Page 7 - Open-Access-June-2020

TECHNICAL PAPER

to fiber bridging and crack controlling tensile strain-hardening initial damage conditions. The study reported the macroscopic
property of ECC in under-reinforced beams and higher residual load-displacement, cracking characteristics and average stress-
strength and high ultimate compressive strain in over-reinforced strain behavior of the plates. Particularly, the attention was
beams [22,24] . focused on the resulting secondary cracks (defined herein as a
series of parallel cracks formed in a different orientation to the
2.1.3 Cracking Behavior and Failure Modes pre-cracks). Finally, the study concluded that the ductility of the
pre-cracked plates were not influenced by the existing cracks.
Under flexural tensile condition, ECC beams generate numerous In pre-cracked ECC plates, the initial cracks were uniform and
small micro-cracks at tension side due to its steady state and continuous and then they were discontinuous.
multiple cracking property. To add, the observed crack width
in ECC beams behaves more or less constant on increasing the Said et al. investigated the flexural performance of ECC slabs
[29]
load until failure. Further, it is also reported that the crack width with varying fiber reinforcing index. The study reported that
observed in ECC beams are one seventh of concrete beams at upto certain value of reinforcing index, the strain-hardening and
limit state . For FRP reinforced ECC beams the observed crack multiple cracking behavior was not observed. After that, increase
[12]
spacing are 6 to 8mm. Under flexural compressive condition, in reinforcing index depicted improved strain-hardening and
the failure of RECC beams is accomplished by very prolonged multiple cracking behavior, which in turn increased the flexural
cracking of ECC due to high residual compressive strength and performance of ECC slab. The increase in reinforcing index also
ultimate strain . increased the deflection at both ultimate load and failure.
[24]
2.1.4 Size Effect 2.3 Flexural Behavior of ECC – Composite
Systems
Lepech and Li reported that the ECC beams with longitudinal
[25]
steel reinforcing bars exhibit insignificant / null size effect due to The flexural behavior of ECC – Composite systems such as
the full suppression of sudden fracture failure and the material extruded panels, slabs and pipes are also investigated for
variability. specific applications in conjunction with other reinforcing
elements like RC slabs, steel joists, modular deck panels, etc.
Kanakubo et al. reported that the size effect on ECC beams The studies have concluded that the performance of ECC-
[26]
exists such that the strength and deformation capacity of ECC composite system was satisfactory and superior to conventional
beams increased as the size of the beam decreases. Such effect system in terms of load carrying capacity, stiffness and
is due to the uniform fiber orientation (one or two dimensions) deformation. Few notable studies from literature are discussed
and distribution of multiple cracks (over the pure bending in the following section.
region). Whereas in large size specimens, the cracks were
[30]
concentrated (not distributed) at certain places with wider crack Rokugo et al. developed ECC-pipe composite (steel
width. The observed crack spacing was also smaller in small size pipe covered with ECC) and ECC-plate composite (steel
specimens. plate covered with ECC) and investigated for their potential
structural applications. The study reported that using ECC with
Asano and Kanakubo also studied the size effect in bond steel members shares most of the external force, so that the
[27]
behavior between ECC and steel reinforcing bar. They reported maximum mechanical performance of the ECC was utilized for
that the bond strength increases with increase in cover thickness obtaining higher load bearing capacity in composites.
and decrease in reinforcing bar diameter.
Fischer developed an alternative prefabricated composite
[19]
2.2 Flexural Behavior of Plain ECC Slabs and floor panel system containing ECC slab and light gage steel
Plates joists. The load deformation behavior of the ECC composite
floor panel shows favorable characteristics with relatively high
The flexural behavior of ECC elements such as slab and plates flexural stiffness, strength and ductile ultimate failure than
without reinforcement are also investigated for its structural conventional systems. It was also inferred that the interface
performance. The performance of such ECC elements showed degradation, spalling and bucking of steel joist was eliminated
convincing and superior load carrying capacity, deformation and due to the ductile nature of ECC.
stiffness compared to conventional plain concrete elements.
[21]
Few notable studies from literature are discussed in the Larusson et al. developed prefabricated lightweight
following section. composite deck elements, in the form of integrally cast ECC
deck panels with steel joists and ECC modular deck panels. The
Suryanto et al. investigated the mechanisms of stress transfer study concluded that the use of ECC eliminates the transverse
[28]
across multiple cracks in pre-cracked ECC plates with various steel reinforcement and increases of tensile loading capacity

8 The IndIan ConCreTe Journal | June 2020