Structural Lightweight Concrete Incorporating Sustainable Lightweight Aggregates: A Review

Structural lightweight concrete (SLWC) offers substantial advantages over conventional concrete by reducing dead load, enhancing thermal insulation, and lowering seismic vulnerability in multi-storey and long-span structures. Traditional SLWC production has relied heavily on energy-intensive manufactured aggregates, such as expanded clay and sintered fly ash, which pose environmental concerns. This review examines recent advances in SLWC produced using sustainable alternatives—naturally occurring pumice, treated oil palm shell (OPS), recycled lightweight concrete aggregate (RLA) from demolished blocks, and waste crushed bricks (WCB)—in combination with supplementary cementitious materials (SCMs) including metakaolin, silica fume, fly ash, and ground granulated blast-furnace slag. The paper synthesizes findings on aggregate pretreatment, mixture proportioning, and mechanical performance, showing that appropriately designed SLWC systems achieve 28-day compressive strengths of 25–45 MPa at equilibrium densities below 2000 kg/m³, thereby satisfying major code requirements (ACI 213R, ASTM C330, DIN 1045-1). Pumice-based concretes incorporating 15–18% metakaolin demonstrate strengths up to 40 MPa and sharply reduced sorptivity, while treated OPS concretes with silica fume or slag attain 25–31 MPa at densities around 1700–1750 kg/m³. Recycled lightweight aggregate concretes with 25–35% RLA maintain structural-grade strengths and thermal conductivities in the range 0.49–0.75 W/(m·K). Full replacement of natural aggregates with WCB yields compressive strengths exceeding 39 MPa when combined with 15% silica fume or metakaolin, alongside favorable interfacial transition zone characteristics confirmed by scanning electron microscopy, X-ray diffraction, and thermogravimetric analysis. Durability assessment reveals that highly reactive SCMs—particularly metakaolin and silica fume—refine pore structure, reduce capillary water absorption, and enhance residual strength after exposure to elevated temperatures up to 600 °C. Among SCMs, slag exhibits superior fire resistance, retaining approximately 85% of ambient-temperature strength after 600 °C exposure. However, existing data remain largely short-term and specimen-scale, with limited information on long-term freeze–thaw resistance, chloride ingress, carbonation, and full-scale structural behavior under service conditions. The review identifies critical research gaps, including the need for integrated durability testing programs, multi-parameter response-surface models linking strength, stiffness, sorptivity, and thermal conductivity, and pilot field applications with real-time monitoring of deflection, cracking, and thermal performance. Future work should also translate validated performance into explicit design provisions—density–strength reduction factors, bond and shear coefficients for alternative aggregates, and fire-rating guidelines—to facilitate the wider adoption of these eco-efficient structural lightweight concretes in routine design practice.