Properties and microstructure of concrete masonry blocks incorporating chrysotila carterae microalgal biomass

Chrysotila carterae (coccolithophore) produces CaCO₃ through biomineralization. To utilize this sustainable resource, the effect of incorporating harvested microalgal biomass of Chrysotila carterae into concrete masonry blocks (CMBs) as a partial replacement for cement at 5 and 10 % by mass has been investigated. The hydration kinetics, mechanical properties, electrical resistivity, and microstructural characteristics of the resulting CMBs were assessed. The findings indicate that the addition of microalgal biomass improved the degree of hydration reaction, with 5 % replacement increasing compressive strength to 24.5 MPa and hardened density to 2284 kg/m³. These values exceed the minimum requirements specified by standards for load-bearing CMBs. However, at a 10 % replacement level, a significant decline in properties, including a 45 % reduction in compressive strength and a 7 % decrease in density, was observed, rendering these CMBs more suitable for non-load-bearing applications. Additionally, an increase in water absorption from 5.5 % to 7.1 and 9.2 %, and in permeable voids from 15.5 % to 18.5 and 22.0 %, was reported as the biomass content increased from 0 % to 5 and 10 %, respectively. Nevertheless, the values remained within acceptable thresholds for load-bearing CMBs. Microstructural analysis revealed that the mix incorporating 5 % biomass exhibited a dense matrix, while increasing the biomass to 10 % led to a porous microstructure with various microcracks. This case study highlights the potential of using microalgal biomass to enhance the sustainability of construction materials, with 5 % cement replacement by biomass offering superior performance to the cement-based mix while also reducing cement-induced consumption of natural resources and emission of carbon dioxide.