The effects of the different curing conditions and the role of added aggregate in the strength of repair mortars

Four ready-mix commercial available repair mortars—that are used for porous limestone repair—were studied under different laboratory conditions. To have better compatibility with porous limestone, not only pure mortars but also mortars with 50 wt% of limestone aggregate was tested. The reason why limestone aggregate was added to mortar was to modify the strength and porosity. Samples kept under climate control, dry and humid conditions were tested to understand the influence of environmental conditions. The bulk density and uniaxial compressive strength of cubic specimens were measured 3, 7, 14, 28 and 90 days after casting. The microscopic analyses revealed that tested repair mortars contain Portland cement and also non-hydrated cement particles even after curing. The strength of mortars in time does not show similar changes; however, specimens kept under dry conditions show the lowest strength 90 days after casting. High humidity leads to lower strength than normal humidity for tested mortars, but there is one mortar with added limestone aggregate, which has higher strength under humid conditions. In general, adding 50% of porous limestone aggregate reduced the strength and increased the density of repair mortars kept in climate chamber. Limestone aggregate that has larger pores causes a shift in effective pore radii toward smaller pores of 50% limestone aggregate mortar mixtures compared to pure mortars, with one exception. Tests results indicate that these commercially available repair mortars, even though they are suggested to be used for porous limestone, behave very differently under different environmental conditions and that adding limestone aggregate do not shift properties of the mortars toward appropriate compatibility.