The pH effect of sulfuric acid on the physico-mechanical properties of Atashkuh travertine, Central Iran

Sulfur dioxide (SO₂) is one of the most hazardous pollutants in the atmospheres of industrial cities. This pollutant, in combination with rainfall, forms acid rain. Acid rain can affect the physico-mechanical properties of stones and decrease their durability over time. In this paper, the pH effect of sulfuric acid was investigated on the physico-mechanical properties of travertine, including porosity (n), point load index (PLI), and Brazilian tensile strength (BTS). For this purpose, a travertine sample was obtained from the Atashkuh quarry in Mahallat (central Iran). Next, 30 cycles of wetting and drying were performed on the sample in H₂SO₄ solutions with pH values of 2, 3.5, and 5, followed by measuring its physico-mechanical properties after every 5 cycles. Parameters of the decay constant (λ) and half-time (N_1/2) were obtained from regression curves developed between the measured physico-mechanical properties and cycles of wetting and drying in H₂SO₄ solutions. The N_1/2 and the rate of loss (RL) these properties were used for comparing the effect of H₂SO₄ solutions with pH of 2, 3.5, and 5 on the sample. The results of data analysis showed that with an increase in the number of wetting and drying cycles in H₂SO₄, the n increased while PLI and BTS decreased with varying degrees. Furthermore, the variations in the physico-mechanical properties of the sample and their λ and N_1/2 indicated that the durability of the sample changes after the interaction of the H₂SO₄ solution with various pH values.