Study On Durability Analysis And Quantitative Design For Recycled Coarse Aggregate Concrete Structure Under Carbonation Environment

Carbonation of the recycled coarse aggregate (RCA) concrete is a complicated physical diffusion and chemical reaction process, which is largely affected by the material parameters (such as water to cement ratio, mineral admixtures, recycled coarse aggregate replacement rate, et al.) as well as the environmental parameters (such as temperature, relative humidity, CO2 concentration, et aL). Meanwhile, there are lots of influential factors for the carbonization of the RCA concrete, which is difficult to analyze and predict accurately. Therefore, the quantification of carbonization environmental action as well as quantificational durability analysis model and design methodology for the RCA concrete structure were investigated in this study. The main contents of this thesis are as follows:(1) Based on the micro-structure, mortar adhesion rate and water absorption of the RCA, a porosity model of the RCA concrete was established by taking into account the influences of the air content of fresh RCA concrete, the amount of water per unit volume concrete, cement hydration, second hydration of mineral admixtures, additional water of the RCA. The influences of mortar adhesion rate and water to binder ratio on the porosity of the RCA concrete were also analyzed. Finally, the proposed porosity model was validated by comparing with the tested data, which provides a foundation for the carbonation analysis of the RCA concrete.(2) According to the mechanism of concrete carbonation and taking into account the influence of the mortar adhesion rate of the RCA, a multi-field coupled numerical model for the carbonation analysis of the RCA concrete was developed by combining the diffusion rule of CO2 within the RCA concrete with the conservation law of mass for the carbonatable substances. The effective diffusion coefficient of CO2, the coefficient of carbonation reaction rate, and the amount of the carbonatable substances were adopted as the major control parameters. In addition, the concentration distribution of each substance within the RCA concrete with different replacement ratios of the RCA was comprehensively analyzed.(3) The influence of the RCA replacement rate, environmental temperature, relative humidity, CO2 concentration on the carbonation depth of the RCA concrete were investigated quantitatively based on the proposed multi-field coupled numerical model. Then, a practical prediction model for the carbonation depth of the RCA concrete was established by introducing the environmental coefficients of temperature, relative humidity, and CO2 concentration and based on the theoretical model for carbonation analysis. In addition, the efficiency and applicability of the proposed model was validated by comparing with the tested data.(4) The quantification index of the carbonation environmental action of the RCA concrete structure was established based on the investigation of the influence of the RCA replacement rate, environmental temperature, relative humidity, CO2 concentration on the carbonation depth of the RCA concrete. Then, a quantitative durability design method for the RCA concrete structure was proposed by adopting the coefficient of carbonation reaction rate as the durability design parameter.