Drying shrinkage of Portland cement mortar

AUG 5 1959

LIBRAR"I

DRYMG SIRNJG1G OF PORTLAID CD[WT MORTAR by

ENREUT M. PRILUCK

Submitted in Pertial Nifillament of the Raquirments for the Degree of Baohelor of Soienoe

at the

WASSACHUSETTS INSTITUTE OF TZ=NOIGY Jie, 1959

Signature redacted

Signature of Author . -. o . . . . .- % *

Departuent of Civil and Sanitary Engineering, May 25, 1969 A 9

Signature redacted

Thesis Supervior

,/f

Signature redacted

Aooqftod by ~ 4 6 j ; 4* '-** L* q;"

irman, Departmental Comnittee on Theses

Abstract Sebtion I Theory ad Definitions 1 Seotion II kperimental Procedure 4 Section III Test Results 6 Section IV Ceolusions 17 Appendix Lab Data 19

ABSTRAOT

Portland oement mortar shrinks when eposed to drying oonditions subsequent to moist ouringe The principal factors

influencing shrinksge behavior are the water-oment ratio, the proportion of send in the mortar, and the amount of air in the paste.

The series of tests conducted indicate that the

shrinkage of the water cement paste increases as the percentage air is inoreesed. With higher sand content there is a greater degree of internal cracking*

1

I

Upon exposure to drying conditions subsequent to moist curing, portland cement mortar has been found to shrink. It is the purpose of this thesis to obtain a qualitative picture of what takes plaoe within the mortar during shrinkage and to determine quantitatively

the magnitude of shrinkage for varying mortar proportions.

A pertland oement mortar ( hereafter referred to simply as mortar ) has four ingredients; cement, sand, water, and air. The mortar has two main oomponents. First there is the matrix of oement-water paste plus air. Seond there are the sand partioles within the matrix. The importemt paremeters in the mortar system would sest to be the water-oment ratio of the paste, A the amount of air entrap-ped in the paste, and the proportion of sand to matrix.

It is assumed that the volume of the sand resins constant and that changes in the mortar volume are caused by expension or shrinkage of the matrix.

Based upon the assamption made above there are three shrint-ages" taking plaoe which are defined as followst external shrinkage is the total decrease in volume of the mortar; actual shrinkage is the decrease in volume of the matrix whioh causes external shrinkage and internal cracking; calculated shrinkage is that decrease in volume of the matrix which manifests itself in external shrinkage.

The initial arrangement of the sand grains within the matrix will fall into one of the two oases described below.

In the first oase the sand partioles are well separated and oan move freely as the matrix shrinks. This is shown schematioally

2

In the sesond oae the struoture of the said partioles restriots their novement as the matrix shrinks. This is shein

sohimatioally in Figure 2.

Calculated shrinkage will be equal to aotual shrinkage in Case I (Fig. Se). When struotural intorferenoe *sours, ealoulated

shrinkage will be less than aotual shrinkage ai oraoking of the matrix will develop (Fig. 3b). As the mortar shrinks struotural interferenee mq develop in a mortar that initially had free more-sent (Fig*So)e

In order to investigate the effeets of the pwremeters mentioned above upon the drying shrinkage of mortar, a series of tests and experiments were performed in the laboratory. A desorip-tion of the lab work is given in Secdesorip-tion II.

.

Case

I

Free Movement

FIG. I

Case

If

Structural Interference

FIG. 2

(a)

__

(b)

(c)

0 CP C)

L-

ft-%I

FIG. 3

-+V

14,

II

The first step in the lab work was to set aside a supply of

type I portland oment a"l sand so that the materials used in taking

various mortars would be uniform. The following tests were performed on the sand and ement set aside: sieve analysis; absorbtion, and bulk speoifie gravity of the seed; normal consisteney3 of the emeont.

Using five waternoment ratios (w/Oz .65, .60, .65, .50, .45)

and three ement to sand ratios (/s a 1/4, 1/3, 1/2), fifteen

mortar nixes were made. These mortars had the following proportions by weight:

Cment Sand Water

1 4 .65 1 4 .60 1 4 .65 1 4 .50 1 4 .46 1 3 .65 1 3 .60 1 3 .56 1 3 .50 1 3 .45 1 2 .65 1 2 to0 1 2 06 1 2 .50 1 2 .45

A batoh of each mortar was ixed of suffieient amount for flow and density measurements and for the =iking of three length ohange specimens. 5

A maller batch of eash of the five pastes was made for density measurement.

I as per AMUI C136-46 2as per ASWK ClM-42 3 as per AMM C187-66 4 as per LSTM C124-39

The speoimens were cured in the molds for one d$. The molds were then removed sad the speoimens were cared for six d@as under water at 70 degrees P.. They were then renoved from the water

and exposed to uniform drying at 70 degrees F., 50% relative humidity for the duration of the test.

The speoimens were measured6 and weighed at one da, seven days, eight days, and intervals of three or four days thereafter up to

twenty-one days. Thereafter measuroments were made at seven day inter-vals until the osased to show aq appreoiable length ehange

(4.0005.-.0006 inwhes for two oonsecutive weeks).

The lab data is presented in the appendix. In seotion III, whioh follows, will be found a flow oontour map, mortar proportions

by volume, peroentage air entrapped, and ealoulated shrinkage in

peroent. The method of calculation of these results from the lab data is also illustrated.

III

/5

-

-II

so

1/4

-

X

x

90 SI ooI0 I3Z0 (f53 5O m 39~...u'5~" 140 0 50 60 00 70 100 1 ,5 2103,5 _,50

1/2

- '20 X 130 140 ISO I I I I I I I

0.40

0.45

0.50

0.55

0.60

065

0.70

0.75

W/C

8

Mortar Proportions by Weight and VoIme 0.0. per 100 g. of oement batob

Vt _Vp Kix by weight 1:2:.65 1: 2:.60 1:

2:.55

1:2:.50 1:2: .45 1:3:.65 1:3: .60 1:3:.55 1:3:.50 1:3:.45 114:.65 1:4:.60 1:4:.55 1:4 .50 1:4:.45 98.2 91.4 86.6 81.1 76.7 98.2 91.4 86.6 81.1 76.7 98.2 91.4 86.6 81.1 76.7 vs v. 76.0 76.0 76.0 76.0 76.0 114 114 114 114 114 152 152 152 152 152 0.0 0.0 0.0 3.4 0.0 0.0 5.0 8.0 11.0 30.5 9.8 16.6 24.4 41.9 59.3

%

Air entrapped "'POS, 0.0 0.0 0.0 4.0 0.0 0.0 6.2 8.5 11.9 21.1 9.1 15.4 24.2 34.0 43.6 Vt = Total volme Vp = Volume paste Vs = Sand volume Vs = Air volume 174.2 167.4 162.6 160.5 152.7 212.2 210.0 06.0 26.0 211.0 50.0 50.0 283.0 275.0 58.0

9

Qaloulabod Shrinkage in Peremnt

%A~o 25 S 35 4 %Ar0.0 21.1 43.6 0 0 0 0 1 0189 .153 .234 4 .372 *413 .500 8 .542 e542 *640 11 .62? .638 .896 15 .875 *692 0722

a1

.771 .762 .754 28 0810 .795 0785 53 .917 0838 .785 .50 1w/0 2 8 383 4 8

%

Air 4.02 11.94 34.0 Days 00 0 0 1 .159 0195 .223 4 .333 0428 .457 80503 0554 0638 116.81 o643 .690 15 .655 .78 0 0744 2a .735 .786 o770 38 0780 .880 .7 53 .882 .882 .830 .55 W/0 2 8 353 483 % Air 000 8.45 24.2 Days 0 0 0 0 1 A160 0179 .20? 4 o350 0425 .432 8 .517 0580 .622 11 .590 o658 .677 15 .667 0744 .740 21 0735 .796 0775 38 076 .842 0805 53 o853 0900 o862

10 .60

w/o

2 8 0.0 0 .133 .361 .536 .610 .692 .767 .806 .840 3 8 5.18 0 .143 .388 .53 .645 .746 .818 8657 .895 4 8 15.4 0 .197 .408 .618 .672 .738 ,811 .840 .876 .65 w/o 2 8 *.0 0 .116 .330 .522 .606 .683 .730 .752 .79 3 8 0.0 0 .104 .389 .627 .674 .752 .842 .875 .900 4 8 9.07 0 .215 .411 .579 .68 .732 .788 .818 .884

*days at 70 degrees F., 50% relative hbmidity % Air Dqys* 0 1 4 8 11 15 21 28 53 % Air 0 1 4 8 11 15 21 go

1.0

0.9

W/C

0.45

0.8

c0.7-0.6 _{C/ 4, % A =43.6} c/ I

% A

210.1

%A

0..

.3

0.2 0.-0 10

20

30

40

50

6

I ~% I.'.

0.9

W/ C

0.50

,0.8

E

0.7

0.6-

_{C/= /4}

_%A

_34.0

hY4 c I ,% . S0.4 -S 13 %A21. 0

0.2

00 -4

~0.31-00.2

0.1

SI

I

0

10

20

30

40

50

60

I.0

0.9

W/C

0.55

0.8---0,

c

0.7

0.6

c

,/4,

1

%A x14.2

Oo0.5

₁

_{, %A}

a

8.45

o 0.4 _{Z 2 ,%A a 0.0} O

0.,2-

0.-0

10

20

30

40

50

60

I.o

0.9

W/C

0.60

0.8

-&

0.7--cI

0.6

-s

/

4

,

% A

5.4

S0.5 -s

3

,%A

5.2

Cs

'2, %A= 0.0

0.4 03

0.2

0.I

0

10

20

30

40

50

60

1.0

0.9-

W/C=0.65

0.8

.r 0.7

0.6

C =

/

4,% A

a9.1

2

0.45- 0.-03

0.2

0. I

0

10

20

30

40

50

60

16

Nethods of caloulation

Volmes Per 100

g.

of Coment Patoh TakIng the It 4.45 mix for example, the volumes were ealeulated as followzs

Wt. of batoh a 100 g. oment + 400 g. sand + 45 go water a 545 g.

Total volume Vt - wt* of jatoh a g% *I 0. *.

density of mortar 1.89 g/oo

Volme of paste Yp wt. of paste : 45 g 2 76.7

.

.

density of paste 1:gr/..

Volume of sand y* z wt. of sand z 400 g .152 o.o.

bulk specific gravity 2.63 g/00

Volume of air Ya Yt- (Vp + Vg) a 288 - (76.7 + 152) . 9.3 a. a. Peroent Caloulated Shrinkage The length of the speoimen

at age seven days, whiob eorresponds to sero drying days ( TO degrees F., 50% relative buaidity), is the reference length for subsequent

shrinkage oaloulations. The length of a spooinen, in inohes, on amy subsequent day is found by subtracting the measurement on that day from the 7 day readings The pesoent length ohange for a mortar is taken as the average length ohange of the three speoimens of the mortar divided by the guage length of the speoimens (5 in.) times 100. The per.ent external volumetria shrinkage is taken as three times the peroent length ohange. One 1/100 times the peroent external shrinkage times total volume (Vt) equals oubio oentimeters of external shrinkage. The 0.0. of external shrinkage divided by the volume of the matrix

(Vp a) times 100 gives the peroent oaloulated shrinkage of the

matrix whioh is equal to or less than the aotual shrinkage of the matrix. % oaloulated shrinkage . A readings

y!

100 A 3 X t

17

IV

In this seotion are presented the oonolusions about mortar shrinkage drem from the results of the lb vark given in the preoeeding seotion.

The flow oontour plot shows two trends. For a oonstant proportion of sand, flow increases with increasing W/O and hence inoreasing amounts of water. At a oonstant W/O, flow deoreases as the proportion of sand is increased.

The matrix shrinkage results indioate that shrinkage of the matrix beoomes highr with deoreasing W/O. There is some exception to this rule in the late shrinkage of the 48 mortars vhioh is probably due to struotural interferenoe.

From the mortar proportions by voluae it is seen that the peroentage air entrapped in the matrix is increased with increasing proportions of sand.

The graphs of oaloulated matrix shrinkage show that initially the caloulated shrinkage inoreases with increasing percentages of entrapped air. As shrinkage oontinues this order is partially or oompletely reversed. The reason for this behavior seins to be as follows: Aotual matrix shrinkage increases with inoreasing peroentage of entrapped air throughout the test. The higher air oontents ooour in the high sand mortars. Struotural interference develops to a

greater degree ith inoreasing proportions of sand causing internal oraoking to ooour and oaloulated shrinkage falls off in the latter part of the test. The relation between actual and oalculated matrix

Time

FIG. 4

is

0 CP ~0 Z 0

W/c

x

constant

MO/O

MN,

%WI

AM =

a

-

a-,-Cc/S

cAu=

C/S

x

Calculated

----Actual

19

hlk speoifie gravity of sand = 2.63

Fineness modulus of sand = 2.35

Absorbtion of sand z 1.16%

mormal oonsisteney of eent : 25.8%

Paste Density W/o Density (g*/**.) .65 1.66 .60 1.75 .55 1.79 .50 1.85 .45 1.89