Efeito da proteção superficial (pintura imobiliária) na difusão e captura de CO2 em argamassas de revestimento

Abstract

The construction industry is responsible for a large part of the environmental impacts due to the extraction and consumption of natural resources on a large scale, changes in built spaces, energy consumption, waste generation and emissions. In the cement production process, CO2 is emitted by decarbonating limestone, burning fossil fuels and electricity in factories, with the cement industry being responsible for ~7% of world emissions of anthropogenic CO2. However, cement-based materials can capture CO2 through the carbonation process, which occurs through the reaction of atmospheric CO2 with hydroxides present in the matrix, precipitating calcium carbonate. The potential for capture by this reaction depends on factors, such as the diffusibility of CO2 through the cement-based matrix. In this context, the present work aims to evaluate the effect of paint-type surface protection on CO2 diffusion in coating mortars. For this purpose, mortars were produced (1:1:6 and 1:2:9 cement: lime; sand), which 28 days after production received a real estate painting type surface finish, varying the ink base type (PVA and acrylic), finish (semi-gloss, matte) and color (white and grey). Mortar samples (7x9x16 cm specimens and 40x40x2.5 cm boards) underwent natural and accelerated carbonation, with the carbonation depth evaluated at 28, 101, 127 and 164 days. Carbon fixation was evaluated at 28 days through the thermogravimetric analysis test. A statistical test showed a significant difference in the different treatments, in which the diffusion of CO2 was greater for the reference matrix (without protection), followed by the matrix with protection type PVA, matte acrylic, and semi-gloss acrylic due to a greater protection given to the substrate due to inks. For the same exposure time (164 days) the mortars suffered a decrease in the carbonation rate when compared to the reference ones. The reduction was up to 3.6 times for mortars with standard acrylic paint with a semi-gloss finish, from 2.5 to 2.0 times less for mortars with acrylic protection with a matte finish, regardless of color. In the lowest reduction PVA paint, the carbonation speed was 1.20 times slower than the reference mortar. The effect of reducing the carbonation velocity and carbon fixation was verified, due to the lower diffusion of CO2 in samples with surface protection. Protection systems based on PVA are more permeable to CO2, which application should be preferred for greater carbon capture in the short term. However, considering the coating mortars life cycle (20 to 40 years), it can be stated that all systems can completely carbonate over time, regardless of the surface protection applied, considering an average thickness of 20 mm Therefore, carbon capture studies in coating mortars should be carried out considering a lower CO2 diffusion coefficient when there is a protective barrier applied to the surface of the material.