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.