持压荷载与干湿循环作用下再生混凝土氯盐侵蚀行为

Chloride ingress behavior of recycled aggregate concrete subjected to sustained compressive loading and drying-wetting cycles

  • 摘要: 采用干湿比为3∶1和质量分数为5wt%的NaCl溶液,开展了持压荷载与干湿循环共同作用下不同再生粗骨料取代率(r=0%、30%、50%、100%)混凝土的氯离子传输试验,分析了持压应力水平(λc=0.1、0.3、0.5)对氯盐侵蚀性能的影响。基于非饱和混凝土的氯离子对流-扩散模型,提出了考虑应力水平和再生骨料取代率影响的水分和氯离子扩散系数模型,并验证了该模型的有效性。结果表明:相同再生粗骨料取代率的混凝土内自由氯离子含量、氯离子扩散系数和表面氯离子浓度均随应力水平的增加呈先减小后增大的趋势,同一应力水平下与再生粗骨料取代率呈正相关,再生粗骨料取代率为100%的试件承受0.1fc、0.3fc、0.5fc (fc为再生混凝土(RAC)立方体抗压强度值)应力作用的氯离子扩散系数分别是无应力状态的0.97、0.88和1.48倍;所建立的持压荷载与干湿循环作用下RAC氯离子传输模型,为再生混凝土耐久性分析提供理论依据。

     

    Abstract: The chloride attack environment with cyclic drying-wetting ratio of 3 : 1 and 5wt% mass fraction of NaCl solution was simulated to conduct the chloride ingress test of recycled aggregate concrete (RAC) with diffe-rent replacement rates (r=0%, 30%, 50%, 100%) subjected to sustained compressive loading and drying-wetting cycles. Effect of different sustained compressive stress levels (λc=0.1, 0.3, 0.5) the chloride ingress performance of RAC was studied. Based on the chloride convection-diffusion model of unsaturated concrete, the models of water diffusivity and chloride diffusion coefficient considering the effects of recycled coarse aggregate replacement rate and stress level were proposed and validated. The results indicate that at the same replacement rate of recycled coarse aggregates, the free chloride content, chloride diffusion coefficient and surface chloride concentration in RAC decrease first and then increase with the increase of sustained compressive stress level. Under the same stress level, they are positively correlated with the replacement rate of recycled coarse aggregates. The chloride diffusion coefficients of specimens with the replacement rate of 100% subjected to 0.1fc, 0.3fc and 0.5fc (fc means the cubic comprssive strength of RAC) are 0.97, 0.88 and 1.48 times than that of unstressed state, respectively. The established model of the chloride ingress in RAC under sustained compressive loading and drying-wetting cycles can partly provide the theoretical basis for the durability of RAC.

     

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