Performance of concretes with surface treatment based on silicate solutions (liquid glass)

ABSTRACT: Concrete, one of the most widespread building materials, may be affected by many chemical and physical deterioration processes as a consequence of the penetration of aggressive substances. The improvement of concrete durability is a subject of great interest to researchers and the use of surface treatments, aimed at making hydrophobized mortars and concretes, is becoming a quite common practice. The study presented in this paper examines the effectiveness of some inorganic products based on alkali silicates as hydrophobic agents; it also tries to connect the chemical and physical characteristics of the silicates to the results obtained in concretes with different characteristics and quality, in terms of resistance to capillary absorption and drying for hydrophobic impregnation. It was found that the water repellent effect is dependent on the intrinsic porosity (amount and size of pores) of the cement matrix; in particular it is more evident when the porosity is lower. However, when the test is carried out with water under pressure, the opposite happens. The humidity loss by evaporation is maintained at about the same rate regardless of the type of conglomerate. The results obtained with several silicates do not show significant differences; furthermore one aspect improves when another worsens. The results don’t seem ascribable to the chemical composition of the silicates used, maybe to their fluidity that means different depths of impregnation, reduction of the open porosity and/or formation of surface film.