This research studied the effect of sodium
hydroxide (NaOH) concentrations on chloride penetration
and chloride binding capacity of fly ashbased
geopolymer concretes. The geopolymer concrete
were prepared from Mae Moh fly ash with sodium
silicate (Na2SiO3) and sodium hydroxide (NaOH)
solutions. The concentration of NaOH was varied at
8, 10, 12, and 14 molar and the Si/Al ratio was kept
constant at 1.98. The 200-mm geopolymer concrete
cube specimens were cast. The specimens were
cured in air for 28 days then were exposed to tidal
zone of marine environment for 180 days. Subsequently,
the specimens were tested to determine the total
(acid soluble chloride) and free (water soluble chloride)
chloride contents in geopolymer concrete. A regression
analysis of investigated data was carried out and
Ficks second law of diffusion was applied to calculate
the chloride diffusion coefficient (Dc). In addition,
the chloride binding capacity was analysed in term
of percentage chloride binding capacity compared to
the total chloride content. The results showed that
chloride penetration and chloride diffusion coefficients
of geopolymer concrete significantly decreased with
an increase in concentration of NaOH. It was also
found that the percentage of chloride binding capacity
compared to total chloride content increased with an
increase of NaOH concentration in the fly ash-based
geopolymer concrete.