Concrete improvement incorporating recycled powder and aggregates treated via a combination of calcination and carbonation: The impact behaviors

Abstract

Property improvement is a key process for achieving high value-added utilization of recycled powders (RPs), recycled fine aggregates (RFAs) and recycled coarse aggregates (RCAs) in concrete. The purpose of this study is to improve the quality of recycled concrete (RC) incorporating recycled powder and aggregates by optimising the combined calcination and carbonation pretreatment, focusing on the effect of recycled powder and aggregates pretreatment on the impact behavior of RC. For this purpose, a series of impact tests were conducted by using a Ø 100-mm splitting Hopkinson pressure bar apparatus to examine the influence of the reaction conditions on the physical and microstructural properties of the modified RCs. The various tested parameters included the following: (1) calcination temperature (25 °C, 200 °C, 400 °C, 600 °C and 800 °C); (2) carbonation time (0, 3, 6, 12 and 24 h); (3) RP content (0 and 10%); (4) RFA content (0 and 25%); (5) RCA content (0, 50 and 100%) and (6) strain rate (20 s−1 to 120 s−1). In addition, the test results from the impact properties of the modified RCs were compared with those under quasi-static loadings. The results showed that a combination of calcination at 400 °C (for RP at 600 °C) and carbonation for 24 h significantly improved the performance of RPs, RFAs, and RCAs and reduced the negative impact of their addition on the impact resistance of RC. X-ray diffraction (XRD) and scanning electron microscopy (SEM) results showed that the coupling pretreatment was beneficial for the development of the RC microstructure; a stronger bond between the matrix and recycled material was achieved, and the interfacial transition zone (ITZ) was also effectively improved. Finally, a recalibration model based on the RPs, RFAs and RCAs was proposed to predict the dynamic increase factor (DIF) of the RC under impact loading.