a study of the effect of moisture content upon the ......torata matsumoto student in the graduate...

HI L L I NOI SUNIVERSITY OF ILLINOIS AT URBANA-CHAMPAIGN

PRODUCTION NOTE

University of Illinois atUrbana-Champaign Library

Large-scale Digitization Project, 2007.

UNIVERSITY OF ILLINOIS

ENGINEERING EXPERIMENT STATION

BULLETIN No. 126 DEC. 5, 1921

A STUDY OF

THE EFFECT OF MOISTURE

CONTENT UPON THE EXPANSION AND

CONTRACTION OF PLAIN AND

REINFORCED CONCRETE

BY

TORATA MATSUMOTOSTUDENT IN THE GRADUATE SCHOOL OF THE

UNIVERSITY OF ILLINOIS

ENGINEERING EXPERIMENT STATIONPUBLISHED BY THE UNIVERSITY OF ILLINOIS, URBANA

CONTENTS

PAGE

I. INTRODUCTION . . . . . . . .. . . . . . 5

1. Object of Investigation . . . . . . . . 5

2. Acknowledgments . . . . . . . 6

II. MATERIALS USED IN TEST SPECIMENS . . . . . . .

3. Materials . . . . . . . . 7

4. Coefficient of Expansion of Mortar and Concrete . 8

III. EFFECT OF MOISTURE CONTENT ON LENGTH OF SPECIMEN 9

5. Cement Mortar and Plain Concrete . . . . . 9

6. Sandstone and Limestone .. . . . .. . 16

IV. SHRINKAGE STRESSES IN REINFORCED CONCRETE . . . . 19

7. Analysis of Shrinkage Stresses . . . . ..... . 19

8. Measurement of Shrinkage Stresses in ReinforcedConcrete Specimens .. . . . . . 21

V. CONCLUSION . . . . . . .. . . . . 28

9. Comments .. . . . 28

LIST OF FIGURES

NO. PAGE1. Change in Length with Change in Moisture Content of Mortar . . . 10

2. Change in Length with Change in Moisture Content of Concrete . . . 11

3. Loss of Moisture from Mortar and Concrete when Dried at 150 deg. F.after Preliminary Storage Noted in Diagram . . . . . . . 13

4. Absorption and Corresponding Expansion of Mortar and Concrete Im-mersed in Water . . . . . .. . . . . . . . . . 14

5. Absorption and Corresponding Expansion of Nine-Year-Old ConcreteImmersed in Water .... . . . . . . . . 16

6. Absorption and Corresponding Expansion of Lake Superior Red Sand-stone Immersed in Water ... . . . . . . . . . 17

7. Absorption and Corresponding Expansion of Indiana Oilitic LimestoneImmersed in Water ... . . . . . . . . . . . 18

8. Distribution of Shrinkage Stresses in Reinforced Concrete Specimen . 19

9. Shrinkage Stresses in Reinforced Concrete Specimens . . . . . . 22



12. Comparison of Measured and Calculated Shrinkage Stresses . . . . 27

LIST OF TABLES

NO. PAGE

1. Mechanical Analysis of Sand . . . . .. . . . . . . . 7

2. Change in Moisture Content of Mortar and Concrete and CorrespondingChanges in Length .... . . . . . . . . . . 12

A STUDY OF THE EFFECT OF MOISTURE CONTENT

UPON THE EXPANSION AND CONTRACTION OF

PLAIN AND REINFORCED CONCRETE*

I. INTRODUCTION

1. Object of Investigation.-While the properties of concretehave been investigated for many years, attention has largely beengiven to considerations of strength alone. Studies of the less im-portant properties, however, are also needed to explain phenomenathat are observed in reinforced concrete structures, and to give infor-mation on questions relating to the appearance and durability of thematerial.

Aside from the action of direct load, deformations are producedin concrete by changes in temperature and in moisture content. Withreference to temperature changes in reinforced concrete, it is wellknown that, regardless of differences in the mixture, concrete haspractically the same coefficient of expansion as steel, so that the twomaterials contract or expand together. Moisture content, on the otherhand, has the undesirable property of affecting concrete alone. Con-crete, like wood, clay, and some other materials, expands when itabsorbs moisture and contracts when it is dried; steel has no suchaction. After the concrete is poured the steel remains unchanged withchanges in moisture conditions, while concrete ordinarily shrinks aconsiderable amount. Aside from the stresses set up in steel andconcrete by the shrinkage of the latter, the resulting formation ofcracks large or small will produce a condition which may be favorableto the corrosion of the steel or the disintegration of the concrete afterrepeated changes from dry to wet condition.

*This bulletin contains some of the results of experiments made by T. Matsumoto. agraduate student in Theoretical and Applied Mechanics at the University of Illinois, in 1918.Owing to his years of experience as an engineer on harbor works on the Island of Formosa,he was particularly interested in the question of the durability of concrete exposed to seaair and to the conditions found in a tropical climate. It is felt, however, that the resultsobtained apply to our ordinary conditions and may have many practical applications. Thepaper has therefore been revised by members of the Department of Theoretical and AppliedMechanics and prepared in form for publication as a bulletin of the Engineering ExperimentStation.

6 ILLINOIS ENGINEERING EXPERIMENT STATION

The tests which are described were made to investigate the amountof shrinkage which may be expected in a mortar or a concrete, therelation between the change of moisture content and the change oflength of these materials, the difference in shrinkage of plain andreinforced concrete, and the internal stresses set up in the latter. Forpurposes of comparison with the results obtained with concrete, a fewtests were made on the effect of the absorption of water by sandstoneand limestone.

2. Acknowledgments.-The work reported in this bulletin wasdone in the Laboratory of Applied Mechanics of the University ofIllinois. Acknowledgment is made to PROFESSOR ARTHUR N. TALBOT,PROFESSOR 11. F. GONNERMAN, and others, for helpful suggestions andaid.

THE EFFECT OF MOISTURE CONTENT UPON CONCRETE

II. MATERIALS USED IN TEST SPECIMENS

3. Materials.-The materials used in making the concrete test

pieces were all of good quality. Universal portland cement, whichpassed the specifications of the American Society for Testing Materials

as to fineness, soundness, tensile strength, and other qualities, was used.The fine aggregate was a well graded sand from Attica, Indiana. Anaverage mechanical analysis from ten samples of the material isgiven in Table 1. The specific gravity of the sand was 2.69. Theweight per cu. ft. when tamped into the mold with a rod was 111 lb.,from which the voids in the dry material were estimated to be 34 percent.

The coarse aggregate was gravel from Attica, Indiana. It was allscreened to a size between 1/4 and 1/2 in.; larger sizes were not usedbecause of the small dimensions of some of the test pieces. The gravelconsisted of well rounded pebbles having a specific gravity of 2.71; itsweight per cu. ft. was about 97 lb., making the voids in the coarseaggregate about 42 per cent. The steel used in the reinforced concretetest pieces consisted of plain round mild steel bars. In none of thetests did the measured stress in the steel approach the elastic limit ofthe material.

TABLE 1

MECHANICAL ANALYSIS OF SAND

SIEVE OPENING PER CENT PASSINGSIEVE NO. IN INCHES THE GIVEN SIEVE

3 0.263 98.6

4 0.185 95.3

8 0.092 71.4

14 0.046 42.3

28 0.0232 18.0

48 0.0116 7.1

100 0.0058 2.6

ILLINOIS ENGINEERING EXPERIMENT STATION

All concrete was hand mixed, and each test piece was made from

a separate batch of material. Since the size of the test pieces and the

conditions of their storage varied greatly in, the different tests, these

details will be noted in the descriptions of the several sets of tests.

In the various mortars and concretes used, the proportions of the

ingredients are given by volume.

4. The Coefficient of Expansion of Mortar and Concrete.-The

coefficient of expansion of mortar and concrete was measured for usein making a temperature correction of measurements. It was ob-

tained from perfectly dried specimens only, so that there was no error

due to the change in length with a change in moisture content of aspecimen. The measurement of length was made by the use of a Berrystrain gage, and the temperature was measured by a thermometerwhich was so placed among the test pieces that radiation of heat didnot affect the reading.

The results obtained indicate that the coefficient of expansion ofmortar and concrete is practically the same for different proportionsand ages, provided that the same materials are used in all mixtures.The average values of the coefficient of expansion of 1: 1, 1: 2, and 1:3mortar, and 1:1: 2, 1:2:4, and 1:3: 6 concrete, varied from 0.0000050to 0.0000058 for one degree Fahrenheit, with no particular variationwith the age or with the richness of the mixture.


III. EFFECT OF MOISTURE CONTENT ON LENGTH OF SPECIMEN

5. Cement Mortar and Plain Concrete.-Thirty test pieces, 2 by3 by 24 in. in size, containing 2 steel plugs which formed a 20-in. gageline, were made of 1:1, 1:2, and 1:3 mortar, and 1:1:2, 1:2:4, and1:3:6 concrete, five test pieces for each mixture. One day after thetest pieces were made the molds were taken off, and initial measure-ments of the length and weight were made. All test pieces were thenstored in a damp room and covered with double sheets of burlap whichwere kept wet. The measurements of length were made with a Berrystrain gage of 20-in. gage length, using as a standard a steel bar im-mersed in water of known temperature. All measurements were cor-rected for the effect of temperature change. Changes in weight weretaken to mean gains or losses in moisture content.

After 60 days of damp storage all tests pieces were stored inair in a room where the relative humidity varied from 40 to 60 percent when the room was heated by steam. As soon as the steam heat-ing was discontinued with the advance of the season the relativehumidity of the room increased, and it reached 90 per cent on cloudydays; whereupon the mortar and concrete absorbed moisture fromthe air and began expanding instead of contracting. After beingkept 90 days in the air of this room the specimens were dried for14 days in an oven at a temperature of 150 deg. F., and then for 15days at 200 deg. F. The amounts of change of moisture and lengthduring the test are shown in Table 2 and are indicated in Figs. 1 and 2.

As may be seen from Fig. 1, 1: 1 mortar at seventy days contracted0.025 per cent, notwithstanding the fact that it contained moremoisture than its initial amount. From this phenomenon it can beconcluded that the water which goes into the concrete may exist intwo different ways, either combined with cement in a chemical com-pound or remaining in a state which affects the volume of the concrete.It also appears that concrete in which the total moisture content iskept constant for some length of time is liable to contract slightly.This slight contraction was observed on several occasions during thetest. It follows that the absolute amount of contraction of concrete


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due to drying is indeterminate, because it depends upon the age ofthe concrete and the duration of the drying period. Figs. 1 and 2 showthat in general these specimens of mortar and concrete expandedwhen they were kept wet. The richer mixtures absorb more water andconsequently expand more than the leaner ones. Mortar and concretelose moisture rapidly when placed in dry air and the loss is morerapid in lean mixtures than in rich ones. In air storage the shrinkageis greater for mortar than for concrete, and with artificial drying theshrinkage is greater for the richer mixtures.

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For the specimens tested, the contraction of mortar and concreteat a temperature of 150 deg. F., which is somewhat higher than thehighest outdoor temperature in summer in a tropical climate, was0.12 per cent for 1: 1 mortar, 0.10 per cent for 1: 2 mortar, 0.09 percent for 1: 3 mortar, 0.07 per cent for 1: 1: 2 concrete, 0.06 per centfor 1: 2: 4 concrete, and 0.06 per cent for 1: 3: 6 concrete. The amountof expansion when specimens were kept wet reached 0.012 per cent in1:1 mortar, and 0.002 per cent in 1:3:6 concrete, at the end of 60days. Judging from these tests, shrinkage of concrete in a structurefreely exposed to the air may be as much as 0.05 per cent in a 1:2:4

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concrete.* In a structure such as a retaining wall or a road pavement,where one side of the structure is against a mass of earth, the shrinkageshould be considerably less.

In a second set of tests twenty-four test pieces, having the samesize and form as those in the tests previously described, were preparedfrom the same materials, half of mortar with the proportions of 1:2,and half of concrete with the proportions of 1: 2: 4. The test pieces

Length ofryi/,ng Period/i7n LDns

FIG. 3. Loss or MOISTURE FROM MORTAR AND CONCRETE WHEN DRIED AT 150

DEG. F. AFTER PRELIMINARY STORAGE NOTED IN DIAGRAM

* Quantitative information regarding the shrinkage of concrete over varying periods oftime has been reported by a number of investigators, among whom are the following:

McMillan, F. R. "Shrinkage and Time Effects in Reinforced Concrete." Studies in* Engineering, No. 3, University of Minnesota, 1915.

White, A. H. "Destruction of Cement, Mortars, and Concrete Through Expansion andContraction." Proc. A. S. T. M., Vol. XI, 1911.

Nichols, C. S. and McCullough, C. B. "The Determination of Internal TemperatureRange in Concrete Arch Bridges." Engineering Experiment Station, Ames, Iowa,Bul. No. 30, 1913.

Goldbeck, A. T. "The Expansion and Contraction of Concrete While Hardening." Proc.A. S. T. M., Vol. XI, 1911.

Abrams, D. A. "Effect of Fineness of Cement." Structural Materials Research Laboratory, Lewis Institute, Chicago, Bul. No. 4, 1919.


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FIG. 4. ABSORPTION AND CORRESPONDING EXPANSION OF MORTAR AND

CONCRETE IMMERSED IN WATER

were stored in a damp room and covered with burlap which was kept

wet. Three specimens of each kind were taken out of the storeroom

when they had hardened 7, 14, 28, and 60 days, respectively, in the

damp condition, and were then dried in an oven at a temperature of

150 deg. F. until the loss of weight did not exceed 0.20 per cent during

24 hours. The test pieces were then immersed in clean water in a

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of temperature changes in the instrument. The results obtained are

shown in Figs. 3 and 4, the loss in moisture being given in terms of

weight of the mortar or concrete. The mortar weighed from 140 to

145 lb. per cu. ft., and the concrete weighed from 145 to 155 lb. per

cu. ft.From Fig. 3 it is seen that the rate of loss of moisture in mortar

and concrete by drying decreases with the age of the specimen. In

the mortar, the rate of loss in specimens 28 days and 60 days old, re-

spectively, becomes nearly the same. The total loss in moisture in

mortar does not seem to be greatly different from that in concrete atthe four ages used.

A number of significant features of the second set of tests arebrought out in Fig. 4:

(a) Dry mortar and concrete expand as soon as they absorbwater.

(b) The rate of absorption upon immersion is much less forthe older specimens during the first two or three days of immer-sion, although the total amount of absorption does not changevery greatly for specimens of different ages.

(c) The rate of expansion due to immersion is also less forthe older specimens during the first two or three days of immer-sion. For longer periods of time the amount of expansion is nearlythe same for all ages of each material; but in every case the ex-pansion is considerably greater for mortar than it is for concrete.

(d) The amount of the expansion of mortar and concrete issmall until an absorption of nearly 2 per cent is reached. Afterthis point the expansion becomes nearly proportional to the addi-tional absorption of moisture. This holds true until a suddendecrease in the absorption occurs after about one day's immersion,beyond which point additional absorption gives a greatly in-creased expansion.

(e) The absorption of moisture by mortar or concrete ismuch more rapid than the drying out of moisture from the samematerial. As a result, the expansion due to wetting is more rapidthan the contraction produced by drying. For example, a mortar7 days old gained as much moisture in 2 hours' immersion ascould be dried out by heating to 150 deg. F. for 24 hours.


Another experiment on the relation between absorption of mois-ture and expansion of concrete was made upon two specimens of 1: 2: 4gravel concrete taken from a floor of the Western Newspaper UnionBuilding in Chicago. The concrete was 9 years old. The sizes of thetest pieces were 3.5 by 5 by 21 in., and 3.5 by 5 by 26 in. The speci-mens were dried for 13 days in an oven at a temperature of 150 deg. F.In drying, the average contraction of the concrete was 0.016 per centfor the two specimens. After immersion in water for 15 days theaverage absorption was 5.09 per cent and the resulting expansion 0.042per cent. The results of the test are shown in Fig. 5.

6. Sandstone and Limestone.-For comparison with the behaviorof mortar and concrete, a few tests' were made on the absorption ofwater by stone. The specimens used were sandstone and limestonewhich had nearly the same porosity as the mortar and concrete tested.If the expansion of such material is due to the separation of particles,the same amount of expansion might be expected with stones of thesame porosity.

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RED SANDSTONE IMMERSED IN WATER

Two specimens of a reddish brown sandstone of good quality,obtained from the Lake Superior region for use in the constructionof a University building, were used in the test. The sizes of thespecimens were 3 by 4 by 24 in. and 3.5 by 4 by 25 in. Both pieceswere dried for 6 days in an oven at a temperature of 150 deg. F.After immersion in water for 13 days, the average absorption for thetwo specimens was 5.75 per cent, and the corresponding expansion was0.080 per cent. By referring to Figs. 4 and 5 this amount of expansionis seen to be much greater than that of mortar or concrete after thesame period of immersion. The results of the test are shown in Fig. 6.

The limestone specimens used in the test were a good quality ofo6litic limestone of the kind used for building purposes, commonlyknown as Bedford Indiana stone. The stone has a porous structure.The two test pieces were 3.5 by 3.7 by 11.1 in., and 3.5 by 4.75 by 12.5

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in. in size. The first specimen was dried for 7 days in an oven at 150deg. F., with consequent loss of moisture, due to the drying, of 1.04per cent, and no measurable contraction. The second specimen wasdried for 11 days in an oven at 150 deg. F., with consequent loss ofmoisture of 1.42 per cent and no measurable contraction. They werethen immersed in water. Fig. 7 shows that after an immersion of 6days the average absorption was 6.1 per cent with practically no ex-pansion.

The very rapid absorption and the lack of expansion of the lime-stone are in decided contrast to what occurred with all the othermaterials used. The behavior of the limestone throws doubt upon thetheory that moisture entering a porous substance causes an expansionof material through separation of the particles.

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IV. SHRINKAGE STRESSES IN REINFORCED CONCRETE

7. Analysis of Shrinkage Stresses.-In the preceding tests onplain concrete, a considerable amount of information was obtainedregarding the changes in length corresponding to changes in moisturecontent. It is desirable to know how such information can be appliedto the action of reinforced concrete specimens. It is known that thereis a well defined difference between the shrinkage in a set of plainconcrete test pieces, and that in a set of reinforced concrete testpieces made from the same materials. This difference may be takenas due to the resistance of the reinforcement to the shrinkage of theconcrete, which thus produces compressive stress in the steel and tensilestress in the concrete. It has been found possible to estimate theactual shrinkage stresses, both in steel and concrete, by comparisonwith the shrinkage of plain concrete under similar conditions.

When a plain concrete prism is dried out in air all particles havea tendency to move toward the middle of the prism, thus decreasingits length without causing cracks unless external' forces resist thistendency. Consider one half of the length of a reinforced concreteprism as shown in Fig. 8. If there was no bond resistance between theconcrete and the reinforcing bar, when shrinkage occurred the relative

P/a4n Reinforced Bond Compress1-eConcrete Concrete Stress Stress' /,Spec/1Men Specm/ry2 Re1Inforcemr'ent

FIG. 8. DISTRIBUTION OF SHRINKAGE STRESSES IN REINFORCED CONCRETESPECIMEN


displacement of concrete particles with reference to the reinforcementwould be maximum at the end of the prism and zero at the center.Since resistance to this displacement actually is offered by the bondresistance between the concrete and the bar, the bond stress developedshould be proportional to the amount of the tendency toward displace-ment. This bond stress is, therefore, greatest at the end of the bar andsmallest at the center. If there is *no slipping of the bar, a fairlyreasonable assumption is that the bond stress varies uniformly from amaximum at the end of the bar to zero at the middle of the length ofthe bar.

The following notation will be used:

e = shrinkage in a unit length of plain concrete;el

s = 2 total shrinkage in a half-length of a plain concrete

prism;s' = total shrinkage in a half-length of a reinforced concrete

prism;l = length of the prism;a = pA = cross-sectional area of the reinforcing bar;A = cross-sectional area of the prism;o = circumference of the bar;u = maximum bond stress at the end of the bar;

P,= total compressive stress in bar = total tensile stress inconcrete, at any section y distant from the center;

E, = nE, = modulus of elasticity of steel;E,= modulus of elasticity of concrete.

Since the total compressive stress P,, produced at any section,must equal the summation of the bond stresses between the sectionand the end of the bar, it follows that the maximum value of P, occurs

uolat the middle of the bar and is equal to~ . At any other point the

stress P, is given by the expression

P = uol[ 1 -( 2........ (1)

This is the equation of a parabola with its vertex at the center of thebar as shown in Fig. 8.


The total deformation of the half-length of the bar is

, P, dy uol2

s (2)aE 12aE.

Since the total stresses in steel and concrete are equal in amount

at any section, the total deformation in the concrete is

, el , 2 P• dy _[ uol2 1=2 AE, (1 - p) =12 AE(1l-p)J 3

From equations (2) and (3), disregarding the factor (1 - p), the

maximum bond stress is found to be

6 eaE,u ......... (4)ol (l+np)

The total stress P= 1.5 eaE1+np

1.5 eE,whence the maximum compressive unit stress f - - (5)

and the maximum tensile unit stress

f A= f pf .. . . . . . . . .. . . . (6)

The shrinkage stresses in the steel and concrete are thus seen tobe directly proportional to the amount of shrinkage in plain concrete.It is seen that the stress in the steel decreases and the stress in theconcrete increases with an increase in the percentage of reinforcement.

It must be remembered that equations (5) and (6) give maximumstresses; the average stresses over the length of the specimen are two-thirds as great. In the following experiments gage lengths wereused which were five-sixths and five-twelfths of the length of the speci-men; in these cases the average measured stresses should be 77 percent and 94 per cent, respectively, of the maximum stress at themiddle of the bar.

8. Measurement of Shrinkage Stresses in Reinforced ConcreteSpecimens.-Two sets of tests were made for the purpose of measuring


the shrinkage stresses in reinforced concrete specimens. For the first setof experiments six test pieces, 2 by 3 by 24 in. in size, were prepared,two of them being of plain concrete, two having two 3

8 -in. round steelbars (p - 3.68 per cent), and two having two 1/2-in. round steel bars(p = 6.54 per cent). The proportions of the concrete were 1:2:4.The specimens were dried in the air of a room for 22 days; then they

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FIG. 9. SHRINKAGE STRESSES IN REINFORCED CONCRETE SPECIMENS

T


were dried in an oven for 13 days at a temperature of 150 deg. F.;and finally they were dried for 6 days at a temperature of 200 deg. F.

The change of length was measured on a 20-in. gage line betweenpoints on each embedded steel bar in the reinforced concrete testpieces, and between points on steel plugs embedded in the plain con-crete test pieces. The results, which were very uniform in companionspecimens, are shown in Fig. 9. The measured stresses in the steelwere obtained by multiplying the measured deformation in the steel bythe modulus of elasticity of steel; the curves marked "measured stressin concrete" were obtained by multiplying the measured stress inthe steel by the percentage of reinforcement, see equation (6), andrepresent the average stress over the cross-section of the concrete.The calculated stress is the average calculated stress over the 20-in.gage length, or 77 per cent of the maximum stress given by equations(5) and (6).

As may be seen from Fig. 9, even reinforced concrete having avery high percentage of reinforcement contracts rapidly in air. Whenthe specimens were 22 days old the shrinkage stress in the concretereached 166 lb. per sq. in. in the specimens having 3.68 per cent rein-forcement, and 204 lb. per sq. in. in the specimens having 6.54 per centreinforcement.

The same specimens, after being dried 13 days longer at a tem-perature of 150 deg. F., developed stresses of 190 lb. per sq. in. and240 lb. per sq. in., respectively, which nearly correspond to the ulti-mate'tensile strength of the concrete. Furthermore, being dried at atemperature of 200 deg. F., the concrete failed in tension and showedtwo transverse cracks at points about 8 in. from each end.

This last case, however, may not be representative, because theremay have been some injury to the texture of the concrete when it washeated beyond 200 deg. F. But the fact that the shrinkage stress inthe concrete reached 170 to 200 lb. per sq. in. in 22 days, in the air of aroom, may be sufficient reason for concluding that cracks will eventu-ally be formed in concrete which has a high percentage of reinforce-ment.

The sudden drop of the shrinkage stress in the concrete whenheated beyond 200 deg. F., as shown in Fig. 9, indicates injury to theconcrete at this temperature; so that the use of reinforced concreteexposed to a temperature higher than 200 deg. F. may be dangerousunless proper precautions are taken.


A second set of tests was made in which smaller percentages of

reinforcement were used. The size of the test pieces was 6 by 6 by 24in. and they were made of 1: 2:4 concrete. Deformations were meas-

ured on a gage length of 10 in. One piece was made without rein-forcement, one with four 1/4-in., one with four 3/s-in., and one withfour 1/2-in. round steel bars. A similar set of test pieces was madewith the same amount of reinforcement, but which had in additionthree anchor-lugs welded to each end of the reinforcing bars toguard against a slipping of the reinforcement during the setting ofthe concrete; a test piece of plain concrete was also included in thisset. The size and form of the test pieces are shown in Figs. 10 and 11.

These specimens were left in the air of the room for 99 days. Theywere then dried in an oven at a temperature of 200 deg. F. Thecontraction which took place during the drying and the measuredshrinkage stresses in both steel and concrete are shown in Figs. 10, 11,and 12. The measured stresses in steel and concrete were determinedas in the preceding tests. The calculated stress is the average calculatedstress over the 10-in. gage length, or 94 per cent of the stress given byequations (5) and (6).

In the case of the plain concrete, the results of the two sets oftests were quite uniform, both as regards the loss of moisture andthe resulting contraction during setting and hardening. The differ-ence between the contraction of plain concrete specimens and thosehaving different amounts of reinforcement was quite regular at allconditions of storage, and is very instructive. The deformation inthe reinforcing bars provided with lugs was greater than the deforma-tion in the plain bar. This indicates that slipping of the bars tookplace with the latter during the shrinking of the concrete; the shrink-age stress is seen to be greater in reinforced concrete having goodanchorage of the reinforcement. In general some slipping must beexpected.

The measured stress in the steel reached 18 000 lb. per sq. in. inthe specimen having reinforcement of 0.55 per cent, and the stressin the concrete reached 250 lb. per sq. in. in the specimen having rein-forcement of 2.18 per cent. This stress in the steel exceeds theaccepted working stress of soft steel and the stress in the concrete isnearly equal to the ultimate tensile strength of concrete of this kind.

When these specimens were heated above 200 deg. F. thesestresses both in concrete and steel suddenly dropped down, probablydue to injury of the concrete by the heat.


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V. CONCLUSION

9. Comments.-The following comments are offered; part of themrelate to the concrete used in the tests and part are inferences based onthe writer's general experience and observation:

1. Concrete expands when it absorbs moisture and contractswhen it is dried. Concrete of a 1: 2: 4 mixture is likely to contractduring hardening as much as 0.05 per cent in an ordinary struc-ture.

2. Contraction of concrete by the loss of moisture causesstress in the concrete when it is restrained by an external force.The amount of this stress is not as small as is generally supposed.

3. The shrinkage stress caused in the steel in reinforced con-crete may reach the usually accepted working stress of steel whenthe amount of reinforcement is less than 1.5 per cent.

4. The shrinkage stress developed in 1:2:4 concrete mayreach the ultimate tensile strength of the concrete when theamount of reinforcement is greater than 1.5 per cent. Withricher mixtures the increase in shrinkage stress may be relativelygreater than the increase in ultimate strength.

5. The greater the percentage of reinforcement the greaterthe tensile stress that may develop in the concrete, and concretehaving a higher percentage of reinforcement than 1.5 per cent islikely to have cracks formed unless proper provision is made.

6. In reinforced concrete out of doors, subject to alternatewet and dry conditions, cracks may readily be formed under therepeated stress which is nearly equal to the tensile strength of theconcrete.

7. Reinforced concrete does not appear likely to be a durablematerial in a place where a corrosive influence on steel, such assea air, is active, unless proper protection against the formation ofshrinkage cracks is made.

8. It is suggested that the prevention of shrinkage stress inconcrete might be accomplished in two ways, either by finding a

THE EFFECT OF MOISTURE CONTENT UPON CONCRETE 29

cement giving less expansion and contraction, or by the use of aperfect waterproofing treatment.

9. It may be expected that an integral waterproofing com-pound might lessen the change of volume for a short time, but itwould not prevent the final diffusion of moisture with consequentchange in volume.

LIST OF

PUBLICATIONS OF THE ENGINEERING EXPERIMENT STATION

Bulletin No. 1. Tests of Reinforced Concrete Beams, by Arthur N. Talbot.1904. None available.

Circular No. 1. High-Speed Tool Steels, by L. P. Breckenridge. 1905. Noneavailable.

Bulletin No. S. Tests of High-Speed Tool Steels on Cast Iron, by L. P.Breckenridge and Henry B. Dirks. 1905. None available.

Circular No. S. Drainage of Earth Roads, by Ira 0. Baker. 1906. Noneavailable.

Circular No. 3. Fuel Tests with Illinois Coal (Compiled from tests madeby the Technological Branch of the U. S. G. S., at the St. Louis, Mo., Fuel Test-ing Plant, 1904-1907), by L. P. Breckenridge and Paul Diserens. 1908. Thirtycents.

Bulletin No. 3. The Engineering Experiment Station of the University ofIllinois, by L. P. Breckenridge. 1906. None available.

Bulletin No. 4. Tests of Reinforced Concrete Beams, Series of 1905, byArthur N. Talbot. 1906. Forty-five cents.

Bulletin No. 5. Resistance of Tubes to Collapse, by Albert P. Carman andM. L. Carr. 1906. None available.

Bulletin No. 6. Holding Power of Railroad Spikes, by Roy I. Webber. 1906.None available.

Bulletin No. 7. Fuel Tests with Illinois Coals, by L. P. Breckenridge, S. WParr, and Henry B. Dirks. 1906. None available.

Bulletin No. 8. Tests of Concrete: I, Shear; II, Bond, by Arthur N. Tal-bot. 1906. None available.

Bulletin No. 9. An Extension of the Dewey Decimal System of ClassificationApplied to the Engineering 'Industries, by L. P. Breckenridge and G. A. Good-enough. 1906. Revised Edition, 1912. Fifty cents.

Bulletin No. 10. Tests of Concrete and Reinforced Concrete Columns, Seriesof 1906, by Arthur N. Talbot. 1907. None available.

Bulletin No. 11. The Effect of Scale on the Transmission of Heat throughLocomotive Boiler Tubes, by Edward C. Schmidt and John M. Snodgrass. 1907.None available.

Bulletin No. 1S. Tests of Reinforced Concrete T-Beams, Series of 1906, byArthur N. Talbot. 1907. None available.

Bulletin No. 13. An Extension of the Dewey Decimal System of Classifica-tion Applied to Architecture and Building, by N. Clifford Ricker. 1906. Noneavailable.

Bulletin No. 14. Tests of Reinforced Concrete Beams, Series of 1906, byArthur N. Talbot. 1907. None available.

31


Bulletin No. 16. How to Burn Illinois Coal without Smoke, by L. P. Breck-enridge. 1907. None available.

Bulletin No. 16. A Study of Roof Trusses, by N. Clifford Bicker. 1907.None available.

Bulletin No. 17. The Weathering of Coal, by S. W. Parr, N. D. Hamilton,and W. F. Wheeler. 1907. None available.

Bulletin No. 18. The Strength of Chain Links, by G. A. Goodenough andL. E. Moore. 1907. Forty cents.

Bulletin No. 19. Comparative Tests of Carbon, Metallized Carbon, and Tan-talum Filament Lamps, by T. H. Amrine. 1907. None available.

Bulletin No. 20. Tests of Concrete and Reinforced Concrete Columns, Seriesof 1907, by Arthur N. Talbot. 1907. None available.

Bulletin No. 21 Tests of a Liquid Air Plant, by C. S. Hudson and C. M. Gar-land. 1908. Fifteen cents.

Bulletin No. 22. Tests of Cast-Iron and Reinforced Concrete Culvert Pipe,by Arthur N. Talbot. 1908. None available.

Bulletin No. 23SS. Voids, Settlement, and Weight of Crushed Stone, by Ira 0.Baker. 1908. Fifteen cents.

*Bulletin No. 24. The Modification of Illinois Coal by Low Temperature Dis-tillation, by S. W. Parr and C. K. Francis. 1908. Thirty cents.

Bulletin No. 25. Lighting Country Homes by Private Electric Plants, byT. H. Amrine. 1908. Twenty cents.

Bulletin No. 26. High Steam-Pressure in Locomotive Service. A Review of aReport to the Carnegie Institution of Washington, by W. F. M. Goss. 1908.Twenty-five cents.

Bulletin No. 27. Tests of Brick Columns and Terra Cotta Block Columns, byArthur N. Talbot and Duff A. Abrams. 1908. Twenty-five cents.

Bulletin No. 28. A Test of Three Large Reinforced Concrete Beams, byArthur N. Talbot. 1908. Fifteen cents.

Bulletin No. 29. Tests of Reinforced Concrete Beams: Resistance to WebStresses, Series of 1907 and 1908, by Arthur N. Talbot. 1909. Forty-five cents.

Bulletin No. 30. On the Rate of Formation of Carbon Monoxide in Gas Pro-ducers, by J. K. Clement, L. H. Adams, and C. N. Haskins. 1909. Twenty-fivecents.

Bulletin No. 31. Tests with House-Heating Boilers, by J. M. Snodgrass. 1909.Fifty-five cents.

Bulletin No. $S. The Occluded Gases in Coal, by S. W. Parr and PerryBarker. 1909. Fifteen cents.

Bulletin No. 88. Tests of Tungsten Lamps, by T. H. Amrine and A. Guell.1909. Twenty cents.

*Bulletin No. 84. Tests of Two Types of Tile-Roof Furnaces under a Water-Tube Boiler, by 3. M. Snodgrass. 1909. Fifteen cents.

* A limited number of copies of bulletins starred are %vailable for free distribution.

PUBLICATIONS OF THE ENGINEERING EXPERIMENT STATION 33

Bulletin No. 35. A Study of Base and Bearing Plates for Columns andBeams, by N. Clifford Ricker. 1909. None available.

Bulletin No. 36. The Thermal Conductivity of Fire-Clay at High Temperatures, by J. K. Clement and W. L. Egy. 1909. Twenty cents.

Bulletin No. 37. Unit Coal and the Composition of Coal Ash, by S. W. Parrand W. F. Wheeler. 1909. None available.

Bulletin No. 88. The Weathering of Coal, by S. W. Parr and W. F. Wheeler.1909. Twenty-five cents.

*Bulletin No. 39. Tests of Washed Grades of Illinois Coal, by C. S. McGovney.1909. Seventy-five cents.

Bulletin No. 40. A Study in Heat Transmission, by J. K. Clement and C. M.Garland. 1909. Ten cents.

Bulletin No. 41. Tests of Timber Beams, by Arthur N. Talbot. 1909. Thirtyfive cents.

*Bulletin No. 42. The Effect of Keyways on the Strength of Shafts, by Her-bert F. Moore. 1909. Ten cents.

Bulletin No. 43. Freight Train Resistance, by Edward C. Schmidt. 1910.Seventy-five cents.

Bulletin No. 44. An Investigation of Built-up Columns under Load, byArthur N. Talbot and Herbert F. Moore. 1910. Thirty-five cents.

*Bulletin No. 45. The Strength of Oxyacetylene Welds in Steel, by HerbertL. Whittemore. 1910. Thirty-five cents.

Bulletin No. 46. The Spontaneous Combustion of Coal, by S. W. Parr andF. W. Kressman. 1910. Forty-five cents.

*Bulletin No. 47. Magnetic Properties of Heusler Alloys, by Edward B.Stephenson. 1910. Twenty-five cents.

*Bulletin No. 48. Resistance to Flow through Locomotive Water Columns, byArthur N. Talbot and Melvin L. Enger. 1911. Forty cents.

*Bulletin No. 49. Tests of Nickel-Steel Riveted Joints, by Arthur N. Talbotand Herbert F. Moore. 1911. Thirty cents.

*Bulletin No. 50. Tests of a Suction Gas Producer, by C. M. Garland andA. P. Kratz. 1911. Fifty cents.

Bulletin No. 51. Street Lighting, by J. M. Bryant and H. G. Hake. 1911.Thirty-five cents.

*Bulletin No. 5S. An Investigation of the Strength of Rolled Zinc, by HerbertF. Moore. 1911. Fifteen cents.

*Bulletin No. 53. Inductance of Coils, by Morgan Brooks 'and H. M. Turner.1912. Forty cents.

*Bulletin No. 54. Mechanical Stresses in Transmission Lines, by A. Guell.1912. Twenty cents.

*Bulletin No. 55. Starting Currents of Transformers, with Special Referenceto Transformers with Silicon Steel Cores, by Trygve D. Yensen. 1912. Twentycents.

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34 PUBLICATIONS OF THE ENGINEERING EXPERIMENT STATION

*Bulletin No. 56. Tests of Columns: An Investigation of the Value of Con-crete as Reinforcement for Structural Steel Columns, by Arthur N. Talbot andArthur R. Lord. 1912. Twenty-five cents.

*Bulletin No. 57. Superheated Steam in Locomotive Service. A Review ofPublication No. 127 of the Carnegie Institution of Washington, by W. F. MGoss. 1912. Forty cents.

*Bulletin No. 58. A New Analysis of the Cylinder Performance of Reciprocat-ing Engines, by J. Paul Clayton. 1912. Sixty cents.

*Bulletin No. 59. The Effect of Cold Weather upon Train Resistance andTonnage Rating, by Edward C. Schmidt and F. W. Marquis. 1912. Twenty cents.

Bulletin No. 60. The Coking of Coal at Low Temperature, with a PreliminaryStudy of the By-Products, by S. W. Parr and H. L. Olin. 1912. Twenty-five cents.

*Bulletin No. 61. Characteristics and Limitations of the Series Transformer,by A. R. Anderson and H. R. Woodrow. 1912. Twenty-five cents.

Bulletin No. 6S. The Electron Theory of Magnetism, by Elmer H. Williams.1912. Thirty-five cents.

Bulletin No. 6S. Entropy-Temperature and Transmission Diagrams for Air,by C. R. Richards. 1913. Twenty-five cents.

*Bulletin No. 64. Tests of Reinforced Concrete Buildings under Load, byArthur N. Talbot and Willis A. Slater. 1913. Fifty cents.

*Bulletin No. 65. The Steam Consumption of Locomotive Engines from theIndicator Diagrams, by J. Paul Clayton. 1913. Forty cents.

Bulletin No. 66. The Properties of Saturated and Superheated AmmoniaVapor, by G. A. Goodenough and William Earl Mosher. 1913. Fifty cents.

Bulletin No. 67. Reinforced Concrete Wall Footings and Column Footings,by Arthur N. Talbot. 1913. None available.

Bulletin No. 68. The Strength of I-Beams in Flexure, by Herbert F. Moore.1913. Twenty cents.

Bulletin No. 69. Coal Washing in Illinois, by F. C. Lincoln. 1913. Fiftycents.

Bulletin No. 70. The Mortar-Making Qualities of Illinois Sands, by C. C.Wiley. 1913. Twenty cents.

Bulletin No. 71. Tests of Bond between Concrete and Steel, by Duff A.Abrams. 1913. One dollar.

*Bulletin No. 72. Magnetic and Other Properties of Electrolytic Iron Meltedin Vacuo, by Trygve D. Yensen. 1914. Forty cents.

Bulletin No. 7"3. Acoustics of Auditoriums, by F. R. Watson. 1914. Twentycents.

*Bulletin No. 74. The Tractive Resistance of a 28-Ton Electric Car, by HaroldH. Dunn. 1914. Twenty-five cents.

Bulletin No. 75. Thermal Properties of Steam, by G. A. Goodenough. 1914.Thirty-five cents.



Bulletin No. 76. The Analysis of Coal with Phenol as a Solvent, by S. W.Parr and H. F. Hadley. 1914. Twenty-five cents.

*Bulletin No. 77. The Effect of Boron upon the Magnetic and Other Prop-erties of Electrolytic Iron Melted in Vacuo, by Trygve D. Yensen. 1915. Tencents.

Bulletin No. 78. A Study of Boiler Losses, by A. P. Kratz. 1915. Thirty-five cents.

*Bulletin No. 79. The Coking of Coal at Low Temperatures, with Special Ref-erence to the Properties and Composition of the Products, by S. W. Parr andH. L. Olin. 1915. Twenty-five cents.

* Bulletin No. 80. Wind Stresses in the Steel Frames of Office Buildings, byW. M. Wilson and G. A. Maney. 1915. Fifty cents.

Bulletin No. 81. Influence of Temperature on the Strength of Concrete, byA. B. McDaniel. 1915. Fifteen cents.

Bulletin No. 8R. Laboratory Tests of a Consolidation Locomotive, by E. C.Schmidt, J. M. Snodgrass, and R. B. Keller. 1915. Sixty-five cents.

*Bulletin No. 83. Magnetic and Other Properties of Iron-Silicon Alloys,Melted in Vacuo, by Trygve D. Yensen. 1915. Thirty-five cents.

Bulletin No. 84. Tests of Reinforced Concrete Flat Slab Structures, byArthur N. Talbot and W. A. Slater. 1916. Sixty-five cents.

*Bulletin No. 85. The Strength and Stiffness of Steel under Biaxial Loading,by A. J. Becker. 1916. Thirty-five cents.

Bulletin No. 86. The Strength of I-Beams and Girders, by Herbert F. Mooreand W. M. Wilson. 1916. Thirty cents.

"Bulletin No. 87. Correction of Echoes in the Auditorium, University of Illi-nois, by F. R. Watson and J. M. White. 1916. Fifteen cents.

Bulletin No. 88. Dry Preparation of Bituminous Coal at Illinois Mines, byE. A. Holbrook. 1916. Seventy cents.

Bulletin No. 89. Specific Gravity Studies of Illinois Coal, by Merle L. Nebel.1916. Thirty cents.

*Bulletin No. 90. Some Graphical Solutions of Electric Railway Problems, byA. M. Buck. 1916. Twenty cents.

Bulletin No. 91. Subsidence Resulting from Mining, by L. E. Young andH. H. Stock. 1916. None available.

'Bulletin No. 9S. The Tractive Resistance on Curves of a 28-Ton ElectricCar, by E. C. Schmidt and H. H. Dunn. 1916. Twenty-five cents.

*Bulletin No. 93. A Preliminary Study of the Alloys of Chromium, Copper,and Nickel, by D. F. McFarland and 0. E. Harder. 1916. Thirty cents.

*Bulletin No. 94. The Embrittling Action of Sodium Hydroxide on Soft Steel,by S. W. Parr. 1917. Thirty cents.

*Bulletin No. 95. Magnetic and Other Properties of Iron-Aluminum AlloysMelted in Vacuo, by T. D. Yensen and W. A. Gatward. 1917. Twenty-five cents.



*Bulletin No. 96. The Effect of Mouthpieces on the Flow of Water througha Submerged Short Pipe, by Fred B Seely. 1917. Twenty-five cents.

*Bulletin No. 97. Effects of Storage upon the Properties of Coal, by S. W.Parr. 1917. Twenty cents.

*Bulletin No. 98. Tests of Oxyacetylene Welded Joints in Steel Plates, byHerbert F. Moore. 1917. Ten cents.

Circular No. 4. The Economical Purchase and Use of Coal for HeatingHomes, with Special Reference to Conditions in Illinois. 1917. Ten cents.

*Bulletin No. 99. The Collapse of Short Thin Tubes, by A. P. Carman. 1917.Twenty cents.

*Circular No. 5. The Utilization of Pyrite Occurring in Illinois BituminoisCoal, by E. A. Holbrook. 1917. Twenty cents.

*Bulletin No. 100. Percentage of Extraction of Bituminous Coal with SpecialReference to Illinois Conditions, by C. M. Young. 1917.

*Bulletin No. 101. Comparative Tests of Six Sizes of Illinois Coal on a Mikado Locomotive, by E. C. Schmidt, J. M. Snodgrass, and 0. S. Beyer, Jr. 1917.Fifty cents.

*Bulletin No. 102. A Study of the Heat Transmission of Building Materials,by A. C. Willard and L. 0. Lichty. 1917. Twenty-five cents.

*Bulletin No. 108. An Investigation of Twist Drills, by B. Benedict and W.P. Lukens. 1917. Sixty cents.

*Bulletin No. 104. Tests to Determine the Rigidity of Riveted Joints of SteelStructures, by W. M. Wilson and H. F. Moore. 1917. Twenty-five cents.

Circular No. 6. The Storage of Bituminous Coal, by H. H. Stock. 191P.Forty cents.

Circular No. 7. Fuel Economy in the Operation of Hand Fired PowerPlants. 1918. Twenty cents.

'Bulletin No. 105. Hydraulic Experiments with Valves, Orifices, Hose, Nozzles,and Orifice Buckets, by Arthur N. Talbot, Fred B Seely, Virgil R. Fleming, andMelvin L. Enger. 1918. Thirty-five cents.

*Bulletin No. 106. Test of a Flat Slab Floor of the Western Newspaper UnionBuilding, by Arthur N. Talbot and Harrison F. Gonnerman. 1918. Twenty cents.

Circular No. 8. The Economical Use of Coal in Railway Locomotives. 1918.Twenty cents.

*Bulletin No. 107. Analysis and Tests of Rigidly Connected Reinforced Con-crete Frames, by Mikishi Abe. 1918. Fifty cents.

*Bulletin No. 108. Analysis of Statically Indeterminate Structures by theSlope Deflection Method, by W. M. Wilson, F. E. Richart, and Camillo Weiss. 1918.One dollar.

*Bulletin No. 109. The Pipe Orifice as a Means of Measuring Flow of Waterthrough a Pipe, by B. E. Davis and H. H. Jordan, 1918. Twenty-five cents.

*Bulletin No. 110. Passenger Train Resistance, by E. C. Schmidt and H. H.Dunn. 1918. Twenty cents.



*Bulletin No. 111. A Study of the Forms in which Sulphur Occurs in Coal, byA. R. Powell with S. W. Parr. 1919. Thirty cents.

*Bulletin No. 112. Report of Progress in Warm-Air Furnace Research, byA. C. Willard. 1919. Thirty-five cents.

*Bulletin No. 113. Panel System of Coal Mining. A Graphical Study of Per-centage of Extraction, by C. M. Young. 1919.

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*Bulletin No. 115. The Relation between the Elastic Strengths of Steel inTension, Compression, and Shear, by F. B. Seely and W. J. Putnam. 1920.Twenty cents.

Bulletin No. 116. Bituminous Coal Storage Practice, by H. H. Stock, C. W.Hippard, and W. D. Langtry. 1920. Seventy-five cents.

*Bulletin No. 117. Emissivity of Heat from Various Surfaces, by V. S. Day.1920. Twenty cents.

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*Bulletin No. 119. Some Conditions Affecting the Usefulness' of Iron Oxide forCity Gas Purification, by W. A. Dunkley. 1921.

*Circular No. 9. The Functions of the Engineering Experiment Station of theUniversity of Illinois, by C. R. Richards. 1921.

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*Bulletin No. 121. The Volute in Architecture and Architectural Decoration, byRexford Newcomb. 1921. Forty-five cents.

*Bulletin No. 122. The Thermal Conductivity and Diffusivity of Concrete, byA. P. Carman and R. A. Nelson. 1921. Twenty cents.

*Bulletin No. 123. Studies on Cooling of Fresh Concrete in Freezing Weatherby Tokujiro Yoshida. 1921. Thirty cents.

*Bulletin No. 124. An Investigation of the Fatigue of Metals, by II. F. Mooreand J. B. Kommers. 1921. Ninety-five cents.

*Bulletin No. 125. The Distribution of the Forms of Sulphur in the Coal Bed,by H. F. Yancey and Thomas Fraser. 1921.

*Bulletin No. 126. A Study of the Effect of Moisture Content upon the Ex-pansion and Contraction of Plain and Reinforced Concrete, by T. Matsumoto.1921. Twenty cents.


THE UNIVERITY OF ILLINOISTHE STATE UNIVERSITY

UrbanaDAVmi KImL y, Ph.D., LL.D., P r esident

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