Evaluation of moisture diffusion characteristics and the effect of moisture treatment on flexural properties of expanded perlite-based building material

The expanded perlite-based building material for drywall application consisting of sodium silicate solution as a binder was manufactured by varying the degree of compaction and sodium silicate content to investigate moisture diffusion behavior and the effect of moisture treatment on flexural properties of the composites. Moisture treatment was conducted on specimens in a climatic chamber at a temperature of 37°C and a relative humidity of 90% until saturation. Results show that moisture absorption decreased with increasing compaction ratio for a constant sodium silicate content in binder and increased with increasing sodium silicate content in binder for a constant compaction ratio. A range of volume fractions of solid sodium silicate in the foam is identified, in which the fully Fickian diffusion gradually transformed to non-Fickian diffusion as sodium silicate content in foam increased. The concentration-dependent diffusion method was found to be suitable to explain this behavior. The moisture diffusion below this transition range showed an entirely Fickian diffusion and changed to concentration-dependent diffusion above the range. As a result of moisture treatment, the flexural strength of medium density foams was decreased but the lowest- and highest-density foams were not affected while the flexural modulus was increased only for the highest density foam and no significant effects were seen in other cases. The bending failure mechanism of the composite was not affected by the moisture treatment.