Effect of tie bars on the field performance of full-depth repair on concrete pavement

Many Full-Depth Repairs (FDRs) have suffered recurring failures and thus there is a critical need to enhance the understanding of the failure mechanisms. Three premature failure projects were investigated. Recurring pumping, settlement and cracks are strongly related to poor Load Transfer Efficiency (LTE), which was obtained with a falling weight deflectometer. Cores were taken to examine the condition of the tie bars. The results from highway IH20 reveal that recurring failures occurred on the same slabs that had poor anchoring to the adjacent slabs. There was zero resistance on the pull-out test before the concrete was poured in 2009. Low LTEs of less than 40% were measured in 2010. Cores taken in 2010 revealed significant surrounding voids at the tie bar, indicating that the epoxy did not ever develop sufficient anchoring strength. The deflections at the joints were 3-5 times higher than those at the center slab. Similar failure mechanisms were observed on the IH35 and US75 projects that had poor LTE. There was a good correlation between lower LTE, higher deflections, visible pumping, and settlement. Tie bars were not properly anchored in the IH35 pavement. Tie bars were ruptured in the US75 pavement. Because of these ineffective tie bars, pumping and settlement were prevalent. In contrast, a good performing FDR on SH78 also was investigated. All LTEs had remained above 90% even after 16 years of trafficking. It was concluded that when LTE exceeds 90%, it lead to a successful FDR. By comparison, if was concluded when LTE was less than 40%, premature failures occurred. Additional data is needed to verify what will be the performance when the LTE is between 40% and 90%. A threshold value can be established for acceptable LTE value. The superior performance of the SH78 pavement suggests that proper procedures are critical when anchoring the tie bars. Pull-out tests should be performed to ensure that proper anchoring and sufficient strength is developed on the tie bar before concrete is placed.