Civil Engineering Reference
In-Depth Information
angularity and surface roughness of RCA aggregate as well as the effectiveness of
interfacial bonding due to the orientation of larger coarse RCA along the speci-
men's length compensated the negative impact of the weakness of RCA and
therefore maintained a FS similar to that of conventional concrete.
Chen et al. (
2010
) observed a slight increase in FS due to the replacement of up
to 40 % of coarse NA by RCA and similar values to that of conventional concrete
above this replacement level. In this study, the ratios of FS to CS were in the range
of 0.11-0.13 when 10-100 % coarse NA was replaced by RCA. Ahmed (
2011
)
observed similar 28 and 56 days FS of concrete due to the replacement of 25 and
50 % of natural fine aggregate by fine RCA. However, at 75 and 100 %
replacement level, the FS was lower than that of conventional concrete. The 28-
day FS of RCAC prepared by replacing 50 and 100 % of coarse NA by RCA in the
Malesev et al. (
2010
) study were respectively 5.7 and 5.2 MPa in comparison to
the 5.4 MPa of conventional concrete.
Yang et al. (
2011
) observed a 7.5-13.8 % reduction in FS due to replacement of
100 % coarse NA by RCA at various ages. Gull (
2011
) observed a reduction of
around 37 % in 28-day FS of concrete due to the replacement of fine and coarse
natural aggregates by RCA when both mixes were prepared at w/c ratio of 0.5.
However, the 28 day FS of RCAC prepared at the same w/c ratio but by using a
water reducing agent was similar to that of conventional concrete. Casuccio et al.
(
2008
) observed a 5-21 % reduction in 28-day FS of concrete due to the
replacement of 100 % coarse NA by RCA. Mas et al. (
2012
) observed 20, 13 and
30 % reductions in FS due to the replacement of up to 75 % (by volume) of coarse
natural aggregate by low quality RCA in three types of concrete prepared at w/c of
0.65, 0.72 and 0.45 respectively.
Singh and Sharma (
2007
) observed a 4-15 % reduction in 1- to 28-day FS of 20
and 25 MPa concrete mixes due to replacement of coarse natural aggregate by
RCA aggregate. James et al. (
2011
) observed a 28-day FS about 2.5 % lower due
to the replacement of 25 % by mass of NA by RCA at a w/c ratio of 0.55. Like in
conventional concrete, the FS increased with curing time. The differences in FS
between conventional concrete and RCAC are lower at higher w/c ratios than at
lower ones. The authors did not observe any effect of the w/c ratio on the CS of
RCAC either.
Yong and Teo (
2009
) observed higher 3-day FS for RCAC than for conven-
tional concrete up to a 100 % substitution level of coarse NA by RCA. However,
the FS of conventional concrete was higher than that of RCAC when the curing
age increased to 28 days. They also reported that the FS performance of RCAC
was not as good as that observed for CS and STS due to the lower modulus of
elasticity of RCA than NA's; therefore RCA tended to deform more than NA. In
comparison to CS, Akbarnezhad et al. (
2011
) observed a lower reduction in the
modulus of rupture as the replacement of coarse NA by RCA increased. At 100 %
replacement, the reduction in modulus of rupture and CS was 15 and 30 %
respectively. The higher water absorption capacity of RCA might enhance the
bond
strength
between
the
new
mortar
and
aggregate,
which
can
partially
