Uso de água cinza na hidratação do cimento portaland PCII Z 32 e seus reflexos na cura: um estudo reológico da pasta fresca

Abstract

The increasing scarcity of drinking water represents one of the most urgent challenges of the 21st century, impacting several sectors, including the construction industry. In this context, the reuse of gray water emerges as a viable and sustainable alternative for the production of mortars. This study analyzes the feasibility of using gray water from washing machines in the hydration of mortars, focusing on its rheological behavior. The fresh paste was prepared with CPII-Z32 Portland cement, with a w/c ratio of 0.43 and 0.57, for utility water (AR) and low-organic gray water (AC), respectively. After hydration, the mortars were studied by rotational rheometry at times of 20 and 60 minutes through the analysis of the hysteresis areas that allow a better understanding of the stress limits of the fresh mixtures, indicating how much they can withstand structural collapse. The sample AC 50% and w/c ratio 0.57, after the rheological study carried out at 60 minutes, reached the highest shear stress, indicating greater formation of agglomerates and resistance, favoring applicability on the surface. The use of reference water (AR) and gray water (AC) without dilution in high quantities can significantly impact the cement hydration reaction. This effect occurs due to the presence of impurities, dissolved salts and other chemical compounds in gray water, which can interfere in the chemical reactions involved in the formation of cement hydration products, such as hydrated calcium silicate (C-S-H) and calcium hydroxide (CH). The study of the chemical composition using FTIR demonstrated an intensification of the sulfate and carbonate bands for 50% AC 0.57 of water-cement ratio, suggesting the participation of gray water compounds in the reactions, altering the morphology of the cement products. It is also noted that the increase in the proportion of AC (gray water) negatively influences the cement hydration. Therefore, the use of AC in larger proportions should be analyzed with caution to avoid undesirable impacts on the quality of the material. With the curing time (7, 14 and 28 days), an increase in the intensity of the hydrated silicate peaks was observed, evidencing the progressive formation of the cementitious matrix. In summary, this study highlights the feasibility of reusing gray water in the proportion of 50% AC, highlighting the importance of using it in adequate proportions to optimize results and minimize negative effects. The reuse of greywater in civil construction is a promising strategy to reduce the consumption of drinking water. Making its use viable contributes to the advancement of more sustainable practices in the civil construction sector.