Improving the Durability of Lime Finishing Mortars by Modifying Them with Silicic Acid Sol

Lime materials are in great demand for the restoration of the walls of historical buildings. However, lime coatings have insufficient resistance during operation. The purpose of this work was the modification of lime mortars with silicic acid sol in order to obtain more durable crystalline materials for construction purposes. A technology has been developed for obtaining a silica-containing additive, which consists in passing a liquid glass solution with a density of 1.053 kg/m³ through a cationic column and obtaining a silicic acid sol with a pH of 3-4 and a charge of (-) 0.053 V. The regeneration time and the amount of sol have been determined. Regularities of change in the radius of particles of silicic acid sol depending on age are determined. It is established that at an early age (up to 5 days), the radius of sol particles can be determined in accordance with the Rayleigh equation, and at a later age, in accordance with the Heller equation. The results of the calculation show that at the age of 1-5 days, the radius of the sol particles is 17.1-17.9 nm, and then the particles become coarser and the particle radius is 131.2-143 nm at the age of 19 days. The work of adhesion of silicic acid sol to lime and the heat of wetting are estimated. It is shown that the work of adhesion of water to lime is 28.9 erg/cm², and that of the sol is 32.8 erg/cm². The amount of heat Q released when lime is wetted with SiO₂ sol is 15.0 kJ/kg, and when lime is wetted with water, it is 10.6 kJ/kg.