Improving the performance of full-depth repairs by understanding the failure mechanisms

Abstract

In order to understand the reoccurring failures on the slabs or adjacent slabs that received Full-Depth Repair (FDR) treatments, efforts were made to investigate the causes of the failures on IH35W and US75. In addition, one successful FDR project on SH78 was studied to verify and validate the hypothesis of the failure mechanisms. Load Transfer Efficiencies (LTEs) were evaluated with a falling weight deflectometer, and the base and subgrade moduli were determined by Dynamic Cone Penetration (DCP). Cores were taken to examine the condition of the tie bars. Furthermore, design and construction practices were reviewed and evaluated. The common symptom for both IH35W and US75 projects was the poor LTE (less than 40%). When the LTE was lower, there were higher deflections, visible pumping, and settlement. Settlement is strongly related to the poor LTE. Tie bars were found to be ruptured in the US75 pavement, and they were not properly anchored in the IH35W pavement. Because of these ineffective tie bars, poor LTE and settlement was prevalent. On SH78, all LTEs remain above 90% even after 14 years of trafficking. The superior performance of the SH78 pavement suggests that proper procedures are critical when removing concrete and drilling holes for new tie bars, to avoid damage to, and subsequent failure of the adjacent slabs. The anchoring of the tie bar is critical to the performance of the FDR. Pull out tests should be performed to determine the type of epoxy, time before concrete pouring, embedment depth, and other construction parameters will provide adequate strength. Based on the DCP and field performance results, it is concluded that the most accurate indicator of joint performance is LTE, while the base and subgrade support are secondary.