Effect of Original Mix Proportion on Rapid Removing of Attached Mortar for Recycled Concrete Aggregate Through a Freeze-thaw Approach

The fundamental reason to the unsatisfied performance of recycled aggregate concrete (RCA) is the existence of attached mortar in recycled concrete aggregate. A new physical method to remove the attached mortar is proposed in this study, which is a multiple process based on freeze-thaw cycles (FTCs). This study adopts the freeze-thaw modification technology and explores its efficiency in treating RCA with different strength and water to cement ratio. The effectiveness of such modification method is also evaluated, where the results show that for w/c=0.68, 10-15 freeze-thaw cycles are needed, for w/c=0.54, 15-20 FTCs are required and for w/c=0.38, 20-25 cycles are necessary. The mechanical properties of unmodified recycled aggregate concrete (RAC) are related not only to the strength of the parent concrete, but also to the content of attached mortar of recycled concrete aggregate and its durability which is further related to the water-cement ratio (w/c). On the other hand, modified recycled aggregate concrete (mRAC) could achieve satisfied mechanical properties and long-term properties as using natural aggregate concrete (NAC).