Adição de cal aos concretos com ar incorporado visando a redução da frente de carbonatação

Abstract

Air-entraining admixtures are widely used in civil construction, either to control the deleterious action of the freeze-thaw cycles, in self-compacting concretes or to change specific masses, in order to obtain a more economical structure with better thermal performance. The air entraining process generates small spherical air bubbles, stable, and uniformly distributed in the paste of the concrete. Carbonation is a reaction that occurs from the penetration of carbon dioxide (CO2) into the pores of the concrete, where it diffuses into the moisture present in the structure forming carbonic acid (H2CO3). This acid reacts with the compounds of the cement paste - mainly with calcium hydroxide [Ca(OH)2] - resulting in water and calcium carbonate (CaCO3). The consumption of calcium hydroxide in this reaction results in a decrease in the pH of the concrete, which can result in corrosion of the reinforcement. The present work aims to evaluate the viability of the addition of hydrated lime [Ca(OH)2] to the concrete formulation so that it acts as a sacrificial product, leaving free the Portlandite produced in the cement hydration process to guarantee the alkaline pH responsible for passivation of the steel reinforcement.