Study of durability of Portland cement mortars blended with silica nanoparticles

•There are few studies on mortars of OPC/NS exposed to aggressive agents.•NS diminished the total volume of pores, especially capillary pores.•NS helped in the formation of pores with diameter below 10nm.•NS improved compressive strength significantly in samples with 10wt.% of NS.•NS controlled the expansion under MgSO4 attack. In this paper the effects of nanosilica (NS) on porosity, capillary suction (UNE 8398:2008), compressive strength (ASTM C 349), and sulfate resistance (ASTM C 1012) were evaluated for mortars made with Portland cement (control) and partially replaced with a commercial NS suspension, in percentages by weight of 0%, 1%, 3%, 5%, and 10%. Mortars with a water/binder (w/b) ratio of 0.55 and addition of superplasticizer, for flow correction, were prepared. NS showed that, it has an important role in pore refining, decreasing the total volume of pores and their diameters. Samples containing NS showed an important positive effect on the capillary suction and sulfate resistance. In the case of expansion due to sulfate attack, mortars with 5% and 10% of NS decreased expansion by 90% and 95% respectively after 2years of immersion.