再生粗骨料混凝土干燥收缩特性理论模型

为研究再生粗骨料混凝土的干燥收缩特性，收集了现有12项研究与32组收缩数据并进行了比较，试验时间跨度为41~480 d，分析参数包括水灰比(0.36~0.68)、普通混凝土抗压强度(27~60 MPa)、再生粗骨料替换率(20%~100%)、相对湿度(43%~65%)、湿养护时间(1~28 d)和测量收缩的时间(41~480 d)；通过比较试验数据和理论预测结果，利用基于天然骨料混凝土干燥收缩试验数据的多个统计指标，评估了现有ACI 209R-92模型、Bazant-Baweja B3模型以及FIB MC2010模型；采用基于Fathifazl等研究的方法来评估混凝土的干燥收缩增量；通过上述选定模型来评估再生粗骨料混凝土的干燥收缩率的增量，并使用评价残差、欧洲国际混凝土委员会(CEB)变异系数、CEB均方差与CEB偏差等统计指标评价了试验数据。研究结果表明:当将已知收缩行为的天然骨料混凝土的部分或全部粗骨料替换为已知残留砂浆含量的再生粗骨料，可以最准确地预测总收缩的演变；通过将残余砂浆系数应用于天然骨料混凝土的实测收缩量，可以相对准确地预测再生骨料混凝土的收缩；当再生粗骨料混凝土的替代率为20%~33%时，残余砂浆系数为1.03~1.08，当再生粗骨料混凝土的替代率为50%时，残余砂浆系数为1.07~1.16，即再生骨料混凝土的干燥收缩率比天然骨料混凝土的干燥收缩率增加了约16%或更小；当再生粗骨料混凝土的替代率为100%时，残余砂浆系数为1.18~1.76；当天然骨料混凝土的替代率大于50%时，再生粗骨料混凝土的干燥收缩率的增加相比天然骨料混凝土的干燥收缩率的增加更明显。由此可见，当前的研究方法可用于利用扩展的数据库进一步改进再生粗骨料混凝土干燥收缩行为的理论预测。 

Theoretical model of drying shrinkage behavior of recycled coarse aggregate concrete

To investigate the drying shrinkage behavior of recycled coarse aggregate concrete, 12 studies and 32 sets of shrinkage data were collected and compared. The test period was between 41 and 480 d, and the analysis parameters were as follows: the water-cement ratio (0.36-0.68), compressive strength of normal concrete (27-60 MPa), replacement ratio of recycled coarse aggregate (20%-100%), relative humidity (43%-65%), time for wet cure (1-28 d), and time of shrinkage measurement (41-480 d). Three existing theoretical models, such as the ACI 209R-92 model, Bazant-Baweja B3 model, and fib MC2010 model, were evaluated by comparing the test data with the theoretical predictions using multiple statistical indicators based on the experimental drying shrinkage data of natural aggregate concrete. The approach proposed by Fathifazl et al. was used to evaluate the increase in the drying shrinkage of concrete. The increments of the drying shrinkage rate of recycled coarse aggregate concrete were also evaluated by the three selected models, and the experimental data were evaluated by the statistical indicators including the residual evaluation, as well as the variation coefficient, mean square error, and mean deviation of Comité Euro-International du Béton (CEB). Research results show that the most accurate predictions of the total shrinkage evolution are possible when part or all coarse aggregates of natural aggregate concrete with known shrinkage behavior is replaced with the recycled coarse aggregate with known residual mortar content. When the residual mortar coefficient is applied to the measured shrinkage of natural aggregate concrete, a relatively accurate prediction of the shrinkage of recycled coarse aggregate concrete is possible. The residual mortar coefficient ranges from 1.03 to 1.08 when the replacement ratio of recycled coarse aggregate is 20%-33%, and it is between 1.07 and 1.16 when the replacement ratio is 50%. In other words, the increase in the drying shrinkage rate of recycled aggregate concrete over that of the natural aggregate concrete is about 16% or smaller. When the replacement ratio of recycled aggregate concrete is 100%, the residual mortar coefficient ranges from 1.18 to 1.76. When the replacement ratio of natural aggregate concrete is greater than 50%, the increase in the drying shrinkage rate of recycled coarse aggregate concrete is more significant than that of the natural aggregate concrete. It can be seen that the current research methodology can be used to further improve the theoretical prediction of the drying shrinkage behavior of recycled coarse aggregate concrete using an expanded database.