Page 544 - New Trends in Eco efficient and Recycled Concrete

492 New Trends in Eco-efficient and Recycled Concrete

For the water absorption value, it was calculated based on the saturated surface

dry and oven-dried mass (at 105 C for 24 h) of the RAC cylinders with the size of
Φ100 3 200 mm after 56 days curing in water. The bulk electrical conductivity of
the concrete specimen was determined in accordance with ASTM C1760-12. The
chloride penetrability of RAC was tested in accordance with ASTM C1202 using a
Φ100 3 50 mm concrete disk, which was cut from the cylindrical specimens of
Φ100 3 200 mm. The gas permeability test was carried out on the basis of the
Darcy’s law by a gas permeability tester. In general, the permeability of concrete is
related to its porosity and pore size distribution. The porosity and pore size distribu-
tion of the tested concrete were also measured by a mercury intrusion porosimeter
(MIP).

16.3.6.1 Water absorption values versus porosity of RAC
Fig. 16.12 shows the water absorption values of RAC prepared with different types
of NRCAs. With the increase of NRCAs, the water absorption values of RAC line-
arly increased. The RAC prepared with 100% non-carbonated NRCAs was approxi-
mately two times higher than that of the reference normal concrete. It was also
observed that when the C-NRCAs were used, the water absorption value was signif-
icantly decreased by about 6% 15%, depending on the replacement level of C-
NRCAs. This should be mainly attributed to the reduction in the porosity of
NRCAs after carbonation.
The total porosities of the tested concrete specimens were measured by MIP as
shown in Fig. 16.13. It can be observed that the RAC prepared with the C-NRCAs
had a significantly lower porosity compared with that of the non-carbonated
NRCAs, in particular for NRCA replacement levels of higher than 20%. It is known
that the water absorption of RCAs is influenced by the porosity of concrete.

Figure 16.12 Water absorption values of RAC prepared with NRCAs. RAC, Recycled
aggregate concrete.