Effects of chemical admixtures on the shrinkage of cement mortar

shawlaskewvilleUrban and Civil

Nov 29, 2013 (3 years and 7 months ago)

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Effects of chemical admixtures on the shrinkage of
cement
mortar

Rakesh Gopinath and Ravindra Gettu


Department of Civil Engineering, Indian Institute of Technology Madras, Chennai, India.

Abstract
:

Restrained

shrinkage

cracking

is

a

major

problem

in

mortar

or

concrete

construction,

not

only

from

the

durability

point

of

view,

but

also

in

reference

to

aesthetics
.

The

main

objective

of

the

study

is

to

monitor

the

long

term

shrinkage

evolution

of

mortar

mixes

having

polypropylene

glycol

based

shrinkage

reducing

admixture

(SRA),

a

polycarboxylate

based

superplasticizer

and

the

combination

of

the

two
.

The

restrained

shrinkage

test

ware

also

performed

to

better

understand

the

effectiveness

SRA

mortars

towards

cracking
.

The

shrinkage

tests

are

performed

on

mortar

prisms

maintained

at

50
%

r
.
h

and

27
°
C
.

The

test

results

show

that

SRA

helps

in

reducing

the

shrinkage

and

delays

the

age

of

visible

cracking
.

Whereas

the

combined

effect

of

SRA

and

superplasticizer

brings

down

the

efficiency

of

the

SRA

in

reducing

shrinkage

and

associated

cracking
.

INTRODUCTION

RESTRAINED RING TEST


Cracking

due

to

the

restraining

of

shrinkage

deformation

is

common

in

mortar

and

concrete
.

The

shrinkage

reducing

admixture

(SRA)

is

getting

popular

in

reducing

shrinkage
.

These

glycol

based

admixtures

act

by

reducing

the

surface

tension

of

the

capillary

water

that

causes

a

reduction

in

the

angle

of

contact

of

the

surface

of

the

menisci,

thereby

reducing

capillary

stresses

that

lead

to

shrinkage
.

The

superplasticizer

is

another

type

of

chemical

admixture,

which

is

mainly

used

for

improving

workability

of

mortar

or

concrete
.

Along

with

the

improvement

of

workability,

shrinkage

is

also

influenced

by

the

presence

of

these

admixtures
.


MIX PROPORTIONS

Mortar

Compressive Strength in MPa

Flexural Strength in MPa

7 Day

28 Day

7 Day

28 Day

MPa

S.D

MPa

S.D

MPa

S.D

MPa

S.D

Ref

36.85

1.33

47.37

1.05

4.89

0.32

5.07

0.43

SC

37.10

3.66

47.36

1.59

4.54

0.20

4.82

0.50

SRA1

34.31

4.31

43.52

0.98

4.79

0.41

5.22

0.30

SRA2

34.46

2.76

43.27

1.41

5.02

0.18

5.56

0.20

SCR1

36.52

3.68

41.98

1.52

5.30

0.27

5.31

0.20

SCR2

35.77

4.47

42.01

1.50

5.42

0.30

5.45

0.40

INFLUENCE OF SRA ON STRENGTH

Mean Values and Standard Deviations (S.D.) of Compressive and
Flexural Strengths


0
20
40
60
80
100
120
140
160
180
T
i
m
e

(
d
a
y
s

a
f
t
e
r

c
a
s
t
i
n
g
)
0
0.2
0.4
0.6
0.8
1
S
h
r
i
n
k
a
g
e

d
e
f
o
r
m
a
t
i
o
n

i
n

m
m
/
m
R
e
f
S
C
S
R
A
1
S
R
A
2
S
C
R
1
S
C
R
2
SHRINKAGE EVOLUTION

Mortar

Ref

SC

SRA1

SRA2

SCR1

SCR2

Age at
cracking
(days)

5

6

21

20

14

14

CONCLUSIONS


The

incorporation

of

the

shrinkage

reducing

admixtures

results

in

40
-
45
%

reduction

in

shrinkage
.

This

increases

the

resistance

to

restrained

cracking

due

to

shrinkage
.


T
he

presence

of

superplasticizers

could

reduce

the

efficiency

of

the

SRA

in

reducing

shrinkage
.


The

addition

of

the

SRA

results

in

a

slight

decrease

in

the

compressive

strength
.


International Conference on Rehabilitation and Restoration

o
f Structures, IIT Madras, Chennai, India

Acknowledgements

Mortar
designation

Cement:sand
ratio, by
weight

w/c

El

Tr

Gl

Ref

1:1.6

0.4


-----


-----

------

SC

------

------

0.15%

SRA1

2%

------

------

SRA2

------

2%

------

SCR1

2%

------

0.15%

SCR2

------

2%

0.15%