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CHAPTER 4

EXPERIMENTAL INVESTIGATIONS ON SELF COMPACTING CONCRETE

4.0 GENERAL

In this chapter, the mechanical behaviour of Fibre Reinforced

Self-Compacting Concrete Wall Panels of M30 grade made with Steel

Fibres, Glass Fibres and Hybrid Fibres with a mixture of glass and

steel fibres is examined. For this, experimental investigations were

carried out on the fresh and hardened properties of fibre reinforced

self compacting concrete of M30 grade. Then wall panels were cast

and investigations were conducted to study the behaviour of wall

panels of plain SCC, Steel Fibre Reinforced SCC (SFRSCC), Glass

Fibre Reinforced SCC (GFRSCC) and Hybrid Fibre Reinforced SCC

(HFRSCC) under Axial and Eccentric Loads. The experimental

programme was taken up in various steps to achieve the following

objectives:

1. to develop plain SCC of M30 grade and obtain its fresh and

hardened properties.

2. to develop Steel and Glass Fibre Reinforced SCC of M30 grade

separately and study their fresh and hardened properties.

3. to develop Hybrid Fibre Reinforced SCC with a combination of

glass and steel fibres and study its fresh and hardened

properties.

4. to study the Stress–Strain behaviour of SCC, SFRSCC,

GFRSCC and HFRSCC and develop mathematical models.

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5. to study the behaviour of wall panels cast with plain SCC,

GFRSCC, SFRSCC and HFRSCC under axial and eccentric

loads.

4.1 Materials

4.1.1 Cement

Ordinary Portland cement of 53 grade available in the local

market was used in the present investigations. Tests were conducted

to establish various properties in accordance with IS: 4031–1988 and

found to conform to IS: 12269–1987.

4.1.2 Coarse Aggregate

Crushed angular granite available from a local market was used

in the investigations. The aggregate was tested as per IS: 2386–1963

and found to be conforming to the specifications.

4.1.3 Fine Aggregate

River sand available in the local market was used as fine

aggregate. The fine aggregate was tested for its properties as per IS:

2386–1963 and found to be conforming to specifications.

4.1.4 Fly Ash

Fly ash from a thermal power station in Andhra Pradesh was

used in the investigations. The physical and chemical properties of the

fly ash as used in the investigations conform to grade I fly ash of IS

3812–2003.

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4.1.5 Super Plasticizer

Super plasticizer with Sulphonated Naphthalene based

Formaldehyde (SNF) conforming to IS: 9103–1999 was used in the

present investigations.

4.1.6 Viscosity Modifying Admixture (VMA)

Viscosity modifying agent from a standard agency conforming to

standard specifications was also used.

4.1.7 Water

Potable water conforming to IS: 3025–1986 part 22 & 23 and IS:

456–2000 was used in the investigations.

4.1.8 Glass Fibres

Anti Crack High Dispersion Fibres having a Modulus of

Elasticity (E) of 72 GPa and 857 Aspect Ratio were used.

Fig. 4.1.1: Glass Fibres

4.1.9 Steel Fibres

Plain steel fibres of 0.4 mm dia and Aspect Ratio of 30, cut from

steel wire were used in the investigations.

Fig. 4.1.2: Steel Fibres

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4.2. PHASE I: DEVELOPMENT OF PLAIN SCC AND INVESTIGATIONS ON ITS FRESH AND HARDENED PROPERTIES In this phase of investigations, M30 grade SCC mix is developed

using mineral and chemical admixtures to study its fresh and

hardened properties. For developing SCC of M30 grade, the mix

proportions were designed based on the method suggested by Nan-Su

et al(2001) and SV Rao et. Al(2010) using fly ash as mineral admixture

and chemical admixtures like Super Plasticizers (SP) and Viscosity

Modifying Agents (VMA). Finally, SCC mixes which have given required

compressive strength with satisfactory fresh properties were taken for

the next phase of investigations. This is explained in detail as given

below.

4.2.1 Mix Design and Trial Mix Proportions of Self Compacting Concrete An SCC mix of M30 standard grade was aimed and the initial

mix proportion was obtained using the mix design methods as

mentioned above. The mix proportion thus obtained was fine-tuned by

incorporating different guidelines available and making various trial

mixes to obtain the mix which satisfies the required fresh and

hardened properties. The detailed mix design calculations are given in

Appendix I. The final mass of ingredients for 1m3 of SCC are as

follows:

Mass of Cement = 330.0 kg

Mass of filler (Fly Ash) = 150.0 kg

Mass of water = 186.0 kg

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Mass of Coarse Aggregate (CA) = 794.4 kg

Mass of Fine Aggregate(FA) = 860.6 kg

Super plasticizer dosage = 1.5% by weight of cement (bwc)

VMA dosage = 0.6% by weight of cement (bwc)

4.2.2 Mixing of Ingredients

The mixing of ingredients was carried out in a power operated

pan type concrete mixer. Initially coarse aggregate, fine aggregate,

cement and fly ash were put in the pan mixer and mixed in the dry

state for a few seconds. Then Superplasticizer (SP) was added to the

water, thoroughly mixed and added to the material in the concrete

mixer. The required amount of VMA was added and further mixed till

a mix of required uniform consistency was achieved.

To obtain the Glass Fibre Reinforced SCC, anti-crack high

dispersion glass fibre dosage was added to the already developed mix,

maintaining the fresh SCC requirements. Similarly, Steel Fibre

Reinforced SCC was made by adding suitable dosage of steel fibres

Fig. 4.2.1: Pan Mixer Fig. 4.2.2: Developed SCC Mix

maintaining the fresh SCC requirements. The Hybrid Fibre Reinforced

SCC was prepared by adding glass and steel fibres in different

proportions till fresh SCC properties were satisfied.

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4.2.3 Methods of Evaluation of Workability of SCC

Workability test methods available for conventional concrete

mixes are not adequate for evaluation of workability of Self-

Compacting Concrete mixes as they are not sensitive to ascertain all

the requirements of Self-Compacting Concrete mixes. Different test

methodologies were developed to characterize the fresh properties of

SCC mixes. No single method was available till date, to assess relevant

workability requirements. Hence, the SCC mixes have to be tested

using more than one test for measuring different workability

parameters. The following are the test methods available to

characterize the desired workability requirements and for the

finalization of fresh Self-Compacting Concrete mixes.

4.2.3.1 Slump Flow Test and T 50 cm Test

The slump flow test is used to ascertain the free flow of Self

Compacting Concrete without obstructions.

Fig. 4.2.3: Slump Flow Test

� About six litres of SCC is required to perform this test.

� First moisten the base plate and the inside surface of slump

cone. Place base plate on level stable ground and the slump

cone centrally on the base plate and hold down firmly.

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� Fill the slump cone with SCC using a scoop. Do not tamp the

concrete. Strike off the concrete surface with the top level of the

cone with a trowel.

� Any surplus concrete in and around the base of the slump cone

has to be removed.

� Lift the cone vertically and allow the SCC to flow freely.

� Start the stopwatch simultaneously, and record the time taken

for concrete to spread upto the 500mm circle marked. (This is

called T50 cm test).

� Afterwards, measure the final diameter of the concrete spread in

two or more perpendicular directions.

� Then calculate the average of the measured diameters which is

termed as the slump flow.

Interpretation of the results:

Higher slump flow value indicates greater ability to fill the

formwork under its own weight. A minimum value of 650mm is

recommended for SCC. The T50 time is also an indication of SCC flow.

A lower time means greater flowability. The research suggested a time

range of 3-7 seconds for general civil engineering applications and 2-5

seconds for general housing applications (T.Suresh Babu,2008).

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4.2.3.2 V-Funnel Test

This test is performed to determine the filling ability (flowability)

of the Self-Compacting Concrete.

Fig. 4.2.4: V-Funnel Test

Procedure for V-Funnel Test :

� Take about 12 litres of concrete to perform this test.

� Keep the V-funnel on level ground.

� Moist the inside surface of the V-funnel

� Open the trap door to drain out any surplus water.

� Now close the trap door and keep a bucket underneath the V-

funnel.

� Now fill the V-funnel apparatus completely with the SCC

without any compaction or tamping. Then strike off the excess

concrete and level the top with the help of a trowel.

� Open the trap door within 10 seconds after filling the funnel.

� Now allow the concrete to flow out of the funnel under gravity.

� Start a stopwatch immediately after the trap door of the funnel

is opened. Record the flow time taken for the concrete to

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discharge completely from the funnel. This is recorded when

light is seen from the top through the funnel.

� The test is to be completed within 5 minutes time.

4.2.3.2.1 Procedure for flow time at T5 minutes

� Take the same setup as above of V-Funnel test and do not clean

the inside of the funnel again.

� Close the trap door and fill the V-Funnel apparatus completely

with concrete, again without compaction. Strike off the excess

concrete on top and level the top surface with a trowel.

� Place a tub underneath the funnel.

� Open the funnel door after 5 minutes after the filling of the

funnel the second time and allow the concrete to flow freely

under gravity.

� Start the stopwatch simultaneously when the door is opened,

and record the time taken for the concrete to completely come

out. This is the flow time at T5 minutes. This time is to be

recorded when the light is seen from the top of the funnel.

Interpretation of results:

The above test measures the ease of flow of the SCC; shorter

flow times indicate greater flow ability. For SCC, 10 seconds flow time

is considered appropriate. Five minutes after settling, segregation of

concrete indicates a lesser flow with an increase in the flow time.

4.2.3.3 L Box Test

The test is for assessing the flow of the SCC and the blocking

resistance.

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Fig. 4.2.5 : General Assembly of Fig. 4.2.6 Test in Progress L Box Test

Procedure:

� Take about 14 litres of self-compacting concrete for performing

this test.

� Place the apparatus on a level ground and ensure free opening

and closing of sliding shutter. Moisten the inside surface of the

L Box apparatus.

� Fill the vertical section of the apparatus with the SCC sample.

� Lift the sliding gate and allow the SCC to flow out into the

horizontal section.

� Start the stopwatch simultaneously, and the time taken for the

SCC to reach the 200mm and 400mm marks are to be recorded.

� The heights “H1” and “H2” are measured, when the SCC stops

flowing.

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� Calculate the ratio H2/H1, which is the blocking ratio.

� The complete test is to be performed within a time of 5 minutes.

Interpretation of results:

If the concrete flows freely without any resistance, H2/H1 will be

unity. Therefore the nearer the ‘blocking ratio’ to unity, the better the

flow of the SCC. The European Guidelines[84] suggests a minimum

value of 0.8.

4.2.3.4 Testing of SCC in Fresh State

The SCC mix in fresh state was tested to get fresh properties

like filling ability, passing ability and segregation resistance by

performing Slump cone, V-funnel, and L-box tests as explained above.

4.2.4 Casting of Specimens

After satisfying the requirements of SCC in fresh state, the mix

was placed in moulds and allowed to flow and settle by itself. Any

excess SCC on the top of the moulds was removed with a trowel.

Fig. 4.2.7: Casting of SCC Cubes

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4.2.5 Curing of SCC Specimens

The SCC specimens were kept undisturbed at room temperature

for 24 hours after casting. Then the specimens were removed from the

moulds and transferred to curing ponds containing fresh potable

water as shown below.

Fig. 4.2.8: Curing pond

4.2.6 Testing of Hardened SCC

A proper time schedule for testing of hardened SCC specimens

was maintained in order to ensure proper testing on the due date. The

specimens were tested using standard testing procedures as per

IS : 516 – 1959.

4.2.6.1 Compression Test

After the required curing period, the SCC cubes were taken out

of the curing tanks and the moisture was wiped off to make the

surface dry. They were placed in the Compression Testing Machine

(CTM) in such a way that the face perpendicular to the direction of

pouring of SCC mix was on the bearing surfaces and the load was

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applied centrally at a uniform rate of 140 Kg./sq.cm./minute until the

failure of the specimens, in accordance with IS 516–1959. The testing

was done on a 3000 kN capacity Compression Testing Machine.

Fig. 4.2.9: Compression Test Set-up

4.2.6.2 Split Tension Test

The split tension test was carried out on a cylindrical specimen

of diameter 150mm and 300mm long as per IS specifications.

Fig. 4.2.10: Split Tension Test Set-up

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The horizontal stress = 2P / ̟ LD

Where P = compressive load applied on the cylinder,

L = length and D = diameter of the cylinder.

In order to reduce the concentration of high compressive stress

near the points of application of the load, narrow strips of suitable

packing material, such as plywood, are placed in between the

cylindrical specimen and the loading platens of the testing machine.

4.3 PHASE II: DEVELOPMENT OF FRSCC AND STUDIES ON FRESH AND HARDENED PROPERTIES

4.3.1 Addition of Anti Crack High Dispersion Glass Fibres to SCC Mixes

Anti-crack high dispersion glass fibres were added in different

dosages to the selected SCC mixes in the first batch of investigation

and Glass Fibre Reinforced Self-Compacting Concrete (GFRSCC) was

developed. After adding glass fibres to SCC mixes, its influence on

fresh and hardened states was observed by conducting tests on fresh

and hardened GFRSCC. The tests on fresh and hardened GFRSCC

were conducted in the same way as they were conducted for SCC.

Fig. 4.3.1: Addition of Fibres to SCC mix

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4.3.2 Development of Steel Fibre Reinforced Self-Compacting Concrete and Hybrid Fibre Reinforced Self-Compacting Concrete Mix Proportions

The GFRSCC mix with an optimum dosage of glass fibres,

satisfying the fresh and the hardened properties, was considered for

the next phase of investigation. Similarly, the dosages of steel fibres in

Steel Fibre Reinforced Self-Compacting Concrete (SFRSCC) with a

fixed aspect ratio and Hybrid Fibre Reinforced Self-Compacting

Concrete (HFRSCC) consisting of a mixture of glass and steel fibres,

were developed by trial mixes. The ratio of steel fibres to glass fibres

was determined in the laboratory by trial mixes satisfying the fresh

and the hardened properties.

4.4 PHASE III: STUDIES ON STRESS- STRAIN BEHAVIOUR OF SCC AND FIBRE REINFORCED SCC MIXES IN UNCONFINED AND CONFINED STATES

In this phase of investigations, the stress-stain behavior of SCC

and FRSCC were taken up. The stress-strain behaviour was studied

for the SCC and FRSCC mixes in unconfined and confined states. The

confinement was given in the form of steel hoops in the cylinders, 3

hoops (0.798%), 4 hoops (1.062%), 5 hoops (1.327%) and 6 hoops

(1.591%) as shown in Fig 4.4.1 (a) and (b).

Fig. 4.4.1 a: Steel Hoops Fig. 4.4.1 b

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The tests were carried out on the standard cylindrical

specimens of diameter 150mm and height 300mm. After casting, the

cylinders were capped with cement mortar and cured for a period of

28 days in curing tanks as shown in Fig: 4.2.8. The specimens were

then taken out and made surface dry. The samples were placed in a

microprocessor strain controlled universal testing machine of 1000 kN

capacity and tested under uni-axial compression as per IS 516:1959.

The test setup is shown in Fig. 4.4.2 and the tested samples are

shown in Fig. 4.4.3.

Fig. 4.4.2: Cylinders Test Set-Up

Fig. 4.4.3: Tested Cylinders

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The stress–strain behaviour as obtained was plotted. The values

of secant modulus, initial tangent modulus, plasticity indices and

ductility factors for different SCC and FRSCC mixes were determined

from the stress-strain curves.

After determining the stress-strain behaviour of SCC and

FRSCC, empirical equations were developed based on the relevant

simplified models proposed by (1) Derivated Saenz model based on

Madrid parabola as adopted by the European Concrete Committee,

(2) Modified Saenz model(1964), and (3) model of Mansur et al(1997).

to present uni-axial stress-strain behaviour of SCC and FRSCC mixes

and these models were compared with experimental stress-strain

behaviour.

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Fig 4.4.4 Cylinder without Confinement

Fig 4.4.5: Cylinders with different Confinements

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4.4.2 Non-Dimensional Stress-Strain Curves

A general examination of the stress-strain behaviour of SCC

indicates that the behaviour is almost similar for all the SCC mixes

with and without fibres. The only difference that is observed is that

the FRSCC mixes have shown higher stress values for the same strain

levels compared to those of plain SCC mixes. This leads to the

conclusion that the stress-strain curve as a unique shape, if

expressed in non-dimensional form. This can be obtained by dividing

the stress at different levels by peak stress and the strain at different

levels by strain at peak stress. Thus the stress-strain curves have the

same point (1,1) at the peak stress. By the non- dimensionalisation of

the stresses and strains, the behaviour can be generalized.

The stress- strain data obtained experimentally for SCC and

FRSCC mixes were normalized as explained above and normalized

stress-strains values were calculated for different SCC and FRSCC

mixes in unconfined and confined states.

4.5 PHASE IV: STUDIES ON FRSCC WALL PANELS

In this phase of investigations, the studies were extended to

investigate the behaviour of Fiber Reinforced wall panels of size

1500mm × 1000mm × 75mm thick made with plain SCC, GFRSCC,

SFRSCC and HFRSCC. Standard moulds were prepared for casting

the above panels maintaining exact dimensions as shown in Fig.4.5.1

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Fig. 4.5.1 Casting Frame of FRSCC Wall Panels

The panels were cast with pouring concrete with horizontal spread.

They are provided with single grid of 6mm mild steel bars at the centre

of the specimen to maintain a minimum of 0.12% of steel as per IS:

456:2000 specifications as shown in Fig.4.5.2.

Fig. 4.5.2 Reinforcement Details in FRSCC Wall Panels

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The samples cast were cured as per BIS specifications and tested for

load carrying capacities under axial load and minimum eccentric load

with a minimum eccentricity of t/6 i.e 12.5mm. The test setup is

shown in Fig. 4.5.3.

Fig. 4.5.3 Experimental Test Set-up for FRSCC Wall Panels

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The specimens were tested until failure in 6000kN capacity

loading frame for compression, and the failure loads and pattern were

reported in Table 7.7.1. The wall panels were also tested for out-of-

plane bending in 400 kN capacity bending machine for obtaining the

flexural strength and the failure loads and pattern were reported in

Table 7.7.2. The test setup for flexural strength is shown in Fig. 4.5.4.

Fig. 4.5.4: Experimental Set-up for Flexure Test of FRSCC Wall Panels

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4.4.1 MATHEMATICAL MODELING FOR STRESS-STRAIN BEHAVIOUR OF SCC AND FRSCC

After obtaining the stress-strain behaviour of SCC and FRSCC

mixes experimentally, an attempt was made to get the analytical

stress-strain curves for SCC and FRSCC mixes.

A good number of empirical equations were proposed to

represent stress-strain behaviour of conventional concrete. Most of the

equations can be used for the ascending portion of the curve only. In

1997 Mansur et al. have adopted Carriera and Chu(1985) model,

which was based on the model proposed by Popovics(1973). As such,

model proposed by Mansur et al includes both ascending and

descending portions of the stress-strain curve for the confined

concrete with introduction of two constants for the desending portion

of the curve. Several researchers proposed various empirical equations

for stress-strain behaviour as briefly reported in the previous chapter.

Most of the equations proposed are for conventional concrete

with or without fibres, but limited literature is available on the

mathematical modeling of stress-strain behaviour of SCC and FRSCC.

An attempt has been made in this study to develop mathematical

models for SCC and FRSCC mixes of GFRSCC,SFRSCC and HFRSCC

in unconfined and confined states.

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The test results obtained for the load carrying capacities of

different types of wall panels were validated using the principles of

structural mechanics. The procedure adopted for validation of the

results is shown in Annexure II. Using the experimental values,

principles of structural mechanics and model analysis, the load

carrying capacities of prototype wall panels of 3000mm ×1000mm ×

150mm thick, and 3000mm × 1000mm × 200mm thick, are arrived at.

The two thicknesses of 150mm and 200mm are based on different

applications and codal provisions. The analysis part of arriving at

prototype load is shown in Annexure II.