双轴受压下再生混凝土氯离子扩散规律

Chloride Diffusion Law in Recycled Concrete Under Biaxial Compression

为了研究复杂应力状态下再生混凝土的氯离子传输特性,首先通过破碎不同水灰比的母体混凝土得到不同性能的再生粗骨料,并对天然混凝土和不同性能再生混凝土进行双轴受压试验。然后利用电场加速氯离子扩散和双轴受压装置测试了不同类型再生骨料混凝土和天然骨料混凝土在不同应力水平和不同应力比下的氯离子扩散系数,并利用压汞仪测试了混凝土内部的微观孔隙结构。最后建立了考虑双轴应力水平、再生骨料吸水率和粗骨料体积分数的再生混凝土氯离子扩散系数理论模型,并进行了试验验证。结果表明:来自不同母体混凝土的再生骨料中的附着老砂浆具有不同的孔隙结构,再生混凝土中老砂浆的孔隙率随着母体混凝土水灰比的增加而变大,进而影响再生混凝土的氯离子扩散性;应力比相同时,随着双轴受压应力水平的增加,再生混凝土氯离子扩散系数普遍呈现先下降再上升的趋势,在应力水平约为0.5时再生混凝土氯离子扩散系数出现最小值;在双轴受压荷载作用下,母体混凝土水灰比分别为0.4,0.5,0.6的再生混凝土氯离子扩散系数最多分别下降到无荷载时的0.76%,0.78%,0.78%。

In order to study the chloride ion transport characteristics of recycled concrete under complex stress state.Firstly,recycled coarse aggregate with different properties was obtained by crushing the parent concrete with different water cement ratio,and biaxial compression tests were carried out on natural concrete and recycled concrete with different properties,then combined with electric field to accelerate chloride diffusion and biaxial compression device,the chloride diffusion coefficients of different types of recycled aggregate concrete and natural aggregate concrete under different load levels and stress ratios were tested.The micro pore structure of the concrete was tested by mercury porosimeter.Finally,a theoretical model of the chloride diffusion coefficient of recycled concrete considering biaxial stress level,water absorption of recycled aggregate and volume fraction of coarse aggregate was established and verified experimentally.The results show that the attached old mortars in the recycled aggregates from different parent concretes have different pore structures,and the porosity of old mortar in recycled concrete increases with the increase of water cement ratio of parent concrete,which will affect the chloride ion diffusivity of the recycled concrete.For the same stress ratio,with the increase of biaxial load stress level,the chloride ion diffusion coefficient of recycled concrete generally shows the trend of decreasing first and then rising,and the chloride ion diffusion coefficient of recycled concrete appears the minimum when the stress level ratio is about 0.5.Under biaxial compressive load,chloride ion diffusion coefficient of recycled concrete from parent concrete with water cement ratio of 0.4,0.5 and 0.6 decreases to 0.76%,0.78%and 0.78%at most than that without load,respectively.