Estudo da pasta de cimento com substituição parcial e total da água de hidratação por manipueira

Abstract

Cement paste is the union of two inputs: water and cement. From it, concrete and mortar are prepared, which are the most consumed elements in the construction industry. Given this great demand, some questions arise about the environmental impact of the high consumption of natural resources. In this sense, researches have been developed to minimize the consumption of non-renewable goods by replacing them with products from other productive activities. Within this perspective is manipueira, a liquid by-product resulting from the pressing process of cassava roots with a high content of hydrocyanic acid and high biochemical oxygen demand. Its disposal is normally done in water bodies, causing changes in the self-purification and eutrophication capacity, or through accumulation in small areas surrounding the production site without prior treatment. Considering that in 2020 Brazil was responsible for the production of 18.96 million tons of cassava root, studies to mitigate this environmental impact are relevant. The objective of this research is to analyze the behavior of cement paste produced with manipueira as a substitute for water, in terms of physical and mechanical properties and microstructure. The materials were characterized and seven pastes prepared with different replacement contents (10%, 15%, 20%, 25%, 50%, 75%, and 100%) for analysis of properties in the fresh and hardened state. In the fresh state, the presence of manipueira caused a delay in setting time up to 66% about the reference paste and plasticizing behavior to the cement pastes in all the proposed formulations. In the hardened state, an increase in compressive strength of 28% was found in the formulation with 20% replacement, and a sharp drop in the proportions of 75% and 100% replacement when compared to the reference paste. It was also verified a decrease in specific mass, increase in the void index, and capillary absorption in all replacement ratios. From the results found, microstructural analyzes were performed on samples of 20% and 100% compositions. It was noticed the formation of hydrated silicate flakes (CSH) in the paste with 20% replacement, and late ettringite in the paste with 100%. Thus, it is concluded that the studied manipueira can be used in cement pastes replacing up to 20% of the hydration water since its properties have been improved. However, the incorporation of manipueira in higher levels of replacement harmed the cement hydration process.