Civil Engineering Reference
In-Depth Information
Table 5.9
Reduction in CS (%) due to the addition of CDW aggregate
References
Type of aggregate
Reduction in strength,
(substitution level %)
Comment
Oliveira and
Vasquez
(
1996
)
Coarse/RCA
10
Varied depending on moisture
content in RCA aggregate
Topçu and Sengel
(
2004
)
Coarse/RCA
23.5
C16 type concrete
33
C20 type concrete
Sani et al. (
2005
)
Coarse/fine/RA
40
At constant water to cement ratio
Gomez-Soberon
(
2002
)
Coarse/RA/10 min
pre-soaked in
water
*2, (15)
Substitution level (v/v): 15, 30 and
100 %
* 5, (30)
*11.5, (100)
Coarse/RCA/SSD
a
Kou and Poon
(
2008
)
4-6, (20)
Substitution level (v/v): 20, 50 and
100 %; strength decreasing with
increasing mortar content;
13-17, (50)
16-22, (100)
Khatib (
2005
)
Fine/RCA
*24.5-25, (25-75)
Substitution level (w/w): 25, 50, 70
and 100 %; prepared at free water
to cement ratio of 0.5
*36, (100)
Yang et al. (
2011
)
Coarse/RCA
5.7, (100)
Prepared at w/c of 0.47 with a slump
of 24 mm
a
SSD Saturated surface dry
admixture. They also observed an inverse relationship between CS of RAC and open
porosity of RA. The addition of fly ash to replace a part of fine RA can recover part of
the CS and therefore in this case a reduction of about 30 % in CS was observed.
Dapena et al. (
2011
) did not observe any change in 28-day CS of resulting concrete
due to 20, 50 and 100 % (by volume) replacement of coarse NA by coarse RA owing
to the small amount of impurities in RA (\2 %) and an initial reduction of water to
cement ratio of RAC due to higher water absorption capacity of RA. The 5 and 10 %
(by volume) of fine (\4 mm) content in RCA did not affect the strength behaviour of
concrete containing 20 and 50 % RCA; however, a drop of around 3.6 MPa in CS
was observed in concrete containing 100 % RCA. Poon et al. (
2009
) observed a
reduction in compressive strength of RAC containing RA as the only coarse
aggregate as the replacement of fine natural aggregate by fine RA increased.
Etxeberria et al. (
2007a
) reported that concrete prepared by replacing 25 % (v/v)
coarse NA by coarse RA can be used as medium strength (30-45 MPa) concrete
having similar CS to conventional concrete, when both mixes are prepared with the
same cement content and effective water to cement ratio of 0.55. However,
a reduction of effective water to cement ratio of 0.52 or an increase of 6 % in cement
content was necessary for RAC containing 50 % RA to achieve a CS similar to that
of conventional concrete. These values became 0.50 and 8.3 %, respectively,
for RCAC containing 100 % RCA. Gonzalez-Fonteboa and Martinez-Abella (
2005
)
also increased the cement content by about 6.2 % without changing the w/c
(including moisture content in aggregate before mixing) in RAC where 50 % (by
volume) of natural coarse aggregates were replaced to obtain CS and consistency
