Use of Construction and Demolition Waste as Aggregate: Properties of Concrete - Recycled Aggregate in Concrete - page 320

Fig. 5.80 Carbonation depth
of concrete versus
replacement ratio of fine NA
by fine RCA (Evangelista and
de Brito 2010 )

20 weeks to a carbon dioxide atmosphere at 20 C and 55 % room humidity.
Gomes and de Brito ( 2009 ) observed higher carbon dioxide penetration depth in
concrete with coarse RCA or coarse CBMRA than in conventional concrete
(Table 5.24 ). Evangelista and de Brito ( 2010 ) observed a linear increase of car-
bonation depth with the replacement ratio of fine NA by fine RCA similarly to the
capillary water absorption and chloride permeability performances (Fig. 5.80 ).
Zega and Di Miao ( 2011 ) observed similar carbonation depth of NAC and
RCAC's prepared by replacing 20 and 30 % by volume of fine NA by fine RCA,
when concrete was exposed for 620 days to urban-industrial environmental con-
ditions. Shayan and Xu ( 2003 ) observed comparable depth of carbonation of
conventional concrete and RCAC with coarse RCA as full replacement of coarse
NA or fine RCA as 50 % replacement of fine NA, even though a marginally higher
carbonation depth was observed in concrete containing fine RCA. However, the
use of sodium silicate and lime treated coarse or fine RCA significantly increased
the depth of carbonation of the resulting concrete.
Sagoe-Crentsil et al. ( 2001 ) observed higher carbonation depth in concrete with
RCA as complete replacement of coarse NA than in conventional concrete. The
use of slag cement or a 5 % increase in cement content can decrease the car-
bonation depth of the RCAC, which was more pronounced for RCAC with higher
cement content (Fig. 5.81 ).
Buyle-Bodin and Zaharieva ( 2002 ) observed significantly higher carbon pen-
etration depth of concrete due to the complete replacement of coarse and fine NA
by RCA (Fig. 5.82 a). The carbonation depth of water cured RCAC was around
half that of air-cured RCAC. They also observed that the kinetics of carbonation
for conventional concrete and RCAC can both be designed according to basic law
of diffusion (Fig. 5.82 b):

p t

x ¼ C

where, x, C and t are depth, rate and time of carbonation.
Razaqpur et al. ( 2010 ) observed comparable or even lower carbonation depth in
RCAC prepared by mixing two methods (conventional and EMV) than in