The relationship between water absorption, volume of permeable
voids and NH concentration of GCs are presented in Fig. 5. The
water absorption of GL and GR varied in a narrowrange of 5.3e6.5%
and 9.6e11.2%, while the volume of permeable voids were
14.5e17.5% and 22.1e25.3%. The water absorptions of geopolymer
concrete in this study were nearly the same as 5.8e7.1% of selfcompacting
concrete (Siddique, 2013). The use of 12 M NH
seemed to give low water absorption and volume of permeable
void as shown in Fig. 5(a) and 5 (b). The low water absorption and
volume of permeable void are mainly influenced by the denseness
and limited open porosity of the matrix. The high compressive
strength of GC was related to the low water absorption and volume
of permeable void. The use of RCA in fly ash based geopolymer
concrete gave higher water absorption and volume of permeable
void than those with LS. This was due to the high porosity from
attached mortar of RCA particle which served as a potential conduit
for water transport in the matrices.
As shown in Fig. 6, the relationship between volume of
permeable void and water absorption of GC in this study gave a
good correlation. As the water absorption increased, the volume of
permeable void also increased correspondingly. This result is in the
same direction of that of Portland cement concrete reported by
Dinakar et al. (2008).
Fig. 7 shows the effect of NH concentration on the sorptivity of
geopolymer concrete containing RCA compared with natural
aggregate. The geopolymer concrete containing RCA exhibited
higher sorptivity than that with LS. The lowest sorptivity was
6 103 and 15 103 mm/s1/2 for GL12 and GR12 concretes.
These results were in the line with water absorption and volume of
permeable void results. In addition, the correlation between
compressive strength and sorptivity were very good with a correlation
coefficient (R2) of 0.92 as shown in Fig. 8. The high
compressive strength concretes showed low sorptivity.