Effect of old mortar pore structure on relative humidity response of recycled aggregate concrete

In this paper, based on the pore structure characteristics of old mortar attached to recycled concrete aggregate (RCA) surface, recycled aggregate concrete (RAC) internal relative humidity (RH) response process and mechanism were investigated, considering different temperatures, RCA replacement ratios and load condition. The RH was determined by the embedded probe, pore structure was measured by mercury intrusion porosimetry (MIP), and micro-cracks of the old and new mortar were observed through scan electron microscope (SEM). The experimental results indicated that: (1) The range of critical pore size distribution and the proportion of large capillary pores volume in the old mortar was larger than in new mortar, resulting in RH response rate in RAC being faster than natural aggregate concrete (NAC). The obstruction of saturated small pores (pore neck) on the diffusion of gaseous water in the connected large pores causes the RH response hysteresis. (2) The RH response rate in the pores increases with the increasing temperature, especially in RAC. (3) Under the bending load, the pore network of old mortar creates more micro-cracks than the new mortar which provided additional channels for the diffusion of gaseous water. These conclusions will be helpful for further understanding to the durability of RAC. (C) 2020 Elsevier Ltd. All rights reserved.