Evaluation of silicon-based strengthening agents on porous limestones

Deteriorated porous bioclastic limestones from the archaeological area of Aptera, Crete, Greece, were treated with silicon-based strengthening products, tetraethoxysilanes, elastified silicic acid ethyl esters, an aqueous colloidal dispersion of silica particles, as well as an oligomeric siloxane water repellent. Changes in color, water vapor permeability, water absorption by capillary suction, porosity and pore size distribution were evaluated after treatment. Energy dispersive X-ray fluorescence and Fourier transform infrared spectroscopy indicate the penetration depth of the applied products. The effectiveness of strengthening was also evaluated by measuring the tensile strength. The pore size distribution was insignificantly modified decreasing only the ratio of coarse pores. The applied products penetrated up to a depth of 30 mm. All the studied products create linkages across the interface between calcite and the alkoxysilanes-derived gels, due to the hydroxyl groups of the quartz included in the limestones. Better reinforcing results were obtained by applying the elastified silicic acid ethyl ester. The elastified silicic acid ethyl ester confers chromatic stability on the stone, shows insignificant modification of the water vapor permeability and reduces the absorbed quantity of water.