Deconvoluting The Effects of Chemical Composition and Structural Confinement of Algal Biomatter on The Hydration Reactions of Portland Cement

Decarbonization of cementitious materials, which contributes to 10% global carbon emissions, is one of the primary targets to achieve carbon net zero by 2050. Utilizing the abundance, easy cultivation and carbon-sequestering ability of algal biomatters to reduce cement usage has received rising attention. We recently reported that certain algal strains in the unprocessed form hinder the hydration reactions of ordinary Portland cement, preventing the application of replacement at high algae content. Here, to understand the interactions between the algal biomatters and cement further, we aim to deconvolute the effects of chemical composition and structural confinement of algal biomatters on the performance of algae-cement composites. We first study the influence of algae-related biopolymers, including carbohydrates, lipids, and proteins, on the resulting hydration products using thermal gravimetric analysis (TGA) and scanning electron microscopy (SEM), and their contribution to composites’ compressive strength. We then apply pretreatments, involving grinding, self-bonding induced by heat and pressure, and biopolymer extraction, to the macro- and microalgae respectively to investigate the impact of particle size, bonding structure, and chemical composition on the algae-cement interactions. The effects of varying particle size and morphology of biomass on the binding interfaces and distribution in cement matrix are evaluated by SEM. The modified bonding environment and chemical composition of biomass are measured with Fourier transform infrared spectroscopy (FTIR) and x-ray photoelectron spectroscopy (XPS), and then correlated with the hydration products and mechanical properties of the algae-cement composites. Compared to the unprocessed algal biomatter, we significantly improve the strength of composites by twofold using specific pretreatment for both algal biomatters. The proposed processing method and mechanisms enable higher algae replacement in cement with low energy trade-off, showing great potential for reducing cement usage and carbon footprint.