Innovative Biological Technique Utilizing Microalgae to Improve the Stability of Gypsum

Gypsum is widely used in the construction industry, but its rapid setting time often requires the addition of retarders. Traditionally, these retarders are chemical agents that require energy-intensive production processes and result in carbon dioxide emissions. In our study, we introduce a novel retarder alternative, microalgae, which is carbon-negative during its growth, offering a more sustainable option. Additionally, we investigated the effects of both algae powder and its pyrolytic product, biochar, on the setting characteristics of gypsum. Our results indicate that algae powder significantly delayed the setting of gypsum; adding 3% algae powder extended the setting time by 146 min compared to plain gypsum. Biochar did not exhibit a retarding effect due to the absence of these relevant functional groups, specifically the −COOH and −OH groups. Moreover, the algae powder increased the yield stress and viscosity of gypsum, altering its rheological properties. These results demonstrate that algae powder can serve as an eco-friendly retarder for gypsum, providing a valuable approach for the construction industry to mitigate carbon emissions.