With regards to the effect of NH concentration on chloride
penetration depth, the results showed that the chloride penetration
depth decreased with the increasing NH concentration for
both GL and GR concretes. The reduction in chloride penetration
depth from 8 to 12 M NH was higher than that from 12 to 16 M.
For example, the chloride penetration depth at 90 days immersion
of GL with 8 and 12 M NH were 39.0 and 21.0 mm; while the 16 M
NH concrete was 18.9 mm. The result was consistent with
Chindaprasirt and Chalee (2014) who reported that the increase
NH concentration resulted in decreasing chloride diffusion and
steel corrosion in geopolymer concrete. A number of researchers
(Mikuni et al., 2007; Li et al., 2011) indicated that the dissolution
of Si and Al in fly ash increased with increased NH solution concentration.
The higher amount of dissolved Si and Al produced a
better polycondensation reaction in geopolymer matrix and
reduced porosity and chloride ingression. Fig. 10 shows the
boundaries of chloride penetration depths of GC for 30 and 120
days of immersion.