Shrinkage-Based Analysis for Control-Joint Spacing in Slabs-on-Ground

A rational approach is developed to link standard drying shrinkage values and environmental parameters to control-joint spacing for slabs-on-ground. The analysis includes the combined effects of shrinkage, tensile creep, reinforcement, and sub grade friction. The result of the analysis is a set of equations to calculate the control-joint spacing, establishing a rational framework for shrinkage performance specifications. Thermal effects are not included in the model, thus limiting the applicability of the equations to slabs-on-ground in an environment where thermal gradients are minimized. The calculated control-joint spacing values for plain concrete compare favorably with the commonly used empirical PCA recommendations. Reduction in drying shrinkage is shown to increase control-joint spacing. The examples provided show that reinforcement provides marginal increases in control-joint spacing if intermediate cracks are not allowed. When tight intermediate cracks are allowed, reinforcement and low-shrinkage concrete are shown to have a synergistic effect and can provide significant increases in joint spacing.