The effect of activator ratio on the thermal and hygric properties of aerated geopolymers

Studies on the factors that influence the thermal and hygric performance of aerated geopolymers are limited. One key factor that affects their hygrothermal performance is the activator ratio. In this work, the effect of the activator ratio on the thermal conductivity, porosity, moisture buffer capacity, vapor permeability, and adsorption-desorption isotherms of geopolymers is investigated. The moisture buffer capacity of the samples ranged from 4.32 to 5.20 g/(m2%RH). The moisture inertia of the specimens increased with increasing silicate content but only until a certain critical threshold. This is attributed to an increase in the number of pore networks. The decrease in moisture buffer capacity with a further increase in water glass is because the viscid system prevents the colloidal reaction. This results in unreacted material, desperate geopolymeric agglomerates, and sodium carbonate in the pores. Moreover, a large amount of silicon prevents structural reorganization during the condensation stage of geopolymerization and decreases the formation of capillary pore networks. The vapor permeability of the samples also follows a decreasing trend with increasing sodium hydroxide in the reaction mixture. This is because the resulting matrix becomes less porous as the reaction moisture becomes more alkaline. In addition, the negative impact of efflorescence on the moisture buffer capacity and vapor permeability becomes significant as the hydroxide content increases. The highly hydrophilic crystalline salt that forms because of carbonation inhibits moisture transport. According to the absorption-desorption isotherms the specimens have meso and macro porous microstructure. The isotherms also indicated that alkalinity facilitates the formation of a continuous geopolymer matrix and the decomposition of the foaming agent. This increased the moisture capacity and macro porosity of the samples.