Applications of Alginate in Geotechnical Engineering and Construction: A Review

Alginate, primarily sodium alginate, is a biopolymer derived from brown algae or bacterial sources that forms hydrogels via ionic crosslinking with certain divalent cations. Its incorporation into soils, earthen materials, cementitious composites, and asphalt mixtures improves mechanical performance and durability. This review collates recent advances in alginate-based treatments for geotechnical and construction applications, highlighting how alginate dosage, substrate type, gelation method, mixing strategy, and curing regime influence mechanical strength, physical properties, and self-healing efficiency. In soil stabilization, alginate treatments increase unconfined compressive strength (UCS) by 0.2–1.5 MPa in sand, with some studies reporting increases of over 2 MPa. Reported UCS improvements in alginate-treated clayey soils generally fall within the range of 50–150% compared to untreated samples, although isolated studies document increases exceeding 200%, depending on material composition and curing conditions. In cementitious systems, alginate-based capsules and hydrogels facilitate self-healing, achieving high closure rates of 70–100% for microcracks <0.4 mm, with some studies achieving complete sealing of macrocracks up to 4 mm while also recovering significant mechanical strength. Depending on dosage and formulation, alginate can also serve as a viscosity-modifying admixture, increasing the plastic viscosity and yield stress of the fresh mix, with this thickening effect becoming pronounced at dosages above approximately 0.1 w/w% by cementitious binder mass. For asphalt pavements, alginate-encapsulated rejuvenators facilitate high healing efficiency under cyclic loading and thermal cycling; rheological tests confirm elevated complex modulus and improved viscoelastic response. This review also synthesizes an explanatory framework for the divergent results found in the literature, advocates for standardized experimental protocols and material characterization, and outlines future research directions to advance alginate as a suitable alternative to conventional stabilizers.