Eco-Friendly Concrete Incorporating Fly Ash, GGBS, and Coconut Shell Aggregate: A Comprehensive Review

The global concrete industry consumes over 4 billion tonnes of ordinary Portland cement (OPC) annually, contributing approximately 8% of anthropogenic CO₂ emissions. The search for sustainable alternatives has generated substantial research interest in supplementary cementitious materials (SCMs) — particularly fly ash (FA) and ground granulated blast furnace slag (GGBS) — and in bio-derived aggregates such as coconut shell (CS). This review synthesizes findings from 25 peer-reviewed publications (2013–2025) to present a comprehensive, evidence-based assessment of their application in M20 grade concrete. Objective of this paper is to systematically compile, compare, and critically evaluate published experimental evidence on the mechanical properties, workability, microstructural behavior, environmental impact, and economic viability of eco-friendly concrete systems incorporating FA, GGBS, and CS aggregate, and to identify priority research gaps. The findings reveal that ternary blends of OPC+FA+GGBS at combined replacement levels of 20–40%, when paired with 15–25% CS aggregate, achieve 28-day compressive strengths of 20–23 MPa — satisfying M20 structural requirements per IS 456:2000. Flexural and split tensile strengths are comparable to or marginally above those of conventional OPC concrete in optimized ternary systems, attributed to pozzolanic densification of the interfacial transition zone (ITZ) and the interlocking surface texture of CS. CO₂ reductions of 22–35%, density reductions of 8–15%, and material cost savings of 10–20% are widely reported. Critical gaps remain in long-term durability, fire resistance, and structural-scale validation.