Chloride ion penetration in concrete is one of the major causes of deterioration of reinforced concrete structures by depassivation of reinforcing bars. Since testing of the natural chloride penetration is time consuming, utilising an accelerated test method is more desirable. Surface resistivity (SR) test is increasingly being used, due to its relative speed and ease of performing combined with the non-destructive nature, to assess the permeability of concrete and its resistance to chloride ion penetration. The test has been standardised as AASHTO TP 95 which consists of measuring the resistivity of water-saturated concrete cylinders using a four-pin Wenner probe array.
This paper present the results of an experimental investigation on the surface resistivity (SR) of a low-calcium fly ash-based geopolymer concrete (GPC). SR test results show that the resistivity of GPC samples are very low, this does not necessarily mean that they are having a high level of chloride penetrability since the AASHTO TP 95 limits are only applicable for conventional OPC concrete and not for the GPC. In case of geopolymer concrete, there are a large amount of mobile metallic ions such as Na+ in the pore solution which could probably affect the resistivity test measurements. A further study is required to directly measure the chloride permeability of the GPC such as natural diffusion or ponding test to be able to properly correlate the surface resistivity measurements of GPC to its actual chloride permeability level.