Avaliação multiescalar do efeito da carbonatação na durabilidade de argamassas de revestimento

Abstract

The present work aims to evaluate by macro and nanostructural techniques the effect of thermal cycles on the durability and bond strength of rendering mortars submitted to carbonation. Specimens were made of ceramic substrates coated with cement and sand mortar, which were cured in a saturated environment for 150 days. The non-carbonated specimens were kept in a 60±5% humidity and CO2 free chamber and the carbonated specimens were kept in a 60±5% humidity and 5% CO2 chamber. Non-carbonated and carbonated samples were subjected to an accelerated aging process by thermal shocks, resulting from 20 cycles of heating and wetting. The renderings were analyzed on a macro-scale by their tensile bond strength, capillary absorption, voids index, and mortar shrinkage. Carbonation generates an improvement in the bond strength of the renderings, but when aged these mortars are equal to noncarbonated mortars. Carbonation generated a shrinkage of 18% in the mortars, which was almost completely compensated throughout the thermal cycling process, where expansion occurred. Accelerated aging increased the variation coefficient in all tests performed. In nanoscale, using an atomic force microscope, scanning and indentations were made in the interface between mortar and substrate, and only in the mortar. The carbonation generated an increase in the elasticity modulus, both at the interface and in the mortar. The average modulus of the interfaces analyzed was higher than the modulus of the mortar, besides presenting distribution curves with higher standard deviation, which suggests that it is a heterogeneous region and that hydrates differently from the rest of the matrix. In all samples analyzed, aging decrease the elasticity modulus, generating greater damage in non-carbonated mortars.