Carbonation Modification of Recycled Fine Aggregate and Its Effect on Rheological Properties of Mortar

Recycled fine aggregate (RFA) seriously affects the fresh and hardening properties of concrete due to the presence of attached old mortar.The purpose of this study is to reveal the influence of replacement rate and carbonation methods on the rheological properties of recycled mortar (RM),where standard carbonation and carbonation after limewater spraying process (CH carbonation) were adopted to modify the quality of RFA,respectively.The results show that the dynamic yield stress and plastic viscosity of mortar were closely related to the time variation of water absorption,which exhibits a good effect on predicting the quality of RFA.As the replacement rate of RFA increases,the dynamic yield stress of fresh mortar decreases and the growth rate of plastic viscosity increases significantly within 30min.Both the two carbonation methods can improve the quality of RFA and the rheological properties of RM.Compared with standard carbonation,the dynamic yield stress and plastic viscosity of RM after CH carbonation decreased by 26.6% and 25.1% respectively at 30min,and their growth rates decreased by 50.0% and 83.5% within 30min,respectively.In addition,the compressive and flexural strengths of RM were both improved after carbonation modification.