Physical changes of porous Hungarian limestones related to silicic acid ester consolidant treatments

Abstract

AbstractPorous limestones are widely used in the monuments of Hungary, and are often treated using stone consolidants on site during restoration works. Two types of porous Miocene limestones from Sóskút were treated with dilute and concentrated silicic acid ester under laboratory conditions. The aim of the experiments was to assess the performance of the consolidants of different concentrations on fine- and medium-grained limestones, and to detect physical changes caused by consolidation. The pore-size distribution and fabric of the limestones were also different with initial porosities of 37 and 23%, respectively. In the open pores only a few per cent (3.2–5.2%) of silica gel was precipitated even under vacuum saturation. The loss of porosity was higher when concentrated consolidant was used. The decrease in porosity was found not to be proportional to the changes in strength. Indeed, the dilute consolidant caused a greater increase in strength than the concentrated one. The increase of tensile strength was higher for the less porous medium-grained limestone than for the fine-grained one. The differences in strength between non-consolidated and treated specimens were also detectable using ultrasonic pulse velocities. The tests have shown that the efficacy of silica acid ester treatments in terms of strength is less influenced by the concentration of the consolidant, but rather its ability to reach the micropores of porous limestones.