Civil Engineering Reference
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Fig. 5.37 Performance of normalized rupture modulus with the water absorption capacity of
natural and CDW aggregate (Yang et al.
2011
)
predicts a significantly lower FS value then the experimental value. In the James
et al. (
2011
) study, the existing ACI 318 (2008) code underestimated their FS
results. Katz (
2003
) observed higher values of 28-day FS of conventional concrete
and RCAC than the value predicted according to ACI 363R.
5.3.4 Modulus of Elasticity
Similarly to the strength properties, the modulus of elasticity (MO) of concrete
containing CDW aggregate is normally lower than that of conventional concrete
and it decreases as the content of CDW aggregate in concrete increases. Some
typical results are presented in Table
5.16
. The causes for reduction in concrete's
MO due to the incorporation of CDW aggregate indicated in various references
are: (1) the loss of concrete stiffness, which depends on properties such as stiffness
of mortar, concrete porosity and aggregate-cement paste bonding; these properties
deteriorate due to the addition of RCA to concrete; (2) the lower MO of CDW
aggregate than that of natural aggregate, since the concrete's MO is primarily
dependent on the MO of the aggregate.
Depending on factors such as substitution ratio, quality and size of aggregate,
w/c ratio, the reduction in MO of RCAC may reach 50 % when compared to
conventional concrete. The reduction in concrete's MO due to the incorporation of
CDW aggregate is generally higher than the corresponding CS reduction. Saf-
iuddin et al. (
2011
) observed a reduction of about 17.7 % in the 28-day MO in
comparison to a 12.2 % reduction in CS of concrete with 100 % coarse RCA when
compared to conventional concrete. Chen et al. (
2003
) observed a 22 % reduction
in MO in comparison to a 15 % reduction in CS of concrete due to the inclusion of
