Sulfate Resistance of Nanosilica and Microsilica Contained Mortars

Presented is a side-by-side comparison study intended to identify the effects of nanosilica (nS) on chemical sulfate attack resistance of portland cement (PC) mortars and its effectiveness in comparison to similar replacement levels of the more widely implemented microsilica (mS). Several mortar mixtures were prepared with a 4.1 and 7.2% tricalcium aluminate (C(3)A) PC by progressive cement replacement with nS or mS. The mortars tested were measured for expansion, compressive strength, and mass loss. Results indicated that nS replacement benefited the studied mortars. However, in the dry powder form and method of mixing used in this study, poor dispersion and agglomeration of the nS was suspected to hinder mortar permeability in comparison to mS and low-C(3)A cement mortars. Replacement with nS in aqueous dispersion, however, proved to be significantly more effective than equivalent replacement of dry powder nS and mS.