Length change behavior of autoclaved aerated concrete at various relative humidity: Comparison between Japanese and Vietnamese AACs

This paper presents an experimental study on the sorption isotherm and length change behavior of autoclaved aerated concrete (AAC) in both desorption and adsorption processes. Two types of Vietnamese AAC and one type of Japanese AAC with different pore size distributions were used for the tests. The experimental results show that the length change strain of AAC during the adsorption process is mostly larger than that in the first desorption process even though the water content in the adsorption process is lower. Interestingly, a clear expansion in the desorption process at relative humidity (RH) from about 90% to 65% is observed in Japanese AAC but not in Vietnamese AACs; and a significant shrinkage hysteresis at high RH (RH > 65%) is observed in all types of AAC. Both of these behaviors can be explained by capillary tension model taking into account the effect of pore size distribution of each AAC and the explanation is further supported by the reduction of shrinkage in desorption process of AACs that are immersed in solution with shrinkage reducing agent. In addition, the surface energy model is applied to explain the length change during the adsorption process and at lower RH in desorption process for all types of AAC.