Uso dos resíduos do processo kraft de celulose – dregs e grits – como adição mineral na produção de matrizes cimentícias.

Abstract

The Portland cement manufacturing process accounts for approximately 7% of total CO2 emissions worldwide. To minimize its environmental impacts, cement industries have been adopting some mitigating measures, such as the incorporation of mineral additions in partial replacement to clinker. The waste dregs and grits generated during the production of cellulose, consisting mainly of calcium oxide, can be an alternative of supplementary material in the production of cementitious materials. In this sense, the present study aims to analyze the effect of the use of dregs and grits residues as mineral addition in the production of cementitious matrices. For this, the residues were ground to obtain particles lower than 75 μm, granulometry similar to Portland cement. The evaluation of the potential use of the residues was made by partially replacing the cement in levels of 0%,5%,10%,20% and 30% by mass by dregs or grits in the production of pastes and mortars. In the paste study, the influence of these on the kinetics of hydration, carbohydrates formed, was observed. Pastes with 20 and 30% dregs had a higher induction period than the reference, while grits in levels higher than 10% had a reduced induction period. Typical hydrates of Portland cement, CSH, CH, ettringite, monosulfoaluminate and calcium carbonate were verified, in addition to pirssonite (except for the content of 5%) and hydrated magnesium silicate (M-S-H) in pastes with 10, 20 and 30% dregs. The results showed that the use of grits promoted an increase in the consistency index of mortars. And in terms of compressive strength, the substitution of cement by both residues at different levels, provided a reduction in mechanical properties due to the dilution effect, however it was still possible to obtain resistances of 25MPa replacing in up to 34% of cement with dregs or grits at 28 days.