Civil Engineering Reference
In-Depth Information
Fig. 5.10 Effect of moisture
content in RCA on CS
(Oliveira and Vazquez
1996
)
60
3-day
28-day
45
30
15
0
Control
Dry
88.1%
89.5%
Saturated
moisture
moisture
cement matrix region due to movement of water from SSD aggregate weakens the
cement paste/aggregate bond and lowers the compressive strength. On the other
hand, the opposite movement of water from cement matrix to aggregate
strengthens the bond and led to higher CS of concrete containing OD RCA.
Concrete containing larger RCA has higher CS than similar concrete containing
smaller RCA as the mortar content in larger RCA is generally lower than in
smaller RCA (Tavakoli and Soroushian
1996
; Hansen and Narud
1983
).
Corinaldesi (
2010
) reported that the CS of RCAC containing larger coarse RCA is
higher than that for smaller coarse RCA at the same water to cement ratio and at
30 % (by volume) substitution ratio of natural coarse aggregate (Fig.
5.11
). Both
types of aggregate were generated in same crushing plant at the same crushing
period. According to the authors, the coarser RCA came from concrete with a
higher CS and hence less friability than the other concrete, which generated the
finer RCA. In this study, two classes of concrete (C30/37, C32/42) were prepared
from coarse and fine RCA aggregate at the water to cement ratios of 0.5 and 0.4,
respectively. Nagataki et al. (
2004
) observed the dependence of mechanical
properties including CS on the size of coarse aggregate of the original concrete as
well as on the amount of sand particles present in RCA. The stress concentration at
the zone between RCA and mortar in RCAC is lower for smaller coarse aggregate.
Low amounts of sand particles in RCA also enhance the CS of RCAC.
A strong relationship between the CS of RCAC and the properties of the source
concrete from which RCA originated was reported in various studies. Hansen and
Boegh (
1985
) observed that the 47-day CS of high and medium strength concrete
containing RCA generated from high and medium strength concrete were higher
than that of the original high and medium strength concrete; however, the CS of
low strength concrete containing RCA originated from medium and low strength
concrete was lower than that of conventional low strength concrete. Their results
are presented in Fig.
5.12
.
Tavakoli and Soroushian (
1996
) reported that the CS of concrete containing
RCA depends on several factor such as the strength of the source concrete from
which RCA is generated, the mixing procedure, the water to cement ratio and the
