Civil Engineering Reference
In-Depth Information
Fig. 5.38 MO of concrete at
various ages due to the
replacement of coarse NA by
coarse RCA (Gomez-Soberon
2002
)
MO gradually slowed down with increasing content of RCA in concrete. The MO
of concrete containing RCA at 100 % replacement level was almost the same at
the various curing ages. The authors could not establish a relationship between
total porosity and MO even though the MO decreased as the open porosity
increased up to around a 15 % porosity level. Safiuddin et al. (
2011
) observed a
smaller increase in MO as curing time increased than that observed for FS and
STS. In this study, the 28-day MO of RCAC was only 11.2 % higher than 7-day
value, whereas the FS and STS increases were respectively 40.3 and 17.3 %. The
MO increased with the concrete's CS too.
Domingo-Cabo et al. (
2010
) found a decrease of the 28-day MO due to the
incorporation of a good quality coarse RCA as a 0, 20, 50 and 100 % (by volume)
replacement of coarse NA in mixes with similar w/c ratio. Unlike most investi-
gations, the RCA used in this one was not pre-saturated before concrete mixing;
instead a super-plasticizer was used to prepare a workable mix. After the RCAC
were prepared at constant slump by considering the amount of water absorbed by
RCA, the 28-day MO was similar to that of conventional concrete. Padmini et al.
(
2009
) observed a significant reduction in MO of concrete with the incorporation
of RCA as coarse aggregate owing to the increase of porosity of concrete due to
that incorporation. The higher reduction in percentage of the MO was observed for
concrete made with smaller coarse RCA due to their higher porosity. However, no
effect was detected of the strength of original concrete from which the RCA were
generated on the MO of RCAC. Corinaldesi (
2010
) observed a reduction of around
23 and 13 % in 28-day MO of concrete prepared at w/c of 0.40 and 0.45
respectively, due to the replacement of 30 % of fine and coarse gravel (6-12, FR
and 11-22 mm, CR) by similar sized RCA (Fig.
5.39
). However, these values for
fine and coarse gravel RCA became 22 and 32 % respectively at the w/c ratio of
0.60. Thangchirapat et al. (
2008
) observed a reduction of around 11 % in the 28-
day MO due to a 100 % replacement by weight of coarse NA by RCA. The
replacements of fine NA by fine RCA in the concrete with 100 % coarse RCA
further lowered the MO. The reduction in MO of mixes with 50 and 100 % fine
RCA was respectively around 14 and 24 %.
