Civil Engineering Reference
In-Depth Information
hydration of the nano-silica particles were the major causes for the observed CS
improvement due to the nano-silica treatment of RCA.
Topçu and Saridemir (
2008
) successfully predicted the 3- to 90-day CS of
RCAC by applying artificial neural networks and fuzzy logic systems. Lin et al.
(
2004
) used the optimal mix proportioning of RCAC by orthogonal array,
ANOVA and significance test with F statistics to prepare a RCA concrete mix with
suitable mechanical strength. The optimum RCAC mix observed in this investi-
gation contains RCA and natural river sand as 100 % coarse and fine aggregates,
respectively, with water/cement ratio of 0.5 and volume ratio of recycled coarse
aggregate in RCAC 42.0 %. The mix should contain no crushed brick and
unwashed RCA should be used. The slump and 28-day CS of this optimum mix
was 180 mm and 30.17 MPa, respectively.
The use of fine fraction (\4 mm fraction) of CDW aggregate in preparation of
concrete is not as thoroughly studied as the coarse fraction. It is believed that the
greater water absorption capacity of the fine fraction of CDW waste can jeopardize
the use of this fraction as fine aggregate in concrete (Evangelista and de Brito
2007
).
Merlet and Pimienta (
1993
) observed 19-39 % lower CS of concrete made with
fine and coarse recycled aggregate than that of a control concrete. Leite (
2001
), on
the other hand, observed increasing and decreasing CS of concrete due to
increasing incorporation of fine and coarse recycled aggregate (FRA and CRA,
respectively), respectively (Fig.
5.20
). The author justifies the results with the
stronger bond created between FRA and the matrix, because of the precipitation of
cement crystals inside the FRA.
Khatib (
2005
) observed a reduction in CS with increasing content of fine
recycled concrete aggregate (FRCA) in concrete. The particle size of FRCA was
\5 mm. The concrete was prepared at free water to cement ratio of 0.5. The
reduction in 90-day CS was in the range of 15-27 % when 25-100 % by weight of
fine natural aggregate (FNA) was replaced by FRCA. However, 28-day CS of
concrete containing 25-75 % and 100 % FCRA were about 25 and 36 % lower
than that of the control, respectively. The relative CS of FRCA concrete (FCRAC)
in the 28-90-day period increased due to the hydration of un-hydrated cement
Fig. 5.20 CS of RCAC due
to incorporation of fine (FRA)
and coarse (CRA) recycled
aggregates (Leite
2001
)
