Effect of acid rain on mechanical properties of sandy soil stabilized with cement

The everyday increase in population, the increase in the activity of industrial factories and workshops, and the expansion of transportation system lead to the release of metal pollutants and acid-forming compounds, such as nitrogen and sulfur, into atmosphere. The presence of these polluted compounds in atmosphere lowers the natural rain pH and gives it an acidic property. Acid rain, as one of the sources of soil pollution, has devastating effects on soil. A variety of natural and chemical materials are used to stabilize different types of soil. In the present study, the effect of acid rain on mechanical behavior of cement-stabilized sandy soil is investigated. Primarily, the cement was added to the sandy soil, with percentages of 3%, 5% and 7%, and then the samples were tested after saturation in solutions with pH values of 1, 3, 5 and 7.8. The results show that the increase in cement percentage enhances the optimum moisture, maximum specific dry weight, shear strength, Secant modulus (E50), and shear strength parameters of samples. Nonetheless, the acidification of environment reduces the Secant modulus, cohesion, and internal friction angle of soil. The results indicate that the decrease in uniaxial compressive strength and Secant modulus, due to the acidification of environment, are more pronounced with higher percentages of cement. According to the results, the increase in shear strength parameters, due to the increase in curing time and decrease in environmental acidity, is more significant in cement-stabilized samples than lime-stabilized ones. Finally, the effect of pH and cement on the cohesion between sand and cement particles was investigated using image processing and getting binary images from samples, the results of which revealed that the increase in acidity and the reduction of cement percentage drastically reduces the cohesion between sand and cement particles.