Uso da cinza de casca de arroz em cimentos álcali-ativados como fonte alternativa de sílica

Abstract

Rice bark is an agricultural residue from the processing of the grain. With a global production of 120 million tons per year, it is used in the production of energy for drying, thus generating rice husk ash (RHA), a pollutant residue that is commonly discarded inappropriately. The use of RHA as a source of silica in cements has been studied in order to improve its properties and reduce the environmental impacts of the cement industry. Thus, this research aims to incorporate the RHA of the rice husk as a source of silica in activated alkali cements. Activated alkali cements are basically composed of industrial by-products such as fly ash, blast furnace slag and slag and are gaining space by presenting a reduced environmental footprint. In order to analyze the influence of the SiO2/Al2O3 and CaO/SiO2 ratios on the development of mechanical strength and hydrated compounds of the AAC, two different chemical composition slags were used together with RHA and Metacaullim, activated with NaOH. Compositions with CaO/SiO2 ratio close to 1, obtained better mechanical resistance, around 35-40 MPa at 28 days. The SiO2/Al2O3 ratio did not influence the results. X-ray diffraction and thermal analysis presented the formation of hydrated calcium silicate (C-S-H) and hydrotalcite as hydrated compounds. The heat of hydration of the pastes containing RHA were smaller than the AAC composed only of slag. It can be seen that the RHA can be used in the AAC in order to obtain better results and that the chemical composition of the materials used influences the performance.