再生细骨料混凝土流变性及其对强度和耐久性的影响

The high porosity and water absorption of recycled fine aggregate (RFA) are caused by the presence of old mortar, lead to the degradation of the properties of fresh and hardened concrete and thus hinder its application in practical engineering. To solve this problem, the effects of the replacement rate of RFA (0, 25%, 50%, 75% and 100%) on the rheological properties, mechanical properties and chloride ion penetration resistance properties were studied by conducting both the conventional workability test, rheological test, compressive strength test and chloride penetration test. Experimental results show that the replacement of RFA will increase the time loss of both the slump and slump flow values of fresh concrete, with the corresponding increased yield stress and the decreased plastic viscosity. When the replacement ratio of RFA is within 50%, the rheological properties of fresh concrete, including the plastic viscosity, can be effectively improved by adjusting the amount of superplasticizer. On the contrary, the effect of superplasticizer will be significantly reduced when the replacement ratio is higher than 50%. When the replacement ratio is 50%, the 28-day compressive strength and chloride diffusivity of recycled concrete are about 71% and 200% of that of the normal concrete, respectively. While the 28-day compressive strength of recycled concrete with 100% RFA is only about 55% of the normal concrete. In this study, the RFA can be applied in high fluidity concrete to replace natural sand, and the recommend replacement rate is between 25% and 50%.