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首先,将裂缝弥散化并将裂缝的影响耦合到再生混凝土中CO_2的扩散系数中,基于Fick定律建立受力状态下再生混凝土中CO_2扩散方程,根据质量守恒定律,推导出考虑应力状态影响时再生混凝土中CO_2的传质方程;然后,通过加速碳化试验,确定了传质方程中应力水平影响系数的大小;最后,采用MATLAB编制有限元程序求解传质方程,确定了再生混凝土梁截面的碳化深度分布。结果表明,对于顶面不传质的再生混凝土梁,截面上的碳化深度分布很不均匀,受压区角部再生混凝土碳化深度最小,而受拉区角部再生混凝土的碳化深度最大,其值为受压区一般边再生混凝土碳化深度的2.2倍,为相应的无应力状态下同配比普通混凝土梁一般边的2.4倍。
Firstly, the cracks are dispersed and the influence of cracks is coupled to the diffusion coefficient of CO_2 in recycled concrete. Based on Fick’s law, the CO_2 diffusion equation in recycled concrete under stress is established. According to the law of mass conservation, Then, through the accelerated carbonation test, the influence coefficient of the stress level in the mass transfer equation was determined. Finally, the finite element program was used to solve the mass transfer equation by MATLAB, and the carbonation depth of the section of recycled concrete beam was determined distributed. The results show that the distribution of carbonation depth is not uniform for the regenerated concrete beam with topless mass transfer and the carbonized depth is the least in recycled concrete at the compression zone and the carbonized depth is the highest at the corner recycled concrete beam. It is 2.2 times of the carbonation depth of recycled concrete in the compression zone and 2.4 times of that of normal concrete beam under the corresponding stressless state.