BOND STRENGTH AND MODULUS OF ELASTICITY OF ENGINEERED CEMENTITIOUS COMPOSITES

The compressive strength of plain or conventional concrete is high, but plain
concrete possesses a very low tensile strength, limited ductility and little resistance
to cracking. New generations of concrete such as high strength concrete and ultrahigh
strength concrete have been successfully developed. Although these new
generation concrete have extremely high compressive strength, their tensile strength,
ductility and resistance to drying shrinkage cracking have not been significantly
improved which limits their use for structural applications. All current methods to
improve the ductility and tensile strength of concrete members such as the addition
of discontinuous discrete fibers to concrete during mixing, the use of reinforcement
steel bars and restraining techniques are not cost effective. Established literatures
show that Engineered Cementitious Composites (ECC) exhibits ductile behavior
under uniaxial tension load. ECC has been repeatedly reported by different
researchers to be characterized by high ductility, tight crack width control and
exhibition of pseudo-strain hardening behavior with several percent tensile strains as
compared to brittle and quasi-brittle behaviors for plain concrete and Fiber-
Reinforced Concrete (FRC) respectively. Thus, the objectives of this project are: 1)
to develop polyvinyl alcohol (PVA) fiber reinforced self-consolidating ECC, 2) to
investigate the bond strength between the developed PVA-ECC and reinforcement
bars and 3) to determine the Modulus of Elasticity of the developed PVA-ECC. To
achieve the above project objectives, the following activities were performed:
mixing / casting, curing and testing of 100 mm x 100 mm x 100 mm ECC cubes and
ECC cylinders of heights 200 mm and 300 mm with diameters 100 mm and 150 mm
respectively. The tests conducted include slump flow, Visual Stability Index, Vfunnel,
L-box (for self-compacting concrete requirements), pull-out and modulus of
elasticity tests. The values of slump flow, V-funnel and L-box measured in this
project all satisfied the requirements for self-consolidating concrete (SCC). It has
also been found out that the bond strength between reinforcing steel and ECC
increases with increase in PVA fiber contents. The modulus of elasticity of PVAECC
also increases with increasing PVA fiber content and increasing compressive
strength of PVA-ECC.