The influence of four factors (water-binder ratio, recycled coarse aggregate replacement rate, fly ash substitution rate, and superplasticizer content) on the workabilities and mechanical properties of recycled coarse aggregate self-compacting concrete (RCASCC) was studied using the orthogonal test method. Based on the orthogonal test design and range analysis method of the fresh and hardened properties of RCASCC, the optimal mix is as follows: water-binder ratio of 0.269, recycled coarse aggregate replacement rate of 30%, fly ash substitution rate of 40%, and superplasticizer content of 0.50%. Then, the porosity and aperture size distribution of nine groups of RCASCC were tested by mercury intrusion porosimetry (MIP) at the microlevel. The macroscopic and microscopic relationship was established by combining the results of mechanical property tests and MIP. Fractal dimension D of the B.B. Mandelbrot model was used to study the fractal characteristics of pore volume of RCASCC. Results showed that porosity and strengths are negatively correlated, and the relative strength can be roughly judged according to the porosity. The pore structure of nine groups of RCASCC materials has evident fractal characteristics of irregular shape. The complex pore structure adversely affects strength.
The purpose of this paper is to explore the numerical simulation of damage process and results of a new environmentally friendly material, recycled coarse aggregate self-compacting concrete (RCASCC). Random aggregate model of mesoscopic viewpoint was used for the experimental simulation of RCASCC. Results show that the specimens with 50% substitution rate exhibited the best performance among the specimens (i.e., with rates of 25%, 50%, 75%, and 100%). The stress-strain curves after dimensionless treatment were fitted using the uniaxial compressive principal equation of concrete with control parameters a = 0.9 and b = 11, and the fitting degree of the curve was relatively good. Meanwhile, the change process of internal cracking was shown intuitively. The crack expansion process became more obvious in the specimens and beams with a high substitution rate of RCA. The simulation results of the bending process of RCASCC beams analyzed by the concrete damaged plasticity (CDP) model and extended finite element (XFEM) were compared with the test results. Both simulation results validated the applicability of the CDP model and XFEM in the mechanical tests of RCASCC and can provide valuable reference for future research on the mechanical properties of recycled aggregate self-compacting concrete.
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