Use of Construction and Demolition Waste as Aggregate: Properties of Concrete - Recycled Aggregate in Concrete - page 264

Fig. 5.25 STS versus total
porosity curve of RCAC
(Gomez-Soberon 2002 )
The presence of impurities in RCA such as crushed clay brick and tiles has
positive or negative effects on the STS of resulting RCAC depending on the
substitution ratio. Yang et al. ( 2011 ) observed lower 7- and 28-day STS in RCAC
prepared by replacing 20 and 50 % of RCA by crushed brick than in conventional
RCAC (Fig. 5.26 ), owing to the higher porosity of crushed brick aggregate than of
RCA. In crushed brick containing concrete, most of the tensile failures occurred
within the crushed brick particles while for other mixes, failure seemed to occur
between the aggregate and the mortar matrix interfaces. The STS of concrete
paving blocks containing RCA decreased with increasing replacement of fine or
coarse RCA by crushed clay brick in the Poon and Chan ( 2006 ) study too. Kou
et al. ( 2011a ) also observed lower STS for RAC than for RCAC especially at the
later stages of hydration.
However, Poon and Chan ( 2007 ) observed higher STS in concrete paving
blocks due to the 10 % replacement of RCA by crushed tiles or a 1:1 mixture of
crushed tiles and bricks. Mixing crushed glass with tiles or tiles/bricks gave
strength comparable to that of conventional RCA concrete. On the other hand, the
addition of crushed wood drastically lowered the STS. Strengthening of the
Fig. 5.26 Effect of crushed
brick content in RCA on the
STS performance (Yang et al.
2011 )