考虑湿度时效分布影响的再生混凝土收缩预测模型

Shrinkage distribution model of recycled aggregate concrete considering time-dependent relative humidity distributions

为预测单面传湿边界条件下再生混凝土内部收缩变形的时效分布,结合传湿学基本理论与CEB-FIP 90规范中建议公式,建立再生混凝土水分扩散系数的表达式,并采用现有的相对湿度分布实测数据验证表达式的准确性;在此基础上进行参数分析,量化再生粗骨料取代率与湿度边界条件等因素对再生混凝土内部相对湿度分布的影响;引入混凝土自由收缩与相对湿度的数学关系,建立并验证再生混凝土在单面湿度边界条件的收缩变形时效分布模型。研究结果表明:考虑再生粗骨料取代率影响提出的再生混凝土水分扩散系数公式,可有效预测再生混凝土内部相对湿度分布,预测结果与实测结果相差在15%以内;再生粗骨料取代率和湿度边界条件对混凝土内部相对湿度分布的影响明显,取代率为100%的混凝土较取代率为0%的混凝土中部湿度增大0.6%~4.2%,相同厚度时,单面传湿条件下混凝土内部相对湿度的不均匀分布程度较双面传湿条件时更明显;基于相对湿度分布提出的混凝土收缩分布模型,可有效预测单面传湿条件下的再生混凝土收缩分布,预测结果与实测结果相差在15%以内。

To investigate the time-dependent internal shrinkage distributions of recycled aggregate concrete(RAC)under single-side diffusion boundary condition,by combining the basic theory of moisture transfer and the empirical formula of existing CEB-FIP 90 specifications,the expression of RAC moisture diffusion coefficient was established and verified against the existing relative humidity(RH)distribution test data.A parameter analysis was further conducted to quantify the influential factors on the internal RH of RAC,e.g.,recycled coarse aggregate(RCA)replacement ratio and diffusion boundary condition.The time-dependent shrinkage distribution model of RAC under single-side diffusion boundary condition was proposed by introducing the correlation between concrete free shrinkage and RH values.The results show that the proposed diffusion coefficient can effectively predict the RH distributions inside the RAC by considering the effect of the RCA replacement ratio,and the average error between the predicted and the measured results was with 15%.The effects of the RCA replacement ratio and the diffusion boundary conditions on the RH distributions inside the concrete were obvious.The RH in the middle of the concrete specimen with RCA replacement ratio of 100%was 0.6%-4.2%higher than that in the concrete specimen with the replacement ratio of 0%.Under the condition of the same thickness,the non-uniform RH distributions inside the concrete with single-side diffusion condition was more obvious than that under two-side diffusion condition.The concrete shrinkage distribution model proposed can effectively predict the shrinkage distribution of RAC with single-side diffusion boundary condition,and the average difference between the predicted results and the measured results was with 15%.