Civil Engineering Reference
In-Depth Information
Fig. 5.40 Effect of curing
conditions on the MO of
concrete (Poon et al.
2006
)
Fig. 5.41 Effect of curing
conditions on the MO of
concrete containing various
ratios of coarse RCA
(Fonseca et al.
2011
)
Oliveira and Vasquez (
1996
) observed comparable 28-day MO for concrete
containing coarse RCA with various moisture levels; the MO of RCAC was about
75 % that of conventional concrete. Chen et al. (
2003
) observed insignificant
influence of the quality of RCA whether it was washed or unwashed with impu-
rities such as sand particles, bricks and tiles on the MO of the resulting concrete.
The differences in MO of conventional and RCA concrete were also similar with
the w/c ratio (Fig.
5.42
). Chen et al. (
2003
) also found an insignificant effect of
brick and tile contents on the MO of RCAC (Fig.
5.43
).
Tam et al. (
2007
) observed higher MO for concrete prepared using a two-stage
mixing approach (in which mixing of the water was divided into two parts: the first
one added to the mixed aggregate and the remaining part to the mixed aggregate
and cement) than that observed for concrete prepared using a one-step mixing
approach (in this approach the whole amount of water was added to the mixed
aggregate and cement). In this study, the replacement of 31.3 % of NA by RCA
gave the highest improvement in 28-day MO of RCAC prepared by the two-stages
mixing when compared to conventional concrete. In another study, Tam and Tam
(
2008
) observed an improvement of about 16 % in the 28-day MO of concrete
containing coarse RCA as a 30 % replacement of NA due to the incorporation of
silica fume as a 2 % replacement of OPC where the concrete was prepared by a
