Analysis of the effects caused by accelerated weathering on red porous sandstone samples

Abstract

The sandstones of the Botucatu formation are extensively used in the region of São Carlos and Araraquara, even having been used in several historical buildings of these cities. One of the formation’s lithotypes, known as red porous sandstone (APV), has been traditionally viewed as a waste product of the extraction of yellow and red sandstones; the quarries of the region have, however, shown an increasing interest in selling this lithotype due to a major effort in reducing waste generation. This study aimed to determine the effects caused by the use of muriatic acid on surfaces made of APV, in order to expand upon lithotype feasibility studies conducted by other researchers from the federal university of São Carlos and to verify the veracity of reports on the negative effects caused by use of this acid on this APV. For this, tests of hard body impact resistance and determination of physical indices according to current norms and a non-standardized chemical alteration test were performed on two sample groups that had previously been exposed to natural weathering for a period of around 1 year. These tests showed that, after prolonged exposure to the acid, the samples: lost around 1/4 of the mass, lost on average 30% of their tenacity, adopted unwanted stains and had changes in their physical indexes consistent with loss of cementation and deposition of salts in the voids. With this, it was concluded that the use of muriatic acid for cleaning surfaces composed of APV is strongly contraindicated, as it negatively affects all tested aspects of the rock.