Properties of fly ash blended magnesium potassium phosphate cement cured in presence of sulfuric acid

Abstract

Magnesium potassium phosphate cement (MKPC) is a new fast hardening and high strength cementitious material, which have attracted more attention in the field of repair and reinforcement for damaged concrete structures due to aggressive aqueous environments. The performance of MKPCs under severe environment are however not be sufficiently investigated. In this work, the effect of fly ash (FA) on the compressive strength development and micro-characteristics of the plain MKPC and FA/MKPC cured for a short of time and then exposed to air/water/sulfuric acid solution, were systematically investigated. The results show that, FA replacement ranges from 25% to 35% is beneficial to the sulfuric acid resistance properties of the MKPCs, in light of the compressive strength retention ratio and compressive strength. The acidic environment obtained by adding the sulfuric acid altered the reaction path of the plain MKPCs and FA/MKPCs with the probable formation of products not identified in the present work, which was detrimental to the properties of MKPC. In the presence of appropriate pH, Mg tends to be trapped to form precipitation of MgSO3·H2O. However, the MgSO3·H2O is quite instable which tends to destabilize when the environment changes. When the plain MKPCs were exposed to sulfuric acid solution, sheet-like crystal groups which were composed of acicular-like crystals, formed and intermixed at the surface of a compact structure.