A Conceptual Framework for Engineered Lightweight Aggregates Using Dissolved EPS and Fly Ash

Expanded polystyrene (EPS) waste and fly ash are commonly available waste materials and have been widely studied in the field of lightweight concrete. In most existing studies, EPS is mainly used as a lightweight filler to reduce density, while fly ash is applied as a supplementary cementitious material in cement-based mixtures. However, the combined use of both materials as an integrated system at the aggregate level is still limited. This paper presents a conceptual framework for the development of artificial lightweight aggregates using dissolved EPS and fly ash. In this concept, dissolved EPS is assumed to act as a binding matrix, while fly ash functions as a mineral filler that contributes to the basic structural characteristics of the aggregate. The proposed framework discusses the general material concept, possible aggregate formation mechanisms, and the expected role of material composition on aggregate behaviour. The position of this conceptual approach is also discussed in relation to previous studies on EPS-based lightweight concrete and artificial aggregates. This study is intended as an initial step to support future experimental investigations on EPS–fly ash composite aggregates for lightweight concrete applications.