Civil Engineering Reference
In-Depth Information
Fig. 5.31 FS of concrete
containing dry NA and RCA
with various moisture content
(D: dry; S1, S2 and S3: 89.5,
88.1 and 100 % water
saturated RCA) (Oliveira and
Vazquez
1996
)
compensate the negative effect related to the weakness of the old ITZ in RCA as
the FS is largely dependent on the bond strength between aggregate and mortar
matrix.
The concrete containing RCA from high-strength concrete exhibited higher FS
than the one containing RCA from low strength concrete Limbachiya et al. (
2000
).
Topçu and Sengel (
2004
) observed a systematic decrease in the FS of 16 and
20 MPa (cylindrical) concrete classes as the content of coarse RCA in concrete
increased. The reduction was 13 and 27 % for the 16 and 20 MPa mixes
respectively at a 100 % substitution level. Padmini et al. (
2009
) observed lower FS
for RCAC than for conventional concrete and the differences in terms of CS and
FS decreased with a reduction of the design CS (Fig.
5.30
).
Takavoli and Soroushian (
1996
) observed higher FS for RCAC using smaller
coarse RCA than for bigger coarse RCA and in some cases the FS was higher than
for the control concrete. Oliveira and Vazquez (
1996
) observed a reduction from
the control concrete of about 10 % in the 3- and 28-day FS of mixes made with
coarse RCA with different moisture levels (Fig.
5.31
). The FS of concrete con-
taining dry RCA or around 90 % saturated RCA were comparable; however, the
FS of concrete containing saturated surface dried RCA was significantly lower
than that of the others.
Katz (
2003
) observed similar 28-day FS for conventional and concrete with
coarse RCA and a mixture of fine RCA and natural sand, obtained from 1-day
cured concrete; however, the FS of RCAC with RCA obtained from 3- and 28-day
concrete was 11.5 % lower than that of conventional concrete. On the other hand,
the reduction in FS was respectively 29.9, 20.9 and 31.3 % in concrete with white
Portland cement as binder for 1-, 3- and 28-day cured RCA. Yang et al. (
2011
)
observed 3 and 9 % reductions from the control concrete in the 7- and 28-day FS
of concrete with RCA as sole coarse aggregate. The addition of crushed brick up to
a 50 % substitution level of RCA slightly increased the FS due to the low Young
modulus of brick and therefore improved the tensile stress along the matrix-
aggregate interface (Fig.
5.32
). The failure modes for control and RCA concrete
occurred at the aggregate and mortar matrix's interface while both interface and
aggregate failure occurred in RCAC containing crushed brick.
