To evaluate the effect of the mix proportioning method on drying shrinkage and freeze-and-thaw resistance of recycled concrete aggregate (RCA) concrete, two series of concrete mixes were made using the modified equivalent mortar volume (EMV) method and the conventional ACI method. In this study, different sources of RCAs were manufactured from on-site plants on air bases and at a commercial recycling plant. Keeping the total mortar at the same level, concrete mixes were proportioned by the modified EMV method, using different scale factors: S = 1 (with RCA substitution of 23%), S = 2 (with RCA substitution of 47%), and S = 3 (with RCA substitution of 73%). It was assumed that the residual mortar volume in the RCA concrete was represented in the sum of the volume of mortar and the volume of aggregate, in variance to the scale factors. Test results showed that the modified EMV method for all the mixes yielded the drying shrinkage property of the RCA concrete comparable to that of the companion concrete with natural coarse aggregate. On the other hand, it was observed in the freeze-and-thaw test that the modified EMV method could be marginally applied to the limited condition with S = 2.

Abstract:This study aims to show the effect of a modified equivalent mortar volume (EMV) method on the flexural performance of recycled concrete aggregate (RCA). To verify this, an experimental study was carried out firstly by testing fresh and hardened material properties of RCA concrete specimens made by two different mixture design methods, i.e., the modified EMV method and the conventional American Concrete Institute (ACI) method. The flexural performance of five reinforced recycled concrete (RRC) beams mixed with different mixture designs was then investigated. Test results confirmed that the elastic moduli of the RCA concrete specimens made using the modified EMV method are greater than those of the conventional ACI mixture, while the drying shrinkage tended to decrease. The ultimate strengths of RRC beams mixed with the modified EMV method are as much as five percent greater than that achieved with the conventional ACI mixture.