Enhancing the strength and durability of mixed biochar-blended mortars after Accelerated Carbonation Curing (ACC)

Rapid growth and urbanization have led to an increase in the CO₂ content of the environment. Biochar has the potential to replace ordinary Portland cement (OPC) because of its high carbon content, and its porous nature reduces the carbon footprint of cement composite materials. In this study, 0 %, 3 %, 5 %, and 10 % by weight of mixed biochar (50 % rice husk (RH) and 50 % Saw dust (SD)) were incorporated into the mortar cubes, and their mechanical, durability, and microstructure analysis using Thermogravimetric analysis (TGA), Field Emission Scanning Electron Microscopy (FESEM), and X-ray diffractometer (XRD) were investigated after 28 d of carbonation curing. Further, workability, compressive strength, water absorption, fire resistance, acid attack, and package density tests were performed to analyse the durability properties of the biochar-incorporated mortar samples. Mixed-biochar incorporation improved the strength by enhancing the pore structure and promoting the internal CO₂ uptake of the cement mortar. Moreover, the compressive strength of samples exposed to the 5 % Na₂SO₄ solution for sulphate attack and NaCl solution for chloride attack for the duration of 30, 60, and 90 d showed improvement in the strength at 30 and 60 d compared to 90 d. Use of biochar up to 5 % replacement showed positive result on durability, attributed to improvement in hydration (more C-S-H gel formation), filler effect, which resulted in denser microstructure and improved the capillary action, and the pore blocking action of the biochar mitigated the microstructure damage caused by the sulphate attack. The mixture of the developed biochar has the potential to be incorporated into cementitious materials, aiding in reducing cement demand and promoting waste management.