Comparison Between Visual and Ultrasonic Tomography Joint Deployment Detection Methods

Thin bonded concrete overlays placed on existing asphalt (BCOA) pavements perform best when they are designed and constructed with small square panels. The closely spaced contraction joints help to control the location of slab cracking that develops due to the restraint stresses caused by concrete shrinkage and thermal contraction, reflective cracking forces, differential movement between the concrete overlay and asphalt, and curling and warping stresses. These joints are only able to fulfill their function if they deploy shortly after hardening of the concrete. Due to common observations of sequential joints not deploying, experimentation has begun with applying early loads to the panels to encourage more frequent deployment. While visual observation of joint deployment along the side of the concrete overlay is possible before shouldering material is placed, it becomes difficult thereafter. Questions also arise whether visual observation of a cracked joint on the side of the pavement reflects that the joint is fully deployed across the lanes. This study examined the efficacy of visual joint deployment detection along the side of a BCOA project that had been loaded early, compared to ultrasonic tomography conducted across those same joints. Analysis shows both that visual observations and ultrasonic tomography can be used to reliably detect joint deployment, and that it is uncommon that joint deployment is not fully engaged across lanes.