COMPARISON OF STRENGTH PROPERTIES OF CONCRETE ON ADDITION OF ADMIXTURES

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JOURNAL OF INFORMATION, KNOWLEDGE AND RESEARCH
IN

CIVIL ENGINEERING

ISSN: 0975


6744|
NOV 09 TO OCT 10

| Volume 1, Issue 1


Page
7


COMPARISON OF STRENGTH PROPERTIES OF
CONCRETE ON ADDITION OF ADMIXTURES


1
GEETHA M AND

2
DR. R.MALATHY




1
Research Scholar, Faculty in Civil Engineering, CSI Polytechnic College,

Salem 636 007,Tamil Nadu, India.

2
Principal, Excel Engineering College, Ko
marapalayam ,

Namakkal 637 303, Tamil Nadu, India.


geethacsi@yahoo.co.in
,

malathycivil@kongu.ac.in


ABSTRACT

:

Curing of concrete is maintaining moisture in th
e concrete during early ages specifically with in
28 days of placing concrete, to develop desired properties. Curing concrete plays a major role in developing
the concrete microstructure and pore structure. Good curing is not possible in most of the cases.

Good curing is
not always practical in many cases. Concept of self curing is to reduce the water evaporation from concrete and
hence increase the water retention capacity of the concrete compared to conventional concrete. Improper
curing can easily cut t
he strength of concrete. Curing simply means keeping the water in the concrete where it
can do its job of chemically combining with the cement to change the cement into a tough glue that will help to
develop strong durable concrete. Good curing means keep
ing concrete damp and at about 70
o

F until the
concrete is strong enough to do its job. It is found that water soluble polymers used as admixtures in concrete
influences the strength properties of Concrete
.

Curing of concrete plays a major role in devel
oping the
concrete micro structure and hence improves its durability and performance



1.
INTRODUCTION


Curing is the process of maintaining enough
moisture and temperature for a definite period of
time.

Unless, otherwise

cured properly,
concrete
would n
ot gain sufficient strength and durability
and performance would not the improved


In the last few decades, there has been a great
amount of knowledge generated of how to make
concrete better through the incorporation of
specifically engineered ingredient
s and methods of
batching and mixing


Internal curing makes good concrete better (1) It
can make up some of the deficiencies brought on
by human beings not following the best practices
with external curing. It can even make up for some
of the problems brou
ght on by hot or windy
weather. For very low w/c (
≤ 0.35 ) concretes,
Inter Curing may be necessary.


Internal curing agent is added to reduce water
evaporation from concrete and there by to increase





water retention capacity of concrete comparing to
that of conventional concrete.






2.
NOMECLATUR
ES


f
t

= splitting tensile strength



of the specimen in MPa

P = maximum load in N applied to the


specimen

D = measured diameter of the


specimen in mm, and

L = measured length
of the specimen


in mm.



3
.
PURPOSE OF INTERNAL CURING


Internal curing refers to the process by which the
hydration of cement occurs because of the
availability of additional internal water that is not
part of the mixing water. The ad
ditional water
being supplied by using relatively small amounts of
saturated light weight fine aggregates (or) super
absorbent polymer particles in concrete (3)



Aim of the paper is to find a water soluble
polymer as self curing agent. The use of self cur
ing
admixture is very important from the point of view
that water resources are getting valuable every day
more over requirement of water for concreting is
also high. (ie.,)
1
m³ of concrete requires 3 m³ of
water for construction, most of which is needed f
or
curing (4) At present, the benefit of

self curing
JOURNAL OF INFORMATION, KNOWLEDGE AND RESEARCH IN

CIVIL ENGINEERING


ISSN: 0975


6744|
NOV 09 TO OCT 10

| Volume 1, Issue 1


Page
8


agent is realized in desert areas and dry seasons of
dry areas and soon may be felt in all areas.



In this study Mechanical property of
admixture added
concrete compared to
conventional concrete.


4
.

RE
SEARCH SIGNIFICANCE

Of late, the consciousness of the labor is going
down, the workers and the contractors could not be
relied. It is better to fix more of responsibility on
the Engineers, rather than on the contractors.
Having this in mind, and more ove
r the increasing
scarcity of water , day by day necessitate the
Internal curing. A few research findings are
published related to Internal curing of concrete


5
.
EXPERIMENTAL PROGRAMME



5
.
1 CUBE COMPRESSIVE STRENGTH

For cube compression testing of concr
ete, 150 mm
cubes were used.
T
he cubes were tested in
f
or
each trial mix combination, three cubes were tested
at the age of 1 day, 3 days, 7 days, 14 days, 28
days of curing using compression testing machine
as per BIS : 516
-

1959

.


Figure 1.
Compres
sion test on cube specimen


The tests were carried out at a uniform stress of
140 kg/cm
2
/minute after the specimen has been
centered in the testing machine. Loading was
continued till the dial gauge needle just reversed its
direction of

motion. The revers
al in the direction
of motion of the needle indicates that the specimen
has failed. The dial gauge reading at that instant


was noted which was the ultimate load. The
ultimate load divided by the cross sectional area of
the specimen is equal to the ultima
te cube
compressive strength. The test set up for
compression strength on cube specimen
is
shown in
Figures 1.



5
.2
CYLINDER COMPRESSIVE STRENGTH

Cylinder compressive strength tests were carried
out on cylinder specimens of size 150 mm diameter
and 300 m
m height at the age of 28 days, using
compression testing machine of as per BIS : 516
-

1959 . The test set up for compression strength is
shown in Figure
2
.





Figure 2 Compression test on cylinder specimen


5
.3
SPLITTING TENSILE STREN
GTH

This is an indirect test to determine the tensile
strength of cylindrical specimens. Splitting tensile
strength tests were carried out on cylinder
specimens of size 150 mm diameter and 300 mm
length at the age of 28 days compression testing
machine of
1
000 KN capacity as per BIS : 5816
-

1970 . To avoid the direct load on the specimen,
the cylindrical specimens were kept below the
wooden strips. The load was applied gradually till
the specimens split and readings were noted. Figure
3

Patterns of typical

splitting tensile failure mode
shapes of cylinder specimens are shown in Figure
4
. The splitting tensile strength has been calculated

using the
follow
ing


formula:




f
t


π
DL






Figure 3 Test set up for splitting tensile strength


on cylinder specimen



JOURNAL OF INFORMATION, KNOWLEDGE AND RESEARCH IN

CIVIL ENGINEERING


ISSN: 0975


6744|
NOV 09 TO OCT 10

| Volume 1, Issue 1


Page
9




Figure4 Patterns of typical splitting tensile

failure


mode shapes of cylinder specimens



5
.4 STRESS
-

STRAIN CURVE AND ELASTIC
MOD
ULUS

To start with, the average compressive
strength of concrete at the age of 28 days curing
was determined by conducting compression test on
cube specimens using
1
000 KN capacity
compression testing machine. After that, cylinder
specimens of size 150 mm
diameter and 300 mm
height were used to determine the modulus of
elasticity of concrete in compression at the age of
28 days
as
per BIS : 516
-
1959. The test cylinder
was attached with a longitudinal compressometer
to measure compressive strain over middle

2
/
3 of
the specimen (gauge length = 200 mm). The
modulus of elasticity was found out by
plotting the stress
-

strain curve. The modulus
of elasticity

was obtained with reference to tangent
modulus. The experimental set up for the
compressi
ve strain measurements on cylinder
specimen is shown in Figure
5





Figure 5 Test set up for compressive strain



measurements on cylinder specimen




COMPRESSIVE STRENGTH OF CUBES IN N/mm2
0
5
10
15
20
25
GREEN
10.62
14.44
17.82
19.5
20.71
WHITE
11.8
11.8
14.5
16.4
17.3
POLY
10.5
16
17.3
18.3
18.7
CURING
9.5
14.8
15.1
17.64
17.8
3 DAYS
7 DAYS
14 DAYS
21DAYS
28 DAYS

Table 1:
Compressive strength of cubes on various


day
s of curing




Green admixture

White admixture

Cylinder
compressi
ve stress

Split
tensile
stress

Cylinder
compressiv
e stress

Split
tensile
stress

ample1

1.06

0.223

0.92

0.121

Sample2

1.29

0.210

0.61

0.111

Sample3

1.11

0.223

0.61

0.118

Sample4

1.30

0.
220

0.62

0.108

S
ample5

1.32

0.188

0.64

0.111

Table 2: Cylinder compressive and Flexural


strength tests



Stress strain curve
0
2
4
6
8
10
12
14
16
0
0.0005
0.001
0.0015
0.002
0.0025
Strain
Stress
Series1

Figure 6 : Stress strain curve for white admixture



Stress strain curve
0
2
4
6
8
10
12
14
16
0
0.0002
0.0004
0.0006
0.0008
0.001
0.0012
0.0014
Strain
Stress

Figure
7

: Stress strain curve for
green
admixture


JOURNAL OF INFORMATION, KNOWLEDGE AND RESEARCH IN

CIVIL ENGINEERING


ISSN: 0975


6744|
NOV 09 TO OCT 10

| Volume 1, Issue 1


Page
10



6

RESULTS AND DISCUSSIO
NS


CUBE COMPRESSIVE STRENGTH


Compressive strength of cubes Table 1 shows the
compressive stress of cubes of after 3,7,14,21 and
28 days of casting and the strength of concrete by
addition of the admixtures with out any external
curing proves to be almos
t equal to that of
conventional curing and the addition of green
admixture proves to give the highest strength.


CYLINDER COMPRESSIVE STRENGTH
AND SPLIT TENSILE STRENGTH

From the tests conducted the cylinder compressive
strength and split tensile streng
th of concrete with
green admixture proves to be higher.


MODULUS OF ELASTICITY

From the stress strain curve drawn, it is clear that
the Modulus of Elasticity of both the concretes, that
is with the addition of white admixture and green
admixture , the Mo
dulus of elasticity is equal to
greater than the relation 5000


f
ck

.


7

CONCLUSION

1.
Percentage Increase in Strength
in concretes
with admixtures c
ompar
ed

to Conventional
Concrete



DAYS

GREEN

WHITE

POLY

3

11.78

24.21

16.35

7

-
2
.43

-
2
0.27

8.18

14

18.01

-
3.97

1
4.38

21

10.54

-
7.
03

3.41

28

16.3

-
2.81

5
.06


2. From the above table, it is clear that the strength
of admixture added concretes are almost equal to
that of conventional concretes and except that of 7
days curing the strength of green admix
ture added
concrete proves to be higher than the other two.



3. In the same manner , the split tensile Strength
and cylinder compressive strength of green
admixture concrete proves to be higher.



8

REFERENCES

1. Weber .S; Reinhardt,H .W., Modeling t
he
internal curing of High strength concrete
using Light weight Aggregates, Theodore
Bremner Symposim on

High
performance Light weight concrete , sixth
CANMET / ACI / international conference on
durability, Thessaloniki ,Grace PP 45
-
64 June
2003


2.

Bentz,

D.P. Stutman, P.E; Effects of early
age curing on long term Micro Structure,
April, ACI Spring convention, New York
(2005)


3.

Bentz .D.P., Lura .P ; Roberts J.W.,
Mixture proportioning for Internal curing
concrete International , Vol 27, No 2, 35
-
40, Feb 2
005.


4.

A.S El
-

Dieb , Self curing concrete, water
retention, hydration and moisture


5.

Bentz.D.P., Snyder .K.A, Protected paste
volume in concrete. Extension to internal
curing using saturated light weight fine
aggregate .


6.

Lura .P ., Internal wat
er curing with
Liapor aggregates.


7.

7.Zhutovsky , Kovler.K & Bentur.A .,
Efficiency of Light weight Aggregate for
internal curing of high strength concrete to
eliminate autogenous shrinkage