Sacrificial mortars for surface desalination

Abstract

Four absorbent mortars were designed in this study and used as sacrificial desalinating media. The mortars comprised lime, sepiolite, nanosilica (72/3/25 by weight) and three admixtures (H2O2 and two commercial aerators) and had a liquid/solid ratio of 0.9, a mean porosity of 40% and a mean pore size of 0.8–0.7 μm. These mortars were applied three times to ashlars exhibiting surface saline efflorescence on a church at Talamanca del Jarama, a town in the Spanish province of Madrid. The salts impregnating the wall were characterised with XRD, FTIR and Micro-Raman spectroscopy. The ion concentrations in the ashlars was studied with ion chromatography at 0.5 cm, 1.5 cm and 3.0 cm from the surface after each application and the inner and outer surfaces of the mortars were analysed with Micro-Raman spectroscopy to determine the desalinating efficacy of the mortars.The mortars designed mobilised and absorbed the soluble salts in the ashlars; as a rule, elimination was most effective in anions with a smaller ionic volume and therefore greater ionic mobility and when the salt concentration was high and superficially located. Three years after application of the desalinating mortars, the salt concentration in the ashlars treated was 50% lower than prior to treatment.