Variation in the sulfate attack resistance of iron rich-phosphoaluminate cement with mineral admixtures subjected to a Na2SO4 solution

Abstract

Phosphoaluminate cement (PAC) has excellent resistance to sulfate attack due to its unique hydration product and dense hardened matrix. Mineral admixtures (MAs) are also known to enhance the performance of conventional cementitious systems. Thus, in this study, the effects of three kinds of admixtures (limestone powder, fly ash and gypsum) on the performance of iron rich-phosphoaluminate cement (IR-PAC) against sulfate attack were analysed using XRD, MIP, DSC and MTS to examine any synergistic effects resulting from their combination. The results indicated that excessive limestone powder incorporation (more than 9%) was detrimental to the IR-PAC performance. The addition of fly ash resulted in fluctuation of the flexural strength of the mortar due to the reduction in cement content and the micro-aggregate action of fly ash particles. The resistance coefficient of the IR-PAC mortars (against sulfate attack) with fly ash replacement of 9% (by weight) at 90 d could reach 1.13–1.16, and at a 12% replacement, the value could even reach 1.12. The addition of gypsum could transform etched components in IR-PAC mortar into ettringite in the early stage of cement hydration. As a result, the IR-PAC could maintain the stability of its own components under external sulfate erosion. However, excessive gypsum at the expense of cement would cause a decrease in the strength of the mortar and result in a slight reduction in the sulfate attack resistance coefficient.