Use of Construction and Demolition Waste as Aggregate: Properties of Concrete - Recycled Aggregate in Concrete - page 240

5.3 Hardened Concrete Properties
As the properties of CDW aggregate are significantly different from those of NA,
the various hardened properties of conventional concrete change with the addition
of CDW aggregate. In this section, the hardened properties of concrete containing
various types of CDW aggregate are discussed from information available in
various references. As indicated in the introductory section, a similar terminology
(RA and RCA) will be used to indicate recycled aggregate with different origin.
5.3.1 Compressive Strength
In this section, the compressive strength (CS) of concrete containing CDW
aggregate (both RA and RCA) is highlighted. Results will be analysed in terms of
size and composition of CDW aggregate. The relationship with fresh properties is
also presented.
Normally, the CS of concrete decreases with the addition of CDW aggregate
(Oliveira and Vazquez 1996 ; Dhir et al. 1999 ; Topçu and Sengal 2004 ) and the
reduction in strength can reach 40 % (Katz 2003 ; Chen et al. 2003 ). In some
studies, it was pointed out that the reduction in CS was between 12 and 25 %,
when 25-30 % (Corinaldesi 2011 ; Etxeberria et al. 2007a ) or 100 % NA was
replaced by CDW aggregate (Li et al. 2009 ; Rahal 2007 ; Safiuddin et al. 2011 ).
However, a negligible influence is observed when the coarse or fine recycled
aggregate is used to replace up to 30 % of coarse NA (Gomez-Soberon 2002 ;Li
et al. 2009 ; Limbachiya et al. 2004 , 2012 ; Rao et al. 2011 ; Yang et al. 2011 )or
20 % of fine NA (Dhir et al. 1999 ), respectively. Some typical results are presented
in Table 5.9 . An increase in concrete porosity due to the addition of CDW
aggregate (due to old mortar content) and weak aggregate-matrix interface bond
are the major reasons for the reduction in CS of CDW aggregate concrete (Kwan
et al. 2012 ).
The reduction in CS due to the addition of CDW aggregate can be controlled by
changing various factors of the concrete mix such as adjusting the water to cement
ratio, changing the mixing procedure, treating the aggregate and using a mineral
addition. The information gathered so far on the use of CDW aggregate in concrete
shows that modifications in the concrete mixing procedure are the key step to
develop a good quality concrete containing any type of CDW aggregate.
Etxeberria et al. ( 2007a ) observed that the 28-day CS of concrete made with
100 % coarse RA (RAC) was 20-25 % lower than that of conventional concrete.
A similar trend was reported by other researchers (Gonzalez-Fonteboa and Martinez-
Abella 2005 ; Sani et al. 2005 ). Sani et al. ( 2005 ) observed about 40 % lower 90-day
CS in RAC than in conventional concrete due to the incorporation of RA as complete
replacement of coarse and fine aggregates. The mix was prepared with the
same cement content and water to cement ratio without using any water-reducing