A scientometric review of the synthesis and application of expanded clay aggregate in cementitious composites

Expanded clay aggregate (ECA) are lightweight aggregates (LWAs) synthesized through high-temperature clay sintering, featuring a unique internal cellular structure comprising numerous air-filled cavities. This unique internal cellular structure, characterized by numerous air-filled voids, together with the inherent ceramic composition of ECA, confers them with exceptional properties i.e., good thermal and acoustic insulation, chemical inertness, and fire resistance. ECA brings about environmental benefits, such as resource efficiency, a sustainable, long-lasting lifespan, and 100% recyclability, which position it as the aggregate of the future. This comprehensive study provides a consolidated overview of the synthesis of ECA, encompassing various additives used with clay, along with its laboratory and industrial-scale production processes. Subsequently, the article delves into the diverse applications of ECA in concrete formulations, highlighting their prominent role in the production of lightweight aggregate concrete (LWAC), geopolymer concrete, high-performance concrete, and fiber-reinforced concrete. Notably, LWAC with compressive strengths exceeding 68 MPa and densities as low as 1000 kg/m3 have been achieved using ECA substitution levels of up to 77%. This review, therefore, serves as a valuable resource, capturing the multifaceted aspects of ECA, their evolution, and their promising potential within the realm of modern construction advancements.