 41. Chapter III THE REVIVAL OF CONCRETE IN EUROPEAN ARCHITECTURE The gradual penetration of an experimental, more scientific method of thinking in the area of construction, amenable to measure- ment and calculation, began in the late Middle Ages, and continued 1 throughout t.he Renaissance . This interest in experimentation, conducted in diverse fields such as statics, architecture, and mineralogy led to a greater scientific understanding of cement and concrete in the eighteenth century. \'Vith the changes in attitude and the rise of experirnent.al sciences, the structure of classical 2 aesthe-tics was altered. The Medieval philosophy of harmonic structure to the universe and the comprehension of God through mathe- matical symools acquired new expression in the Renaissance. The 1 'l'he links between technical activity and scientific preoccu pations, which, in certain periods, notably those of Archimedes and the School of Alexandria, was never cmnpletely lost. Bertrand Gille, Enc:r_inee~ ~:f._ :t;_he Renaissance_ (Cambridge: M.I.T. Press, 1966), p. 32. The quantificz1t.ion or mathematiciz.ation which took place in the six teenth and seventeenth century under the influence of the introduction of the mathematics of Archimedes and its use by Galileo, was in part a product of the initial investigations undertaken at the University of Oxford and Paris in the fourteenth century. Richard Swineshead, "Late Medieval Physics," Osiris, Vol. IX (1950), p. 131. Randall also believes that it is a mistake to accept history's estimate of the pioneer thinkers of the sixteenth and seventeenth cent.uries without realizing their many predecessors in the late Middle Ages. J. H. Randall, Jr., The School_?f ~adna, and !:he -~er_9ence of Hodern .~£ie~ (Padova: Edit.rice Antenore, 1961), p. 18. 2Rudo1f Nittkower, Architecti!::r-al Principles ~~ the Age of_ [-Tu~~ni.sm (New York: Random House, 1%2), p. 153. H3 84 essence of the old theories which made Medieval architecture practi- cal, aesthetically satisfying and scientifically sound, were not feasible in a changing architecture which developed new spacial 3 rep~esentation. Neither a science of statics developed over centu- ries and based on convictions regarding the importance of geometrical proportions for structural stability, nor the tradition of masons' procedures, could be discarded as long as ne\>l humanist concepts had . . . . 4 h given a new dlrectJ.on, but not a new scJ.ence,. to arch1tecture. T ere had been a close theoretical interconnection of structural form and structural stability in Medieval architecture, but the structural 5 strength of round arches constituted a problem in Renaissance 6 architecture, not applicable to the scientia geometria of the past. 3 Howard Saalman, "Early Renaissance Architectural Theory and Practice in Antonio Filarete's Trattato di Architettura," Art ~~_let in, Vol. XVI (March, 1959) , p. 101. 4 Ib1'd.. 5 Filarete argued, "You may say that the pointed arches are also strong and sufficient. That is b:ue. But as long as you make the round arc he, i.e., the half round with good shoulders, it also is strong." Saalman, Art Bu~letin, p. 91. 6 sc~~n_tia ~eometri~ acquired its structural authority before Archimedes. The classical statement of that concept is found in Plato • s •ri~~~~l~_· Here, microcosm and macrocosm are visualized in terms of the 9eomei:rj.c perfection o.f the five regular polyhedra and the sphere and the cognate symmetries of the simple "musical" propor tions. See Rev. R. G. Bury, Plato ~nth an English translation, Book VII, Timaeu~ (Cambridge: Harvard University Press, 1961), pp. 61-69. Evidence of the theory continued in discussions by Filarete, Francesco di Giorgio, Serlio, Philibert de L'Onne, and Roriczer. Rowland l'-1ainsJcone, "Structure and Design Before 1742," Architectural B_ev~~V-1, Vol. XLIII, No. 354, April 1968, p. 303. The overall character of ·the Gothic cathedral wa.s determined on the basis of geometrical grids of lines and dots in \vhich the specific problems of form and structure played little part, however the actual elements 85 (See Figures 24 and 25.) The science of statics which had developed oYer the centuries based on convictions rega.rding the importance of fixed geometrical proportions for structural stability could not be discarded as long as there was no new scientific rules for Renaissance architecture. Early Renaissance architecture marks the beginning of an architecture in crisis, from the standpoint of a coherent struc- 7 tural and aesthetic theory. It only began to be resolved when the eighteenth century gave science to the scientist and art to the . 8 artJ.st. The introduction of the theory of statics and of the strength of materials into building science created a transition from craft 9 to art in t:he sphere of engineering construction. It brought about stat.ical conditions identical with the artistic appreciation of t:he structure. The mechanics of the Renaissance was not, however, the "scientific mechanics" of the modern .,.;orld. Neither the Medieval nor the Renaissance periods lacked the ingenuity or the mechanical skill for mode.rn teclmical achievement, as documented by the array . 10 . . . of amazing contl~J.vances produced. However, J.t was the J.nterest J.n of the cathedral took shape by virtue of a compromise of ideal for mulae and practical know-how. See James Ackerman, "Gothic Theory of Archi·tecture at the Cathedral of Hilan," Art B~lletin, Vol. XXXI, No. 2 (June, 1949), pp. 88-107. 7.Saalman, Jtr"t. Bulletin, p. 102. 8 . IbJ.d. 9 Hans Strau.b , A Hlstory . ~f C:t.'?.:_~_. '1 ~!_1_9.,~neer:t.ng,. . . t rans1 ate d b y Erwin Rockwell (Cambridge: M. I.T. Press, 1964), p. xvi. 10 Herbert Butterfield, The Origins of Modern science, 1300- 18 00 (New York: The Free Press, 1968) • p. 103. 86 Top left, project of 1391. Top right, 1392, bottom left, 1392. Figure 24. Proposals for the Cross Section of Milan Cathedrala a Mainstone, Architectural R~~~ew, p. 303. 87 Figure 25. Francesco di Giorgio, Elevation of an Ideal Churcha 88 mechanical invention that distinguished the mature Renaissance from . . . d 11 t h e earl1er Med1eval per1o . The confrontation of empiricism already present in the West in the practical arts with the rational explanation contained in recently translated Greek and Arabic t.exts 12 opened a door that would lead to the seventeenth century. Important to the later science of statics was Aristotle's Mechanics and Archimedes' Equilibrium of Planes. Aristotle discussed the movement of weights and introduced the germ of virtual \\'Ork (glossary) and mechanical study. Archimedes de:tailed the· concept of the center of gravity and furnished t:he means for calculating its position. Later Hellenistic writers, such as Hero of Alexandria, developed these ideas. These were passed on in turn with the Isla.J.-nic conquest of the seventh centuries into Arabic scientific thought and subsequently became known in the West through Spain and Sicily in 13 the twelfth and thirteenth centuries. Apart from these early beginnings in ancient times, the science of statics, as a branch of 11 Barclay Parsons, Engineers and Engi:,neering in the Renais- sance (Cambridge: M.I.T. Press, 1967) 1 p. 105. During the twelfth century, Ailnoth is frequently mentioned as a military architect or "inqeni.at.or." E. F. Salzman, English Industries of_ the Middle Ages {Oxford: at t:he Clarendon Press, 1923), p. 108. The term "engineer" had h2en applied in Italy, France, and England to the builders of war machines and fortifications. The word may have originated in the fact that the technical aids of warfare and defense used to be known as "Ingenia." Straub, A History of Civil Engineering, p. 118. 12 b" d h .. A. C. Crom 1e, R~bert Grosse·tes_te ~~ t e Or1g1ns of Experi~~-ltal_ Sc~ence, 1100-1700 (Oxford: at the Clarendon Press, 1961), p. 1. 13 Row1and Mainstone, "Structure and Design Before 1742," ~c~~~.ra!:_ Rev~~-~, Vol. XLIII, No. 354 (April, 1968), p. 306. 89 theoretical mechanics was a product of modern thought. The science of statics, known in the Middle Ages as the scientia de ponderibus was the subject of a series of treatises on weights, some of which were Latin translations of earlier ';X)rks from the Arabic or Greek. The most important of the Medieval Treatises on statics 'tJas the 14 De Ratione Ponderibus attribut.ed to Jordanus de Nemore (1237d). In this treatise he discusses the principle of virtual displacemen·t (glossary). The precise definitions of static moment (glossary), of the resolution of a vertical force along an inclined plane and of virtual work were argued. Biagio Pelacani (Blaisine of Parma, l416d) is of historical importance as a transmitter of th8 mechanical tradition of the Northern countries to Italy in the fourtc-;;en-tll 15 century. His Tractatus de Ponderibus is essentially a compilat:ion of the materials found in the treatise of Jordanus. With Jordanus and Blasius there emerges an analytical abstracted, generalized 14 Jordanus de Nemo:::-e is often identified with Jordanus of Saxony who served as master general of the Dominican order from 1227 to 1237. However, the1.:·e is no evidence of any mathematical interes·t, nor use of the name "de Nemore." Some authors believe, such as M. Curtze, that Jordanus, the mathematic-ian, is identical with the Dominican. See Narshall Clagett, The Science of Mechanics in the ~ddle ~9..E::E (London: Oxford University-Press,l·9~p:-72-.- -- 15Nicholas of Cusa (1401-1464} was a fifteenth-century platonist, \vho wrote a treatise on statics entitled De s·taticis .~Jleri-E:l!?nt:J:~-· In the fourth book of his _!?io!:._~ he suggested-that problems concerning relationships between elements could be solved by weighing. See Ernest A. Moody, Marshall Clagett, eds., translated and with notes, T~~- ~edieval Science of ~eights (Madison: The Uni versity of Wisconsin, 1960), p. 236. 90 approach which leads to the first principles of a true science of . 16 stat2cs. Leonardo Di Vinci (1452-1519) demonstra.ted the varying effects of loading on arche.s of different curva·ture, and indicated the places where fa.;t.lure. m1.g . h t occur. 17 (See Figure 26.) Since these were located at the haunches (glossary), he believed that the la·tter should be reinforced with good masonry. He showed in his sketches that the line of thrust did not follow the arch stones, but left them diagonally at some point on the quarters, where it passed into the 18 abutment. 'l'his conforms to the modern concept that the line of thrust must lie at all points within il::he middle third of the arch joints, or else tension will develop at the end of such joints. Had he made his findings public in 1500, the art of structural design would have been revolutionized by Galileo and others. The ability to compute stress would have been of little value, however, without the complementary understanding of the s.trength of materials. During the Renaissance there -was no knowledge regarding this, nor how to arrive at the amount of stress in a meJnber of a structure caused by a given load. There was nothing which \\ 16 rbid., pp. 3-20. 17 Leona.rd o Dl . VlncJ. . . was f aml'1" :~.ar wlth. Jordanus' s work. See Ivor B. Hart, The Mechanical Investigations of Leonardo Di Vinci (Los Angeles: University of California Press, 19G3), p. 70. 91 a :Fm. 22. Leonardo's diagram of how to determine the breaking strength of an arch. (Ms. A, S!r) FIG. 23. Leonardo's diagram showing the point of rupture in an arch loaded only on one side. Figure 26. Leonardo's Diagram of How to Determine a the Breaking Strength of an Arch (Ms.A,5lr) aBarclay Parsons, Engine~rs ~~~- Eng.i:?eering in the Ren~issance (Cambridge: M.I.T. Press, 1966), p. 7L 92 as developed by a supported weight as it passed from the point of . 19 support to t 11e ba se o f · t h e f·oundatJ.ons. Galileo Galilei (1565- 1642) was the first to discuss the bending strength of a beam, thus becoming the founder of an entirely r1ew branch of science: the strength o f materla. 1 s. 20 (See Figure 27.) Among the multitude of physical and mechanical problems engaging the later scientist of the sixteenth and seventeenth century, t'i.>'O are fundamental to ·the undel>- standing of concrete: the composition of forces, the basic problem of statics, and bending (glossary), the fundamental problem of the . 21 e 1 emen tary t 11eory o f t h e strength o·f ma.ter :tal s. The originalit.y 19 Parsons, EJ:!gineers, p. 67. Partial anticipation of the fuller statical understanding of today are seen playing this role in determining arch and vault profiles in some of Leonardo's sketch projects for the tiburio over the crossing of Hil~n Cathedral. No quantitative application of statical theory is recorded before the time of Wren. See Christopher Wren, "Second Tract on Architect:ure," in S. C. vlren, Parentalia -~!_ _!!le Wr~~ Fanlily {London: E. Arnold, 1750), pp. 356-358. 20 Isaac To d hunter, ed1tor,. and completed by Karl Pearson, A ~istory of the Theory of E~as:ticit:_y_~nd_ the Strength of Materials fro~ Gali~ei to Lord Kelvin (New York: Dover Publications, 1960), p. l. Not u;Jtil 1680 was t''lariotte {edme) able to determine relation ships between flextural strengths of prism. See Gernando Luiz Lo:to B. Carneiro, "Galileo, Founder of the Science of the Strength of Ma·terials," !2:~~!-:!~~!J:onal Association of ~~~ting ~nd Res~arcl~ Labor<'-!-_ t.ori~~ for_ ~i'.:t:.e2::.:_~~1E, and Str~<_?tures, Bulletin No. 27 (,June, 1965), p. 107. 21 As properties of a material rather than of an element's, strength is measured in terms of the maximum stress that can be resisted, and stiffness in 'cerms of the stress that is developed by a given proportionate deformation, i.e., deformation per unit of length, kno\\'Tl as strain, in the direction of the stress. For most materials, bOth strengths and stiffness vary according to the type of loading, the values most commonly measured being those for stress in one direction only, either tension (glossary) or compression (glos sary) " Rovdand Main stone, Developmen-ts i~ S't_!.:~.<::_tural Form (London: Hazell, Watson & Viney 1 Ltd., 1975), p. · 4 7. <) . 9,J • FIG. 3. Figure 27. Galileo Galilei's Drawingsa a Gernando Luiz lobo B. Carnei:t-o, "Galileo, Founder of the Science of Testing and Research Laboratories for Materials," Materials and §!:!":_Ectures, Bulletin No. 27 (June, 1965), p. 108. 94 of Galilee's method was his effective use of mathematics and e..xperi- 22 ments. By conceiving of science as a mathematical description of rela.tionships, the excessive empiricism of the past was laid aside. Yet despite the keen interest on the part of Leonardo, and despite 23 the contributions of men like Simon Stevin {1548-1620) and Galileo, it was not until the late seventeenth century that a fully general- ized concept of a force acting in any direction was achieved, and the conditions of equilibrium stated and applied to problems such as the stability of an arch. It was not until. then, that the earlier speculations of Jodranus, Leonardo and Galileo bore fruit in a manner that permitted quantitative calculations on the basis of tests on 24 materials. Leonardo's principle of accepting nothing as final until proven by experiment or experience, anticipated the kind of thinking that would prepare men for a new approcah to scientific procedure vihich would occur in the seventeenth century. The dis- tinctive feature of the scientific method of the seventeenth century, as compared t.o that of ancient Greece, was the way in which a t.heory 22 The Discources are presented in the form of a dialogue be t\'7een Salviati and Simplicia. The later represents the scholastic ment:ality of the age, dogmatically following the Aristotlian method, which opposed experimental evidence hy aprioristic and arbitrary reasoning. ~alileo g~!~lei, ~ial9gue~ Conc~_ing !WO Ne~ Sciences, translated by Henry Crew and Alfonso De Salvio, introduced by Antonio Favaro (Michigan: Northwestern University Press, 1968), p. 116. 23 Simon Stevin was a Dutch mathematician whose Statics and !-~Yd~ Static::>_ (1586) enunciated the theorem of the triangleof forces. 'l'his gave ne•d impei:us to the study of statics, which had previously been founded on the t.heory of the lever. See "Simon Stevin," Ency cJ:~paedia Bri~nnica., Vol. 21, William Benton, publisher, p. 241~- 24 . Nc:anst.one, "Structural Design Before 1742," p. 306. ,. . 9;) related to the observed facts it explained, and then suhnitting t.eseh f acts to exper1menta. 1 test. 25 'rhe first. architectural edifice that began to suggest the application of scientific method to construction was the Dome of Santa Maria ~el Fiore (1421-1434) by Filippo Brunelleschi (1377- 1446).26 It gave birth to structural engineering during the Renais- sance and began to anticipate ·the statical theory which would follow later. Ih 1418, the Opera Del Duomo_:, a council organized by the guilds to control the construction, anJJounced a competition for a 27 design for the vaulting of the main cupola. Vasari commen-ts: "There was held in the same year a conference of the architects and engineers (ingegneri) of the country on the method of erecting the 25 Cromol.e,. . Grosseteste, pp. 9·-10 • 26 By t.he year 405 A.D. a church was built on the site of the lat.er Florence Cathedral, to celebrate the vic·tory of the Florentines over the Ostrogoths, a victory attributed to St. Raparate. See Piero Borgellini, Guido Mo:r:ozzi, and Giorgio Batini, Looking ~ack to Santa Raparat~; a _g~~::dral Within ~ Cathect!_~_l, translated by Herry Orling (Italy: Bonechi Edi·tore-Firenze, 197l) r p. 21. In 1294 I the Florence Cathe~ral ~Bs begun and w0rk continued sporadically until 1334, when attention was turned to the tmver. Work continued in the 1340's under Andrea Pisano and in the 1350's under Frencesco Talenti. In 1366 foundations for the octagon \vere built by Neri de Fioravante and until 1420, the design of the Cathedral under his direction remained. See Howard Saalman, "Santa t-1aria Del Fiore: 1294-1418," ~h~ Ar!: Bull~·tin, Vol. XLVI, No. 4 (December, 1964), pp. 471-SOC. The general shape of the dome was known before Brunelleschi's time, but whether Neri had a plan for erecting a cupola over the great span of one-hundred and thirty-eight feet is not known. See R. J. Main stoner "Bruenlleschi's Dome S. Marie dei Fiore and Some Related Structures," Transactions of the New·c:_~en Soci<=::tY, Vol. 42 (1969-1970), p. 109. 27 F. Prager and Gustine Scaglia, Brune}leschi (Cambridge: M.I.T. Press, 1970), p. 27. ·96 28 d orne." This open competition ended with the appointment of Brunelleschi, together with Lorenzo Ghiberti and Battista d'Antonio 29 to superintend the construction. Brunelleschi's design resulted in several structural achievements (see Figure 28). Aside from his careful study of the Pantheon, his Dom~ of Florence Cat~~dral shows its indebtedness to the Medieval octagonal clo-ister vaults of the . 30 . Bap:Lstery. Late Roman vaulting tecmLiques reveal cons1stent attempts ·to dispense with centering devices by embedding ribs of brick int.o the vault t.hereby becoming an integral part of the concrete mass. 'rhe inclined bands of vertical brick of herringbone bond in t.he Duomo perform the sa.me function structurally. The ribs in the Te_I!J2.:~'.::. of Mi.ner:·va Medica have a :r.·emarkable resemblance to the ribs and 31 horizontal arches of Brunelleschi dome. In addition, Brunelleschi divided the cupola into an outer and inner shell, each constructed without a.n armature. A description of this method of construction was given by Giovan Bat:ista Nelli ("R<\gionamento sopra la maniera di voltar le cupole senze adoperavi le centine" in Discoursi di Archit.et- tura del Senatore, Florence, 1753) who descril~s the herringbone h)nd 28 GJ.org1o· · Vasar1· 1 L1ves· o:·E Seventy o f t l1e Most Emlnent. _ _!"'ain_"!::_~E._§.r Sculptors and_ Arc~cts 1 ed.i-t·ed by E. H. Blashfield, Vol. I (London: Bell & Sons, 1896), p. 256. 29 . . Ma:Lnstone, "BrunelleschJ..' s Dome 1 " p. 110. 30 Howard Moise, "Brunelleschi, and his Influence on the Development of Renaissance Architecture," Th<::._ ~_Echi tectur~~ Quarterly, Vol. I (June, 1912) 1 p. 50. 31 Ma:tnstone. 1 p. 122 . 97 BRUNBLLE,)'Cili'S DOMh" OF S. MARIA DFL FIORE Figure 28. Brunelleschi' s Dam.e of s. Maria del Fiorea aCowan, Master Builders, p. 112. 98 of the brickwork as the feature which made it possible to dispense 32 with supporting centering. Brunelleschi's use of reinforcement of bo·th the inner and outer shells by iron cramps and stone, timber and 33 2ron. c h a1ns . 11ave c l ose precedents 1n. Roman construct1on.. When Roman architecture was at j_ts height the entire masonry of the vault was reinforced by annular chains, usually with vertical ribs added to 34 distribute the effect of the chains. Brunelleschi' s design shows . that he may have acquired, partly through ·the st.udy of Roman remains, an awareness of the general pattern of stresses within a circular dome--of the tensile hoop stresses .in the lower part, the corres- pending compressive ones alx:Jve, and the outward thrust which v-10uld be exerted at the base if the tensile hoop (glossary) stresses led 35 to radial cracking. (See Figure 29.) Brunelleschi began to abolish 32 b' ~ I lCi,, p. 113. 33 B....1 a k e, Anc1en_!_-· construc t._1on. In c1rcu. ].ar, as we 11 as seml-. circuJ.ar structures, the outward thrust of the roof was counteracted by one or several peripheral chains, consisting of stones inter connected by metal cramps. This was often the practice in pre--Roman t.imes. F. D. Prager, "Brunelleschi's Inven·tions and the Revival of Roman Masonry Work," Osj..ri~, LX (1950}, p. 488. 34 I b',J_Q. I p. 488 . 35 These radial cracks extend up and dovm from the springings cf nearly all large domes or semidomes seen today in some of the remains of the Baths ~f Trajan, and the pantheon. Albert:o Terenzio, "Le restauration du Pantheon de Rome,." I.e ~~!lservatj~on_ des Monuments ~_'ar~ ?e d'HistoirE?;_ (Paris: 1933), pp. 280-285. In this connection, there were telltakes of bronze and marble inserted at numerous points in the dome in 1695 when considering whether the radial cracks ca:J_led for the inserting of new chains. When such chains were proposed :Lt was stipulated that the bars coming from the foundry should be care fully v,~sted. t-1ainstone, "Brunelleschi's Dome," p. 124. 99 IC\~..tl :;if· Bo··• 7tP M~ ;;-o? '!·V.., ?Y:J' (ta*i"'. '1'') ...;.ft · {J>-})\l) (~-1.2-C\~ t - I (r4.r:,) {I+:J-6) {H5?) (v-t=> Figure 29. Stress Configurations for Brunelleschi's Domea a Cowan, ~as_!er ~uilders, p. 119. 100 the interrelated design principles of the reinforcing buttress of the Gothic Cathedral, and thus began anew the re-investigation of Roman building principles. His achievement was basically a technical one, and with the Duomo completion in 1434, the pre-eminance of the 36 Pantheon's Dome was lost. In light of modern methods of construe- tion, Brunelleschi's cupola would be: difficult to build without steel or reinforced concrete. The mortar was exceedingly hard and there is a possibility that Brunelleschi used a hydraulic cement 37 similar to t.hat of the Romans. No m:asonry dome with a greater "1 . h . 38 span h as be~en b Ul. t slnce t at tnne. The dome of s. Maria del Fio£_~ has, like the Pantheon, never given subsequent cause for concern regarding its safety, and in this respect. it differed from most Goth lC. stx·uctures an d f rom St. Peter ' s ln . Rome. 38 (See Figure 30.) 36 Mainstone, "Brunelleschi," p. 107. 37 w. B. Parsons, Engineers an~ Engineering in th~_ Ren~ss~.nce (Cambridge: M.I.T. Press, 1967}, p. 592. 38 Brunelleschi v.;ould not have been able to compute the stresses in the dome because ·they were no·t known. Even if such computations had been possible, there WdS no knowledge of the strength of mat~erials and consequently no means of proportioning the parts to withsta:r;.c1 t.he stresses. He was only a:ble to evaluate correct.ly the qual itat.ive nature of these stresses and their position and direction as a resul·t. ':l'oday, the structure wouLd be built as an octagonal domf~ in reinforced concrete, with enormous savings in material and weigh·t, and with horizontal intermediate ribs rather than vertical ones. Ibid., p. 596. 39 Henry J. Cowan, The Master Bu~i1ders (New York: John Wiley & Sons, 1977}, p. 177. 101 ORT JIOGRi\f'liL\· i'AR TIS· EX TieR! ORI5 TEMPf.l·DIYI·I'F.TRI IN·Vt\Tl\l\.i'\0 ,\l!Cll:\Fl.·,;-..,~,\.:H.VS·lh.':\AI\OT ;\·!NV E~IT SI[P!I\;-..;\'.)·DY PlRAC· ff.ClT Figure 30. The ~_?_!P.e of_ s-t.:.. Peter' s, Rome a a Helen Gardner, Art_ :!'_hro~c;Jh_ -~~Ages, 5th edi-tion (New York: Harcourt, Brace & World, Inc., 1970), P~ 479. 102 The Basilica of old St. Peter's was built in 330 A.D. The original design of the new church was the work of Donato Bramante (1444-1514). The foundation stone for the new St. Peter's was laid in 1506 and construction passed successively from Bramante to Raphael, Baldassare Peruzzi, Antonio da San Gal.lo the Younger, Michelangelo Buonarotti, and Giovanni Della Porta. Upon Michelangelo's death in 1564, others continued to work on the project until it was completed 40 by Carlo Haderna in 1612. (See Figure 31.) Bramante' s inspiration 41 for the design of a solid hemispheric After having experimented with Roman methods of construction he built four great piers upholding the dome and their connecting arches of 42 concrete. Vasari attributes to him a number of technical inven- tions, e.g., a kind of "cast concrete.,. or artificial stone which y,ras 43 pou:r:ed into previously prepared moulds. "Among other instances of this [concrete] was the method of vaulting with gypswn and that of 40 Cowan, Haster Builders, p. 192. 41 Braman·te departed from the precedent set by Brunelleschi by adopting the circle, not the octagon to his design. His selection of curves modified the development of stresses in the dome as well. 'I'he dome was desig·ned as one solid shell instead of the double shell. Bramante failed to take advantage of the engineering principles in the dome of Santa Maria del Fiore because the dome of the Pantheon was nearer by. Parsons, ~ngineers, p. 612. 42 vasari believed that the execution of the great piers up holding the dome and their connecting arches of one-hundred and forty one feet high and seventy-nine feet across, overshadowed everything that. had been achieved in architectureal construction since the days of antiquity. Vasari, Lives, Vol. II, Pw 56. 43 Ib.id. 103 a. Bramante, 1506. b. Bramante-Raphacl, 1515-·1520. 1: •. Sangallo, 1539· d. Michelangelo, 1546-1564. Figure 31. Plans for St. Pet.er' sa a James Ackerman, 'l'he Archi!-ecture.:_ of Hichelangelo (New York: The Viking Press, 1961), p. 90. 104 preparing stucco, roth Jr...nown to the ancients, the secret of which had been lost in their ruin and had remained concealed even to the time 44 of this master." Bramante 's association with Leonardo regarding theoretical principles of vault design may have influenced his work 45 as well. After B.ramante's death, a succession of architects worked on St. ?eter's, including Michelangelo, who took over the supervision of the church. Originally he planned a double-shell dome like that of Brunelleschi' s Cathedral, but did not live to complete it. Giovanni Della Porta completed the dome after Michelangelo's death in 1590. Unfortunately the tension reinforcement proved inadequate, and in 1742-1743 a struct.ural analysis was made to ascertain the cause of i'·_,. t l1e cx-ac k s an d to d evJ.se. remed. J.a 1 measures. 46 Several experts were consulted in 1742-1745. One \!laS Giovanni Poleni, professor of experi.- mental philosophy (equivalent to Physics} at the University of Padua. His theory, published in 1748, had been based on those of J. Stirling and D. Gregory. D. Gregory was a Scottish mathematician whose treatise, "Properties of the Catenaries, .. was published in the 44 Vasarl,. LJ.ves, . Vo 1 . II, p. 56 . 45 carlo Pedritti, "Newly Discovered Evidence of Leonardo's Association with Bramante," Journal of the Society of Archi·tec·tural H~storian~, Vol. 32, No. 3 (October i 973)-; pp. 223~227. 46 rn no great building of the pa.st for which adequate records remain was the form of the superstructure finally determined until its supports were comple·te, e.g., St. Paul's and St. Peter's. At roth these building::.;, extensive re:medialwo~k-on the main piers was necessary before the domes could be safely constructed. Mainstone, "Desi Philosop~ica:t.:_ Transactions of 1692_. Following the example of J. Stirling (1717), Poleni established the effect of the thrust on St. Peter's dome. (See Figures 32 and 33.) His research suggested that the line of thrust was an inverted catenary (g.lossary). Understand- ing this, he could determine the correct shape of arches and domes by finding the shape assumed by a chain carrying unequal weights proportional to the section of a vault or dome segment. Radial cracking (glossary), as well as circmnferential cracking near the springings, would have led to a collapse of the dome. The circum- ferential reinforcement required \l'laS calculated and it was concluded . . 47 that add1t1onal tie rods should be added. In 1743, a report on the subject w-as published under the title Parere da tre mattematica fi_::'1e del_!:_, Anno, 1742. The method of investigation they followed \vas first formulated by Jordanus de Nemore in the thirteenth ceE- tury, and later refined by Daniel Bernoulli in the sixteenth 48 cen·tury. The investigation of the structural behavior of St. 47 rn 1743 and 1744, five additional tie rings were added to the dome by Luigo Vanvitel1i. Cowan, tllaster Builders, p. 198. 48 T h'1s 1s. now known as the l)r1nc1p. . 1 e o f V1rtua1 . Dlsp1acement. . The three authors were Le Seur, Jacg_uier and Boscowich. They presented their information on a graph showing how the dome must have given way. Their error v.-as in treating the tie rings as a con stant force. Their report, however, was epoch-making. Contrary to all tradition, the stability of a structure had been based on science and research. J. Bernouille, "Vertab1e hypothese de la Resistance des Solids avec La Demonstrat:ion de la Courbure des corps qui font ressoit," Memoires ~~- ~aca~mi~ Royale des Sciences (1705), pp. 176- 186. 106 TAVOL\. D. ' - ·-~ I' fiG.XIll. - 'p,-,_.,.J+·: - The parallelogram of forces (X): the "smooth-sphere" analogy fo; the masonry arch {XI); the use of the CJle11ary for the solution of the masonry arch {Xll and Xlll) from Memorie istoriche della Gran Cupola del Tempio Vaticano by Giovanni Poleni, Padua, 1748. Figure 32. The Catenary Clli>in for a Dome of Uniform Weight and for the Dome of St. Peter•sa 107 FIG. XIV. Figure 33. The Parallelogram of Forces from Memorie istoriche della Gran Cupola del Tempio Vaticano by Giovanni ::?oleni, Padua, l748a ctCowan, Master Builders, p. 197. 108 Peter's was the first example of the application of structural mechanics to an architectural problem. Brunelleschi's dome laid the foundation for structural mechanics, but it took another three centuries for the science to develop and pr-oduce visible results in . 49 arc h ltecture. In addition, before the rediscovery of concrete in the eighteenth and nineteenth centuries, the use of stone in archi- tecture had been developed into a proper science by mathematically tralne. d englneers. . 50 49 sm1on Stevin (1548-1620) published De Beghinselen de~ W~~gh const (Elements of Statics) in 1586. He was the first ·to prove formally the theorem of the composition of forces. He thereby laid the founda·tion for "graphic statics" which became an important part of structural analysis in the nineteenth century. Roberval (1602- 1675) wrote _'!r.aite de Ivlechanique, res·tating the principle of parallelo gram of forces a century after Simon's work. Varignon (1654-1722) vms the first to pronounce the doctrine of super position of statical moments. In 1697, David Gregory published a paper on the Properties ?.f.:!:_!~- g_aten_~ia, which stated tlk""lt the theoretically correct line for an arch is an inverted catenary. Mariotte (1620-1684) solved the basic principle of bending. Robert Hooke (1635-1703) discovered that the force with which a "spring" attempts to regain its natural posit.ion is proportional to the distance by which it has been dis placed. Philippe de la Hire published 2;raite_ de Ivlechanique which argued that t.he shape of the arch must be such that for each block the resultant of its own weight and of the pressure of the preceding block is perpendicular to the face of the next block. Both De La Hire's theory and Gregory's \vere used for checking the safety of the Dome of SL Peter. C. A. Coulomb (1736.-1806) and Navier (1785-1836) mo::.de outstanding contributions to the field of st.atical problems and finally integraJced many of i.:he la\v.S and methods ah·eady known into th2 ::;-:r·act~ical tasks of structural engineering. By the time Denison pointed ou·L thac hoop forces can be resisted only by the thickness of the mated.al (!'_~~:_~heo_~) or by buttressing or metal ties, masonry domes had <:=Jiven way to those built with iron. He could not foresee the versa·t:ility of the recently invented reinforced concrete. See Enc '/C! 1.opaec'Li.3. Br i t.ann.ica, 9th edit ion, Adam and Charles Black . -(E.afT;:"i;l"lrgh: ___1975-":L8-BB~ 25 vols. so·· Straub, Engineering, p. 141. 109 Three slightly later analyses were made by Emiland-Marie Gauthey, Jacques-Germain Soufflot, and Jean-Baptiste Rondelet relating t.o the stability of the French Pantheon (Ste. Genevieve) in Paris. (See Figu:ces 34 and 35.) Th:is resulted in one of the most important pioneering efforts made in the scientific investigations of structural form. In 1770, a decision vas reached that the ancient church should be replaced by a more monumental modern edifice, and the design was entrusted to Jacques G. Soufflot (1713-1780). Extensive tests were 51 carried out by Gauthey, Soufflot and Rondelet at the time of construction. (See Figures 36 and 37.} Soufflot's proposal to set the dome on much less massive supports >vas strongly criticized. The piers under t.he dome, according to Gauthey' s calculations, carried an average load of thirty-three tons per square foot. Small speci- mens of the stone tested in Gauthey' s machine carried over eight times that calculated load per unit before fracturing. The calcula- ·tions, however, made no allowance for wind, eccentric loading, or uneven settlement. In a treatise published in 1771, entitled Memoire SUE_ _;!;'Application ?e la Mecanigue ala ~onstruction des voutes et de~ dome.~, Rondelet sought t.o prove that t.he thrust of cupolas was 51 Emiland_,. M. Gauthey (1732-1807) was_,. a pupil of D. C. Trudaive, who.. founded the ------Ecole des Pones et Chaussees. He was a teacher at the Ecole, and became an engineer-in-chief of the province of Burgundy. Later he was appointed director of the Burgundy w-aterways, and finally Inspecteur-·Geneur des Ponts et Chaussees in Paris. V'Jhen he tried to find answers to the question regarding loads which could be safely carried on stonework, he found the existing data so inadequate that he designed a machine which he used for §_te. Genevieve. His nephew was Navier, tbe founder of modern structural analysis. W. H. B. Armytage, !:_ _?ocial Hi~tory o~ ~:ngineering (London: Faber & Faber, 1961), p. 95. 110 ~einforcement in the masonry of. St. Genevieve, Paris, about 1770. Figure 34. Reinforcement in St. Genevieve, Parisa aMainstone, Developme!lts_i:_~ Structural Form, p. 225. 111 Figure 35. Dome of the Pantheon, Parisa 112 _r-______L______ Illustr. 215.-Gauthey's Testing Machine Figure 36. Emile Gauthey's Testing Machinea aAbrahc:tm Wolf, ~ History ~f Science, Technology and Philosophy ir~ :the Eigh_t:_~-~~th Century, Vol. II (New York: Harper & Brothers, 1961)! p. ~)26. 113 Rondelet's Testing Machine Figure 37. Rondelet's Testing Machinea aNolf, A History of Science, '!'~chnology_ and Philosophy, :UlustTation 218-; p~---529. 114 generally overestimated. Nevertheless, when the centering was removed, there were signs of serious damage, and an investigation was initiated. This included the first compression test ever made 52 on 1ron-re1n·orce. . f d stone beams. Before 1742, architectural theory was almost entirely geo- metr1ca. ] .. 53 That date marked a turning-point in architectural design in that it was the date of the first recorded and substantially correct analysis of an existing structure in terms of its static equilibrium. In a general sense, the marriage of art and enginee:r-- ing involved in creating the design of Brunelleschi's dome was to dissolve subsequently with the separation of engineering from architecture. Until physical science was introduced into the art of building in the twentieth century, the increased complexity made it impossible for any one person to be highly skilled with the 52 Straub, Engineering, p. 110. For a further discussion of the problems in this structure, see J. Rondelet, Me~oire Historique sur le Dome du Pantheon Fran~aise (Paris: 1747), pp. l-115. A k~owledge of-the- strength coefficients of the more important building materials was indispensable for any practical application of the theories of statics to structural tasks. (See Figure 38.) Test results published by men like Parent, Musschenbroek, and Buffon would h.~ followed during the eighteenth century when modern civil engineer ing based its designs on scientific calculation. Ibid., p. 109. Not until t.he intl:oduction of beams of cast and wrought iron and later, of cunc~cet:e u.secl in wide-span forms such as suspension bridges, would a fuller undc:n:;tanding of t.he strength of materials be achieved. R. Mainsto:ne, S·tructural Form, p. 292. 53 Essentially this meant that the main lines and forms of a structure such as the heigU1s of vaults and the proportions of piers ann bu·ttresses conform to a certain predete:nnined geometric grid. Ro\'7land Main stone, 11 Structure and Design Before 17 42, 11 Architectural Review, VoL XLIII, No. 3~)4 (April, 1968) , p. 303. 115 Q., 0--- 8.2 Machine for testing small tension specimens. The load was multiplied by a lever. The test specimen was gripped in shackles which were self-aligning to ensure concentric loading (from Physicae experimentales et ge,>met ricae dissertationes, by Petrus v Figure 38. Machine for Testing Small Tension Specimens, from Physicae experimentales et geometricae dissertationes by Petrus van Musschenbroek, l729a a Cov.-a.n, Master Builders, p. 224. 116 technical requirements of the two branches. Almost all phases of building up to this time was largely practiced by the same person, 54 an architect. The first sign of the division between architecture and engineering appeared when natural and applied science moved into 55 the realm of teclmology and industry, and out of the realm of art. The scientific revolution produced a vigorous interest in more prac·tical processes, which resulted in a unification of philosophical 56 thought and the manual skill of the craftsman. This new intellec- tual outlook stimulated the formation of new institutions and academies for the advancement of scientific research. Men with the same scientific interest were able to facilitate their experimental 54 The v.'Ord Architect was a Greek word of great antiquity, originally meaning "a chief artificer, mas·ter-builder, direc'cor of v.urk, architect, engineer." During the Niddle Ages it described "those men who occupied that position, such as the ~~ment§l-rius, the ..:!:_ngeniato:t::_, and the master-mason." Martin s. Briggs, The P...rchitect~ in Hi st~ory (Oxford: Clarendon, 1927} , pp. 3--4. 55 Ada Louise Huxtable, Pier_ IJ~igi Nervi (New York: George . Braziller, 1960) , p. 12. Peter collins, on the other hand, believes "'rhe division occurred when bridge designers increased bridge spans beyond technical capabilities of stereotomy." Peter Collins, review· of Pier Luigi Nervi, by A. L. Huxtable, in Journal of _!.he Society of ~E_~bitectural _!{istorians, Vol. XIX, No. 3 (October, 1960), p. 178. 56 'I' 11e ut1"l. 1tar1an . 1 . d ea l was g1ven. ear l y exp:r::ess1on. b y Franc1s . Bacon in the sixteenth and seventeenth centuries. "I am labouring to lay the foundation not of any sect or doctrine but human utility and power .. " Th~ ~~il~sophY. Works of Franc_:_i.s Bacon, translated and with notes by Ellis and Spedding, edited and with an introduction by John M. Eobertson, "Preface to the Great Instauration" (London: George Eoutledge & Sons, 1905), p. 247. 117 57 v10rk and share similar ideas. These investigations resulted in a growing body of published work. Through published writings, one of the last obstacles to recent information on concrete up to this time, was removed. •rhe knowledge of cement and concrete was practically a mystery up to the eighteenth century. The relationship between statics and strength of material was crucial to the u·tilization of concrete. However, architectural structure and form was dictated by the restriction of the material. Until the chemical knowledge of concrete was better understood, concrete would remain outside architectural tradition. 57 Thi.s movement began in Italy where in 1560 the Academia §ec~~t~rum Naturae wa.s organized. The Accademia_ dei ~inc~i. was founded in Rome in 1603. See Stephen P. Tomishenko, The Hi__:;tory of _!-he Strength of Materials (New York: McGraw-Hill, Inc., 1953), p. 15. Th_£ ~cademi,~ 9-_el Ciment~ at Florence, the Pa:r:i.s Acade'mie_ ?es Scienc~_, and 'l'he Roy~=\:_ Society were founded, and the latter published in 1662 the Philo~~Erdcal Transactions, the first scientific journal in the English speaking world. Three characteristics of their societies \'lere: a c01mnon instinct to share information with the membership; to make their findings available to other circles; to publish and spread their findings to the rest of t.he world. Roger Hahn, The ~nat:-om;t_ -~~ ~ Scientif.:!:_~ Institut~on, Th::=_ ¥aris Acader~y_ o~- Sciences, 1666-1803 (Los Angeles: University of California Press, 1971), pp. 3-49. In 1795, the Ec~-~- Polytechr:-iq~u; was begun in France. All social classes could ent.er. Courses consisted of basic science and engineering. Lat.er, the Ecole l:;ecame a school of basic science, and the Ec~_-!:~ de:::_ !'_on!s et C[l~~ss~~_:~' or the Eco~<:__ de~ ~ines prepared students for engineering. 'l'imoshenko, p. 68. Neit.her the London Royal Society nor the ~c-~de~_:i.-~ de~ ScL~nce_~ were formed by Govern ments, but from an informal gathe:d.ng of devo·tees of experiment.al science, scholars and a.mateLlrs. 'l'he ~_ll:~emi<::_ dE'-~- Scie~ces in France, on the other hand, was able to draw on t.he royal treasury. The French Jl.cademy became a model for: many other academies. Generally the goc,l of these societies was ·to create a climate which encouraged original investigat.ions and allowed for the dissemination of results t.o ·their membership and beyond. Martha Ornstein, Role of Scientific Societies (Chicago: University of Chicago Press, 1928 )-, -p. 73-:------118 During the centuries that spanned the rise and fall of the Roman Empire and the Middle Ages, writers on mineralogical subjects added little until Albertus Magnus (1206-1280). From the achievements of Paris during the thirteenth and fourteenth centuries, Magnus produced a large number o f sc1ent1. 'f' 1c wrltlngs.. . 58 His Book of Hinerals (De Hinera~ibus et Rebus Metallicis) influenced those who wrote on this subject until the time of Georgius Agricola in the six-· 59 te:enth century. Aris·totle had defined hard and soft stones in terms 60 of dry and moist, :cesistan·t or unresistant to pressure. Albertus' s discussion regarding the hardness of building stones~s similar to -~ . 61 t h at o f VJ.~.-.:cuv1us. However, Albertus does not quote Vitruvius, P.liny or Isidores, which indicates that he was thinking in terms of observation rather than the authority of old~-r sources. Albertus lived in .the great age of cathedral buildings, and may have acquired his in:Eormatioa on st.ones directly .by observing workmen either at 58 Albertus Magnus owed muc h to Grosseteste. Grosseteste also met Jordanus De Nemore when the later visited Oxford in 1229-1230. See A. c. Crombie, ~!.. Grosseteste, pp. 190-191. 59 Treat:i.ses on mineralogy were written by Isidore of Seville in the seventh cen'cury and by Harbody, Bishop of Rennes, in the twelfth century, but it was not until Agricola's work in the sixt.eenth century that there was an effort to base information on scientific observation, rather than on Aristotle, Pliny or the supernatural. See Dorothy Wyckoff, Albertus Hagnus, Bo~~ o~ Minera_}s, translated by Dorothy Wyckoff (Oxford: Clarendon Press, 1967), pp. 46-47. 60 The Works 9.!_ AriE~otl~_, translated into English under the editorship of W. D. Ross, Vol. II, De_ Generatione et _s::orruptione by H. H. Joachim (Oxford: at the Clarendon Press, 1953) , Book II, 3, 300. 61 vitruvius, On Architecture, translated by l"lorgan, II, 7, 3,-4, p. 50. 119 Cologne or during his travels. His observations lead him to con·- elude: Stones like chalk, or those softer than chalk, which are very white and leave a white streak on whatever they touch, have surely been mixed with a moisture highly susceptible to evaporation, and have been burnt by a heat exceeding solidification, and have already begun to be calcined. Therefore they are not durable in vmlls. For because their dryness has been calcined they are always rough on the surface, which tends to separate from the grip of the cement, so that the stone as a whole is not held fast by the cementi and so these stones fall out of walls, and after a while a wall made of them becomes lj_ke an earth wall. 62 In 1546 Agricola published _!2~ Natura_ Fossilium (The Natural Stones). Agricola specified the quali·ty of the various limes for use in plastering. He believed that l~tter mortar is obtained if lime and sand are mixed together and allowed to stand for three 63 years. "Certain buildings are not firm and stable because the 64 mortar was prepared too soon aft.er mixing the lime and sand." Agricola refers to maltha_ (glossary), a hydraulic cement usee. to repair aqueducts, castles, and reservoirs in Rome. This natural material "w-ill produce the firmest of vm1ls and the artificial cement 65 is used :i.n the same manner." Agricola cites pitch, wax, eggs, 62 Wyckoff, Book of Minerals, Book I, Tractate, 4, 11, p. 47. 63 Georg1us. Agr1co. 1 a, De N~tura Fos~~~um,'1' translated from t h e First Latin Edition of 1546 by Mark Chance Bandy and Jean Bandy for the Hineralogical Society of America. •rhe Geological Society of America, Special Paper 63, Book VII (November, 1955), p. 163. Vitruvius does not mention such a waiting period. 64 I b'd1 . 65 rbid. 120 ox blood and meal in compositions used fo:r· making lime mortar, indi- eating that many of the "recipes" from the Middle Ages were still in 66 use. Agricola knew of puzzolana, i.e., that it was used in the 67 construction of sea walls. However, in spite of the fact that he was the father of modern mineraology, and wrote the first textbcok on mineraology in the modern sense, Agricola's works were not widely read and did not have the popular appeal of later editions of lapidaries, herbals, and smaller works on mining. In architecture, on the other hand, writers such as Antonio Filarete (1400-1465) suggested that to know the nature of lime and . . 68 sand one shoul d rea d Vltruvlus. Leon Battista Alberti (1404-1472) warned that lime should be carried immediately out of the kiln into a dry place and watered; for if it was kept in the kiln or exposed to t.he air, it crumbled to powder, making it useless. This watering ------·----- 66 Tbl"d .• , p. 164 . 67 Agri.cola does not mention puzzolana in connection with lime. Like Vitruvius, it is discussed in terms of the earth it comes from and its use in aquatic '1.\Drk. Agricola, De Natura Fossilium, nook X, p. 219. 68 Filarete's Treatise on Architecture (Trattato de Architet------· ------·-- tura), translated and with Introduction and No·tes by John R. Spencer, voi-:- I: The Translation (New Haven, Yale University Press, 1965) I pp. 27-28. Filarete refers to puzzolana as well. "They say that it is best because it is well covered by sand, or pozzolana, as they call it." He also refers to a stone called alberese which is used in ------Florence. "They" is not a reference to Vitruvius, but to the work- men. Filerete's Tre~tise on Architecture, Book III, Folio 151, pp. 27-28. 121 69 dissolved the 1' '', and made it suitable only for plastering. By the time Philii :x · de L'Orme (1510-1570_) wrote his treatise on archit.ecture U_<::_C;_']j.tectu_~e, 1567), interest in Roman concrete was widespread. De L'Orme concluded that from observations he had made, people did not know how t.o preserve their limes, and as a result, buildings were poorly constructed. He recomrnended that: At the moment when the lime is removed from the furnace, you assemble it in a large open area, and arrange it evenly in a pile perhaps two to three feet in height. Follo·wing that, you cover the pile with good earthy sand or fluvial sand, to 2 depth of al:x:mt two or three feet. You r:our a gTeat quantity of water over it, such that the sand is so da.TUpened and soaked that the lime can fuse from beneath, without burning it in the least. Having thus completely soaked and slaked the sand, all the stones of ·the lime will be converted into a gelatinous mass, which, when you cut into it at the end of two, three, or even ten years to make mortar, will seem like cream cheese. It will also absorb a great quantity of sand, and will be such a good mortar, that it will adhere to the stones, as though it were a true and excellent cement. But it is arove all necessary to take care when soaking the sand, and of course the lime which the sand covers, so that the \oJhole is not exposed to the air, since the heat and smoke of the lime opens and separates the sand, which can in turn cause its evaporation and.aey-ation.70 In 1662, a paper was written on English building practices by Sir Balthazar Gerbier D'Onvilly. He noted that "buildings crmnbled 69 Leon Bat.tista Alberti's Ten !30oks on Architecture, trans- lated by Cosi.no Bartoli from Italian into English by James Leoni, edited by Joseph Rykwert (London: Alec Tiranti Ltd., 1955), Book II, Chapter XI, pp. 36-37. 70 Ar<;:hitecture de Philibert !!e. ~~ Orme, Onseiller et Avmonsnier, Ordinarie du Roy, et Abbe de fainct Serge les-Angers. (A. Roven, chez David Ferrand, 1648). pp. 28-29. 122 71 to sand and dus·,: 0 • :::.' to the poor laying on of mortar. ,, D'Onvilly ascertained tha': ·the Romans "did not make use of their lilne when it was slaked, but for six months time suffered to pu:cify it, and when so purified, they made a cement which was joined with stone or brick 72 and made an 1.nseparable. unlon.. •• By ana l yzlng . correctl y t h at t h e Romans used cisterns, one higher than the other, D'Onvilly concluded that the water could be drawn down from one to the other. He knew that after being burned and slaked the lime •~s purified. D'Onvilly suggested that two parts of lime with one part of sand was the correct proportion, compared with Vitruvius' three parts of sand . 73 to one o f J.1.me. Sir D'Onvilly did not mention puzzolana or the hydarulic qualities of Roman mortar, but was perhaps the first to discuss the use of clay and lime. John Smeaton' s revelation t.hat clay was the most important ingredient for making good mortar was no·t revealed until the late eighteenth century. Sir D'Onvilly \'las one of the first writers who attempted to analyze the process of lime making anticipating inquiries into the subject which appeared a 71 sir Balthazar Gerbier D'Onvilly, Knight, ?':.Brief pi:>_ ~~l}.r~~ C~!?-~-~~ning the Three Chief !'rincipJ.es of Hagnificent !3uildings: _Soli~~:X_r s:_~nv~ienc~ an~_ Ornament (London, 1662), p. 20. Balthazar Gerbier vm.s a close friend of Inigo Jones. See G. Webb, "Baroque Art," Proceed~gs of the _:I?ritish Academy (1947), pp. 131-148. 72 I b'dl • , p. 20. 73 . . ·h. Vl truvlus, On Arc .2:_tect~;r-e, translated by Morgan, II~ V ,. 1-3' pp. 45' 46. ,, 123 century later. He also refrained from the exclusive use of ancient sources for his information, and reached his conclusionsscientifically. In 1674, Thevenot wrote a book about his voyages t.o India, entitled The_ ::!:ravels of Monsieur de Thevenot_ into_ the _Leva_0t, in which tJ;e process of making lime was described in India: "Walls were covered by quick lime, slaked with milk, and ground toge·t.her with sugar. This mortar is further polished with agate, and it is made as shiny as a mirror, which proves that what the Romans used can be made . h ] . ..74 w;~.. t pure _l.rne . In 1765, Monsieu Loriot asserted that the Romans used quick li.me on their scaffolds. He had written Marquis de Marigny, Surveyor GeneTal of the King's works and described a method for making quick- lime with puzzolana. The lvlarquis refuted Loriot by quoting Vit.ruvius. · However, Lariat's research established several qualities relevant to cement: tenAcity and hydraulicity. 'I'he mixture did not swell or shrink, but. turned to a solid state quickly. He discovered in 1770 that powdered quick lime mixed with slaked lime, and subsequently 75 reduced to a paste, produced the best results. His experimentations 74 Monsieur de Thevenot (1633-1667) attended the University of Paris and traveled widely. rrhe 'l'ravels of Honsieur de 'l'hevenot. into ------~------tft~ ,!~ev~E.!:_, translated by A. Lovell (I.ondon: H. Clark, 1686), Part III, Chapter VII, p. 16. 75 Antoine LToseph Lariat, Practj_cal_ Essay on ~ CeE_J..'§:nt and _?:._Ft~_:ficiaJ::.. ~-!_:-~ne, §2:1J?.POsed to _!?~ tha!:_ of the Gr_~ek~ ~md Roman~ !;:~!ely ~e-disc~_:\-:_ereQ_ !:;_~ ~~'JnS~~u ~orio!:_, translated frorn the French (London: 'l:. Cadell, 1774). Quick-lime is unslaked lime. He and De La Faye rea.lized there was more than one process by which lime could be made; in·to cem2nt. 124 undertaken in 1772·~1773, proved that the mixtures did not deteriorate when exposed to rain. Loriot's cement consisted of water, slaked lime, sand, and brick dust. He prophesized a great future for cement, 76 realizing that it could be made into any shape desired. In 1777, De La Faye published a paper Recherches Sur La Pre- 77 paration que ~es Romains, Donnoient A ~a Chaux. He referred to the writings of Pliny, Vitruvius, Augustine, and Thevenot. De La. Faye believed that if one read the ancient texts and reproduced their experiments, the secret. of Roman cement would be understood. In order to explain the superiority of Roman cement, it was supposed that the Romans possessed a particular method of slacking the lime. De La Faye believed that the solidarity of ancient monuments was due less to the quality of materials than in the way that they were . 78 . . cornb1ned. De La Faye re-d~scovered two bas1c types of mortar for building; that of slaked lime made into mortar, and powdered lime, 76 Loriot l~~lieved that the solidarity of cement in the Aque- 9-uc-t:-_ _?_~ ArcieE_ was due to the use of bullock's blood. It was typical of some of these early investigators such as Loriot to assume that the red color observed in Roman concrete was due to animal blood. As chemistry developed into a science in the seventeenth and eighteenth centuries, these notions were finally disproved. 77 This paper was first presented to the Academy of Sciences in 1775. 78 Once the basic materials and process was discovered that the Romans used, i.e., slaked lime and powdered brick or puzzolana, the next process was to discover the various processes in~ol:;.ed in making mortars with different combinations. Other limestones had to be investigated, 'cypes of hydraulic cements tested, and the addit.ion of o·ther chemical agents studied before construction with a hydraulic cen1ent was possihl.•8. 125 79 which is made into a superior hydraulic lime. He reached the same conclusion as John Smeaton, i.e., lime not calcinated is as durable as l1me. burne d ):or~ a 1 ong tlme. . 80 The older the lime, the less likely it would be used for structural purpo8es. Burned limestone had to be calcinated long enough so-that it would become a powder, and with the aad1t1on" . . o f water, a paste. 81 Start with hard limestone. Cook, lake, cover. Put the lime on the floor, clean, in a dry, co\~ered area. Place large, dry barrels with a big basin full of river water or water without minerals. Two workers are· needed, one with hatchet. to break lj1ne stones until the size of an egg. Then [the] other worker takes a shovel and puts [the] l:L.'Tiestone int.o a flat basket with grat.ed layers, like a sieve. [He] dips that basket into water until the whole surface of the water bubbles. 'rhen 79Pln1y . an d St. August1ne. knew t l1at two ba s1c. processes w2re involved in making mortar. "When limestone is burned, quicklime ;formed, and if sprinkled with water, slaked lime." See Pliny, ~atural History, '-'lith an English translation by D. E. Eichholz, Vol. I, Book 36 (London: Harvard University Pressr 1962), p. 139. St. Augustine called t.he quicklime "living lime." "Lime then poured into water, or water poured over it and though it was cold before, it: is now made hot by the same agent by which all hot things are cooled." St. Augustine, Thr:_ _gity of God Against th~yagans, translated by William W. Green (Cambridge: Harvard University Press, 1972), p. 19. 80 The question of how well limestone wa.s burned had been an unresolved puzzle for centuries. If limestone is only partially burned it will fall into lumps, not po'hcUer. This was a crucial error which persisted for centuries as revealed by Alberti. "Carry your J_,ime, t.herefore, immediately out of the kiln into a shady, dry place, and water it; for if you keep it either in t.he kiln itself, or any where else in the air, or exposed to tl1e Moon or Sun, especially in Summer, it would soon crumble to powder, and be totally useless." Leon Battist.a Alberti, Ten_ Books on_ _Errchitectur:~.-' translated by C. Bar-toli (London: Alec Tiranti Ltd_, 1955), Book 22, Chapter 11, p. 36. 81 Cato, V1truv1us,. . P.1' 1ny an d ot h -er anc1ent . sources d o not specify exact temperatures for burnin~ limestone. Alberti specifies that plaster of paris requires twent.y hours of burning, while lime st:one requj.res thirty hours. L. B. Alberti, :!'en ~~ok~, II, XI, p. 36. 126 he takes (the) basket out of water, and will leave it drip for a short while. Then he puts this lime into a barrel until all the lime has been put in barrels. This lime then heats up and ejects itself in smoke. Falls into a poWder and will lose its heat.82 De La Faye f·u:cther suggested that mortar be obtained by mixing this with sea or river sand together with small stones. Soil sand con- sisting of small square grains was preferable, and one the Romans called follitumi was another. Very fine soft sand was not as 83 desirable, and river sand ~~s better than sea sand, De La Faye recommended that five parts of good hard sand be mixed with two parts of the recently baked lime, so that the mortar is fat and thick. If a hydraulic mor·tar was desired, three measures of sieved povilered 84 stone in addition to one measure of lime was needed. George Semple (1700-1782) argued in ~ Treatis~ on Build~~~ 85 in !ifate:t;:_, that Roman concrete laid in courses between wooden plank- 85 ing was still being used in his time. His motive for writing the 82 Mr. De La Faye, On the Way the Romans were Processing Lime for use in_ their B~i.1.d.ings_ ~~- on the s-:ompos:i.tion and-Use of-their - Hortars (Paris: Imprimerie Royale,· 1777). 83 De La Faye was restating Vitruvius here. Vitruvius mentions several types of pit sand, Sl.l.perior to all other sands: black, gray, red, and carbuncular. However a sand that was good for stucco was not good for cement. Vitruvius, On !'rchitecture, translated by Morgan, II, V, pp. 44-·45. 84 De La Faye, p. 37. 85 1 . . d. . ( George Semp e, !2. Treat~se on_ Bu~l J.ng ~n ~~-t.er_ Dublin: J. A. Husband, 1775), Section II, p. 81. 85 Semple states that Alberti's word Cases (III, V) and Palladia's ~Iord coffer or. coffer-work (I, 9, G) are in fact the same t_;hing, nameJ.y the method for laying foundations and building walls. ~-~_§ltise, p. 77. 127 87 treatJ.se. was ut .. '... 1.tar1an;. . . and h e note d t h at wor km· en were responslb. J .e for imparting t.radit.ions prac·ticed in ancient times originally brought 88 to Ireland by Christian monks. In addition, the method of pouring hot lime lnto the walls to .harden them was not an ancien·t tradition, . d . 89 ·b ut may h av9 b een an acqu1re pract1.ce. In Semple's time, hydraulic mortar was known for aquatic work, as well as the use of crushed 90 b r1c. k s or tl . ] .es w h 1c. h could b e m1xe . d w1t . 1 1 mortar. Semple's treatise was written at a time when the London Building Act of 1774, due to fire, encouraged the use of stucco rat.her than wood for building, and specified that brick stone, or burnt clay stucco, artificial stone, lead and iron be used for external ornaments of buildings. Industrial development increased the need for canals, roads, bridges, tunnels, :r·ai.lroa 87 He addressed himself to the repair and rebuilding of br:i.dges and 1't7aS concerned that quick and cheap methods be used. Ibid. , introduc tion. 88 I b'd1 ., p. 79. 89 . . . . ( 1' Hot: mortar was ment1oned by Pranc1s ?r1ce Sa.__:!:-~>bury_ Cat.h_t=:_- dral) in t:he early eighteenth century. Francis Price, !::._ ~1escript.ion £_~!hat A~n2._:~~able St~uc·ture, the_ S::atl?:_edral Church_ of §_alisbury (London: R. Baldwin, 1774), p. 4. Cato, Vitruvius, Pliny, Augustine, and Alberti did not specifically mention a process of using hot lime or mortar. 1'his may therefore be a process adopted later by craftsmen and perhaps limited to England. 90 Like Vitrivius, Semple discusses hydraulic mortar, or !rass, for aquatic vlOrk. Semple, Treatise, pp. 81-83. 91 Norman Davey, !2_ HJ:s' t or'l_ ~ f ~~ . ld 1ng_. I>iace!:_la ' . l~ ( Lon d on: Phoenix House, 1961) , p. 104. The experimentation of the strengt.h of materials occurred at a time when, between 1784 and 1792, over three hundred acts wm:e passed authorizing the construc·tion of new roads and 128 John Si(c '~tton (1724-1792} was the first Englishman to describe himself as a civil engineer. (See Figure 39.) On March 1771, when the Society £~- ~ivil Engineers first met, it was known as the Smeaton~ ian ~ociety. 92 He was asked to design and build a lighthouse at Edystone, which had been destroyed twice by fire and violent storms. 93 Smeaton's first journey to "The Rock" was in 1756. He wanted to build the new structure of stone, similar to the former lighthouse 94 which stood for fifty years. Smeaton concluded that although the previous building had been adequate and spacious, its base had been too narrow. He decided to decrease the top, broaden the base, and bridges in England alone. Still more acts were enacted for the forma tion of canals and harbors, drainage and numerous other measures for improving industrial activity. Samuel Smiles, Selection from Lives 9£ :=-he _:§!n JOHN SMEATOM, CIVIL ENGINEER. ~orn 1724 ; llitb 17!J2; . . . a Figure 39. John Smeaton£ Clvll Englneer 583. 130 95 dove -tail the :" .:ue. The essential problem was how to build a light- 96 house where the ;ortar was constantly loosened by the sea. Once the basic configura Jon had been worked out (see Figure 40), Smeaton turned 97 to the question of the mortar. Experimentation led him to conclude that two measures of quenched or slaked lime in dry powder mixed with one measure of Dutch tarras "beaten together" with the addi-tion . . 98 o f water, was the correct comblnatlon. Smeaton's work demonstrated that the ha.rdness or strength of the limestone did not result in a: 99 stronger mortar. He was also able to conclude that by t.es·t:i.ng many 95 smeaton's use of dove-tailing was derived from Belidor's description of a stone floor at Cherbourg. Ibid., p. 43. 'l'he fo:nner wanted to use iron clamps, but abandoned this when he estimated t.he amount of lead necessary. Pouring molten lead in wet rocks discour aged him as well. Ibid., p. xii. 96 In addition to this problem, Smeaton observed that t.he s·tone used in otlH~r sea-works resembled a honeycomb, due to a small shell fish which destroyed the stone. Even marble was vulnerable. Ibid., p. 52. 91 Smeaton first employed a hydraulic mortar in 1760 in the construction of a lock for the River Colder in England. The use of a mortar mixed with pebbles for the lock came to him when he saw the ruins of the Saxon Corfe Castle in Dorsetshire, whose walls were filled with pebbles set in lime mortar. Cowan, The Master Builders, p. 262. 98 "Beaten together" was a phrase not defined by Smeaton. See footnote 105. The tarras from Holland 1Bd been known since early times, and by the tTme Smeaton' s v.nrk had been published, several treatises were in print which claimed knowledge of the tarras. Smeaton, Edystone L~ghthouse, p. 103. 99 rbid., p. 103. Vitruvius stated "with regard to lime we must be careful that it is burned from a stone which, whether hard or soft, is in any case white." Vitruvius, On Architecture, II, V, p. 45. Pliny's. accoun·t reads: "As for lime, Cato the censor, dis approves of preparing it from variegated li1nestone for white lime stone produces lx!·t·ter quality lime made from a hard stone." Pliny, ~~tural _!-!?.:-Etor'l_, 36, 53. Alberti states: "But the ancient architects 131 . a Figure 40. Edystone L1ghthouse 132 100 different kinr limestone and burning the stone properly he overcame funck: .-.al errors regarding the mixtures and properties of Roman cement. '':' found that after limestone was exposed to a suffi- cient amount of heat, it would, with the addition of water, become 101 h o t , smo k e and swe 11 1n· t o a d ry powu.er·-" ca 11 e d S..l~a·-ked l;me...... m This he distinguished from a pasty kind of mortar, attained when more \~ter is added to it. If limestone was not sufficiently heated, it greatly praise the lime made of very hard. close stone, especially which t.hey say is not improper for any sort of \'Drk, and is extremely strong in arches." Albert.i, 'l~en Books of Archit.ecture, II, XI, p. 36. 100 smeaton does not define precisely what he means by "burn ing prope:t"J.y." The length of time and temperatures used were crucial, but he does not specify what these sl"'.ould be. 101 vit.ruvius did not specify at what temperature limestone was to be burned. His knowledge rest.ed on the results obtained. "If limestone, without being burned, is merely pounded up small and then mixed with sand, and so put into the work, the mass does not solidify nor can it hold together. But if the stone is first throv-m into the kiln, it loses its former property of solidity by exposure to the great heat of the fire, and so with its strength burnt out and exhaus ted it is left with its pores open and empty. Hence, the moisture and air in the body of the stone being burned out and set free, and only a residue of heat being left lying in it, if the stone is then immersed in v.Bter, the moisture, before the water can feel the influence of the fire, makes its way into the open pores; then the stone begins to get hot, and finally, after it cools off, the heat is :cejected from the lxx1y of the lime." Vitruvius, Or:._ Architect.ure, translated by Morgan, II, V, p. 46. By the mid-nineteenth century three distinct methods of slaking lime were known. First, throwing enough water on the lime as i·t comes from the kiln to reduce it to thin paste. Second, emersing the burned lime in water for only a few seconds. It is then withdrawn before the commencement of ebullition; slakes with the wat.er it has absorbed, and falls to powder. Third, leaving the quick lime exposed to the air. Lime, thus exposed, slakes slowly without giving out much heat, and falls to a powder. J. C. Tot.ten, Essa¥~ ~~ Hydr~~li~:. ~~~- S:?_!r_lmo~. ~~_t:_taJ~f?. ar:d o~ Lim~ Burning (New York: Wiley & Putnam, 1842), pp. 7-B. only partly h · .i.nto slaked lime, the residue not being capable of reduction to a ;;:'J.er .102 Smeaton 'i•l burnt lime. HE; concluded: I conceived t.hat a degree of burning may be so much in ·the confines of what is enough and what is not enough, as that the stone may fall to such a degree of fineness as to pass a coarsed sieve, and yet not fall to that powder necessary to form a paste.l03 S'meaton believed that the use of poorly burnt lime was a \vaste and that even if limestone was poorly burned, it could pass through a f·1ner. s1eve . f or purposes o f exper1ment . and use. 104 :r,inally, Smeaton discovered that the longer the mortar \>.'aS beaten, the stronger it: 105 became. He consnl ted chemists on \•.ays to analyze limestone, 102 A third process of slaking is mentioned by Vitruvius, which was reserved only for use in stucco. "If the best lime, taken in lumps, is slaked a good while before it is to be used, so that if any lump has not been burned long enough in the kiln, it will be forced to thcow off its heat during the long course of slaking in water, and will thus be thoroughly burned to the same consistency." Vitruvius, On Architecture, translated by Morgan, VII, 11, pp. 204-205. 103 &neaten, Edystone Lighthouse, p. 108. l 04 ExperJ.ments. wou ld cont1nue. on ca 1 c1nat1on. . . Dr. J. B l acr.,, experimented with t.he g.3.ses driven off by calcination, as well as wi-tl1 tJ::.e properties of cement. "I lately made a paste or cement v1hich may be useful to you on some occasion. '!'he materials are quicklime rubbed to a fine pm·,U.er (not slaked) and molasses, beaten together to a tough adhesive paste. It adheres to everything: metal, glass, etc." Eric Robinson and Douglas McKie, eds., Partners i~ Science, Letters of Jame~- Watt_ and Jo~eph Black (London: Constable, 1970), p. 172. 105T h e "not1on . of t1e 1 workmen? t h e longer mortar was beaten, the stronger it would set" proved to he untrue. Smeaton, Edyston~ Light.house, p. 105. Vitruvius states~ "The Greek stucco-·worke:cs not only employ t.hese methods to make their works durable, but also cons·truct a mortar 'crough, mix the lime and sand in it, bring on a 134 eliminating centuries of errors. He found that the purergrade of limestone was not the best for making mortar used in hydraulic con- struction, and that statements of workmen prior to this discovery were correct. "The best lime for land was not the best for building 106 purposes." Smeaton' s outstanding discovery was the fact that lime- 107 stone mixed with clay was the best material for aquatic buildings. A century has elapsed since the famous Smeaton completed the building of the Edystone Lighthouse. Not only for sea-faring, but for all humanity this lighthouse stands as a true signal of blessed work, a light in a dark night. From a scientific point of view it illuminated the darkness of nearly two-thousand years. The errors which came to us from the Romans, and which were shared even by the ex~ellent Belidor, were dispersed.l08 The Edystone Lighthouse is the foundation upon which our knowledge of hydraulic mortars has been built and it is the chief pillar of modern construction. Smeaton freed us from gang of men, and beat the stuff wit11 wooden beetles, and do not use it until it has been thus vigorously worked." Vitruvius, On_ !\-rchitecture, t.ranslat.ed by Morgan, VII, III, p. 208, VII, I, p. 203. Rondelet confirmed ·the. same process in his work. J. Rondelet, Traite Theorique ~":_ Pr_~ti_g~'~ de ~·Art de Bati~ (Paris: Didot Freres, 1868):-- . 106 Smeaton, Edystone Lightho~e, p. 108. 107 Vltruv:Lus. . recormnended t ha- t t 11e a dd 2tlon. . o f b urnt brlc . k be added to the~ lime. Vitruvius, On A:r_!?_!lit_ecture, translated by Morgan, II, V, 45. un·til the chemical content of clay was analyzed, it was not. well unde:cstood why brick was a good substitute for puzzolana. BrJck, tile and cruder types of pottery were added to ground rock or pre-v·iously baked clay, and even volcanic ash. The essential raw materials o:f. Portland cement are limestone and clay. •.rhese were ground t.oqethcr into a fine povrl.er. Upon the addition of water, the calcitun, aluminum and silicon combine into crystals of hydrous alumina sil;Lcates, and the material sets. Alfred B. Searle, Clays ant:!_ Clay P:r_·~~ucts (London: Sir Isaac Pitman & Sons, Ltd., 1915), p. 7. 108 Bernard Forest de Belidor (1697-1761) published Science Des In~Jer:!-eurs in 1729 and _?rrchitecture Hydraulique (Paris: Cellot, 1782- 1790). He wrote on statics and the strength of materials. 135 the shackles of tradit.ion by shmving us t:hat the purest and hardest limestone is not the best, and that the source of the hydrauliciti of lime mortar must be sought in the argillaceous admixtures. 09 109 wilhelm Michaelis, Die Hydraulischen Mortel (Leipzig: Quandt & Handel, 1869), introduction. CONCIIDSION The articulation of space in concrete, daringly begun by Rome, was not fully exploited until the twentieth century. Vitruvius had written down the precepts for concrete by the beginning of the first century A.D. Due to the spec:ial qualities of puzz_olana, Roman 1 mortar contained a tenacity which ma.de it last for centu.ries. Curvilinear and multilinear ground plans were made possible by the use of concrete, inspiring architect.s o:f Imperial Rome to create u.nprece- dented architectural designs. The basic structural principle, derived by deductions based on experience and observation, was that. the stability of a vaulted structure did not depend upon friction or pressure as in vaults constructed of cut stone, but upon the cohesion and homogeneity of the Roman concrete mass. The Pantheon anticipat:ed to a certain degree the modern practice of obtaining st.iffness and 2 stability in thin vaults by giving them surfaces of double curvature. By the four'ch century, the stability of a Roman vault was still determined by the quality of the mortar and the size of the 1 Marion E. Blake, Ancient ~om~n ~onstruction in It.aly from the Pre]1isto_ri.c Pe~iod _to Augus·tus (Washing·ton, D.C.: Carnegie Institute of Washington, 1947}, p. 159. 2 WJ~'11' 1arn NacDomL.cl :l , The Architecture of the Roman §!fipi.re (New Haven & London: Yale llniversity Press, 1969), p. 165. 136 137 3 foundation. The idea of a continuous arcaded ambulatory around a central dome opened the way for new building schemes in early Christian architecture. Thrust from the central vault to the ground \'Tc:ts in part transmitted indirectly, traveling alon9a..conical route. The ambulatory vault became a continuous buttress, giving way to 4 new spacial developments in architecture. In the centuries following the fall of Rome's Western Empire, brick and stone supplanted concrete, and buildings were higher and vaults became thinner than those monun1ental buildings erected between the first century A.D. and the beginning of the fourth century. The use of concret.e Han~ed. This was due in part to a lack of under- standing regarding statical theory. Beginning about 1160 and con- tinuing for some one hundred years, the Gothic Cathedral unden.vent 5 a period of gro\Vth to unprecedented size. Former structural solu- tions that had been adequate in Rornanesque contributions \ 1onger applicable in tall Medieval edifices. Craftsmen Here forced to lig·hten the fabric. The most critical technical problem was the maintenance of lateral stability. Flying buttresses were designed to resist these lateral forces. The structural forces within the 3 Boethius, Etruscan and Rom<:!_~ Architecture_, p. 511. 4 wi11iam MacDonald, "Some Implications of Later Roman Con s-truction," ,J~~~rnal of the Societ:'Z_ of_ ~chitectural Historians, Vol. XVII, No. 4 (Winter, 1958), p. 6. 5 M. Wolfe and R. Mark, "Gothic Cathedral Buttressing: The Experiment at Bourges and its Influenc:e," Journal of the Society of ·Architectural Historians (March, 1974), p. 17. 138 masonry frame were distributed as if the frame had been constructed 6 from a perfectly elastic, homogeneousmaterial such as concrete. The ambient stress in the shell was so low that the strength of the mortar was 1rre. 1 evant. 7 Concrete Roman domes were self-balancing while brick Go·thic vaults required an intuitive understanding of t:he laws of equilibrium and gravity. The mortar in Gothic vaults was not simply a bed for the joints of. large stone voussoirs, but constituted a thick blanket-like concrete which was incredibly strong. IJittle advance was made on Roman and Gothic forms until the invention 8 9 of Portland cement and reinforced concrete in the nineteenth and twentie-th centuries. ------6 This assumption has been shown to be adequate for predicting structural behavior in tests of reinforced concre·te structures sub jected to service loadings, even though reinforced concrete .is notoriously .inelastic. Ibid., pp. 17--26. 7 Jacques Heyman, "On the Rubber Vaults of the Middle Ages, and 01:her Matt.ers," Gazette des Beaux Art.s, Tome LXXI (May 22, 1968), p. 182. 8 Prior to Portland cement, lower temperatures of 1100-1300° were used in calcinating limestone in order to. prevent the material from fusing. For the manufacture of Portland cement, the mixture was calcinated at: temperatures of 1400~1500° until the carbonic acid was expelled, ground to a fine powder, and mixed with water, sand and aggregate to produce concrete. Jasper 0. Draffin, "A Brief History of Lime, Cement, Concrete, and Reinforced Concrete," University of .!llinois Eu~_;!-etin, Vol. 40, No. 45 (J1.1ne 29, 1943), p. 13. Joseph A.spdin of Leed's claim to have been t..."l1e discoverer of Portland Cement was refuted by Isaac D. Johnson. See Isaac D. Johnson, "The Origin of Portland Cement," Cement Age, Vol. XIII, No. 6 (December, 1911), pp. 254-·257. 9 The early development of reinforced concrete is difficult to ascertain. Jetmes Frost patented concrete. arches between iron beams in 1822. Thomas Potter, Concrete: Its Uses in Building from Fou~datic~n:; to_ !''inish, 3rd edition {London: B. T. Batsford, 1908), pp. 102-103. Dr. H. H. Fox invent:ed in 1833 and patented in 1844 a sys·tem whereby cast--iron joints were used. 1.39 With the Renaissance, dome construction required a new appli- cation of the knowledge of statics and its relevance to the strength of arches. Today, engineers understand that the strength of an arch does not depend upon its thickness, as the Romans believed, but upon its shape, as in Gothic shells. The curved shell resists loads primarily because of its geometric foxm which thereby generates 10 strength. This basic problem o.f statics was not understood until 11 centuries later. Plaster \vas squeezed in and lime concrete was filled in between. In 1840 M. L. Leconte patented a system of iron flitch plates iri con-· junction wit.h wood filled with plaster of paris. Robert Hallet obtained a patent for using wrought-iron joists with arched plates resting between, upon which concrete vas deposited. N .A. "Concrete and St(~el Supplement," The Builders' J~~rnal and Architectural .!':ngi_:::ee:l?_ (,June 20, 1906). Charles Drake devised a concept of metal form--work rather than timber. From this, his company constructed buildings of concrete "bonded" with hoop iron. Bu.?::_~.ding_ ~~w~, July 4, 1873. VJ. H. Lascelles was an architec1: who devised a system of reinforcement for pre-·cast slab constru.ction. The slabs were cast. in moulds with iron rods embedded in concrete to strengthen the slabs. ::£he_ BuiJ::.~r::.£ 1 August 14, 1875. Philip Brannon took ou·t patents in 1871 and 1875 for a system of monolithic concrete reinforced with :i.ron rods. ~~ilders' Journal, May 20, 1908. H. Y. B. Scott took out a patent in 1867 and stated, "The floor becomes ohe solid beam, having t.be tie-rods and hoop iron in combination with the concrete to take the tensile strain, and the concrete to take the compressive r•ction resulting from the weight of the floor." Ernest L. Ransome and Ale;ds Saurbrey, Iteinforced ~oncrete Buildings (New York: HcGraw Hill, 1912) I p. 23. 10 . . . . 1\la.rJ.o G. Salvador, "Thin Shells, " Arch1.tectural Eng 1.neer 1.ng_, Vol. 116, No. I (July, 1954), p. 176. 11 Jacques Heyman, Gazette ~esBeaux Arts, p. 185. In the sixteent.h cr>.ntury, the parallelogram of forces is credited to Simon Stevin (1586), but it vJa.s not until Edme Mariotte (1620-1684) that this law \vas clearly stated. 140 With the scientific revolution of the seventeenth century, confinement of the knowledge of concrete to the "secrets" of ancient Rome was laid aside. John Smeaton's Edystone Lighthouse in the eighteenth cent.ury provided a basis upon which all future concrete architecture could proceed. Concrete ~Bs first used in the service of utilitarian structures in modern times. However, its true poten- tial, i.e., its plasticity, was largely ignored. While England began using concrete for public .:md utilitarian needs as early as the eighteenth century, France did not employ the material in this way until the beginning of t.he nineteenth century. The cause of the 11eglect was partly due to an inadequate mortar as a binding material. It was also due to the belief that ashlar was the only respectable building material for better class homes. From the Hiddle Ages to the end of the eighteenth century, the rich seldom built their man- sions of anything but finely cut stone, while the idea that important public buildings might be built of another material was only enter-· 12 tained in districts traditionally dependent upon brick. The successful production of a high strength cement and the development . h' 13 o:f relnforced concrete changed ·t lS. However, the research into -----··--- 12 Today, concrete is a highly compacted, smooth material, so fine ·that it can reproduce every grain of form--work in which it is cast. Howevex.,, in the 1870's, concrete was rough, with variegated 1mes which even the most advanced Victorian architect had difficulty accepting. Author. 13 The idea of combining iron reinforcement with concrete was not new, but until a high strength cement could give complete protec ·tion against corrosion and the embedded iron, reinforcement was con side:ced hazardous. Rowland Mainstone, Developments in Struc·tural Form (London: Allen k high-strength cement and the testing necessary to establish safe guidelines for its use meant that for every new structural concept developed for concrete introduced by engineers, exhaustive tests were necessary before the material could be safely employed. As research intensified on the problem associated with reinforcement, so did new questions surface regarding elasticity, stress, moments, . 14 and bending strengths. There was still much uncertainty as to 15 t.eh magn:ttu. d e 01-.c t h e stresses :tn. re1n . f. orc1ng. stee1 an d concrete. As a result, architects tended to confine their buildings to the use of traditional materials, while engineers were limited only by ':lhat s·tructural a;1.alysis demanded, thus enlarging their scope of thea- retical knowledge to such an extent that specialization became inevitable. The civil engineer's predilection for immediately per- cep·Live methods were often based on mathematical deductions which offered little inspiration to persons whose interest and abilities ------14 up to the nineteenth century, Coulcomb's discoveries made in 1776 still formed much of the basic informa·t:ion of structural analysis. In 1821, Navier originated the theory of elasticity of three-dimensional solids and established a set of equations for the equilibrium and vibrations of the interior parts of a solid. In 1894, Coignet and N. De •redesco originated the me-thod for computing nominal stress in reinforced concrete beams for the purpose of design. H. M. Westergaard, "One-hundred and Fifty Years Advance in Structural Analysis," American Society of ~j.vi_l Engineers, Proceed· ingo (April, 1928). 15 For all its familiarity and antiquity, concrete has pre sented th~ chemist and engineer with many puzzles. The setting and hardening of concrete involve a number of complex and simultaneous chemical reactions and the process continues for a remarkably long time. I.. E. Copeland, "'l'he Chemistry of Concrete," Scientific ;\lner~~a, Vol. 210, No. 4 (April, 1964), p. 81. 142 16 were more inclined toward artistic intuition. By the beginning of the twentieth century, concrete architecture v:an ed in spite of wide general interest. Unrestricted by building codes and encouraged by the many engineering applications of concrete, the design possibili- ties of ferr·o-concrete tended to be regarded more and more as the domain of civil engineers. Those who persisted in exploring the potential of concrete in their architecture often met with frustra 17 tion. Concret.:e 1 s ugly grey color continued to violate the general view of what a building should look like. Concrete structures in the style of the early Renaissance or Greek Revival performed reasonably well, but buildings with sculptural decorations were not possible to reproduce successfully in concrete. Iron and steel as products of the industrial revolution, began to replace traditional building materials, while concrete had to wait upon a variety of factors to 16 Straub, Engineering, p. 182. 17 A. __1 ong l'1st o-f v1s1onary . . "-··'lduul · ers 1n. bo t h Europe and t h e United States tried unsuccessfully to convince the public of the unique plast.icity and economy of concrete structures. In France, Francois Co.:i.nteraux, Francois Lebrun and Francois Coignet met with financial disaster. Peter Collins, ~ncrete, pp. 23-35. In England, l:.lexander Payne, George Goodwin and Thomas. Potter proclaimed the advantages of concrete to a skeptical audience. See George Good\vin, "Prize E::>sc:.y upon the Nature and Pro-perti.es of Concrete, and its 1'1pplication ·;:o Construction up to the Present Period, 11 Royal Institute_ of Briti~h -~?hitects (January, 1836}. In the United States, principally in California, Leslie E. Ransome, Charles Whittlesley and Irving Gill pioneered concrei~e engineering and architecture. Gill 1 s work especially aroused suspicion. "A dangerous kind of work. 11 See Esther McCoy, !:!v<: California_ Archit~ct~ (New York: Reinhold Book Corporation, 1968}, p. 87. 143 gain architectural acceptance. The question of finding a proper aesthetic for concrete vms paramount to its final acceptance in architecture. One-hundred and fifty years after the completion of John Smeaton's Edystone Lighthouse, concrete was not used in any remarkable new way. Its plasticity, i.e., its ability to be shaped in any way an architect chose, was ignored except by its most ardent advocates. Even more basic to the introduction of new building materials was &'1dre Lurcat' s observation: "Every discovery of a new building method, or a new medium of construction, implies the 18 abandonment of pre-existing values." A:r:t Nouveau was a clearly defined and conscious attempt to evolve an architectural style entirely independent of tradition. The Deutsch W'erkbund was founded in 1907 with the object of improving the standard of machine made products and encoura91nJ the cooperation 19 between architects, designers, and engineers. The Bauhaus followed in 1919, o.nd theorized a synthesis between technology and art. By 1915, reactions against architectural historicism in both E..'urope and America produced demands for an innovative architec-ture based on new mate1.ials, w-ithout reference to the past. The' architecture of con·- spicuous display \vas divorced from the. practical demands of the industrial a.c;-1e, and a new philosophy of design was needed which not 18 Andre Lur~at, Architecture (Paris: Au Sans Parei1, 1929), p. 41. 19 rrhcmas Howarth, Charles Rennie ~-fackintosh and the Mod~rn ~1ovement (Routledge and Kegan Paul Ltd., 1952), p. 69. 144 only utilized modern tecru1ology but also expressed the underlying attitudes of a new generation. Practitioners of the International Style, with their emphasis on volume, regularity of plain surfaces and new materials, did not fully explore concrete. Although they espoused the technological L advantages of the material, they failed to fully explain its poten- t 1a. 1 • 21 Had the modernist possessed sufficient technical knowledge to have followed the lead of Robert Haillart, and later Pier Nervi, "the movement would have been literally 'modern' in a technological 22 sense, rather than symbolically 'modern' in a metaphysical sense." From John Smeaton's Edystone Lighthouse up to the present century, concrete has often been defined in terms of its limitations, i.e., those boundaries to which its plasticity should be confined. Many of the developments in concrete construction were, in reality, aimed at the very negation of all those technological advances which v1ere creating the modern world. Concrete architecture of the 1920's and 1930's fulfilled a sense of rational purism, aust.ere, elementary shapes of mass and space and machine-like functionalism. Throughout this period the originality being sought in concrete forms resided in 21 Reyner Banh arn, ~Ul-~. 'd to Ho d ern Arc h.1tecture ( London: The Architectural Press, 1962), p. 44. 22 Hodern architects simply lost sight of technology by their choice of symbolic forms and symbolic mental processes and t.heir use of the theory of types. William H. Jordy, "The Symbolic Essence of Modern European Architecture of the Twenties and its Continuing Influence," '!'he Journal of A-rchitectural Historians, Vol. XXII, No.3 (October, l963)~-_p_p-:-i77-is7. --- 145 the originality of artistic inspiration, rather than the originality conferred by new structural methods. "'The mark of a good structural organism is the degree to which the qualities and potentialities of steel or reinforced concrete have been fully exploited which follows 23 natural statical forms." Creating an architecture applicable to concrete was dependent in part upon accurate, scientifically tested data. With no other building material have the limits imposed by technical means been so demanding, nor has creative expression been so dependent on physical laws. The combination of the tensile strength of steel and the com- pressive strength of concrete resulted in the, ability to support enormous loads. 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