Thermo-mechanical behavior of cementitious material with partial replacement of Class-II biochar with Accelerated Carbonation Curing (ACC)

Using carbon-neutral materials is a promising way to mitigate the CO2 emissions of the construction industry. Biochar prepared from agricultural waste has a great potential to sequester CO2. This study demonstrates a new sustainable method for preparing biochar from rice husk having class II category as it has less than 60% carbon content and is derived at a temperature of 500 ℃. The prepared biochar was partially replaced in cement paste and cured under a CO2 environment for 7 and 28 d. X-ray diffraction (XRD) and thermogravimetric analysis (TGA) showed that the replacement of biochar promoted cement hydration and mechanical properties. Addition of 3 wt% and 5 wt% biochar increased the compressive strength of the composite by 34.7% and 35.6%, respectively. However, a further addition to 10 wt% biochar reduced the compressive strength by 16.7%. Replacement of up to 5 wt% biochar successfully promoted the carbonation with 10.2% CO2 uptake after 28 d of accelerated CO2 curing. Carbonation of biochar-cement composite substantially improves thermal conductivity, specific heat, and thermal diffusivity compared to control samples at 7 and 28 d. Field Emission Scanning Electron Microscope (FESEM) analysis revealed the numerous cement hydrates which enhance the bond strength after carbonation, and the carbonate densifies the microstructure, considerably enhancing mechanical strength and carbon binding capability. Biochar-cement composites with CO2 could be innovative low-carbon building materials for sustainable engineering applications.