Synthesis of Acid Resistance Green Concrete using Agricultural Residues' Biochar

Concrete is extensively used in the construction industry. To reduce the production of cement and subsequently reduce air pollution due to the release of  gas into the atmosphere and also to increase the strength of concrete, cement additives can be used. One of the additives that can be used in concrete is biochar from agricultural waste during the pyrolysis process. Pyrolysis is the process in which wastes are decomposed in the absence of oxygen and at high temperatures. Agricultural wastes are pyrolyzed before being added to concrete. It produces biofuels that can replace fossil fuels, and pyrolysis residues can be used as cement additive in concrete. In this study, the possibility of using biochar of rice husk and sugarcane bagasse treated with hydrochloric acid as an additive to replace cement at the values of 0, 5 and 10% was investigated. Sulfuric acid with pH = 1 was used to simulate the wastewater environment. In order to evaluate the effects of acidic environment on the properties of concrete samples, weight loss, compressive strength and tensile strength of the samples were measured and SEM and EDS instrumental analyzes were performed on the samples immersed in acid after 28 days.  The results showed that pretreatment of rice husk and sugarcane bagasse with dilute hydrochloric acid could improve the pozzolanic properties of the samples by reducing the amount of potassium and calcium in the composition. The results of compressive strength showed an increase in compressive strength of samples containing 5% of treated rice husk biochar and sugarcane bagasse biochar by 35.9% and 54%, respectively, compared to non-pozzolan sample (control). The changes in tensile strength of the samples containing pozzolan compared to the control sample were not significant, compared to the compressive strength. The weight and compressive strength of concrete samples decreased in the vicinity of sulfuric acid. The weight loss of all samples was less than the control, but the comparison of the compressive strength of the samples containing pozzolan with the control showed that only the compressive strength of the concrete sample containing 5% biochar of treated rice husk was higher than that of control by 16%. Tensile strength of concrete samples containing 5% biochar of treated rice husk and treated bagasse increased by 12% and 13%, respectively, compared to the control. In general, the results showed the positive effect of biochar pozzolan on the mechanical properties of concrete.