Efeito de ciclos de degradação físico-química na resistência mecânica em argamassas geopoliméricas reforçadas com fibras de poliéster

Abstract

Currently, the cement industry is responsible for a significant amount of carbon dioxide (CO₂) emissions into the atmosphere due to the high demand for ordinary Portland cement (OPC). Its production makes use of clinker, thus causing the release of CO₂. A sustainable alternative to replace OPC is alkali-activated materials (AAMs), formed by the mixture of a solid precursor with an alkaline solution. Therefore, the present study aims to analyze the mechanical strength of geopolymer mortars reinforced with polyester fibers before and after immersion in aggressive solutions. Thus, six types of mixtures were produced by varying the contents of metakaolin and recycled glass powder for two fiber reinforcement contents, and through wetting and drying cycles, the mortars were immersed in solutions containing water(H₂O), sodium chloride (NaCl), and magnesium sulfate (MgSO₄). For the production of the mortars, an activating solution composed of sodium silicate(Na₂SiO₃) and sodium hydroxide (NaOH) with a concentration of 6 M was used, and an activator-to-precursor ratio fixed at 0.8; the binder-to-sand ratio was 1:2. The consistency index test was carried out to determine mortar workability using a flow table. For the hardened state, compressive strength tests were performed to analyze the compressive strength of the samples at 7 and 28 days, as well as flexural tensile strength tests at 28 days for prismatic specimens. The same compressive strength test was also performed for the samples after the degradation cycles in aggressive solutions. In the fresh-state results of the geopolymer mortars, the flow diameter tended to increase when the incorporated fiber content was lower, with 0.1% addition. Regarding compressive strength, samples with higher metakaolin content tended to present higher strength values, reaching 50.35 MPa at 7 days and 57.33 MPa at 28 days. The same behavior was observed for the analysis of flexural tensile strength values. In addition to these data, it was possible to analyze that the immersion of the samples in aggressive solutions caused the appearance of efflorescence on the specimens, with the presence of whitish stains and even salt formation on the surface of those immersed in MgSO₄. Compressive strength after the cycles showed strength gains for the samples immersed in magnesium sulfate and losses for those tested in sodium chloride.