Use of Construction and Demolition Waste as Aggregate: Properties of Concrete - Recycled Aggregate in Concrete - page 317

5.4.2.3 Gas Permeability

The gas permeability performance of concrete with CDW aggregate is also
reported in the literature. Results are available for several types of gases: air,
oxygen, nitrogen.
Kwan et al. ( 2012 ) determined the intrinsic permeability of concrete containing
various percentages of coarse RCA by using nitrogen gas penetration. They
observed a gradual increase in intrinsic permeability of concrete with the content
of coarse RCA and the curing time. The difference in permeability between
conventional concrete and RCAC decreased with the curing period. They also
observed a parabolic inverse relationship between CS and intrinsic permeability,
from which they concluded that concrete would achieve a constant permeability as
the maturity of concrete increased. Limbachiya et al. ( 2000 ) did not observe any
effect of 30 % replacement of coarse NA by RCA on the intrinsic air-permeability
performance of three classes of high-strength concrete with design strength of 50,
60 and 70 MPa. Air permeability increased with RCA content but decreased with
design strength. The increase of air permeability of concrete due to the incorpo-
ration of RCA was attributed to the increase of cement paste content as more
cement was added to reach the design strength of concrete.
Buyle-Bodin and Zaharieva ( 2002 ) observed lower air permeability of concrete
with complete replacement of coarse NA by RCA than that of concrete with RCA
as complete replacement of fine and coarse aggregates (Table 5.24 ). Similarly,
both types of concrete and conventional concrete as well exhibited considerably
lower air permeability after water curing than after air curing. Zaharieva et al.
( 2003 ) observed that pre-soaking of RCA can improve the air permeability of
concrete as dry aggregate can absorb hydrating water and therefore can hinder the
hydration reaction. The air permeability of NAC and RCAC increased significantly
due to an increase in pre-treatment temperature i.e. oven drying of concrete
specimens at different temperatures after curing (Fig. 5.77 ).
Gonçalves et al. ( 2004 ) found a significant increase in oxygen permeability of
concrete due to the replacement of coarse NA by RCA. Permeability as well as the
difference of permeability between conventional concrete and RCAC decreased
with the cement content in concrete due to a cut in porosity. These results are
presented in Fig. 5.78 .
Olorunsogo and Padayachee ( 2002 ) evaluated the oxygen permeability of
concrete various replacement ratios of coarse NA by RCA. They presented their
results in terms of oxygen permeability index (OPI), which is defined as the

Table 5.24 Air permeability of concrete containing RCA and conventional concrete at various
experimental conditions (Buyle-Bodin and Zaharieva 2002 )
Concrete type Conventional RCAC with RCA as the

only coarse aggregate

RCAC with RCA only
(coarse and fine)

Curing condition Water Air Water Air Water Air

Air permeability (910 -18 )m 2 6.00 20.0 2.80 3.10 1.04 1.45