Bark ash mitigation power of rice attacked by sulfates in mortars made with scheelite residues

ABSTRACT

In the last decades, the exploration of the Scheelita mine, located in Currais Novos/RN, generated a large volume of solid waste that is improperly disposed of in the environment, causing negative environmental impacts to the municipality. One of the alternatives found to minimize this problem is the use of these residues in coating mortars, a technique used to promote the proper destination of solid wastes from the mining industry. However, there are no consistent studies on the durability of chemical attacks in this type of alternative mortar. In context, this work aims to verify if the rice husk ash calcined at 800 ºC in partial replacement to cement is able to mitigate the chemical attack by sodium sulfate that occurs in mortars made with scheelite residues in total replacement to the natural aggregate. Scheelite residues and rice husk ash were characterized by x-ray fluorescence and x-ray diffraction. The dosage chosen to carry out the investigation was 1:3, most used in base mortar, with the conventional aggregate replaced entirely by scheelite waste and cement partially by rice husk ash calcined at 800ºC. After defining the dosage, the mortar specimens were molded to be subjected to chemical attack in accordance with the ABNT NBR 13583 standard. The results indicated that the cement substitution content by rice husk ash calcined at 800 ºC was not to mitigate the chemical attack, since the expansion of the mortar bars exceeded the limit established (0.06%) by the ASTM C 452 standard. However, the expansions were not sufficient to cause loss of the mechanical resistance of the specimens for the attack period.

Keywords
Supplementary cementitious material; Pozzolanic material; Durability; Chemical reactivity; Alternative mortars