08-05-2012, 04:57 PM
FLEXURAL BEHAVIOUR OF REINFORCED CONCRETE BEAMS
USING SELF COMPACTING CONCRETE
100034039.pdf (Size: 4.15 MB / Downloads: 187)
INTRODUCTION:
Fibre reinforced concrete is relatively a new construction material developed through extensive
research and development work during the last two decades. It has already found a wide range
of practical applications and proved to be reliable construction material having superior
performance characteristics compared to conventional concrete. Incorporation of fibre in
concrete has found to improve several properties like tensile strength, cracking resistance ,
impact and wear resistance, ductility and fatigue resistance. Many fibres like asbestos, steel,
nylon, coir, etc have been used in the past . Out of these asbestos fibres concrete is successful
although its exposure is detrimental to the health of human beings. Steel fibres improves
ductility, flexural strength and toughness. Corrosion damage and increased density are the
drawbacks of the steel fibres.Further development in the field of fibre reinforced concrete was
due to introduction of high strength fibres like glass and carbon fibres. The initial studies showed
deterioration of glass fibres due to corrosive alkali environment of the cement paste. The alkali
resistant glass fibre, which is developed, recently has overcome this defect and can be
effectively used in concrete. The production of fibre reinforced concrete should always be
considered in two well defined phases i.e the fresh phase and the hardened phase. Each phase
must be considered carefully at mix design stage and each presents its own particular
characteristics and related constructional or structural problems. It is necessary to understand
the interaction between the fibres and the surrounding matrix in both phases to know how the
fibre properties affect the properties of concrete.
LITERATURE REVIEW:
.
Annie Peter.J, Lakshmanan N, Devadas Manoharan. P, Rajamane.N.P and
Gopalakrishnan. S (2) had compared the structural behaviour such as load-deflection
characteristics, crack-widths, spacing of cracks, number of cracks, crack pattern, ultimate loadcarrying
capacity, moments-curvature relationship, longitudinal strain in both concrete and steel
for Self compacting concrete (SCC ) and conventionally vibrated concrete( CVC ) . They
observed through SCC and CVC have different modes of compaction, both mixes yielded to
similar strength levels at ages of 1,3,7, and 28 day. The UPV readings taken on SCC were
similar to those of CVC showing that SCC had flowed through the reinforcement and felled the
beam completely without voids, honey combs etc. The load-deformation behaviour of both SCC
and CVC beams were similar up to the peak load stage. Beyond the peak load stage, CVC
beams showed no drop in load with increased deformation while SCC beams showed drop in
load with increased deformation. While the peak and failure loads were nearly the same for CVC
beams, the failure load was nearly 25 percent lower compared to the peak load in SCC beams.
Crack widths were within the limits specified by IS 456 at all load stages. The average crack
widths of both the types of beams were comparable. The crack spacing of both CVC and SCC
were almost the same.
Ganeshan.N, Indira.P.V and Santhosh Kumar.P.T (3) made an attempt to study the effect of
steel fibres on the strength and behaviour of fibre reinforced SCC structural elements subjected
to flexure. Twenty beams were cast for this study, out of which two were plain SCC beams
without fibres. The variables in this study were aspect ratio (15.25 and 35) and percentage of
volume fraction (0, 0.25, 0.5 and 0.75) of fibres. Based on the Experimental investigation they
observed that the first crack load and the post cracking behaviour were found to have improved
due to the addition of fibres. A marginal improvement in the ultimate strength was observed. The
addition of fibres had enhanced the ductility significantly. The optimum volume fraction of fibres
was found to be 0.5 percent.
Ganeshan.N, Indira.P.V and Santhosh Kumar.P.T (4) made an attempt has been made to
study the effect of steel fibres on the strength and behaviour of Self Compacting Concrete (SCC)
flexural elements. Twenty beams were cast for this study out of which two were plain SCC
beams without fibres. The variables in this study were aspect ratio (0, 15, 25 and 35) and
percentage of volume fraction of fibres (0, 0.25, 0.5 and 0.75).First crack load and the post
cracking behaviour were found to have improved significantly due to the addition of fibres.A
marginal improvement in the ultimate strength was observed. The addition of fibres enhanced
the ductility significantly. The optimum volume fraction of fibres for better performance in terms of
strength and ductility was found to be 0.5 percent. Experimental values of the ultimate moment
were compared with various analytical models. The comparison indicate that Swami and Taan
model compares better with the test results than that of the other models.
Experimental programme:
Flexural behaviour of Glass Fibre Reinforced Self Compacting Concrete beams of M 30
,M 40, M 50 and M 60 with varying percentages of glass fibres from 0 % to 0.1% .
Load deflection characteristics of Glass Fibre Reinforced Self Compacting Concrete
beams of M 30, M 40, M 50 and M 60 with varying percentages of glass fibres from 0 %
to 0.1% .
Materials
Cement
Ordinary Portland cement of 53 grades available in local market is used in the investigation. The
Cement used has been tested for various proportions as per IS 4031-1988 and found to be
confirming to various specifications of are 12269-1987.The specific gravity was 2.96 and
fineness was 3200cm2/gm.
Coarse Aggregate
Crushed angular granite metal of 10 mm size from a local source was used as coarse aggregate.
The specific gravity of 2.65 and fineness modulus 6.05 was used.
Fine Aggregate
River sand was used as fine aggregate. The specific gravity of 2.55 and fineness modulus 2.77
was used in the investigation.
Viscosity Modifying Agent
A Viscosity modified admixture for Rheodynamic Concrete which is colourless free flowing liquid
and having Specific of gravity 1.01+0.01 @ 250C and pH value as 8+1 and Chloride Content nil
was used as Viscosity Modifying Agent.
Admixture
The Modified Polycarboxylated Ether based Super Plasticizer which is Brown Color and free
flowing liquid and having Relative density 1.08+0.01 and pH value as 7+ 1 and Chloride Content
nil was used was Super Plasticizer .
Glass Fibres
The Glass Fibres are of Cem-FIL Anti – Crack HD with Modulus of Elasticity 72 GPA, Filament
diameter 14 microns, Specific Gravity 2.68, length 12mm and having the aspect ratio of 857.1.
The number of fibres per 1 kg is 212 million.
Fly Ash
Type-II fly ash from Vijayawada Thermal Power Station, Andhra Pradesh was used as cement
replacement material. The properties fly ash are confirming to I.S. 3812 – 1981of Indian
Standard Specification for Fly Ash for use as Pozzolana and Admixture.
TEST SPECIMENS:
To study the suitability of the Self Compacting Concrete and Glass Fibre Reinforced Self
Compacting Concrete beams investigations were carried out for ultimate load and load deflection
characteristics. Glass Fibre Reinforced Self Compacting Concrete beams by varying the
percentage of glass fibres from 0 % to 0.1 % of sizes 1200 X 150 X 100 mm were cast with
reinforcement of 2 nos of 12mm diameter HYSD bars as tension reinforcement and 6mm
diameter stirrups spacing at 150 mm c/c as shear reinforcement as given in Table no 1.0. To
hold stirrups in position two hanger rods of 2 nos of 10mm diameter HYSD bars at top were
used. These specimens were cured in water for 90 days and tested for ultimate load , deflections
and failure characteristics under one third point loading . The test setup is made of Heico and it is
shown in plate 1.0.