Abstract: Moisture diffusivity of alkali activated aluminosilicate composite with electrical porcelain aggregates is determined as function of thermal loading up to 1200°C using two different methods. The first method is based on the sorptivity concept and provides a single moisture diffusivity value which can be considered as apparent moisture diffusivity. The second method consists in inverse analysis of moisture profiles measured for characteristic times in a 1-D experiment with simple initial and boundary conditions. It makes possible to determine moisture diffusivity as function of moisture content. Experimental results show that the moisture diffusivity depends on previous thermal load in a very significant way. One-order-of-magnitude increase in moisture diffusivity is observed after heating to 1200°C compared to reference specimens.