RBSM-based mesoscale study of frost deterioration for recycled concrete considering air-entrainment in old and new mortar

Abstract

To describe or predict the frost damage of recycled aggregate concrete (RAC), one should consider the material details of both old mortar and new mortar, especially the air entrainment. In this study, a freezing pressure model with entrained air is embedded into Rigid Body Spring Model (RBSM) to simulate degradation of RAC during freezing-thawing cycles (FTCs). First, quantitative models on frost damage of RAC are developed, and basic concepts of RBSM are introduced. Then the deformation of mortar affected by air entrainment is discussed and RBSM-based model for normal concrete is verified. Furthermore, RAC models are established with the method of RBSM, and the simulated frost damage results are compared with experimental results to validate this model. Finally, the validated model is used to study more cases of RAC, providing a comprehensive picture of frost resistance of RAC with different air entrainment, water to cement ratios and replacement ratios. It is found that while an air content of 6% is enough to protect new mortar from frost damage, weak old mortar still renders RAC vulnerable to frost damage and the damage significantly becomes more severe with the increase of replacement ratio of recycled aggregate. On the contrary, replacement ratio has little influence on frost resistance of RAC with weaker new mortar than old mortar. Besides, a linear relationship between compressive strength reduction and frost-related expansion is obtained.