Effect of Algal Biomass on the Properties of Calcium Sulfoaluminate Cement

Abstract

Calcium sulfoaluminate (CSA) cement is a low-CO2 alternative to portland cement (OPC). To further enhance its sustainability, the use of CO2-storing algal biomass and algal biochar was explored herein as carbon-negative cement retarding admixtures. CSA cement was replaced with 0, 5, 10, or 15% raw algal biomass or biochar derived from the raw algal biomass. Results showed that increasing raw algae dosage led to longer delays in hydration; however, the retardation effect was not observed in samples containing algal biochar due to the absence of hydroxyl and carboxyl functional groups in biochar. Delays in cement hydration due to the incorporation of raw algal biomass corresponded to lower compressive strengths, as anticipated. Despite these reductions, the compressive strengths of the CSA cement pastes were similar to the control OPC pastes due to the inherently high initial compressive strengths of CSA cement compared to OPC. Both raw algae and biochar effectively lowered the net CO2 emissions of CSA and OPC, with biochar samples exhibiting lower CO2 emissions relative to raw algae when normalized for strength performance. Overall, the results suggest that algae may be used effectively with CSA cement for a more workable and sustainable binder system.