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EFFECTS OF CURING AND DRYINGENVIRONMENTS ON SPLITTINGTENSILE STRENGTH OF CONCRETE

By J. A. Hanson

Authorized Reprint from CopyrightedJournal of the American Concrete InstituteJUIY 1968, Proceedings Vol. 65, pp. 535-543.

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EFFECTS OF CURING AND DRYINGENVIRONMENTS ON SPLITTING

TENSILE STRENGTH OF CONCRETE

By J. A. Hanson

P OR TI .AiND C EX4E NT AS S OC IATI ONRE SE ARCH AND lIEVEI .OP ME Nl LAB OK.+ TOK1E3

.5420 OId OrchardRoadSkokie.Illinois 60076

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TITLE NO. 65-40

Effects of Curing and DryingEnvironments on SplittingTensile Strength of ConcreteBy J. A. HANSON

The splitting tensile strengths of lightweight andnormal weight concretes were investigated in twotest series which clea 1+ with the effects of thecuring and drying environments. The first seriesshowed that the duration of the initial moist cur-ing period prior to drying a+ 50 percent relativehumidity had little effect on the splitting tensilestrength. While there was a loss of splittingstrength for the lightweight concrete early in thedrying periods, continued storage in the dryingatmosphere led +0 considerable gain in the split-ting strengths. In the second series, concreteswere subiected to cirying for 2 I days a+ differentlevels of relative humidity after initial moist cur-ing for 7 days. Only minor changes of splittingstrength were found as the relative humidity variedfrom 75 to IO percent.Keywords: age-strength relation; compressivestrength; concretes; curing; drying; drying shrink-age; expanded shale aggregates; fine aggregates;gravel (material): humidity: lightweight aggre-gate concretes; lightweight aggregates; moist cur-ing: moisture con}ent; Monfore relative humidityprobe: research: sand (material): splitting tensilestrength; testing.

W THE SPLITTING TENSILE TEST (ASTM C496-66)has been adopted as a convenient and relativemeasure of the tensile strength of concrete. In thetest, a concrete cylinder is placed on its side in thetesting machine and subjected to diametral com-pression. Such compression induces uniform ten-sile stresses normal to the loaded diameter, caus-ing the specimen to fail by splitting along thediameter. Reference 1 provides a discussion of

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early studies of this test and its concomitant ad-vantages and disadvantages.Over the past few years, several investigational-~have shown that some amount of drying of struc-

tural lightweight concrete may reduce the split-ting tensile strength of concrete cylinders. Similarbut more erratic results have been obtained frommodulus of rupture tests of plain concrete beams.On the other hand, such drying of normal weightconcrete appears to cause only a small reductionof the splitting strength, and some increase mayeven be evident. This same relative behavior hasbeen found with concretes steam cured at at-mospheric pressures and then allowed to cool anddry at room temperatures.~,~ The splittingstrength of the steam-cured normal weight con-crete at 28 days was about 98 percent of that ofcontinuous moist-cured concrete, while the split-ting strength of the steam-cured lightweight con-crete dropped to about 75percent.Close correlation Isghas been shown between

the splitting tensile strength of lightweight con-crete subjected tc~a period of drying and thediagonal tension strength of reinforced beams andslabs containing the same concrete, though littleor no correlation was found with concretes con-tinuously moist cured. This relationship betweensplitting tensile strength and diagonal tension re-sistance was adopted by ACI 318-631) to computethe contribution of lightweight concrete to theshear resistance of reinforced beams and slabs.Section 505 of the Code provides that the splittingtensile strength of lightweight concrete be de-termined after 7 days moist curing followed by 21days drying at 73F (23 C) and 50 percent relativehumidity. Since most research has been performedunder these same curing and storage conditions,questions have arisen as to the minimum strength

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3that may be encountered in practice with othercuring periods, or with drying at other ambientrelative humidities. A further question has beenraised regarding the amount of tensile strengthwhich may be recovered with additional age ofdrying concrete.The two somewhat limited test series reported

herein provide some insight into these questions.Series I was planned to study the effects of variousdurations of initial moist curing on the splittingtensile strength of drying concretes at intervalsof time up to 2 years. Series II concerned theeffect of drying at relative humidities other thanthe generally prescribed value of 50 percent.Such a study is of importance to the humiditycontrol required in commercial testing labora-tories.

TESTING PROCEDUREAggregates and concrete mixesThe concretes used in both test series utilized

a single lightweight aggregate and a single normalweight aggregate, both in their commercial grad-ings. The gradings of the fines of both aggregatesfell within the limits of ASTM C-330-64T andASTM C-33-67, respectively.The lightweight aggregate (No. 14 in the PCA

series) was a rotary-kihi expanded shale. TheLong-time ACI member .). A. Hanson i s manager , Laboratory

Research Section, Construction Methods Department, PortlandCement Association Research and Development Div is ion, Skokie,Ill. At PCA Mr. Hanson has beet? concerned with all types ofconcrete products, Iightweight concrete, concrete masonry,architectural concrete; and prefabricated building elements. Heis the author of numerous papers and reports. Currently, he isa member of the Institutes Technical Activities Committee,chairman of AC! Committee 303, Architectural Concrete, and amember of AC I Committee 213, Lightweight Aggregates andLightweight Aggrqaie Concrete, and Committee 533, PrecastPaceIs. tie is also a member of the Federation Internationalde la Precontrainte Commission on Prestressed LightweightConcrete, and a member of the Building Research Institute.

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6

obtain the compressive strength (two specimensper test) and the splitting tensile strength (fourspecimens per test) as a function of time to 2years age of concrete. In addition, these prop-erties were determined for continuously moistcured concretes. In the case of the Elgin normalweight concrete the same properties were deter-mined only under continuous moist curing, andafter 7 and 28 days of moist storage followed bydrying.Four additional lightweight and two normal

weight specimens, one from each of the initialmoist storage conditions, were inst~umented to ob-tain relative humidity distribution, weight loss,and drying shrinkage. Brass tube wells, 5/32 in.(4 mm) inside diameter to receive the Monforerelative humidity probe,l:] were installed at dis-tances of Y4, 3A, 13A, and 3 in. (6, 19, 44, and 75mm) from the cylinder exterior surface. The wellsallowed a gaging length of 1 in. which was cen-tered at middepth of each 6 x 12-in. (15 x 30-cm)cylinder. The cylinder ends were sealed with anamide epoxy to force all drying of the concrete tooccur in the lateral direction. Drying shrinkagewas obtained witk a 10-in. (25-cm) Whittemorestrain gage. Fig. 1 shows a typical installation ofwells, gage points fo,r Whittemore gage, and directreading relative humidity indicator.Series 11The purpose of this series was to

study the effect of storage at various levels ofrelative humidity on the splitting tensile strengthof concrete otherwise tested in strict accordancewith Section 505 c)f ACI 318-63.1( Ten batches ateach strength level of the three concretes pro-vided four specimens for compressive strengthand eight specimens for splitting tensile strengthat the five levels of relative humidity storage of100, 75, 50, 30, and 10 percent. The specimens were

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7placed in these atmospheres after 7 days of moistcuring and were all tested at 28 days. The ambienttemperatures accompanying each relative humid-ity level were controlled to 73 L 2F (23 L- 1C).Two control cylinders from each batch were testedfor compressive strength after storage at the stan-dard conditions (ASTM C330-64T) of 7 days moistcuring followed by 21 days drying at 50 percentrelative humidity.In both series of tests, with the exceptionsnoted above, compressive strength was deter-mined according to the requirements of ASTMC39-66, and splitting tensile strength accordingto

Fig.

J(JL

ASTM C496-66.

.4$-: - -L.

a

iinstrumentation for relative humidity measurements6 x 12-in. concrete cylinder.in

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TEST RESULTS AND DISCUSSIONSeries IRelative humidity distributionTables 2a and2b present results obtained on relative humiditydistribution, drying shrinkage, and weight lossof the 6 x 12-in. (15 x 30 cm) cylinders over the 3year storage period. Fig. 2 is a typical plot of thesedata for the particular condition of 7 days moistcuring followed bydrying at 73F and 50 percentrelative humidity. Perhaps the most striking fea-ture of the data is the long period of time indicatedfor 6 x 12-in. concrete cylinders to attain moistureequilibrium in the 50 percent relative humidityatmosphere. After 3 years of drying, the relativehumidity at the center of the lightweight concretecylinders varies from 57 to 64 percent, dependingon the length of initial moist curing. The normalweight concretes dried somewhat faster than thelightweight but these too have not reached mois-ture equilibrium. It should be noted that, whileconsiderable moisture gradients still exist in theconcretes, after 1 year of drying the weight lossand drying shrinkage curves have nearly at-tained equilibrium. The low drying shrinkage in-dicated by this particular lightweight concrete,relative to that of the normal weight, has beenfound in other studies.~Such indications with these relatively small con-

crete cylinders point toward the extreme slow-ness with which full-sized structural memberslose moisture. The extremely slow rate of dryingof large concrete sections leads to reduced creepand shrinkage relative to that found in usuallaboratory sized specimens.5Splitting tensile st~engthTable 3 presents the

compressive and splitting tensile strengths of all-lightweight and normal weight concretes after thevarious lengths of initial curing and during the

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TABLE 2aRELATIVE HUMIDITY DISTRIBUTION IN(6X 12-IN. ( 15X 30 CM) CYLINDERS)

Depth-+ I Time of dryinz

9PERCENT

cove,~

in. O I 3 days I 7 days I 14 days I 28 days I 90 days I 180 days I 1 year 12 years I 3 yearsAll-1 ightweight concrete

Moist cured, 3 days% ( 6 lmm) 100 94 88 80 70 60 58 56 52 50?~ (19 )~~) 100 100 97 94 88 70 63 61 58 53

1Y4 (44 mm) 100 100 100 99 95 84 74 69 62 553 (75 mm) 100 100 100 100 97 86 79 72 64 57Moist cured, 7 days% ( 6 mm) 100 94 89 813A (19 mm) 100 100 98 94l% (44 mm) 100 100 100 1003 (75 ]mm) 100 100 108 100Moist cured, 14 days\~ ( (3m,~) 100 95?& (19 mm) Iljo 100

l~g (4kmm) 100 1003 (75 mm) ~100 100Moist cured, 28 daysY4 ( 6mm)?~ (lg mm)

134 (44 mm)3 (75 mm)

91188100100

849899100

100 92 86100 100 99100 100 100100 100 100

7996100100

NormMoist cured, 7 days% ( 6 mm) 100 89% (19 mm) 100 971Y4 (44 mm) 100 1083 (75mm) 100 100Moist cured% ( 6mm)$~ (Ig mm)

1?4 (44 mm)3 (75mm)

28 days100 85100 98100 100100 100

84939899

82949799

778a9496

76879498

73 61 57 56 53 5289 73 65 62 56 5598 87 78 72 64 5799 92 84 78 67 59

76 63 59 58 55 5392 76 68 64 59 5597 88 80 74 65 5799 93 87 81 70 61

71 60 58 57 55 5491 77 70 66 60 5699 92 84 78 69 6199 95 91 84 73 64

weight concrete

68818992

59677678

69 5880 6890 7692 78

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57847073

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52555861

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50525456

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1}o TABLE 2bDRYiNG SHRINKAGE AND WEIGHT LOSS(6X 12-IN. (15X30 CM) CYLINDERS)

%?: I ---= - .=:===== := - cfays i o I 3 days I 7 daY~ I 14 days I 28 days I 90 days I 180 days ] 1 year I 2 YearS ! 3 YearSDrying shrinkage, millionths in. per in..

All-l ightweight concrete310 80 130 I 210 310 490 i 570 640 650

1

67070 60 250

Hlw ,60450 i 560 590 640 680

14 0 80 450 1 560 620 680 71028 ,0 80 , 120 I 170 240 400 480 560 630 , 660. Normal weight concrete

70 I 160 I 260 1..170 460 1 67o 1 720 I 750 79028 D 810150 220 290 380 550 620 6301( 67o 690Weight loss, lb-All-1 ightweight concrete .

lo 0.44 0.60 0.74;:: I M 1 R ;$- ~:,;;~;l: 0.860.28 0.44 0.58 0.700.24 0.38 0.48 0.60 0.84 0.96 1.08 1.24 1.27

28 0 0.20 0.34 0.46 0.58 0.80 : 0.94 1.06 1.18 ; 1.25. Normalweight concrete_. .70 I 0.30 I 0.46 I 0.60 I :2i :H / 0.98 1 1.04 I 1.08 ~ 1.1228 0 0.24 0.34 0.46 0.88 0.94 1.04 1.07*E quivalent metric units: multiply l!b by 0.4536 to obtain kg.

TABLE 3COMPRESSIVE ANID SPLITTING TENSILE STRENGTHS OF CON-CRETES AFTER DIFFERENT DURATIONS OF MOIST CURINGSERIES 1Moist Age of concretecure, days 3 days i 7 days I 14 days I 28 d~ys I 90 days ~180 days I 1year I 2 years

AH light-weight concrete (Aggregate 14)Compressive strength, + psi

3 3500714$,8

Continued I 2620 \ 33OOSpli tti ng tensiI e strength,l PSI

3 1- 1-3107 1428

Continued 276 342

4150 4700 52804130 4850 5320

4760 54005970

4320 5120 5850

313 313 365315 3C7 328

305 332. 343407 420 458

5480 5400 5500-5960 5800 577C5720 5750 53506420 6530 64606620 6840 6760

,396 398 385417 424 385415 404 397373 435 433494 513 492

E lsin sand and sravel ccmcrete ( Agm-egate 8)Compressive strength, + psi

7 4.130 4630 3!310 4740 48602!8

2!XC I 3;0 :- 5600 5940 5300 5460

Continued 3330 4560 5240 5390 5530 5570Splitti ng tensi le strength, ! psi

--17 - I 19 371 4!30 443 505 ~ 506-28 467 525 523

Continued 232 I 2_L:L ;6. -448... - 4:.. ? ~ 506-%Equivalent metr ic units: multiply psi by 0.0703 to obtain kg/cm~.$Average of two .specime Rs.$Average of four specimens. AU JOURNAL

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11100908070gn 60

6050

=--7-7IGHTWEIGHT CONCRETE..

~% Cover iI I I 1E: NORMAL WEIGHT CONCRETE?K -3 CoverL.! I~ Cover\ \>>_ ~~ Cover\ J . _-=-==.:__ )Cover---- _ * . -. _ , .- Tc 0 28 90D 180D IYR 2YR

miyiE:7!??E5?28 90D 180D IYR 2 YR

TIME OF DRYING

Fig. 2TyPical relative humidity distribution, drying shrinkage, andweigh+ loss of 6 x [2-in. cylinders moist cured 7 days (Series I).

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12following 50 percent relative humidity storage.Fig, 3 provides curves of the tabulated data whichhave been augmented by auxiliary tests per-formed during the first few days after start ofdrying. The solid curves of these two diagramsindicate the continuous increase of splittingstrength achieved with continuous moist curing.Comparison of the two curves also indicates theapproximately equal splitting strength of bothtypes of concrete when moist curing pre-vails. PfeiferL found this in his study of concretescontaining seven different lightweight aggregatesand at two levels of compressive strength.As would be expected from the previous

studies, Fig. 3 indicates that drying of the light-weight concrete brings about an early loss ofsplitting strength. Considering only initial moistcuring periods of 7to 28 days, the early splittingstrength of this drying concrete, containing thisparticular aggregate and no natural sand fines, isapproximately 75 percent of the 28-day splittingstrength of the continuous moist cured concrete.The duration of initial moist curing appears tohave little effect on the magnitude of this tensilestrength loss.It is of interest to note that this reduction of

splitting strength occurs during the period ofgreatest moisture gradient in the cylinders, asindicated by Table 2 and Fig. 3. Due to the mois-ture gradient, drying shrinkage will not be uni-form across the concrete cross section, and thepotential shrinkage near the exterior surface willbe reduced through the restraint of the interiormaterial. Tensile stresses will then be self-in-duced near the exterior surface and balancingcompressive stresses in the interior. The inducedtensile stresses will reduce the resistance to ex-ternally caused tensile stresses.

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16strength levels, which were subjected to variouslevels of relative humidity storage after 7 days ofmoist curing. The aggregates in these concreteswere all-lightweight, lightweight coarse with sandfines, and Elgin sand and gravel. Examination ofthe data discloses little effect of the relative hu-midity storage level on compressive strength. Withthe possible exception of the results from 100 per-cent relative humidity storage (continuous moistcuring) only random variations of compressivestrength from that of the standard 50 percentstorage are noted. Under continuous moist cur-ing the lightweight and normal weight concretesaveraged 5 and 10percent lower, respectively, thanthe drying concretes.Splitting tensile stnengthThe splitting tensile

strengths of each of the concretes are shown inFig. 4 as a function of the storage relative humid-ity. Each of these curves for the lightweight con-cretes indicates a drop of the splitting strengthwhen the concretes are allowed to dry after 7 daysmoist curing. This effect is more pronounced forthe higher strength concrete than for the lower,and is also greater for the all-] ightwelght concretethan for the sand lightweight. These indicationsagree with Pfeiferbwho reported as follows: -for 3000 psi all-lightweight concretes, the splittingstrengths varied from 80 to 95 percent of the moistcured strength, and for 5000 psi, these percentagesvaried from 65 to 85; similar results for sand-lightweight concrete were 95 to 105 and 80 to 100percent.A most important observation from Fig. 4 is the

minor change of splitting tensile strength as the21-day drying storage changes from 173F (23 C), 75percent relative humidity to 73F, 10 percent rela-tive humidity. Ivey and ButhA found similar in-dications with other lightweight concretes, except

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17r I I T 35500 ALL LTWT. CONC.400

~~F:,~5500 LTWT. CONC./SAND FINESf~ =5800 psi 30; o400 f:= 3400 psi 25>x300 20_J~F 70+ :

:~:yo:;w::N;~,

100 80 60 40 20 0RELATIVE HUMIDITy,O/o

Fig. 4-28-Day splitting tensile strengths of concretes dried atdifferent relative humidifies for 2 I days, temperature 73*2 F[Series II).

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18that splitting strengths of concretes stored at 80percent relative humidity were about equal tothose of continuously moist cured concretes.Similar to the previous discussion of Series I,the splitting strength of the Series II Elgin normalweight concrete increased as the concrete dried.ASTM C496-66, Splitting Tensile Strength of

Concrete Cylinders, requires that lightweightconcrete, tested in accordance with ACI 318-63()shall be stored at 73 & 3F (23 & 2 C) and 50 & 5percent relative humidity for 21 days after 7 daysmoist curing. Commercial testing laboratoriesseldom have facilities sufficiently refined to con-trol the relative humidity within these limits.From the results of this study and those of Ref-erence 4, it would appear that wider limits, per-haps &15 percentage points, might be allowedwithout sacrifice of uniform splitting test results,although additional studies, incorporating otherlightweight aggregates, may be advisable.

Splitting ratio, F,PThe ACI 318-6310 definesthe shear parameter of structural lightweight con-crete FSPas the ratio of the splitting tensilestrength to the square root of the compressivestrength of the same concrete. Since Series II ofthis study satisfied other Code requirements, thevariation of F,p vvith variation of relative humid-ity storage couldl be determined as indicated inTable 4. Small variations of the F.p of the dryconcretes may be noted. The average F~P (ex-cluding the moist cured) for the al.l-lightweight,sand-lightweight, and normal weight concretes,respectively, are 5.1, 5.8, and 6.9. Pfeifers reportedthe following corresponding data: 4.8-6.4, 5.9-6.4,and 7.0; the range in each case covering the sevenlightweight aggregates which he studied.

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19CONCLUSIONS

This somewhat limited study was planned tofurnish insight into some of the effects of dryingon the splitting tensile strength of lightweightaggregate concrete. Since only a single light-weight aggregate, a single natural sand, and asingle normal weight gravel were used, the datareported may not be precisely applied to all light-weight and normal weight concretes. However,the observed effects of curing and drying en-vironments on t l h e splitting strength should pro-vide information on some little understood aspectsof this property- of concrete, particularly sincethese observations are in general accord withprevious findings.The long-time measurements of relative humid-

ity distribution (Series I) have indicated the ex-treme slowness with which concrete dries. Normalweight concrete, with its lower aggregate absorp-tion, may reach moisture equilibrium with theambient atmosphere faster than lightweight con-crete. However, the accompanying I;ests of dryingshrinkage and weight loss show that these prop-erties attain equilibrium much earlier than doesthe internal relative humidity.The tests have reconfirmed the initial loss of

splitting strength that generally occurs with dry-ing of lightweight concrete. This loss of splittingstrength is little affected by prior moist curingperiods varying between 7 and 28 days. The SeriesI tests have shown that the drying concretes re-gain splitting tensile strength as the concrete ages,reaching perhaps 80 percent of the potential ob-tainable under I to 2 years of moist curing. Thisregain of splitting strength points toward anincreased shear resistance occurring with age ofconcrete structures, though it should be notedthat large structural members dry much slowerJULY 1968

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than 6 x 12-in. (15 x 30 cm) cylinders. This regainindicates curing requirements of AC-I 318-6310 andASTM 496-66 provide conservative values of split-ting strength for design purposes.The Series II tests have shown that any dryingenvironment between 75 and 10 percent relativehumidity has about the same effect on splittingtensile strength measured at 28 days. This wouldindicate that the current requirements of ASTM496-66 for maintaining 50 +5 percent relativehumidity during the 21-day storage period mightbe broadened to a tolerance of perhaps f 15percentage points.

ACKNOWLEDGMENTSThis investigation was carried out in the Productsand ApplicationsDevelopmentSection of the PortlandCement Association Laboratories. Particular credit isdue Emil Greinke, Senior Technician, for conduct of

the SeriesI testsand toAlbert Litvin, Senior Engineer,for thoseof SeriesII.

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21REFERENCES

1. Hanson, J. A., Tensile Strength and DiagonalTension Resistance of Structural Lightweight Concrete, ACI J OURNAL, Proceedings V. 58, No. .1, July 1961,pp. 1-39. Also, P(2A Development Department BulletinD50.2. Grieb, W. E.t$and Werner, G., Comparison of the

Splitting Tensile Strength of Concrete with Flexuraland Compressive Strength, Public Roads, V. 32, No.5, Dec. 1962, pp. 97-106.3. Lewis, R. K., and Blakey, F. A., Moisture Con-ditions Influencing the Tensile Splitting Strength of

Lightweight Concrete, Constructional. Review (Syd-ney), V. 38, No. 8, Aug. 1965, pp. 17-22.4. Ivey, D. L., and Buth, E., Splitting Tension Test

of Structural Lightweight Concrete, ASTM Journalof Materials, V. 1, No. 4, Dec. 1966, pp. 859-871,

5. Pfeifer, D. VV., Sand Replacement in StructuralLightweight Concrete Splitting Tensile Strength, ACI JOURNAL, Proceedings V. 64, No. 7, July 1967, pp.384-392. Also, PCA Development Depc!rtment Bulletin.Dlzo.6. Hanson, J. A., Optimum Steam Curing Proce-dure in Precasting Plants, ACI JOURNAL, Proceedings

V. 60, No. 1, Jan. 1963, pp. 75-100. Also, PCA Develop-ment Department Bulletin D62.7. Hanson, J. A,, Optimum Steam Curing Proceduresfor Structural Lightweight Concrete, ACI JOURNAL,

Proceedings V. 62, No. 6, June 1965, pp. 661-672. Also,PCA Development Department Bulletin D92.8. Ivey, D. L., and Buth, E., Shear Capacity of Light-

weight Concrete Beams, ACI JOURNAL, ProceedingsV. 64, No. 10, Oct. 1967, pp. 634-643.9. Hognestad, E.; Elstner, R. C.; and Hanson, J. A.,

Shear Strength of Reinforced Structural Lightweight.Aggregate Concrete Slabs, ACI JOURNAL, ProceedingsV. 61, No. 6, June 1964, pp. 643-656. Also, PCA De-velopment Depa~tment Bulletin D78.10. ACI Committee 318, Building Cocie Requirementsfor Reinforced Concrete (ACI 318-63) , American Con-crete Institute, Detroit, 1963, 144 pp.11. ACI Committee 613, Subcommittee on Proportion-ing Lightweight Aggregate Concrete, Recommended

Practice for Selecting Proportions for Structural.LightweightConcrete (ACI 613A-59), American Con-creteInstitute,Detroit,1959,10pp.JULY 1968

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2212. Landgren, R.; Hanson, J. A.; and Pfeifer, D. W.,

An Improved Procedure for Proportioning Mixes ofStructural Lightweight Concretes, Jou?maZ, PCA Re-search and Development Laboratories, V. 7, No. 2,May 1965, pp. 47-65. Also, PCA Resem-ch Department.Buttetin 183.13. Monfore, G. E., A Small Probe-Type Gage forMeasuring Relative Humidity, Journal,, PCA Research

and Development Laboratories, V. 5, No. 2, May 1963,PP. 41-47. Also, PCA Research Department Bulletin160.14. Pfeifer, D, W., Sand Replacement in StructuralLightweight Concrete Creep and Shrinkage Studies,ACI JOURNAL, Proceedings V. 65, No. 2, Feb. 1968,pp. 131-140. Also, PCA Development Bulletin D128.15. Hansen, T. C., and Mattock, A. H., Influence

of Size and Shape of Member on the Shrinkage andCreep of Concrete, ACI JOURNAL, Proceedings V. 63,No. 2, Feb. 1966, pp. 267-290. Also, PCA DevelopmentDepartment Bulletin D103.

SinopsisResumeZusammenfassung

Efecto del Curado y Condici~nes de Secado en laResistencia a la Tensi6n por Compression Diametral

del ConcretoSe investigaron las resistencias a la tension por

compression diametral de concreto ligero y de pesonormal en dos series de ensayes que tratan con 10Sefectos del curado y las condiciones de secado. Laprimers serie mostr6 que la duraci6n del periodoinitial de curado htimedo, antes del secado a 50 porciento de humedad relativa, tiene poco efecto en laresistencia a la tensi6n por compresi6n diametral.A pesar de que se produjo una perdida de resistenciaa la tension por cortante para concreto ligero aliniciarse el periodo de secado, un almacenamientocontinuo en atmosfera seca condujo i~ una gananciaconsiderable de resistencia a la tensibn. En la segundaserie, el concreto se sometio a secado durante 21 aliascon diferentes niveles de humedad rela.tiva despu& deun curad.o iniciaI htimedo de 7 alias. Solamente seobtuvieron cambios menores en la resistencia a latension cuando se vario la humedad relativa de 75a 10 por ciento.

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23Influence de IAmbiance de Ressuage sur la

Resistance au Dedoublement en Tension du BetonLes r&istances au dedoublement en tension de

bktons I+gers et normaux ont &6 ~tudi~es lors de deuxs6ries dessais clans lesquels linfluence de lambiancede ressuage et s&chage 6tait consid&-&e. Les premi&ess6ries ont montrh que la durke de ressuage initial &tathurnide pr6c6dent un shchage ii 50 pourcent dhumidit6relative avait peu dinfluence sur la resistance audedoublement en tension. Tandis quon notait unediminution de r&istance au dedoublement pour lebkton 16ger tr$s t6t durant la p&iode de skchage;un stockage conti.nu clans Iatmosphere de s~chageconduisait ~ un gain consid&able dam la r&istanceau d6doublement. Dans les secondes skries, les betonsont ete soumis a un sechage durant ~!1 jours adifferent niveaux dhumidite relative! apres ressuageinitial etat humide de 7 j ours. Seulement deschangements mineurs de r&istance au d6doublementont W trouv% lorsque lhumidit6 relative varie de75 ~ 10 pourcent.

Der Einfluss der Lagerungsbedingungen auf dieSpaltzugfestigkeit von Beton

Die Spaltzugfestigkeit von Leichtbeton undNormalbeton wurde im Rahmen von zweiVersuchsreihen studiert, wobei vor allern der Einflussder Lagerungsbedingungen untersucht wurde. Die ersteVersuchsreihe zeigte, class die Dauer einerFeuchtlagerung, die einer anschliessendenAustrocknungsperiode bei einer Luft feuchtigkeit von50 ZO vorangeht, auf die Spaltzugfestigkeit wenigEinfluss hat. Zu Beginn der Austrocknungsperiodenwurde zwar ein geringer Abfall der S,paltzugfestigkeitbeobachtet; langere Austrocknung fflhrte jedoch zueinem merklichen Anstieg der Spaltzugfestigkeit. In derzweiten Versuchreihe wurden die Bet(mproben nacheiner anfanglichen Feuchtlagerung von sieben Tageneinundzwanzig Tage lang verschiedenen relativenLuftfeuchtigkeiten ausgesetzt. Eine Variation derrelativen Luftf euchte zwischen 10 uncl 75% hatte nureinen geringfiigigen Einfluss auf die Spaltzugfestigkeit.

JULY 1968 PCA, R& D, Ser.1314-2

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Bulletins Published by theDevelopment Department

Research and Development Lak>oratoriesof the

Portland Cement AssociationDIOOIndex of Development Department Bulletins D1-D99. Annotated List with Author

and Subject Index.Published by Portland Cement Association, Research and Development Laboratori es,Skokie, I ll inois (1967).

DIO1Rotational Capacity of Hinging Regions in Reinforced Concrete Beams, by ALANH. MATTOCK.

Reprinted from FLEXUHAL MECHANICS OF REINFOI+CE~ CONCKEZE, proceedings Of the Inter-national Symposium, Miami , Flu. (N ov emb er 1964) p ag es 143-181, joi nt s pon sor sh ip .C op y righ ted 1965 by Am er ica n S ociet y of C ivil Eng {neers.D102Tests of Partially Prestressed Concrete Girders, by DONALD D. MAGUKA and EIVIND

HOCNESTAD.Reprinted f rpr n t he J ou ?m a t of t he ,. St ?w ct ur a ID iv is ion , P r oceed in gs of tize AmericanSociety of C t vZl E n gin eer s, P r oc. P a per 4685, 92, S T 1, 327-350 (F eb ru ar y 1966).

D103In fluence of S ize a nd Sha pe of Member on t he Shrinka ge a nd C reep of Concrete.by TORBEN C. HANSEN and ALAN H, MATTOCK.Reprinted from Jownat of t he Am er ica n C on cr et e I ns tit ut e (F eb ru a ry 1966): P r oc@ed -i rsgs 63, 267-290 (1966).

D IOQCa st -in-P la ce Concret e Residences With Insula ted Wa lls, by HARRY L. SCOG CIN.R eprin ted from J ourn al of t he P CA Resea rch a nd D evelopm en t L abora tor ies, 8, No. 2,21-29 (May 1966).

D 105TensiI e Test ing of C on cret e B lock a nd Wa ll E lem ent s, by RI CH ARD O. H ED STROM.R epr in ted f rom J ou sm a ~ of the P C A R esea rch a nd D evelopm en t L abor at or ies, 8, No. 2,42-52 (May 1966).

D106H igh S t rength B ars a s Concret e Rein for cement . P art 8. S imili t ude in Flexura lCra cking of T-B ea m Fla nges, by P AU L H. KAAR.R epr in ted fr om J ou rn al of the P C A R esea rch a nd D evelopm en t L abor at or ies, 8, N o. 2,2-12 (May 1966).

D 107S esmicic Resist an ce of Rein forced C on cret eA L abora tory Test Rig, by NORMANW. H AN S ON a n d HAROLD W. CONNER.Reprinted from J ot i?vs al o f t he P C A Research a n d D ?v el opr nen t L a bor a tor ies , 8, N o. 3,2 -9 (S ep t ember 1986).

D 108Rot a tiona l Ca pa cit y of Rein forced C oncret e B ea ms. by W. G ENE CORLE Y.Reprint ed from J ourn al of t he S truct ura l D ivision, P roceedin gs of t he Am ert ca n S o-ciet u of C ivi l E n gin eer s, P r oc. P a per 4939, 92, S T5, 121-146 (O ct ob er 1966).

D109La bora t ory S tudies of t he Skid Resist a nce of Concret e. by G . G . B ALMER a ndB . E . COLLEY.Reprinted from ASTM J ou ma [ of Ma teria is 1, No. L 536-559 ( sept em ber 1966).

D l10Connect ions in P reca st Concret e S t ructuresColumn B a se P la t es, by R. W.LAFRAUGH and D. D. MAGURA.

Reprinted from JoumaL of the P rest ~ essed C on c?w !e I nst it ut e, 11, No. 6, 18-39 (D e-c ember 1966).D illLa bora tory S tudy of S hot cret e. by ALB ERTLrrvlN a nd J osE pH J. sHID~L~~.

Reprinted from Symposium on Shotcreting, American Concrete Institute, Paper No.13 in Publ ic a t ion 5P-14, 165-184 (1966).D l12Test s on Soil-C ement a nd Cement -Modified B ases in Minnesot a , by !CORBJORN J .

LARSEN.Reprinted from J ournal of the PCA Research and Development L aboratories, 9, No. 1,25-47 (J anuary 1967).

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D 113S t ruct ura l Model Test ing-Reinforced a nd P rest ressed Mor ta r B ea ms. by D ON-ALDD, MAGURA.Rep ri nt e d f r om J osswra~ of the PCA ReseaTctt and f2ewto~ment L aboratories, 9, No. 1,2-24 (January 1967).

Dl14General Relation of Heat Flow Factors to the Unit Weight of Concrete, byHAROLD W. BREWER.

Reprinted from J oumat of the PCA Research and De Vf?tOpmerzt .Labomtones, 9, No. 1,48-60 (January 1967).Dl15Sand Replacement in Structural Lightweight ConcreteSintering Grate Aggre-

gate:;. by DONALD W. PFEIFE~ and J . A. HANSON.Reprinted from J ouwtal of the American Concrete I nstitute (March, ]967); Proceedings64, 121-127(1967)

D l16Fa tigue Test s of Reinforcing B arsTa ck Welding of S t irrups, by KE NNETH T.BURTONand EIVINDHocNmsrAmR ep ri nt ed f rom J ournal of the American Concrete Institute (May, 1967); Proceedings64, 244-252 (1967)

Dl17Connect ions in P reca st Concret e S t ruct uresEffect s of Rest ra ined Creep a ndShrinka ge, by K. T. BURTON. W. G. COEiLEY, and E . HOGNESrAD.Reprinted from J oumaz of the Pmstressed Coracmte I nstitute, 12,No. 2 , 18-37 (Apr il ,1967).

D l18C asin iP la cece C oncret e Residences w it h Insula ted Wa llsInfluence of S hea r C on-n ect or s on F lexu ra l R es is ta nce, by H AR RY L . S C OG G I Na n d D ON AL DW. P F EI EE R.R ep ri nt e d f r om J OumaZ of the PCA Research and Dewtownent L a bor a tor ies , 9, N o. 2,2 -7 (May 1967),

D l19F a t ijg ue of S oi l-C em en t . by T. J . LARSEN a nd P . J . NU SSB AU M.B :epr in ted f rom J ournat of the PCA Research and D welopm en t La bor at or ies, 9, No 2,37-59(May 1967).

D 120S an d Repla cem en t in S tr uct ur al L igh tw eigh t C on cr et ~ ;S plit tin g Tens ile S tr engt h, by DONALD W. PrEIFER.Reprinted from J ournal of the Anwrican Concrete Inst, tute (J uly 1967); Proceedings 64,384-392 (1967).

D121Seismic Resist a nce of Reinforced Concret e B ea m-Column J oint s, by NORMANW. H AN SON a n d HAROLD W, CONNER.

Fteprinted from J ournal of the Structural Division. Proceedings of the American Societyof civiLEngineers, PTOC. Paper 5537, 93, ST5, 533-560 (October 1967).D 122P reca st Rigid Fr ame B uildingsTest of S ca rf C onn(?ct ions, by P AU L H . K AAR a nd

HAROLD W. CONNERReprinted from J ourna~ of the PCA ReseaTch and D cv et oln nen t L abo~ a t or ies , 9, N o. 3,34-42 (September 1967).

D 123P r eca st R ig id F ra m e B u ild in gs C om pon en t Tests, by H AROL D W. CONNER andPAUL H. KAAR.

Reprinted from J ourma~ of the PCA Re=mch and D=Ve~o~mQ~t ~aboratoties, 9, No. 3,43-55 (September 1967),D 124Aggrega te In t erlock a t J oint s in Concrete Pavements, by E. E. COLLEYand H. A.HUMPHREY.Reprintedfrom Highway ResearchRECORD,umber 189,1-18(196?).D125CementTreated Subbasesfor concrete pavements, by L. D. CHILDS.

R epr ,n ted fr om H ig hw a y R es ea r ch R EcOm , N u mber 1~ 9. 1943 (1967).D126 Sa nd Repla cement in S t ructura l Lightw eight Concret e-Freezing a nd Tha wingTes ts , by DONALD W. PFEIFER.

Repr inted from JournuL of the Amer+can Con c~ e t e I n st i t ut e (Novembe r 1967); Proceed-ings 64, 735-744 (1067).D127 U 1t im a t e Torque of Reinforced Rect angula r B ea ms:, W TH OMAS T. C . Hsu.

Reprin t ed from J ourna l of the Structural Division, Proceedings of the American So-ciety of Civil Engineers, PTOC. PafwT 5814, 94, ST2, 485-510 (Febroary 1968).

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i)128-Sand Replacement in Structural Lightweight Concrete-Creep and ShrinkageStudies, by DONALDW. PFEIFER.Reprintedfrom J ourna l of t he A?ne~ican C or zc~ et e I ns ti tu te (F ebr ua r y 1968); P ~ o-ceedings, 65, 131-140 (1968).D129Shea r a nd Moment Tra nsfer B etw een Concret e S la lbs a nd Columns, by NORMANW. HANSON a nd J OHN M. HANSON.

Reprinted from J ournal of the PCA Research and Development Laboratories, 10, No.1, 2-16 (J a n u a ry 1968)D130Trends in Consumer D ema nds for New G ra des of Rein for cing S teel, by E IVINDHOGnTES.TAD.

R epr in ted f rom Proceedings, Fall Business Meeting, Concrete Reinforcing SteelInsti tute, pages 22-32 (1967 ).D131Influence of Mortar and Block Properties on Shrinkage Cracking of Masonry

Walls, by RICHARD O. HEDSTROM, ALBERT LITVIN, and J . A. HANSON.Reprinted from J ournal of the PCA Research and Development Laboratories. 10,No. 1, 34-51 (January 1968).

D132 Toward a Generalized Treatment of Delayed Elasticity in Concrete, by DOUGLAaMCHENRY.

Repr inted from PUBI.ICATIOXS, I nternational Association for Bridge and StructuralE ngineering (Zurich) , Vol 26, pages 269-283 (1966).D133 Torsion of S t ructura l Concret eA Summa ry of P ure Torsion : by THOMAS T. C.Hsu.Reprinted from TORSION OF STRUCIWIAL CONCRETE, American Concrete I nstitute,Paper SP 18-8 in PUbliCatio~SP-1!3, 165-176 (1968).D 13+ Torsion of S t ructura l Concret eP la in Concret e Reef a ngula r S ect ions, by THOMAS

T. C . HSU .Reprinted from TORSION OF .%RUCWRAL CONCRETE, American Concrete I nstitute,SP 18-8 in Publi cati on SP-18, 203-238 (1968).

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Effects of Curing and Drying Environmentson Splitting Tensile Strength of Concrete uKEYWORDS; age-strength r el at ion ; com pr es siv e s tr en gt h; cou cr ct c$ cu rin g; t tr yi n~ d ry - /ing shrinkage; expanded shale aggregates; fine aggregates; gravel (material); humiclity; ,light weight a ~ yw ga te concret es; light weight a ggrega tes; moist cur ing; moist ure con- ,t en t; r es ea rch ; s an d (m a ter ia l); s plit tin g t en sil e s tr en gt h; t es tin g. ISYNOPSIS: The splitting tensilestrmgdls of lightweight anrf normal wcigbt concretesw ere invest iga ted in tw o test ser ies w hich dt a lt w it h the effect s of t he cur ing a nddrying environment s. The first ser ies show ed tha t t he [Iura tion of the init ia l moistcur ing per iut i pr ior t o dry ing a t 50 percent rela tive humidit y ha d lit t le effect on thesplit t ing t ensile st rength. ~ t bile there w as a loss of split t ing st rength for the light -w eight crmcrct e ea rly in the drying pcr ioct s, cont inued stora ge in the drying a tmo-sphere lcd 10 considera ble ga in in t he split t ing st rengt hs. In t he second ser ies, ct sncrct cswmc subjected to drying for 2!1 c1ays at different levels of rela tivc humidity af terinit ia l moist clu]ing for 7 da ys. Only minor changes of split t ing st r rmgth w ere founda s the rela t ive hnmi(lit y va ried from 75 to 1(I percent .REFERENCE: Hanson, J. A., E ffect of C uriug a nd D ryin g E nviron mrm ts ou S plit t ingTen sile S tr en gt h of C on cr et e, AC I J C )U R NA1. P rocce[lings. V. 65, No. 7, J n]y 1968.pp. 535-543 .

Effects of Curing and Drying Environmentson Splitting Tensile Strength of ConcreteKEYWORDS: age-strength relation; com pressive st rengt h; con cr et es; ct lr ing; dr ying; dr y-ing shrinka ge; expa nded sha le a ggrega tes; fine a ggrega te$ gra vel (ma teria l); humidity ;ligh tw eig ht a gg reg at e con cr et es; lightw eight a ggrega t es; moist cur ing: moisture con-tent ; resea rch; sa nd (ma ter ia l); split ting t ensile st rengt h; t est in~ . ISYNOPSIS: The split t ing tensile st rengths of lightweight a nd norma l weight concret es 1Irere hlVeSl@tted in tw o t est ser ies w hich dea lt w ith the efTcct s of t he curing a nd 1drying environment s. The fir st series show ed tha t t he dura t ion of the init ia l moist Icuring period prior to drying a t 50 percent rela t ive humidit y ba {l I it t Ie effect on the Isplitting ttmsile strength. While there was a loss of splitting strength for the light- 1w eight concret e ea rly in the drying per iods, cont inued stora ge in the drying a tmo-sphere! led t o cor]sidera hle ga in in t he split ting st rengt hs. In the second series, ccmcrctes 1wmw subjected to [lry ing for 21 da ys a t differen t levels of rela t i~ ,c bumidit v a ft er Iinit ia l moist cur ing for 7 da ys. Only minor chmges of split t ing st rength were founda s the rela t i\ c humidit y va ried from 75 to 10 percent , IIREFERENCE: H~IIS~JII> J. A., E ffect of Curing a nd Drying Environment s nn Split t ing ITen sile S tr cn gt h of C on cr et e, ACI J OURN.!L P roceedings, V. 65, No. 7, J uly 1968, IPP . 535-543 i

Effects of Curing and Drying Environmentson Spli tting Tensile Strength of Concrete L!KEYWORDS: a ge-st rengt h rela tiou; compressive st rengt h: concret es; curing; drying; dry- ]ing shrinka ge; cxpandcr t sha le a ggrega t es; fine a ggrw ga tcs; gra vel (ma teria l); humidity ; Ilightw eight a ggreg~ te concret es; lightweight a ggrega tes moist curing; moisture com Itent; xcscal-ch; sand (material); splitting tensile strength; testing. I[SYNOPSIS: The spli t t ing tt !ns ilc strengths of l ightweight an t f normal weight concretes [were investigated in two test series which dealt with the effects of the curing and Idrying eot iro])mcnts, The first scritx showml that the duration of the initial moist 1curiug period priol- to drying at 50 percent relative humidity had little eflect on the 1splitting tensile strength. Wbile there wa s a loss of split t ing st rength for the light - 1nreight concret e ea rly in the drying pcr iocfs, cont inued stora ge in the drying a tmo- 1sphere led to considera ble ga in in the splitting strengths. In the sccrmd series, ~ oncrct es ,w ere subject ed to thying for 21 da ys a t different Ievcls of rela t ive humidit y a ft er Iinit ia l moist cur ing for 7 da ys. Only minor cha nges of split t ing st rength w ere found 1a s the rela t ile humidit y va ried from 75 to 10 percen t . IREFERENCE: Hanson, J . A., E ffect of Curing a nd Drying Environmcnrs on Split t in$ IITensile S t rength of Concrct c, ACI J OURNAL P roceedings, V. 65, RIO. 7, J uly 1~ 16~ , ,pp.535-543. I

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