Use of Construction and Demolition Waste as Aggregate: Properties of Concrete - Recycled Aggregate in Concrete - page 250

due to the replacement of 20 and 50 % by volume of coarse RCA by recycled
crushed brick aggregate. Chen et al. ( 2003 ) observed little effect of brick and tile
content in RCA on the concrete's CS if the ratio was \67 % (Fig. 5.14 ). The use
of unwashed RCA had some effect on the CS of RCAC due to the presence of
powdery impurities and other harmful materials; the effect of impurities on the CS
of RCAC was observed prominently at lower w/c. Gomes and de Brito ( 2009 )
observed an insignificant CS loss due to the simultaneous incorporation of recy-
cled brick and mortar, up to a maximum ratio of 25 % brick-mortar mix and 50 %
RCA, or the incorporation of 100 % RCA, by comparison with conventional
concrete with natural aggregates only.
A beneficial effect of RCA on the strength performance was observed when the
RCAC was subjected to dry curing conditions due to the higher water absorption
capacity of RCA. Buyle-Buddin and Zaharieva ( 2002 ) observed lower CS by
around 9-12 % and 3-6 % for conventional and RCA concrete with 100 %
replacement of fine and coarse natural aggregate by same size RCA respectively,
when the curing conditions for both concrete were changed from water curing to
air curing. The water absorbed by fine RCA gradually made its way to the cement
paste and compensated the water loss of cement paste due to air-drying. On the
other hand, Rao et al. ( 2011 ) observed higher CS for partially moist cured followed
by air-cured RCAC than for moist cured similar RCAC (Fig. 5.15 ). The possible
cause was the higher free water content in the old ITZ of moist cured concrete,
which weakens the ITZ and therefore lowered the CS. Fonseca et al. ( 2011 ) did not
observe any significant changes in CS due to variation of curing conditions. In this
study, after casting, the concrete mixes were subjected to four curing conditions:
(1) laboratory environment; (2) outer environment (atmospheric condition); (3)
wet chamber; (4) water immersion.
Razaqpur et al. ( 2010 ) evaluated the CS of RCAC, prepared by using a new
mixing method (equivalent mortar volume, EMV method). In this method, the
amount of residual mortar present in RCA was included in the total amount of
mortar present in RCAC. The total amount of mortar in RCAC was equivalent to
the mortar amount present in the control concrete. The CS of concrete containing
Fig. 5.14 Effect of brick and
tile content in RCA on the CS
of RCAC (Chen et al. 2003 )