Prediction of Ultimate Shrinkage and Shrinkage Half-Time for Concrete Poured in Hot Climates: Development of the ACI 209 Committee Shrinkage Model

The ACI Committee 209 (ACI 209R- 97) had presented a model for prediction of concrete shrinkage. The included variables in this model are related to mix proportions, member geometry, curing method, and age of concrete. The predictions of this model had not pay adequate attention to the effect of the coarse aggregate on restraining shrinkage strain of concrete and overestimate the shrinkage half- time especially in hot climates. A parametric study was done to investigate the effect of variables other than those included in the ACI model (concrete and aggregate stiffness, aggregate volume, actual added water). Three types of normal-weight aggregate and one light-weight aggregate were included with two moisture conditions (dry and saturated). Teasing program included length change, compression, splitting tensile and static modulus of elasticity tests. The test period for shrinkage strain was extended to 150 days. A mathematical model based on dimensional analysis was built according to current experimental data. The predictions of this model stick close to the actual results (R²= 0.97) and it proves itself as a good tool to predict concrete shrinkage strains at anytime after curing is ceased. Another model was built to calculate shrinkage half-time. This factor is defined as the end of short-term age of concrete shrinkage. Finally, a proposed procedure for ultimate shrinkage prediction was suggested and it was verified reliable throughout statistical tests.