About the research
The objective of this project was to determine the optimum joint spacing for thin concrete overlays based on different concrete overlay thicknesses, support systems, and concrete overlay types with and without structural macro-fibers.
In thin concrete overlays, field observations have sometimes shown that not all contraction joints activate initially and, in some cases, do not activate until many years after construction. Contraction joints that do not activate may be considered an inefficient design that may lead to unnecessary maintenance efforts and costs. The optimum joint spacing design may need to be determined based on factors other than those that are currently considered.
This project included an analysis for recommended joint spacing using pavement design software as well as a field review of joint activation in existing concrete overlays using nondestructive testing. Test sections were also constructed to analyze a wider range of variables and to study early-age joint activation behavior.
The data showed that joint spacing was the most significant factor affecting joint activation. A design parameter, slab length over the radius of relative stiffness (L/ℓ), was identified to have a correlation with joint activation percentage and timing.
The data showed that use of macro-fibers did not affect the percentage or rate of joint activation compared to overlays without macro-fibers.