Prediction of effective chloride diffusion coefficient of recycled aggregate concrete based on multiscale analysis
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摘要: 将再生混凝土视为由砂浆相、再生骨料相和二者砂浆之间的界面过渡区相(ITZ-2)组成的非均质复合材料，其中砂浆相由细骨料、细骨料-新砂浆界面过渡区(ITZ-1)、硬化水泥浆体三相组成，而再生骨料相由旧骨料、附着砂浆及旧骨料与旧砂浆的界面(ITZ-3)三相组成。基于N层球夹杂理论，考虑微观相的影响，建立了再生混凝土有效氯离子扩散系数预测的五相多尺度模型，通过硬化水泥浆体、砂浆和再生混凝土的稳态扩散系数实测值与模型预测值对比分析，验证其模型的准确性和有效性；最后，进一步讨论了氯离子侵蚀时间、再生骨料体积分数和附着砂浆含量等关键参数对其有效扩散系数的影响。结果表明：有效扩散系数预测值与试验值吻合较好，说明模型对预测再生混凝土的有效氯离子扩散系数具有普适性，为氯盐环境下再生混凝土耐久性评估与寿命预测提供理论依据。Abstract: Recycled aggregate concrete is regarded as a kind of heterogeneous composite material composed of mortar matrix phase, recycled aggregate phase and the interfacial transition zone (ITZ-2) phase between new and old mortars. Among them, mortar matrix phase is composed of fine aggregate, hardened cement pastes and the interfacial transition zone (ITZ-1) between them, while the recycled aggregate phase is composed of old aggregate, attached old mortar, old interfacial transition zone (ITZ-3) between them. Based on the N-layer spherical inclusion theory with considering the influence of microscale phase, a five-phase multiscale model of effective chloride diffusion coefficient of recycled aggregate concrete was established. The accuracy and validity of the proposed model were verified by comparing between the experimental and predicted results of steady-state chloride diffusion coefficient of hardened cement paste, mortar and recycled aggregate concrete, respectively. Finally, the influence of the key parameters including the chloride ingress time, the volume fraction of recycled coarse aggregate and the attached mortar content on effective chloride diffusion coefficient was further discussed. The results show that the predicted effective diffusion coefficient agrees well with the experimental results obtained in the literature. It indicates that the proposed model can be universally used to predict the effective chloride diffusion coefficient of recycled aggregate concrete, which provides a theoretical basis for durability evaluation and service life prediction of recycled aggregate concrete exposed to chloride salt environment.
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图 1 再生混凝土(RAC)多尺度模型结构示意图
AFt—Ettringite; AFm—Calcium sulfoaluminate; C-S-H—Hydrated silicate gel; CH—Calcium hydroxide; ITZ-1—Interfacial transition zone between new mortar and fine aggregate; ITZ-2—Interfacial transition zone between new mortar and old adhered mortar; ITZ-3—Interfacial transition zone between old adhered mortar and old aggregate
Figure 1. Schematic diagram of recycled aggregate concrete (RAC) multiscale model structure
图 2 基于N层球夹杂理论的RAC五相复合球体模型
Figure 2. Five-phase composite spherical model of RAC based on N-layer spherical inclusion theory
R1, Ri−1, Rn—Concentric circles of radius
图 5 不同侵蚀时间下硬化水泥浆体有效扩散系数计算值与试验值对比
Figure 5. Comparison of effective diffusion coefficient of hardened cement for different exposure time between predicted and experimental results
图 6 砂浆相有效扩散系数预测值与试验值对比
Figure 6. Comparison of effective diffusion coefficient for mortar phase between predicted and experimental results
图 7 再生混凝土有效扩散系数预测值与实测值对比
Figure 7. Comparison of effective diffusion coefficient of RAC between predicted and experimental results
图 8 侵蚀时间、再生骨料体积分数和附着砂浆含量对再生混凝土有效扩散系数的影响
w/c—Water cement ratio; R—Rate of adhered mortar; V—Volume fraction of RCA; t—Exposure time; RCA—Recylced coarse aggregate
Figure 8. Effect of exposure time, volume fraction of recycled aggregate and attached mortar content on effective diffusion coefficient of RAC
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