Page 7 - Open-Access-Dec-2019

TECHNICAL PAPER

the crack width decreases with increasing fibre dosage in FRC, increase of fibre content shall not have major impacts on
the reduction is rather moderate. As for the ECC specimen, the mass loss of steel reinforcement. Surprisingly, significant
no major crack was found, and a reticular distribution of micro- reduction of steel mass loss in ECC specimen was observed
cracks was observed on the cover surface. The great reduction when 2 vol.% of fibre was used. After 4-d accelerated corrosion,
of crack width from millimeter scale in FRCs to micrometer the mass loss of steel reinforcement in ECC was only 1.2%. This
scale in ECC is a direct result of modified crack propagation phenomenon highlights fibre dosage in cover material alone is
mode from the Griffith type in FRCs to the steady-state crack not the dominating factor of corrosion-induced steel mass loss;
[28]
propagation in ECC . rather the fundamental change of failure mode of cover material
from tension softening FRC to tensile strain hardening ECC is
the key to enhancing the corrosion resistance in R/C.

Figure 4 plots the mass loss rate of steel reinforcement in the
prism specimens. For FRC specimens, the general trend shows
that the rate of mass loss increases with increasing corrosion
duration, which suggests the mass loss of steel bar and thus
the deterioration of specimen accelerate with time (Figure 4a).
This can be attributed to continuously widening of crack width
in the FRC cover leading to accelerated ingress of aggressive
a b c d
substances and migration of corrosion products. Similarly, the
Figure 2: Typical crack pattern of (a) FRC 1, (b) FRC 2, (c) FRC 3, and (d) increase of fibre content in FRC cover moderately reduces the
ECC after 4-d accelerated corrosion. mass loss rate of steel reinforcement, and the efficiency of fibre
addition reduces with increasing fibre dosage (Figure 4b). The
3.3 Mass loss and mass loss rate of steel
steel mass loss rate in ECC specimens increases slightly and
reinforcement remains stable at 0.3 % per day after 4-d accelerated corrosion.
The mass loss of steel reinforcement in the prism specimens The high ductility and damage tolerance together with the self-
are presented in Figure 3. For FRC specimens, mass loss controlled tight crack width of ECC alter the brittle failure mode
of steel reinforcement increases with increasing corrosion of the conventional concrete or FRC cover material to a ductile
duration (Figure 3a). Mass loss of steel reinforcement reduces failure behavior subject to corrosion-induced steel reinforcement
moderately with increasing fibre dosage in FRCs. For example, expansion. Corrosion products may fill the microcracks in ECC
the mass loss of steel reinforcement in FRC 1, FRC 2 and FRC which plug the pathway for the egress of rust and the ingress
3 specimens after 4-d accelerated corrosion are 29.4 %, 20.8%, of harmful substances . Also, confinement provided by ECC
[29]
and 18.9%, respectively. The efficiency of fibre addition reduces cover may densify the rust layer which further reduces the rate
at increasing amount of fibre dosage as the reduction of steel of penetration of water, chloride ion and oxygen to reach the
mass loss is not linearly proportional to fibre content in FRCs uncorroded steel surface. The superior confinement provided
(Figure 3b). In fact, the efficiency decreases exponentially with by the ECC cover thus significantly slows down the corrosion
increasing fibre dosage. As such, it is expected continued rate and mass loss of the steel reinforcement. From the

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