Valorization of spent coffee grounds and casein for a new bio-composite material

Abstract

This study investigates the potential of biopolymers derived from spent coffee grounds (SCG) and casein (Cas) for structural foundation. SCG was adopted for its sand-like physical properties, while Cas served as a binder to enhance mechanical performance. A central composite design (CCD) was used considering three factors: Cas content, NaOH concentration, and curing temperature. Mechanical and statistical analyses revealed that the bio-composite achieved a maximum unconfined compressive strength (UCS) of 7.7 MPa under optimal conditions, with curing temperature being the most influential factor. Linear regression models between secant modulus (E50) and UCS highlighted the enhancement of rigidity with curing time. Fired brick waste (FBW), rich in aluminosilicates, was incorporated into some mixtures, but its limited reactivity reduced interfacial bonding. Microstructural observations confirmed the formation of a dehydrated biopolymer gel coating SCG particles. Overall, the SCG–Cas system appears to be a promising sustainable material for circular economy applications. • Sodium caseinate used to stabilize spent coffee grounds as a cement alternative. • UCS and E50 measurements assess mechanical strength development over time. • Quadratic model highlights dominant parameters and interactions for mixture design. • Fired brick waste added to explore alkali activation within the biopolymer system. • Spent coffee grounds were compared to other soils stabilized with sodium caseinate.