A method of forming a plastic aggregate pellet

The present invention relates to a plastic aggregate comprising the steps of mixing plastic which may be derived from waste plastic-based foam and at least one cementitious binder to form a first composition, wherein the particles of the plastic have a size distribution between 0.1 to 6 mm; mixing at least one inorganic base and water to form a second composition; mixing together the first and second compositions to form a plastic aggregate mixture; and compressing and heating the plastic aggregate mixture to form the plastic aggregate. The base may be sodium hydroxide or sodium carbonate. The cementitious material maybe be a cement such as Portland cement, GGBS, fly ash or mixtures thereof. The plastic may be polyurethane (PUR) or polyisocyanurate (PIR). Further disclosed are a plastic aggregate pellet and methods of manufacturing a concrete composition comprising a plastic aggregate.