Durability of very high volume fly ash cement pastes and mortars in aggressive solutions

The resistance of very high volume fly ash cement pastes and mortars activated by Na2SO4 has been monitored following immersion for up to 90 d in 0.1 M HCl, 4.4% Na2SO4 and ASTM-compliant sea water. Changes in the compressive strengths of mortars and in crystalline phases, bond environments, and the microstructure of pastes following immersion were monitored. Experiments were repeated with a commercially available sulfate resistant cement. Both cements were found to present adequate resistance to both sea water and the Na2SO4 solution. However, both were severely degraded by acid immersion. Differences in potential degradation mechanisms based on the chemistry of the fly ash binder and the reference cement are discussed.