Evaluating the use of accelerated test methods for chloride transport in alkali activated slag concretes using electrical impedance and associated models

The applicability of accelerated chloride transport test methods, viz., the rapid chloride permeability (RCP) and non-steady state migration (NSSM) tests, commonly used for conventional concretes, for alkali activated slag concrete systems is evaluated in this paper. Both powder and liquid sodium silicate activators are used to activate slag. The effects of changing the total Na20 content and the activator modulus of both the powder and liquid activators on the RCP and NSSM values are reported. RCP values of activated slag concretes show that these concretes perform better than conventional concretes. However, NSSM tests provide values that are comparable to conventional concretes either with or without high performance cement replacement materials such as silica fume. Pore structural studies show that the water glass activated concretes have lower porosities than the powder sodium silicate activated mixtures, but their critical pore sizes are larger, resulting in reduced transport resistance. Electrical circuit models are implemented on the impedance spectroscopic response of alkali activated and conventional concretes. The modeled circuit model parameters are similar for the alkali activated and conventional concretes. Moreover, the changes to these parameters induced by the NSSM test are similar in trends and magnitudes for both alkali activated and conventional concretes, demonstrating the adequacy of the test method for alkali activated binders.