Synthesis, characterization and evaluation of biochar from agricultural waste biomass for use in building materials

Cement is a critical material for urbanization and its production is responsible for most of the CO2 emissions in the world. The use of substances capable of substituting the material responsible for greenhouse gases can reduce global warming, which is caused by the emission of greenhouse gases into the atmosphere, especially CO2. Among such materials is agricultural waste ash which has been found suitable to partially replace Portland cement in concrete production and can contribute to a decline of the environmental impact of cement production. The objectives of this study were to evaluate the effect of two agricultural wastes namely: rice husk and bagasse which were burnt in the absence of oxygen at 700 °C, in order to produce biochar, on the mechanical properties of concrete samples containing variable amounts of these substitutes. X-ray diffraction, BET and Scanning Electron Microscopy were applied for biochar characterization and investigation of its feasibility in concrete. A total of 0, 5 and 10% of the cement (by mass) was replaced by the agricultural waste biochar. For these mixtures, mechanical tests were conducted. The results were compared with those of concrete without biochar (control concrete), with compressive strength and splitting tensile strength. The results showed that the synthesized materials can be used as pozzolanic materials based on the XRD, SEM and BET methods. Concrete samples containing pretreated rice husk biochar (5%), unpretreated rice husk biochar (5%), pretreated bagasse biochar (5%), unpretreated bagasse biochar (5%), pretreated bagasse biochar (10%), and unpretreated bagasse biochar (10%) had a compressive strength of 36, 20.4, 54.8, 24.4, 21.1 and 23% higher than the control concrete, respectively. There was a 78% increase in tensile strength for concrete sample with 5% treated bagasse biochar compared to the concrete without any biochar. Overall, it has been concluded that rice husk and bagasse biochars are favorable substitutes and can be used in concrete without any adverse effect on the environment.