Page 546 - New Trends in Eco efficient and Recycled Concrete

494 New Trends in Eco-efficient and Recycled Concrete

16.3.6.2 Permeability of RAC versus with water absorption

Fig. 16.14 illustrates the relationship between the water absorption values of RAC
and the permeability indicators (bulk electrical conductivity, chloride-ion penetra-
tion and gas permeability). The major results can be summarised as follows: (1)
with increasing amount of NRCAs in RAC, the values of the permeability indica-
tors gradually increased; and (2) the permeability of the RAC decreased with the
use of the C-NRCAs. Moreover, a general trend is that all the permeability indica-
tors had good correlations with the water absorption values of RAC. It can be con-
cluded that the water absorption value of RAC tested in this study may be
considered as a good criterion to indicate the permeability of RAC.

16.3.7 Performance improvement of RAC prepared with
C-NRCAs

Table 16.3 lists the improvement of RAC prepared with 100% C-NRCAs. It can be
observed that the improvement on static compressive strength and flexural strength
was 22.6% and 28.7%, respectively. For durability, the improvement was 17.3%,
15.1%, 36.4% and 42.4% for water absorption, bulk electrical conductivity, chloride
permeability and gas permeability, respectively. These improvements should be
mainly attributed to the enhancement of NRCAs as well as the ITZ improvement in
the RAC.
However, the permeability of RAC prepared with the C-NRCAs is still not
comparable to that of the reference concrete prepared with NAs. In order to

Table 16.3 Improvement in mechanical properties and permeability of RAC prepared with
C-NRCAs
RAC RAC Improvement
prepared prepared due to
Performance
with with carbonation
NRCAs C-NRCAs (%)
Mechanical Static compressive 38.6 47.3 22.6
strength (MPa)
Flexural strength 3.2 4.1 28.7
(MPa)
Durability Water absorption (%) 8.8 7.5 14.8
Bulk electrical 25.2 21.4 15.1
conductivity (mS/m)
Chloride-ion 9440 6003 36.4
permeability
(coulombs)
2
Gas permeability (m ) 22.1 12.7 42.4
RAC, Recycled aggregate concrete.