HIGHWAY RESEARCH BOARD DIVISION OF ENGINEERING AND INDUSTRIAL RESEARCH NATIONAL RESEARCH COUNCIL
* * * Wa,•tinie Boad Problen,s
* * *
' No.6 PATCIIING CONCRETE PAVEMENTS 1( • WITH CONCRE.TE
HIGHWAY· RESEARCH BOARD 2101 Constitution Avenue, Washington 25, D, C. July, 1943 ..
HIGHWAY RESEARCH BOARD * * * OFFICERS AND EXECUTIVE COMMITTEE Chairman, F. C. LANG, Engineer of Materials and Research, Minnesota Department of Highways, and Professor of Highway Engineering, University of Minnesota. Vice-Chairman, STANTON WALKER, Director of Engineering, National Sand and Gravel Association · THOMAS H. MAcDoNALD, Commissioner, Public Roads Administration
WILLIAM H. KENERSON, Executive Secretary, Division of Engineering and Industrial Research, National Research Council T. R. AGG,. Dean, Division of Engineering, Iowa State College LION GARDINER, Vice-President, Jaeger Machine., Company PYKE JOHNSON, President, Automotive Safety Foundation W. W. MACK, Chief Engineer, State Highway Department of Delaware BURTON W. MARSH, Director, Safety and Traffic Engineering Department, American Automobile Association CHARLES M. UPHAM, Engineer-Director, American Road Builders' Association Director, RoY W. CRUM Assistant Director, FRED BURGGRAF
DEPARTMENT OF MAINTENANCE W. H. RooT, Chairman COMMITTEE ON SALVAGING OLD PAVEMENTS C. L. MOTL, Chairman Maintenance Engineer, Minnesota Department of Highways Sub-committee on Salvaging Rigid Type Pavements
A. A. ANDERSON, Chairman; Manager, Highways and Municipal Bureau, Portland Cement Association L. L. MARSH, Maintenance Engineer, Kansas State Highway Commission C. W. Ross, Maintenance Engineer, Illinois Division of Highways REX M. WHI'l"roN, Maintenance Engineer, Missouri State Highway Department IV a rti11ie R oa,l Pro b le11is There are two major wartime road responsibilities; to keep the traffic essential to the war effort moving, and to carry the existing roads through the war period in as good condition as possible. Dis charge of these responsibilities entails consideration of many new factors in view of the limitations on time, money, labor, equipment and use of critical materials imposed by the exigencies of the national situation. Obviously, changing emphasis from devising better and more economical methods to a program, within the wartime limita tions, of wartime traffic movement and conservation of the existing roads confronts highway engineers with many new problems and new aspects of old problems. The Highway Research Board believes that it can be helpful by aiding in disseminating in usable form the best available information on those phases of highway technology in which common practice has not become established 01; in which practice must be modified during the war. To this end a series of bulletins on WARTIME ROAD PROBLEMS will be prepared by qualified committees and published by the Highway Research Board. Recommendations in this series of bulletins are based upon wartime restrictions and needs and are only intended for use as guides during the periods in which these conditions prevail. This program has been endorsed by the Executive Committee of the American Association of State Highway Officials. Suggestions for suitable subjects will be welcomed. PATCHING CONCRETE PAVEMENTS WITH CONCRETE The best and most economical results in Figures 1 to 5 illustra te each type and patching with concrete have been ob give dimensions, IO(lll. ~ions and jointing tained where careful consideration has arrangements. been given to: The e types 1u·e brrsed on two-lane rural (1) Det.'l.il s of design of the patch. highway pavement. \:Vhere patching is . (2) Preparation of the area to be done on multi-lane pavement.'! or city patched. st reets, ·o me of tho design details may (3) Proportioning, placing, finishing and require modifi cation as described later. curing the concrete. Good practice requires tha t the longi As patching is usually d9ne without tudinal dimension of the patch be at least closing the road to traffic, methods of 4 ft. when the broken area lies at some dis handling t raffi c and providing nclequate tance from a transverse joint. Rectangu protection to the worker and to the b1· patches adjacent to and on one side f completed patch clming the cnring period a.11 expansion joint t' butt constrMtion are also involved. joint should not be less than 6 ft. long; The first step is to determine what areas those 1Ldjacent to nnd on one side of IL need repair and to mark the size and shape contraction joint should not, be les than of the places to be patched. M f~ rking 4 ft long. Reota11gular patches exteu.di.ng the areas involves consideration of the through n.n expansion joint or butt con condition of the existing pavement and struction joint should not be les than 6 the shape and dimensions of a patch that ft. long on either side of the join t; tho e will best stand up under traffic. at each extending through :i oo t1.trnction join t location. The selection and marking of should not be less than 4 ft. long on eithe1· the areas should be done by the mainte side of the joint. . nance engineer in charge of the road. On full width patches (Fig. 1), whr br.eakage has occurred on each side of .. DESIGN tra nsverse joint, a minimum length of patch may be ust>.d by tihifting tl1 e position Size and Shape of the joint to one end of the p~tch tts The shape and dimenaio11s of a pn.tch indicated in F igure 1. On mult.i-h1110 pave 1,1, ncl its position in the pavement with ments wh ere no median strip is used, it is respect to edges and joint.~, are directly desirable to maintain the original positions related to its ability to stand up under of the transverse joints. In such cases a traffic. For this reason the patches have minimum 12-ft. length of patch (6 ft. on been grouped in five types according to either side of the joint) is used at expansion their location in the pavement as follows: joints and an 8-ft. length at contraction joints. Type When the breakage is in one lane only, 1. Full width patch- constructed a but extends from the edge the center lane-at-a-time. to width patch is necessa-ry. 2. Half width patch, involving a single j,oint,, a half Fo r details see Figure 2. In case rm expansion traffic lane. joint is included, it mu t be extended 3. Exterior edge patch. through the new concrete from its position 4. Interior edge patch. 5. Plug patch. Plug patches may be in the undisturbed lane. Better results rectangJ,Jl.ar or diamond shape. are obtained when the joint material is of The Ja.tter is used where bnd spall the same thickness and general character ing or interior corner breaks occur as that remaining in the original joint. and the concrete on the diagonals Rectangular patches less than one traffic is sound and strong. lane wide at an exterior or interior edge of 4 (
the pavement (Types 3 and 4, Figs. 3 and 4) most effective when the patch extends out have given best service when their width a distance of not less than 4 ft. nor more (transverse dimension) is not less than than 6 ft. from the centerline and is not 4 ft. nor more than 6 ft. so that the longi less than 4 ft. long. tudinal edge of the patch falls where there Diamond shape plug patches have been is a minimum number of wheel load appli used successfully for interior corner break cations. The length or longitudinal di age. Their shape and dimensions are mension should be not less than 4 ft. when shown in detail m Figure 5. They are
[•p.insion Joint
B
A PATCH BETW[[N JOINTS PATCH AT EXPANSION JOINTS
Ste. A·A CONSTRUCTION FIRST LANE
SEC. A-A CONSTRUCTION COMPLETED
4'minimum Nol)•ellrudlng t.lller E,pans 10<1 joint .it end of patch SEC B·B SEC·C·C FIGURE 1-Type 1, Full Width Patch. Construction, lane-at-a-time
the broken area is some distance from a built in one Jane at a time. Best results transverse joint; a minimum of 6 ft. on one have been obtained when the transverse or each side of a transverse expansion dimension on each side of the longitudinal joint; a minimum of 4 ft. on one or each joint is not less than 4 ft. and not greater side of a transverse contraction joint. than 6 ft. The overall longitudinal di Plug p1tches of either rectangular or mension is controlled by the angle formed dia~ond shape may be used for interior between the sides of the patch and the breaks which occur on both sides of the longitudinal center joint. For patches center joint. See Figure 5. some distance from joints this angle should Rectangular plug patches have been not be less than 30 nor more than 60 deg. 5 Le e At transverse expansion joints this angle Where the wheel loads do not exceed the should be not less than 30 nor more than load carrying capacity of the pavement as 45 deg. W11ere the diamond shaped plug a whole and where unsatisfactory sub patch CM be used, it effects a considerable grnde conditious hiw e been corrected, the saving in concrete ov r that required for a follo"ing thioknes es of patching are satis rectangular patch. factory (D in' Jt~gs. 1, 2, 3, 4:, 5) :
E•pai'l9' 10n joint
C
. 6' min.imum II 6'mlnimum I Exist ng longitudinal joint
SEC. A-A
SEC. C-C )
SEC B-B
Details of expansion joint in half ~ .ldth patch at original expanoion JOlnt.
FIGURE 2-Type 2, H alf Width Patch
Thickness of Patches 1. Thickened Edge Slab For simplicity of construction and be A. Center thickness of original slab cause of the wartime limitation on the use multiplied by 1.3 on all patches ,of steel, it is recommended that patches be involving unprotected corners. of uniform thickness and that distributed B. Center thickness multiplied by 1.2 reinforcement, dowels and tie-bars be on those patches involving pro eliminated. The thickness of the patch tected corners. will be determined to a lal'ge extent by 2. Uniform Thickness Slab with Load existing subgrade conditions and the weight and volume of traffic the road will Transfer Devices at Expansion Joints carry durLng its remainiog life. A. De~th bf original slab multiplied 6 (
by 1.1 for all patches involving and 2-A and should be tapered off in a unprotected corners. distance of 5 ft. from the joint. If the B. For all other patches use same original slab is of uniform thickness without depth as existing slab. load transfer devices and th~ subgrade is 3. Uniform Thickness Slab without Load satisfactory, the depth of the new concrete Transfer may be the same as that of the existing A. Use same depth for patch as that pavement. of existing slab. Where the breakage has occurred at a
Existing pavnrnent
SEC A-A
SEC B·B
b' minimum b' minimum
Non-cdruding filler to be.used, s:ame thickness as in undialur bed part of' joint SEC. C·C FIGURE 3-Exterior Edge Patch, Type 3
These recommendations cover patches few locations due to inadequate subgrade for relatively small areas. Where full support and it is possible to correct per width reconstruction of thickened edge manently the subgrade condition, the re pavements or uniform thickness pavemen placement of such areas with concrete of having lond transfer device 11.t joints, the same cross-section as the existing slab extend for 50 ft. r more, it is suggested is satisfactory. that the thickness be made uniform as in 1-B or 2-B respectively, and that the slab Reinforcing ends at transverse expansion joints be In some cases it may be practicable and thickened. The thickness required at the desirable to reuse old dowels and tie-bars expansion joints may be obtained from 1-A found in broken areas to prevent faulting 7 or separation of the slabs. They are not necessary in payements haying deformed • needed structurally for patches of the metal center joints or other forms of longi recommended thickness. In some in tudinal center joints as well as in those stances complete removal and discarding without longitudinal joints because the of dowels and tie-bars may give better pavement in the second lane to be patched access to and permit better preparation of is usually badly broken and tbe impact the subgrade and may facilitate placing of from the wheel loads passing over it will hew concrete. cause detrimental vibration in the new
V:a rl ab10 &"minimum NQt less ttlan 4' nor morn than 6' Existing longitudinal Joint
Existing p:avemonl? j 1<2 Width p>vymtnll
~•AW.Mil . ' •·• ' A • ,A~;.~.:~[~;p~KwXII\Ok*tA" Longitudinal Jolnr...7' I V>ri~blo I 4"to6" SEC A-A
SEC B-B
Non-extruding filler to be used, s:ime thickness as in undisturbed part of joint SEC. C-C AT EXPANSION JOINT
FIGURE 4-Interior Edge Patch, Type 4
Jointing concrete in the first lane patched during Longitudinal Center Joints-Full width the early hardening period unless the new patches must be built a lane-at-a-time if concrete is left free from the broken con traffic is to be maintained. This requires crete in the adjoining lane. a construction joint at the longitudinal The same procedure should be used in center joint. In this case it is necessary placing diam~nd shape and rectangular to break out the concrete of the second lane shape plug patches in which one-half of enough to permit a side form to be set for the patch is constructed at a time. the patch in the first lane. This is shown Where half width patches of type 2 or in detail in Figure 1. This procedure is interior eclge patches of type 4 are to be s (
placed in pavements having deformed original devices may be reused depending metal center joint or dummy groove center upon their condition. joints, the face of the joint should be Expansion joints located in areas to be cleaned and the new concrete placed patched full width (type 1) may be omitted against it. unless inspection of the pavement in the Transverse Joints-If the areas t:i be vicinity of the patch shows that additional patched in types 2, 3, 4 and 5 originally expansion space is necessary. Where space
Nol le55 than 30'nor mor
SEC. A-A
Variable I (>"minimum &"minimum SEC. C·C txisting p~vemant- Non-axtrudlng f lllo Sarne thlck.,noss as that (n undisturbed part of Joint The cross -sections ot the cli amond patch are similar to thosQ of the rectangular patch
FIGURE 5-Plug Patch, Rectangular and Diamond Shape, Type 5
contained transverse contraction or ex for expansion mnst be provided, the joint.s pansion joints, such joints should be re can be placed cit one or both euds of the placed in the patched areas in the same patch as iudico.tcd in Figure 1, and at such relative position as in the original pave intervals in the length. of the patch ns ment. The thicknesses of patches recom deemed necessary. A plain, non-extruding mended does not require the use of load type of joint filler has been found satis transfer devices. However, if the trans factory for use in replacing expansion joints verse joints originally were provided with in or adjacent to patches. If the lengths of type 1 patches are 30 ft. load transfer devices, their replacement is or more, transverse contraction joints are a matter of judgment. In some cases the recommended at intervals that will form 9 • slab lengths of 15 to 20 ft. The dummy striking drills, chisels and sledges· to line groove type of contraction joint is recom and to a plane not more than 1 ! in. from mended for all patches. vertical. On multi-lane pavements, it is desirable Where a patching project involves areas to maintain the original position of joints. which are not too widely scattered, pave This will require placing of expansion ment breaking equipment will be more joints as indicated in Figure 2 regardless economical. A unit employing pneumatic of the number of lanes to be patched unless paving breakers includes a portable air the patch involves aHtraffic lanes. compressor of size sufficient to. service two 80-lb. pneumatic breakers, about 50 ft. of PREPARATION OF AREA TO hose for each breaker, a utility truck for BE PATCHED pulling compressor and carrying signs, barricades, breaker bits (chisel and moil Improving Subgrade Support Ad;. point bits) and small tools, and two 1 !-ton dump body trucks for hauling broken con jacent to Patches crete. A minimum crew for such a unit Where pumping action has caused break would consist of eight men: a foreman, two age, it may be desirable to improve the breaker operators, three laborers and two subgrade support of the pavement adjacent truck drivers. to areas to be patched. This may be Breaker operators first outline the area accomplished by pumping a slurry of soil to be patched by moving chisel bits having and cement or other mixtures under the a 2 to 3-in. face continuously over the line pavement to fill the voids that have devel marking the area, letting the breaker strike oped under the slab as described in the only a few times in one spot. After two Highway Research Board Wartime Road to fom trips over the line, the groove is Problems No. 4, "Maintenance Method generally deep enough to cause the con for Preventing and Correcting the Pumping crete to break along the line. This not Action of Concrete Pavement Slabs." This only insures a clean break but protects the operation, when performed before patch adjacent concrete from being broken o ing, materially improves the subgrade sup damaged. In some cases it may be pre port and life of the pavement adjacent to ferred to score the pavement about 6 in. the patch. inside the area to be patched and break out the remainder with hand tools. Cutting Old Slab The concrete is removed by each operator The size of the crew and kind of equip first working a hole through to the sub ment used in cutting out the old slab will grade in order to have a free face from depend on the amount and nature of the which to work. Moil point bits are gen patching to be done. erally used for this. purpose. Each oper Where only one or a few widely scattered a tor then works back from this face using patches are needed to keep the pavement moil point and chisel bits and breaking in satisfactory service and moving in the concrete into as near one-man size breaking e~uipment is not justified, the blocks as is practicable. Laborers working old pavement may be broken out by hand. with sledge hammers, picks, spike bars, The old slab in the area to be patched may crow bars and shovels remove the broken be broken with 12 to 16-lb. rock hammers concrete and keep it away from in front into one-man sizes. Spikes or crow bars of breakers. The broken concrete is loaded used to raise slabs so that spalls can be into trucks or placed in temporary stock placed under one side of the blocks will piles along the edge of the patch or on the make breaking easier and faster. The shoulder. The truck drivers haul the ma broken material should be removed from terial to a dump or a convenient stockpile the area, disposed of or hauled to a nearby for future maintenance use. stockpile for future use. The edges of the Where the size and number of patches area to be patched are then cut with justify their use, other types of pavement 10
) breakers may be used. One is a mobile tremely difficult to cut out all the subgrade unit which consists of an air compressor under the slab to obtain a trench of the and trip hammer mounted on a flu.t bed proper dimensions and to make sure that t rnck. The trip ha mmer is mounted on a the bottom of the original slab is com semi-circul ar bed on t he rea1· of t he truck pletely exposed. Furthermore, it is also in such a way that the hnmroet· will swing difficult to completely fill the excavation through 180 deg. The trip hammer havi ng under the old pavement with compacted a face 6 to 8 in. in diameter strikes about concrete. If either of these two conditions 100 blows per minute and break. . the old exist after the patch is completed, no added pavement into one.-ma.n sizes. This support for the old slab will be obtained by breaker equipment is used in coJ1junction underpinning. with a porta ble air compressor and _pneu matic breaker u11i t fol' outlini11g the areas Subgrade Preparation to be . patched, to break out areas in the Frost boils, frost heave, seepage from corners of patches and to trim the. edges rock outcrops, or nonuniform soil deposits, vertical and to a neat line. as well as capillary rise from high water The sides of all openings should be cut tables, and numerous other conditions to within 1 ! in. of a vertical plane. To which permit softening of the subgrade obtain best results all edges should be may have contributed to the pavement mn de as stl'aigh t as pm.cticabl and approx breakage. Therefore, if a patch is expected imn.tely at right angles or pat·allel to th to withstand traffic, the subgrade at such center line and ed s of the origini~l slab, locations must be made equal in supporting ex ept in the diamond type plug patch. value to the subgrade under the adjacent The edges of this type are to be at an unbroken pavement. angle with the center line as shown in Where poor drainage is obvious, water Figure 5. must be removed or intercepted by dmins, or the water table lowered, as the case may Trimming Edges require, before patching. The top inch of the vertical face of the In addition to providing drainage it is old slab should be cut as straight and usually necessary to remove wet unstable vertical as possible in order to avoid fins subgrade soils and replace them with suit of either old · or new concrete extending able material, adequately compacted. across the junction of patch and pavement. Where subgrade conditions under the If such fins are left they will cause spalling broken pavement are unusually bad, it may later. It is also advisable to cut the be well worth while to replace the subgrade corners of the opening so as to eliminate material with a selected material having acute angles. higher bearing capacity. In general, it is best to prepare the sub Cleaning Edges grade for patches in the same manner as The edges of the old s_lab must be cleaned would be done on a new project, compacting free from dust, dirt or loose particles. Just it in lifts of_ proper thickness up to sub prior to plo.ciug new eoncrete the edges grade elevation for the patch and wetting should be thoro\1ghly dampened to secure the soil prior to placing the concrete. good bond. Most satisfactory results are obtained if the edge of the original slab THE CONCRETE. is just moist enough to be free of dry Materials foreign matter, but not wet enough to interfere with the new co ncrete adhe1-ing . Portland cement, fine aggregate, coarse firmly to the edge. aggregate and water used in the concrete mix and the materials used for curing the Underpinning Old Slab patches should comply with the standard Undercutting the old slab is not recom speoificati ns for portland cemeut con.qrete mended as a general practice. It is ex- pavement construction of the tate high- .. 11 e Way department or other unit of govern cement content which _will ·be required to ment having jurisdiction over the road. maintain workability of the concrete. Calcium chloride not exceeding 2 per Concrete Mix cent of the weight of the cement may be Proportions of cement and aggregate added to both normal portland cement and and the amount of mixing water for the high early strength portland cement mixes concrete mix to give the desired strength to increase the early strength. The addi and satisfactory durability should be es tional strength that may be obtained in tablished by the supervising division of the this manner can best be determined by highway department or engineer in charge tests with the material to be used. The of the road and furnished to the· patching available data indicate that an admixture crew prior to starting the work. of 2 per cent of calcium chloride may be The concrete for patches should be expected to produce an increase of about mixed as dry as can be properly placed, 160 lb. per sq. in. over the one day flexural compacted and finished in order to mini strength of normal portland cement con mize shrinkage during hardening. A maxi crete without the admixture where both mum slump of 1!-in. as measured by the concrete mixtures have a water-cement standard slump test, American Association ratio between 4 and 6 gal. of water per of State Highway Officials (No. T-119-42) sack of cement and are cured at normal is recommended. temperatures. Similarly, the one day Concrete for patching should be de flexural strength of concrete made with signed so as to obtain high early strength high early strength portland cement will be and permit opening to traffic as soon as increased about 110 lb. per sq. in. by the possible. A modulus of rupture of 500 lb. addition of 2 per cent of calcium chloride. per sq. in. is recommended as the strength For both normal and high early strength at which to open patches to traffic except portland cement concretes having a water in cases of emergency when opening at a cement ratio between 4 and 6 gal. per sack lower strength and probable damage to an of cement and cured at normal temper occasional patch may be justified to lessen atures, an addition of 2 per cent calcium inconvenience to traffic. Generally, it will chloride increases the flexural strength at, be desirable to open patches to traffic in 3 days only 25 to 50 lb. per sq. in. and there 24 to 72 hours depending on the locations is little or no increase at 7 and 28 days. of the patches and the conditions under When used dry, calcium chloride should which the work is done. be placed in the skip of the concrete mixer High early strength concrete may be with the aggregate but not in contact with obtained by use of: the cement. When used in solution, the 1. Low water cement ratios with normal calcium chloride should be introduced into portland cement, the drum of the mixer with the mixing 2. High early strength portland cement, water, the solution replacing an equal vol 3. An admixture of calcium chloride ume of mixing water. with either normal or high early Concrete containing calcium chloride strength cement. hardens more rapidly than plain concrete Data from tests in the State or particular and must be finished soon after placement. locality will provide the best basis for Care must be taken not to use more than designing concrete mixtures to give the the recommended amount of calcium chlo strengths desired at early ages with the ride. More than this may reduce the materials available. In order to avoid ex strength and cause such rapid hardening cessively rich mixes with attendant possible that the concrete cannot be properly placed difficulties of placement and curing and and finished. excessive volume changes, water-cement When facilities are not available for the ratios less than about 4 gal. per sack of design of mixtures based upon tests of cement should not be used. The lower locally available materials, or if standard the water-cement ratio, the higher the specifications for high early strength con- 12 crete do not prevail in the locality, the use specific gravities in a saturated surface-dry of arbitrary mixes from Table 1 is recom condition of 2.65 plus or minus 0.05 for mended. s,<1.ncl, gravel and crushed stone, and 2.25 The mixtures in Table 1 are designed to plus or mjnus 0.05 for crushed slag. 1 r yield concrete slightly better in quality th r pc i!ic gravi ties, the weigllts should than that specified by the American Asso be corrected by multiplyin the weights ciation of State Highway Officials for con , l1own in t;he table by the ratio of the speci crete of strength of 550 lb. per sq. in. at fi c gm.vities of the u.ggrego.tes used and 14 days. 1 They are derived, with a reason tho e u e I in com puting the ta.bJ e. 'I1 he able margin of safety for quality of aggre- bulk specific gravity tests should be made
TABLE I. CONCRETE FOR PATCHING Typical weight proportions which will be rcquired for concrete to be cured 1, 3 or 7 days before opening to traffic Slump: Maximum 1! inches
Approximate Sa turated-&urlncc dry weight of sand and Quantities coarse aggrcgnle per sack of cement Calcium chloride Wl1cn gravel is When crushed stone or Type Cement per sack of used as'"' coarsc crushed slag is used as cement Cement Water aggregate coarse aggregate rie r cu. yd. per sack Sand Crushed' Crushed I Gravel Sand I stone slag (a) When patch is to be opened to traffic after curing 24 hours lb. H)gh-ea~ly-st1:ength ...... · I 0 High-early-st1ength...... 2 (b) When patch is to be opened to traffic after cming 3 days -- - Normal pot·~land ...... 0 8.0 4.2 130 265 150 245 210 Normal portland ...... 2 7.0 4.7 150 300 170 280 240 High-early-strength ...... 0 5.5 6.0 200 400 230 370 315 . .) High-early-sLrength ...... 2 5.0 6 " 225 455 260 420 -355 ------(c) When patch is to be opened after curing 7 days Normal portland ...... , 0 5.5 6.0 I 200 I 400 I 230 370 I 315 High-early-strength...... 0 5.0 6.5 225 455 260 I 420 355 gates, field uonditions an I proportioning, in accordance with A.A.S.H .O. Method from the relationship. between water T-84, Section 6, ::incl Method T-85, Sec cement ratio and mod ulus of rnptu re shown tion 6. (A.S.T.M. Methods C 128 and in Figure 6, with the mod ificntions for use ' L2'7 , respecti vely.) of calcium chloride previously discussed. , 'in ·o the w ight.s given in tho Lable ar Tests of individual materials may show ·omputcd fo r aggregtitcs in a snturnted considerable variation in flexural strength surfncc-dry •ondition, the batch weights for a given water-cement ratio clue to shou Id be corrected to accord with the variations in cha,racte1·istics of aggregates. moisture condition of the aggregates de However, the relative effects of age, type livered to the weighing bin. Absorption of cement and calcium chloride admixture tests should be mnde in accordance with wiJl be 1~J)p1·oximately as indi c11ted. A.A.S.H.O. Methods T-84, Section 8, and The proportions given in Tabl e 1 arc T-85, Section 8. (A.S.T.M. Methods based on tho use of nggreg11.t hnving bulk C 128 and C 127, respectively.) The weights of sand and coarse aggregate •A.A.S.H .O. Specifications for Concrete Pavement Construction (1940). given in Table 1 have been calculated on 13 e the basis of using a well-graded natural done by weight to assure accuracy and sand in combination either with a coarse uniformity in the composition of the con aggregate graded from No. 4 to 1! inches, crete. Small portable scales are com or with a coarse aggregate graded from mercially available for use where the vol No. 4 to 2 inches. The relative weights ume of concrete to be placed does not 'of fine and coarse aggregate may be ad warrant the use of a central proportioning justed by the engineer to insure concrete plant. The mixing water may be meas of satisfactory plasticity and workability, ured by volume or by weight and the
1 Concrete made with Concrete made w ith normal portland cement high early strenglh pqrtlaod c~/nllnt r-...... 600 000 ...... ", ...... I"- " r'-..
4 5 6 7 $ & 7 8 NET WATER-CEMENT RATIO - Gallons per sack
FJGUnE 6-Relationships between llex.ural strengLb and wn.tox-cemc11t ratio of concretes made with o.orn.ml and high el,\rly strength portlancl \V ARTIME ROAD PROBLEMS No. 1. Curing Concrete Pavements Under Wartime Restrictions on Critical Materials. No. 2. Design of Highway Guards. No. 3. Design of Concrete Pavements Requiring a Minimum of Steel. No. 4. Maintenance Methods for Preventing and Correcting the Pumping Act.ion of Concrete Pavement Slabs. No. 5. Granular Stabilized Roads. No. 6. Patching Concrete Pavements with Concrete. No. 7., Use of Soil-Cement Mixtures for Base Courses. No. 8. Thickness of Flexible Pavements for Highway Loads. No. 9. Treatment of Icy Pavements. No. 10. Salvaging Old High Type Flexible Pavements. IN PREPARATION Compaction of Subgrades an_d Embankments Soil-Bituminous Roads. 16 L)