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. 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. Rice husks can be used as building material, fertilizer, insulation material, or fuel. Rice husk ash, a product of the burning of rice hulls, could be used to make amorphous reactive silica which is variously applied in materials science.
As pretreatment, 20 g of biomass were immersed in 400 mL of the solutions (0.1N HCl or distilled water) in a 500 mL glass flask. At a constant temperature, the samples were stored separately, undisturbed for a 24-h immersion period in each solution. A programmable electric furnace was used to heat the pretreated and unpretreated samples. Samples were pyrolyzed at 700°C for 2h at 10°C/min in a flowing N2 environment. The synthesized samples were referred to as TRHB, RHB for pretreated rice husk biochar, unpretreated rice husk biochar. TRHA is related to the treated rice husk ash that is produced at 700°C for 2 h in an electric furnace in the presence of oxygen, in order to compare the effect of rice husk ash and biochar on concrete properties. For the cement paste experiments, biochars were used at 0, 5 and 10% replacement levels by mass of cement. For all concrete samples, a water-cementitious materials ratio (w/cm) of 0.5 was used. Three 10 * 10 * 10 cm specimens (ASTM C109) were designed for compressive strength test and three 20 * 10 * 10 cm specimens (ASTM C496) were designed for tensile strength test.
The incorporation of agricultural wastes biochar into concrete had beneficial effects on the compressive and tensile strengths. The addition of 5% rice husk biochar resulted to the highest compressive strength compared to other concrete mixes and control concrete. The principle impacts of biochars on the mechanical properties of concrete samples could be due to their high specific surface area and amorphous silica levels. Finally, the results indicated that biochar may be an appropriate candidate for the production of green concrete.