High-Calcium Bottom Ash Geopolymer: Sorptivity, Pore Size, and Resistance to Sodium Sulfate Attack

Abstract

The resistance to sulfate attack, compressive strength, sorptivity, and pore size of high-calcium bottom ash geopolymer mortars were studied. Ground lignite bottom ashes (BAs) with median particle sizes of 16, 25, and 32 μm were used. NaOH, sodium silicate, and temperature curing were used to activate the geopolymerization. Results showed that relatively high strengths of 40.0–54.5 MPa were obtained for the high-calcium bottom ash geopolymer mortars. The use of fine BA improved the strength and resistance to sulfate attack of mortars. The good performances were attributable to the high degree of reaction of fine BA and the associated low amount of large pores (0.05–100 μm) compared with those of coarse BA. The incorporation of water improved the workability of mixes, and the compressive strength, sorptivity, and resistance to sulfate attack decreased due to the increase in large pores.