Role of pore size distribution in salt uptake, damage, and predicting salt susceptibility of eight types of Japanese building stones

Eight widely used Japanese building stones were subjected to crystallization attacks by three types of destructive salts to investigate whether it is possible to estimate durability of the stones solely from their pore characteristics. The influence of pore size and their distribution on salt uptake and salt crystallization damage was also evaluated. Total porosity was found to have a significant effect on the amount of salt absorbed and of damage induced. Five different upper limits of microporosity were considered in order to evaluate their relative influences on salt crystallization damage. The experimental results corroborate the theoretical supposition that micropores smaller than 0.05 (also 0.1) µm in radius are a critical influence on salt crystallization damage. However, pores smaller than 5 µm are more important in liquid absorption in the impregnation-drying type of salt weathering test, as confirmed by the pore size distributions of pre- and post-experiment specimens. Moreover, these pores seem to act synergistically with smaller micropores in inducing crystallization damage. The results indicate that pore size distribution plays a very important role in both salt uptake and salt damage processes. Based on these pore characteristics, which can readily be obtained from a single mercury porosimetry measurement, a durability estimator called salt susceptibility index (SSI) is proposed. The estimated outcomes correlate significantly with the actual dry weight loss of the rocks tested.