Civil Engineering Reference
In-Depth Information
RCA as 100 % (by volume) replacement of coarse NA when the concrete was
prepared at w/c of 0.5. In contrast to the CS and STS performance, Etxeberria et al.
(
2007b
) also observed a decrease of the MO caused by the addition of coarse RCA
as a replacement of NA due to the lower MO and higher deformation of RCA than
NA's. The percentage reduction in 28-day MO due to the replacement of 25, 50
and 100 % of NA by RCA was around 4, 12 and 15 % respectively. Rahal (
2007
)
observed a reduction of only 3 % in the MO for concrete with cylindrical strength
between 25 and 30 MPa due to replacement of coarse NA by RCA.
Gonzales-Fonteboa et al. (
2011
) observed considerable decrease in the MO due
to the addition of coarse RCA in concrete, because of the lower MO of RCA than
NA's. They observed 4.7, 10.9 and 18.0 % reduction in MO due to the replace-
ment of 20, 50 and 100 % of coarse NA by RCA in concrete at w/c of 0.65. These
values were 3.8, 14.9 and 29.2 % at w/c of 0.50. Berndt (
2009
) observed a
reduction of about 15 % in the MO due to a 100 % replacement of coarse NA by
RCA. According to them, the low MO of RCAC might have an impact on the
structural response (e.g. a low stiffness material is less susceptible to cracking).
Corinaldesi (
2011
) observed a reduction of around 17 % in 28-day MO due to the
replacement of 30 % coarse NA by RCA. Xiao et al. (
2006a
) observed a 45 %
reduction in the MO of concrete due to the incorporation of coarse RCA as a
100 % replacement of coarse NA when compared to conventional concrete.
Frondistou-Yannas (
1977
) observed a reduction of up to 40 % in the MO in
comparison to a 4-14 % reduction in CS of concrete due to the incorporation of
coarse RCA as a full replacement of NA.
In the Rao et al. (
2011
) study, the MO decreased with the replacement ratio of
coarse NA by RCA due to the weaker ITZ between RCA and cement mortar and
the lower MO of RCA than NA's. The reduction percentage in 28-day MO of
concrete due to the replacement of 25, 50 and 100 % NA by RCA were 14.3, 14.4
and 15.4 % respectively. Evangelista and de Brito (
2007
) observed a reduction of
about 3 % in the 28-day MO of concrete containing fine RCA as a replacement of
30 % by volume of fine NA; however, the MO of concrete containing 100 % fine
RCA was 18.6 % lower than that of conventional concrete. The loss of concrete
stiffness, which depends on properties such as stiffness of mortar, concrete porosity
and aggregate-cement paste bonding was not as significant for smaller incorpo-
ration ratios of fine RCA as for higher ones and therefore the MO of concrete was
slightly affected for small ratios of fine RCA.
Kou and Poon (
2008
) observed a 17-23 % reduction in 28-day MO of concrete
containing three types of coarse RCA as a 100 % replacement of NA when
compared to conventional concrete; however, after 5 years of curing, the reduction
dropped to around 10 % indicating higher gain over time in MO of RCAC than
that observed in conventional concrete. The increase in MO of the mixes con-
taining three types of RCA as a 100 % replacement of coarse NA between 28 days
and 5 years was in the range of 33-40 % in comparison to a 20 % improvement in
conventional concrete. Gomez-Soberon (
2002
) observed a gradual decrease of the
MO as the replacement of coarse NA by RCA increased up to 60 % and then
became similar at 100 % replacement level (Fig.
5.38
). The development of the
