CHAPTER 3 PRELIMINARY INVESTIGATION 3.1 GENERAL Self Compacting Concrete is an innovative concrete for the design of which no codal recommendations are available. Researchers across the world have developed many methods for mix proportioning of sec. Similarly different test methods have been developed to characterise the workability properties of Sec. So far no single method or combination of methods has achieved universal approval.. So each mix should be tested by more than one test method for the different workability parameters. Laboratory trials should be done to verify properties of the initial mix composition. When the advantages of see such as capability of Hawing through congested reinforcement are combined \"v1th that of steel fibres such as increase in ductility and toughness, the resulting material, steel fibre reinforced self compacting concrete (SFRCC) would be a promising material for extending the applications of sec to structures in seismic zones. Fibres are known to bridge cracks, retard their propagation and improve the properties of sec. This chapter deals w1th the tests on constituent materials, mix proportioning for the development of 40MPa see mix, use of lvI-Sand in sec, study on int1uence of steel fibres on fresh and hardened properties of sec. The volume fraction of fibres was varied from 0%, 0..25%, 0.5%,0.75% and 1 % with aspect ratio (lid) 30, 50 and 70. To study the fresh properties slump flow test, V-funnel test, V-box test and L-box test were conducted. Hardened properties like cube and cylinder compressive strength, split tensile strength, flexural strength and modulus of elasticity were determined. For comparisol4 eve mix of similar strength was studied. Studies on the durability properties of sce were also carried out and compared with CVC. 3.2 TESTS ON MATERIALS The constitutive materials used in this study are cement, flyash, manufactured sand (M-Sand); river sand, coarse aggregate, water, superplasticizers, steel fibres and 54
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CHAPTER 3
PRELIMINARY INVESTIGATION
3.1 GENERAL
Self Compacting Concrete is an innovative concrete for the design of which no codal
recommendations are available. Researchers across the world have developed many
methods for mix proportioning of sec. Similarly different test methods have been
developed to characterise the workability properties of Sec. So far no single method
or combination of methods has achieved universal approval.. So each mix should be
tested by more than one test method for the different workability parameters.
Laboratory trials should be done to verify properties of the initial mix composition.
When the advantages of see such as capability of Hawing through congested
reinforcement are combined \"v1th that of steel fibres such as increase in ductility and
toughness, the resulting material, steel fibre reinforced self compacting concrete
(SFRCC) would be a promising material for extending the applications of sec to
structures in seismic zones. Fibres are known to bridge cracks, retard their
propagation and improve the properties of sec.
This chapter deals w1th the tests on constituent materials, mix proportioning for the
development of 40MPa see mix, use of lvI-Sand in sec, study on int1uence of steel
fibres on fresh and hardened properties of sec. The volume fraction of fibres was
varied from 0%, 0..25%, 0.5%,0.75% and 1% with aspect ratio (lid) 30, 50 and 70. To
study the fresh properties slump flow test, V-funnel test, V-box test and L-box test
were conducted. Hardened properties like cube and cylinder compressive strength,
split tensile strength, flexural strength and modulus of elasticity were determined. For
comparisol4 eve mix of similar strength was studied. Studies on the durability
properties ofsce were also carried out and compared with CVC.
3.2 TESTS ON MATERIALS
The constitutive materials used in this study are cement, flyash, manufactured sand
(M-Sand); river sand, coarse aggregate, water, superplasticizers, steel fibres and
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HYSD bars. These materials were tested as per the standard testing procedures to
check the acceptability of the materials and the properties of the same obtained are
given below.
3.2.1 Cement
Ordinary Portland Cement 53 grade conforming to IS 12269:1999 was used.
Laboratory tests were conducted on cement to determine standard consistency, initial
and final setting time, and compressive strength as per IS 269: 1998 and IS 4031 :2000
and its results are tabulated in Table 3.1. The results conforms to the IS
recommendations.
Table 3.1 Properties of Cement
Sl. No Test conducted Result
1 Standard consistency 32%
2 Initial setting time 170 minutes
3 Final setting time 480 minutes
4 3 day compressive strength 27.67N/mmk
5 7 day compressive strength 39.93 N/mmk
6 28 day compressive strength 54.22 N/mmk
3.2.2 Flyash
Fly ash is a fine inorganic material with pozzolanic properties, which can be added to
cement to improve its cementitious properties. A high quality flyash generally permits
a reduction in water content of a concrete mixture, without loss of workability. The
flyash of specific gravity 2.1 obtained from Hindustan Newsprint Limited, Kottayam,
was used for experiments. The test results collected from the manufacturer are given
in Table 3.2.
Table 3.2 Chemical Composition of Fly Ash
Sl. No. Constituents Quantity (%)
1 Silica (Si02) 59.42
2 Alumina (Ah03) 32.36
3 Ferric Oxide (Fe203) 4.07
4 Calcium oxide (CaO) 0.18
5 Loss of ignition 3.75
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3.2.3 Fine Aggregate
In see, the quantity of fine aggregate is normally more than that of coarse aggregate.
Presently, there is an acute shortage of river sand and quite often the river sand
obtained from local vendors does not meet all the requirements of fine aggregate. In
this circumstance manufactured sand (M-Sand) offers a viable alternative to river
sand. A combination of river sand and M-Sand was used as fine aggregate in this
study.
3.2.3.1 River sand
Laboratory tests were conducted on river sand to determine the different physical
properties as per IS 383:1970. River sand passing through 4.75 mm sieve was used for
the experiments. Sieve analysis was done to determine the fineness modulus and grain
size distribution. The gradation curve is shown in Fig. 3.1. The test results conforms
river sand to zone II of the IS recommendations and are tabulated in Table 3.3 and
Note: 1. V represents volume fraction of fibres2. R represents aspect ratio of fibres
V-funnel test results indicated reduction of filling ability on fibre addition. The results
indicated that similar to slump flow test, increase in fibre volume fraction and aspect
ratio reduce the filling ability of see. V-funnel at TSmin indicated the influence of
fibre addition on segregation resistance of the mix. Increase in the volume fraction
and aspect ratio of fibres reduced the segregation resistance of see. For mix with
aspect ratio 70, maximum amount of fibre that could be added without imparting
segregation was 0.25%. U-box and L-box values indicate the passing ability of see.Passing ability indicated by both tests decreased on increase in volume fraction and
aspect ratio. Except for fibres of aspect ratio 70, all the mixes showed required
passing ability upto fibre volume fraction 0.75%.
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3.5.2 Tests on Hardened SFRSCC
To determine the mechanical properties, standard specimens were prepared using
see mix with fibres. The hardened properties of mix were determined by conducting
standard tests such as cube compressive strength, cylinder compressive strength, split
tensile strength, flexural strength and modulus of elasticity. The hardened properties
It was observed that addition of 0.25% volume fraction of fibres did not show much
influence in the hardened properties. Addition of higher volume fraction of fibres and
increased aspect ratio had shown enhancement in all the mechanical properties.
Presence of 0.75% fibres with aspect ratio 50 exhibited best results showing an
increase of 17% in cube compressive strength, 18% in modulus of elasticity, 59% in
flexural strength and 34% in split tensile strength. Test results on hardened properties
showed that all the mechanical properties of see increased considerably by fibre
addition. Enhancement in hardened properties was in rise when higher volume
fractions and larger aspect ratio of fibres were used. The notable increase in the
flexural strength and split tensile strength are of much importance when see is used
for flexural members.
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3.5.3 Discussion of Results
Test results of fresh properties inferred that increase in volume fraction and aspect
ratio reduces the flow properties of see. Increase in fibre aspect ratio drastically
affected passing ability of see. The passing ability requirement of see limits the
aspect ratio of fibres as 50 at 0.75% volume fraction. Mix with fibre aspect ratio 70
showed 0% passing ability. For assuring all the fresh properties of see, the
maximum volume fraction had to be limited to 0.75% for fibres of aspect ratio 50.
Test results on hardened properties showed that all the mechanical properties of seehas been considerably increased by fibre addition. Enhancement in hardened
properties was considerable when higher volume fractions of fibres were used. It has
been observed that fibre aspect ratio beyond 50 causes the loss of both fresh and
hardened properties. Similarly the mix with volume fraction of I% failed in respect of
fresh properties. Fibres with aspect ratio 50 and volume fraction 0.75% exhibited best
results. 0.25% fibre addition did not influence any of the mechanical properties
significantly. Hence 0.25% fibre addition was not considered in further study.
3.6 DURABILITY PROPERTIES
3.6.1 General
One of the important factors which influences the durability and long term
performance of concrete structures is the proper compaction of concrete. Proper
compaction eliminates air voids in the concrete mass making it impermeable and
durable. On many occasions, reinforced concrete elements contain heavy and
congested reinforcement necessitated either by structural requirement or
constructional need. The use of normal concrete in such situations may often result in
poor compaction and consequent defects in the placed concrete such as
honeycombing, bleeding, segregation etc. Self compacting concrete which possesses
superior flowability becomes an ideal material for such situations. In this
investigation, the durability properties of eve and see were compared by
conducting various tests like permeable voids and water absorption, acid attack,
sorptivity and alternate wetting and drying.
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3.6.2 Permeable Voids and Water Absorption
It is a usual practice to find water permeability when assessing durability of concrete.
Permeability can be measured by conducting water permeability test, percentage of
water absorption test and initial surface absorption test. The absorption and permeable
voids were determined on 150 mm cubes. The surface dry cubes after 90 days
immersion in water were kept in a hot air oven at 105°e till a constant weight was
attained. The ratio of the difference between the mass of saturated surface dry
specimen and the mass of the oven dried specimen at 105° e to the volume of the
specimen gives the permeable voids in percentage as given below: (Dinakar et al.,
2008)
Permeable voids = [(A - B)/V]xl 00 (3.1)
where
A = weight of surface dried saturated sample after 90 days immersion period.
B = weight of oven dried sample in air.
V = Volume of sample
The oven dried cubes after attaining constant weight, were then immersed in water
and the weight gain was measured at regular intervals until a constant weight was
reached. The absorption at 30 min (initial surface absorption) and final absorption (at
a point when the difference between two consecutive weights at 12 hr interval was
almost negligible) was determined. The final absorption in all cases was determined at
96 hr. The absorption characteristics indirectly represent the volume of pores and their
connectivity. (Dinakar et al). The results of permeable voids and water absorption for
eve and see are presented in Table 3.20. From the result it can be seen that eve
has higher permeable voids and water absorption than see. The permeable voids are
influenced by the paste phase; primarily, it is dependent on the amount of
interconnected capillary pores present in the paste. Because of the self compacting
property and the presence of fly ash, the paste phase becomes denser. Thus the test
results indicate that there are less interconnected pores and less permeable voids in
see than in eve. According to the recommendations given by eoncrete Society
(CEB, 1989) initial absorption of "good concrete" is less than 5% for 30 min
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absorption. This shows that eve and see had lower absorption than the limit
specified for "good" concrete.
Table 3.20 Permeable Voids and Water Absorption
Tests eve see
Initial absorption % 2.63 1.19
Final absorption % 10.13 7.38
% Permeable voids 23.15 16.79
3.6.3 Acid Attack
The chemical resistance of the concrete was studied by immersing them in an acid
solution of 3% H2S04• After 90days period of curing the specimens were removed
from the curing tank and their surface was cleaned with a soft nylon brush to remove
weak reaction products and loose materials from the specimen and the weight was
measured. Mass loss of specimens due to acid attack were determined and expressed
as a percentage of initial weight and the results are shown in Table 3.21.
Table 3.21 Acid Attack
Test Mass loss %
eve see
Acid attack 4.53 1.82
It can be seen that the mass loss of see is considerably lower than that of eve. This
may be attributed to puzzolanic property of fly ash by which ea(OH)2 present in
concrete is converted into cementitious material which makes the paste structure
dense. The see and eve after 90 days in acid is shown in Photo 3.2. It can be
inferred from the photos that eve is subjected to severe acid attack than see.
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Photo 3.2 see and eve Specimens After 90 Days in Acid
3.6.4 Sorptivity
Sorptivity test measures the rate of absorption of water by capillary suction of
unsaturated concrete placed in contact with water (Neville, 2005). The sorptivity test
determines the rate of capillary rise absorption by a concrete specimen which rests on
small supports in a manner such that only the lowest 2 to 5 mm of the specimen is
submerged. The increase in mass ofthe specimen with time is recorded. There exists a
relation ofthe form
(3.2)
where
i increase in mass in glmm2 since the beginning of the test per unit of
cross sectional area in contact with water; as the increase in mass is
due to the ingress of water, 19 is equivalent to 1 mm3, so that i can be
expressed in mm
t time, measured in minutes, at which the mass is determined, and
S sorptivity in mmlmin0.5
Test was conducted on samples of 50mm diameter and lOOmm long cylinders. The
samples were preconditioned to a certain moisture condition by drying in an oven for
7days at 500 C. After cooling, sides of the concrete samples were sealed using
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electrician's tape. After taking initial weight, samples were kept in a tray such that 2
5mm depth was immersed in water as shown in Photo 3.3.
Photo 3.3 Sorptivity Test
At selected times (1, 4, 9, 16,25,36,49,64,81, 100 minutes and 24 hrs) the samples
were removed from water, excess water blotted off and weighed. It was again
replaced in water. A straight line is fitted to the plot of the increase in mass, or the rise
of the water front, versus the square root of time. The point of origin (and possibly
also the very early readings) is ignored because there is a small increase in mass at the
instant when the open surface pores in the lowest 2 to 5mrn of the specimen first
become submerged. The slope of the line of the best fit of these points is reported as
sorptivity. The result of sorptivity test is given in Table 3.22 and is plotted in Fig. 3.6.
Some typical values of sorptivity are: 0.09mm/min°'s for concrete with a water/cement
ratio of 0.4, and O.17mm/min°.5 at a water/cement ratio of 0.6 (Neville, 2005). It can
be seen that eve exhibits higher sorptivity than sec.