Avaliação do desempenho frente ao ataque por ácido sulfúrico de argamassas e concretos com adição de quitosana

Abstract

Concrete is the main component used in civil construction and, in spite of being a resistant material, it is prone to physical and/or chemical deterioration, which usually is the biggest problem in terms of finances and safety, as is the case of sulfuric acid attack. Therefore, the use of additions, such as polymers, has been studied as a way to mitigate deterioration mechanisms. In this sense, the present work aims to evaluate the performance under sulfuric acid attack of mortars and concretes, produced with different cements, with additions of chitosan biopolymer. For this, the work was divided into two parts: tests with mortars and tests with concrete pipes. For the production of mortars, three different cements were used (CP V ARI, CP V ARI-RS and CP IV-RS), two different traces (A = 1:3 [cement:sand], v:v and B = 1:2 :6 [cement: hydrated lime:sand], v:v:v) with chitosan additions of 1 %, 2 % and 3 % (chitosan mass/cement mass). Mechanical tests were carried out, as well as the evaluation of the phases formed through FTIR and SEM analysis. The attack was performed via mortar bars expansion when subjected to solutions with 5% sulfuric acid. For the concrete production, CP V ARI and CP IV-RS were used, since they presented the best performance in mortar tests, with chitosan additions of 1% and 3%. Mechanical tests were performed and phase characterization were carried out by XRD and TGA, also pHPCZ analysis and the quantification of basic and acidic groups were performed by Boehm titration. For sulfuric acid attack, cylindrical chambers were produced with the concrete that received a 5% sulfuric acid solution, the pH was of the acid was monitored and the Ca2+ concentration was evaluated by flame photometry. FTIR and DRX were performed before and after sulfate attack to verify the formation of attack products. Partial results show that the mechanical properties of cementitious materials are sensitive to chitosan incorporation. The addition of chitosan to mortar bars promoted a better performance against sulfuric acid attack. The FTIR shows a good incorporation of the biopolymer with the mortars, and shows a smaller formation of gypsum and ettringite in the mortars after the attack. The FTIR and XRD analyzes show that the interaction of the biopolymer with the cements hydration products can occur through the coordination reactions of chitosan with the Al3+ and Ca2+ ions, the other hypothesis is that the chitosan addition promotes changes in the porous microstructure of the cementitious materials, which could be observed in the SEM images and the results of the TGA analysis. The chitosan addition in the mortars promoted expansion reductions of up to 60.51% for the mortars when compared to the reference ones. In the sulfuric acid attack with the concrete pipes, an increase in pH and a greater release of Ca2+ by the CP V ARI cement pipes were observed. The addition of chitosan promoted a decrease on the release of Ca2+ from the concrete to the acid medium. In the carbonation test, the addition of chitosan provided a better performance against concrete carbonation for both concretes types.