This study aimed to describe the mechanism and reaction characteristics of the adhered mortar removal of recycled aggregate (RA) using microwave irradiation (700 W) and a mixed solution of HCl and H2O2. The HOCl concentration increased to 29.7 M at 35oC and 40 min of reaction time without RA in the mixed solution, which shows that HCl reacts with H2O2 to form HOCl and water. However, after nitrogen purging, the HOCl concentration decreased to 2.71 M in 20 min, which proves indirectly that HOCl reacts with HCl to form Cl2 and water. The HOCl concentration decreased from 29.7 M to 1.88 M at 35oC in 40 min with RA in the mixed solution, and the Ca2+ concentration increased to 9,750 mg/L, which demonstrates indirectly that mortar mainly composed of Ca(OH)2 reacts with Cl2 to form Ca(OCl)2 and CaCl2. The reaction rate (k) with microwave heating was about 2.3 times faster than that with conventional heating, and k at a reaction temperature of 50oC was about 1.3 times faster than that at 35oC. The treated RA was improved in density, water absorption, abrasion loss, and absolute volume.

This study aimed to determine adhered mortar content of recycled aggregate (RA) using microwave irradiation (700W)and mixed solution of hydrochloric acid (HCl) and hydrogen peroxide (H2O2). The optimum condition was first to soakRA in tap water for 30 min and then RA was soaked in mixed solution of 30% HCl and 15% H2O2 (HCl:H2O2=1:2) for 70-90min after 15-min microwave irradiation. The mortar of RA in the condition was completely removed within2.3 hrs. Reaction rate (k) with the condition was −0.6408hr−1, which was about 190 times faster than that with HCl only(k=−0.0034hr−1).

This study aimed to completely remove adhered mortar from recycled aggregate (RA) using microwave irradiation (700 W) and mixed solution of hydrochloric acid (HCl) and hydrogen peroxide (H2O2). The optimum condition was first to soak RA in tap water for 30 min and then RA was soaked in mixed solution of 30% HCl and 15% H2O2 (HCl : H2O2 = 1 : 2) for 70-90 min after 15-min microwave irradiation. Therefore, the mortar of RA in the condition was completely removed within 2.3 hrs. Reaction rate (k) with the condition was –0.6408 hr-1, which was about 190 times faster than that with HCl only (k = -0.0032 hr-1).