Civil Engineering Reference
In-Depth Information
Fig. 5.2 Slump of concrete
containing two types of CDW
aggregate (Khatib
2005
)
weight of sand and then gradually decreased and, at 100 % replacement level, the
slump of concrete mix was about 80 mm in comparison to 145 mm of the control
mix. These results are presented in Fig.
5.2
.
Li et al. (
2009
) observed higher slump in mixes containing coarse RCA coated
with pozzolanic powder than in mixes containing coarse RCA prepared by con-
ventional methods. The poor workability of the mix containing RCA due to the
presence of attached mortar was significantly improved due to the surface coating
of RCA by pozzolanic powder, and therefore reduced the amount of water
absorbed by RCA.
Katz (
2003
) observed similar slump and comparable contents of free water in
conventional concrete and mixes containing coarse recycled aggregate (RCA)
from crushed concrete cured for 1, 7 and 28 days. However, due to insufficient
content of fine aggregate in RCA, an extra amount of fine natural aggregate was
added to the mix containing RCA to maintain workability and cohesivity. Kou
et al. (
2011a
) reported that the addition of silica fume (SF) and metakaolin (MK)
can reduce the slump of concrete mix containing RCA, which otherwise increases
due to the addition of extra water to compensate the increased water requirement
of RCA present in the mix. On the other hand, fly ash and granulated blast furnace
slag addition to similar concrete containing RCA can further increase the slump.
Tu et al. (
2006
) reported that the workability loss of high-performance concrete
(HPC) containing RCA was much higher than that of conventional HPC. The RCA
with higher water absorption capacity had a slight influence on the workability at
the initial stages of mixing of HPC; however, the workability of the HPC mix
deteriorated after 1 h of mixing as the added water amount was insufficient to
satisfy the water demand of the mix.
5.2.2 Density
Fresh concrete density is the mass of fresh, normally compacted concrete,
including its remaining voids per unit volume. This property depends on several
