National Concrete Pavement Technology Center

Project description

Magnetic imaging tomography (MIT) scanning is a nondestructive method for measuring the alignment of dowels placed at transverse joints of jointed plain concrete pavements (JPCPs). Several highway agencies across the United States have adopted specifications for dowel alignment, with many using the joint score measure. However, this measure was developed intuitively and not based on any laboratory or field tests. National Cooperative Highway Research Program (NCHRP) Report 637 provides a methodology to determine an equivalent dowel diameter measure based on dowel misalignment (Khazanovich et al. 2009). This procedure was developed from laboratory tests and with limited field validation. The relationship between dowel misalignment and the performance of JPCP is unclear, but understanding it is imperative for developing construction guidelines. This report presents results of MIT scanning data collected on Long-Term Pavement Performance (LTPP) test sections and data analysis to assess the effects of dowel misalignment on JPCP performance. As part of this study, MIT scanning was performed on 121 Specific Pavement Studies-2 and 3 General Pavement Studies-3 test sections. Dowel alignment parameters, joint score, and equivalent dowel diameter were calculated as part of the analysis. Statistical analysis was performed to determine any relationship between the joint score and cracking and between the joint score and spalling. The analysis did not indicate any definitive relationship between the joint score and cracking or the joint score and spalling within the analysis range for most States, although some effect was observed for three States. This lack of relationship does not mean severely misaligned dowels have no effect on pavement performance, particularly localized distresses. Analysis of the equivalent dowel diameter as a measure of dowel misalignment for use with AASHTOWare Pavement ME Design software suggests that using the equivalent dowel diameter is a less-biased estimator of long-term load-transfer efficiency (LTE), as modeled using AASHTOWare Pavement ME Design, than using the actual dowel diameter, suggesting a relationship between dowel misalignment and long-term LTE (AASHTO 2014). However, there is considerable scatter in the LTE modeled using AASHTOWare Pavement ME Design versus actual LTE. The remaining bias and scatter suggests that the models (i.e., equivalent dowel diameter and LTE in AASHTOWare Pavement ME Design) could potentially be improved using data collected as part of this study.