Abstract: To study the mechanism of thermal damage of concrete caused by steam when mixed with waste plastics， the compressive strength tests of concrete with different contents of polystyrene foam （EPS） particles were carried out， and the effect of EPS-particle incorporation on the porous structure characteristics and microscopic evolution of steam-cured specimens was revealed through mercury intrusion test and SEM observation. The results indicated that the strength of steam-cured specimens increased slightly with an increase in the EPS content. The introduction of EPS particles is beneficial for the development of the later strength of the steam-cured concrete. The thermal stress caused by steam curing was significantly alleviated， and the number of micro cracks and through cracks decreased， effectively suppressing the thermal damage caused by steam curing. The presence of EPS particles refined the pore structure of the steam-cured concrete and reduced the crack width on the interface of the EPS particle and cement matrix.

Key words: polystyrene foam granular concrete, steam curing damage, random aggregate model, pore structure