Potential of acidic volcanic rocks from the Serra Geral group as a partial replacement for Portland cement

Abstract

Searching for natural elements whose processing does not require burning and/or decarbonation, this research aimed to test acidic volcanic rocks from the Serra Geral Group as a partial substitute for Portland cement. After selecting relevant areas from consolidated bibliographies, rocks were selected in Caxias do Sul, Cambará do Sul, and São Joaquim in southern Brazil. Petrography confirmed the presence of volcanic glass in all samples. Pozzolanic activity was analyzed using standardized tests, including lime fixation, electrical conductivity variation, and amorphous material content. Both met the standardized chemical requirements but showed limited performance in pozzolanic activity with lime over 7 days. In physical tests, only Caxias do Sul and São Joaquim achieved the minimum required compressive strength. Caxias do Sul stood out for containing 52% amorphous material and having the highest consumption of Ca(OH)₂. Evaluating electrical conductivity, Caxias do Sul and Cambará do Sul showed variable pozzolanicity, while São Joaquim was considered non-pozzolanic. In summary, the rocks demonstrated pozzolanic properties, validating the use as supplementary cementitious materials. Therefore, this study contributes to the development of eco-efficient binders that are in line with the principles of the modern circular economy.