Christopher Hall De~artmentof Bulldlnq I On the Historv oi Portland after University of Manchester . Institute of Science and Technology Manchester. England M60 1QD 1 150 Years

Cementitious building materials have a long history, and began to build the third Eddystone lighthouse off the the date 1824, traditionally taken as the origin of portland southwest coast of Britain (4),apparently a labor of Hercu- cement, is in fact only the date of a patent (I) granted to les in the absence of a good hydraulic cement. Smeaton, ap- Joseoh Asodin (1778-1855) of Leeds. Eneland. who mav preciating the need to obtain the best component materials not at that'time have made portland cemeit at all. ~oday; fur the lime-pozzolana cement he intended to use, exam- cement is the successor to a line of materials with a historv ined a number of mixtures, and found that the quality de- reaching hack to the ancient world; it has a chemistry o? pended on the limestone (5). He made the important dis- perhaps unsurpassed complexity amongst major inorganic covery that the best mortars were made from limes con- industrial materials and is still the subject of intense study. taining clay impurities. We recognize now that the alumi- At some ~ointin the second quarter of the 19th century, nosilicate clay minerals are closely related to those in the about 150 ago, the cement as we know it now was fir& pozzolana, with this essential difference: that they are produced. burned intimately with the lime in the calcining process. It The very simplest of the mineral cements are those based soon emerged that certain heavily clay-bearing limestones on gypsum, hydrated calcium sulfate. Gypsum loses its were hydraulic in the absence of the pozzolana (6).Such water of crystallization easily on gentle heating to yield materials became known as Roman cements. Various natu- various olasters. These dehydrated suhstances when mixed ral cements of this kind (whose properties depended in an with water reform a crystalline mass of synthetic gypsum, erratic way on the composition of the mineral taken from which however is mechanically weak and is slowly dissolved the ground) achieved prominence in various places in the hv water. There is evidence that the ancientEevotians".. earlv vears of the 19th centurv. The essential roles of lime mixed burnt gypsum with sand to make masonry mortars andsikca in producing hydra;lic cements were established 12). Such mortars were unsuited to less arid climates. and some time before 1818 hv the Frenchman Vicat in his sci- the early bu~ldrrsOII [he nurthtm shores of the Xlediterra- entific studies of innumerable artificial mixtures of lime- nean dt.wlc>oed the ;k~ll; of lime-hurninr ,conversion of stones and clays (7). calcium carbonate to the oxide). The quickkme produced is Thus about the year 1824, a good many people in several slaked with water to yield a lime putty, to which can he European countries were interested in trying to make their added sand to produce a mortar or coarse mineral to pro- fortunes by perfecting these cements. Some were spurred duce a concrete. Such pure lime mortars and concretes on by the belief that the Romans had had a secret for mak- harden slowly and often incompletely by reaction with the ing fine cement which had been lost, and many unlikely carbon dioxide of the air to give calcium carbonate once substances were added in the hope of stumbling upon a more. The Roman builders could achieve superb quality in missing ingredient. Lacking any clear notion of the nature pure lime mortars of this kind-many examples remain of the cementing reactions and using the most variable of today-hut these materials did not set from within the raw materials. thev labored lareelv in the dark. Scientifical- . . u A mass of the paste, nor did they have the quality of hydraul- ly speaking the nature of portland cement did not emerge icily: the capacity to set in contact with water, so valuahle until well into the second half of the 19th centurv. Todav's in many engineering situations. cement is made by heating an intimate mixture of finely Hydraulic limes were produced by hoth Greeks and Ro- eround limestone and clav.. (in ~rouortions. . carefullv " adiust-- mans by adding to the lime putty fine volcanic ash or ed by reference to analyses of raw materials) to a tempera- crushed volcanic minerals, the Romans using the deposits ture sufficientlv. high.. for oartial meltine" to occur (8).The at Pozzuoli, so that now all such materials are known as cooled granular product, a complex multiphase clinker, is pozzolanas. The Romans also discovered that crushed tiles ground to a powder of large surface area. This is portland could act as artificial pozzolanas. Both natural and artifi- cement. It consists primarily of a number of calcium sili- cial pozzolanas are composed chiefly of silica with some cate and aluminate comoounds. When mixed with water it alumina in forms which on mixing with water will react forms a hydraulic paste which sets and hardens to a strong readily with calcium hydroxide from the lime to give hy- solid, larpelv com~osedof hydrates of calcium silicates but drated calcium silicates and aluminates. These important with a remarkahfy intricate physical microstructure. The suhstances are closely similar to the cementing compounds critical variables closely controlled in manufacture are the in portland cements themselves. Because hoth the pozzola- composition of the feed (chalk:clay, 7525) and clinkering na and the lime are present in the mortar, the setting pro- temperature (over 1400°C). Neither Aspdin nor anyone ceeds from within the mass; the extreme insolubility and else for a long time after 1824 fully understood these basic useful strength of these hydrates leads to the property of facts. What then is the basis of Aspdin's claim to be the in- hydraulicity. Lime-pozzolana cements were the only ce- ventor of portland cement? ments available for work in contact with water from the On November 6, 1824, the gossip column of the newspa- Roman period until as late as the 19th century (3). per the Leeds Mercury was preoccupied with its usual In the 18th and 19th centuries, we see the beginnings of business of warning the honest citizens about the dishonest an understandine of whv it is that lime-oozzolana mixtures ("Last Saturdav.-. three females. handsomelv dressed. and Iln\,e thrw rcmarknhle hydraulic pr,,ptrries, and !he ;tart having the appearance of respectable ladies, paid a five of .a I,?horwus ernoiricnl itrun~lp10 make Iwtter and herter ~ound. . . hnnknote.. . to a haberdasher in Leeds, which is cements. But the understanding was a long time coming, not worth a farthing") and gave only a single passing sen- and the early pioneers had very little help from the chem- tence to Aspdin's news. "We hear that Joseph Aspdin, ists of the day. In 1757 the great engineer John Smeaton bricklayer of this town, has obtained a patent for a superior

222 1 Journal of Chemical Education sign (12). The understandine of the nature of the cement cement representing Portland stone." His patent BP 5022: -.. w 1824, "An Improvement in the Modes of Producing an Ar- reactions-both the composition and phase relationships in tificial Stone" consisted of two hrief pages and the rough- the clinker and the details of the hvdration reactions- ness of his manufacturine methods is apparent. His Drocess have been more recent, and the materials science of cement calls for the use of a "specific quantityGf limestoneand of and concrete remains an active and important area of clav hut sadlv. thev . are not specified. Information about the study. burning temperature is of course also absent, as are all de- Advances in knowledae have been brought about by a tails of the kiln which might have helped to establish this. number of modern experimental methods,-such as X-ray However, Aspdin did introduce the name portland cement, diffraction techniques for compound identification, optical a shrewd idea to link the unproven qualities of his new ce- and electron micr©, diffeiential thermal analysis, ad- ment with those of a fine building stone. Unfortunately lit- sorption isotherm techniques, and so on (13). tle is known of Aspdin's manufacturing activities at this There is no doubt that for the first few decades the pro- time. The scanty records have been examined with great duction of portland cement was a primitive manufacturing care by Halstead (6,9).Aspdin was carrying on business as enterprise, even by the standards of the day. The material patent portland cement manufacturer at times during the took a considerable time to penetrate into constructional next ten years both in Leeds and Wakefield, and certainly and civil eneineerine". nractice. and indeed not until the de- later in Wakefield, hut few details have come to light. His velopment of the techniques and structural theory of rein- son William entered the business, and spent the rest of his forced concrete construction were its full potentialities re- rather short life in the cement industry, moving from one alized. venture to the next without ever apparently really prosper- These facts help explain why portland cement was not ing (10). produced in the US until 1871 when David 0. Saylor was The question of whether what Aspdin made in the early eranted his US patent (14). The earlv American portland davs of his business. sav from 1824 to 1830. should be re- cement manufac&ers had to face strong dual competition ga;ded as a true portland cement is a debated but still open from the natural cement industry and from the portland auestion. No specimens appear to he available, though it cements imported from Europe. ~aturalhydrauliE cement may yet he to establish his connection with some had been discovered as earlv as 1818 in New York State, existing building of that period. His product may simply and later in a number of other Eastern seaboard states, and have been yet another artificial hydraulic lime (excess Kentucky and Illinois. The natural cement rocks were lime) or Roman cement (excess silica). No record has been found much more abundantly in these areas than in Eu- found of his early kiln, hut the claim made by a commenta- rope and many of the products established good reputa- tor much later in the century that he used a glass-making tions in the middle of the 19th century. They were used in kiln rather than the cooler lime-hurnine- kiln at least holds huge quantities in the great canal construction projects of out the possihility that he attained the temperatures neces- those years-starting with the Erie Canal in the 1820's. sarv for clinkerine-. (that is. for more complete reaction of The importation of European portland cements started lime and clay), today regarded as essential to cement for- in the later 1860's. The trade was viable only because the mation. cement could travel free of charge westwards across the At- Other evidence which bears on whether Aspdin's early lantic as ballast in tramp careo ships seekine erain or cot- cement should be considered a portland is inferential. Pro- ton cargoes. The ~uropeanindustry at thisdate was well fessor Skempton's detailed studies (11) of the cements of established. The product was reliable and auicklv earned a the middle of the 19th century (including those produced good name. By thk 1890's however the ~mericanmarket for by William Aspdin) provide the basis for making a case cements was expanding so rapidly that the indigenous that Joseph Aspdin had stumbled upon the essential facts portland cement industry was able to establish dominance. of manufacture. Briefly the argument is this. In 1841 Wil- liam Aspdin entered into an agreement with a firm of Literature Cited Roman cement manufacturers, Maude, Son & Co., of Roth- ill Aspdin. J.,"An lmprovemenlin the Modes of Produeinpan Artif~eialStone." Brit~ erhithe, in East London to make the Aspdin cement. There irh Patent 5022:1824. is no suggestion that the son made any innovations to his (21 Lea. F. M., "The Chemistry of Cement and Concrete: 3rd Ed.. Edward Arnold Ltd.. London. 1970. father's process. At this time work was under way on the (31 D~~~~:N., S& Enainaar. 52,193 (197"). building of the new Houses of Parliament following the fire (41 Smeaton. J.. ',A narrative of the buildins and a description. of the construction of of 1834 and in 1843 the contractors carried out tests to the Edystone 1i~hthou~e:'C.NICOI. ~~ndm. 1791. (51 For a life of Smeaton. see Smiles, Samuel, '"Lives of the Engineers: vol. 2, pl, 6. re- compare Maude's new cement with the available Roman print of the 1862 ed., David and Charles. Newton Abbot. England, 1968; Turner. cement. The results of these tests seem definitely to show T.. Endenuour, 33.29 (1974. (61 Halstead. P.. Trow Necueomen Sor ,3437 (1861.2). that the new cement was almost twice as strong- in com- (71 Vicat. L. J., "Treatise on Calcareous Mortars and Cements," John Weale. London. pression as the finest Roman cements available, compelling 1837. I81 For a de~criptionof the modern manufacturing process, see Pollitt. H. W. W., in evidence that this was indeed a true portland cement. If Tsylor. H. F. W.. "The Chemistrv of Cements.'' Academic Presi. Landon and William Aspdin's Rotherhithe cement in 1843 was a port- ~&York.LSbd, p. 27. land, there can be little doubt that Joseph Aspdin's prod- (91 Goading, P.. and Halstead, P. E.. Pior Thirdlnli. Symposium on the Chemistry of Cement. London. 1962. Cement and Concrete Annociation, London. 1954. uct at that time was also. However, whether this was the (10) Much interesting information an the history of the Aspdin iamily, especialiy the same cement as that which he was producing as earlv as suns .lamer and William. has been eathered toeether in a recent ertic1e bv Bar- i0ot.R. .I., Conemla. R, 18i1974). 1824 we cannot at present say. (11) Skempton. A. W.. Trons. N~wcomsnSoc., 35,117 11962). Once the comparative tests of the 1840's showed publicly 112) A vier of the sate of cement msnufaeture at the heginning of this century is pro- vided by Butlor, D., "Portland Cement: its Manufacture, Testing and Uses." the superiority of portland cements over the other calcare- Soon. Ltd..Londonand New York. 1905. ous cements production began in a number of places in Eu- rope and the gradual empirical improvement of the process and the material gathered speed. The development of sound test methods, especially for strength, played an im- portant part in this, as did the refinement of methods of chemical analysis of raw materials and changes in kiln de-

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