New perspectives into the rheology of earth suspensions modified with algae-derived biopolymers

Earthen materials provide a sustainable, low-carbon alternative for construction due to their natural abundance and minimal processing requirements. This study investigates the incorporation of algae-derived biopolymers to enhance the rheology and mechanical performance of cement-stabilized earth materials, aiming to improve construction efficiency while preserving environmental advantages. Three biopolymers extracted from red (carrageenan), brown (alginate), and green (ulvan) algae, each characterized by its principal polysaccharide, were incorporated into cement-stabilized earth suspensions to evaluate their effects on hydration kinetics (isothermal calorimetry), phase evolution (XRD), bleeding, pore solution chemistry (ICP-OES), rheology (visco-elastoplastic behavior), and compressive strength. The algae-based viscosity-modifying agents (VMAs) altered hydration process and improved suspension stability, with the degree of modification depending on the biochemical composition and pre-treatment of the biopolymers. The most significant hydration delay was observed with preheated brown algae, extending the induction period to approximately 88 h, while the highest 28-day compressive strength (4.8 MPa) was achieved with direct incorporation of biopolymer. SEM analyses revealed that algae-based biopolymers promoted a denser microstructure by refining the C-S-H gel, improving the interfacial transition zone (ITZ), reducing portlandite crystal size, and promoting the formation of biogenic calcite, collectively contributing to improved mechanical performance and durability. • Algae-derived VMAs show origin-dependent effects on hydration and reactivity. • ICP analysis reveals algae act as both ion donors and strong Ca 2 + , Al 3+ , Mg 2+ chelators. • Algae-based biopolymers enhance yield stress, viscosity, and structural build-up. • Reduced bleeding and improved rheology promote stability and uniform hydration. • Later-age strength gains confirm algae-derived VMAs as eco-efficient admixtures.