Use of Construction and Demolition Waste as Aggregate: Properties of Concrete - Recycled Aggregate in Concrete - page 318

Fig. 5.77 Air permeability
of NAC and RCAC at various
pre-treatment temperatures
(Zaharieva et al. 2003 )
Fig. 5.78 Oxygen
permeability of conventional
and RCAC's with various
cement contents (Gonçalves
et al. 2004 )
negative logarithm of oxygen permeability coefficient. They observed a gradual
decrease of OPI as the replacement of NA by RCA increased; however, the
increase in OPI of RCAC's with respect to the curing time was similar to that of
conventional concrete. After 56 days of curing, the OPI of conventional concrete
was 10 % higher than that of the RCAC with 100 % RCA. These results are
presented in Fig. 5.79 . The concrete mixes containing 0, 50 and 100 % coarse
RCA after 56 days of curing can be considered as excellent, good and poor,
respectively, according to the Alexander et al.'s ( 1999 ) classification (Table 5.21 ).
5.4.3 Depth of Carbonation
In a reinforced concrete structure, the steel reinforcement is chemically protected
from corrosion by a passive oxide layer due to the presence of the surrounding
alkaline environment. However, with time and in the presence of other chemical
and physical factors, the alkali content in concrete gradually decreases due to the
carbonation of concrete by atmospheric carbon dioxide and therefore the corrosion