Abstract
In 1990, the Arizona Department of Transportation (ADOT) constructed a Specific Pavement Studies (SPS)-6 experiment on eastbound Interstate 40 (I-40) east of Flagstaff, AZ, as part of the Long-Term Pavement Performance Program. The SPS-6 experiment was designed to evaluate treatment and rehabilitation options for an existing concrete pavement. Nineteen sections were constructed, one of which was a 10 in. thick unbonded concrete overlay (UBCOL). Additionally, ADOT planned to construct an 11 in. unbonded portland cement concrete (PCC) overlay on the adjacent I-40 westbound to investigate benefits of additional concrete thickness. The eastbound unbonded PCC overlay has significantly outperformed all other pavement sections and remains in good condition after 27 years of service. However, the westbound PCC section is severely distressed and in need of immediate rehabilitation. An investigation was conducted to evaluate why two similar unbonded PCC overlays performed with vastly different results. It was found that the westbound “unbonded PCC overlay” was not an overlay after all, but instead a 12 to 13 in.thick jointed plain concrete pavement (JPCP). The high level of distress in the westbound JPCP is likely related to the presence of a weak subgrade that infiltrated the aggregate base. Additionally, during coring, water filled the core holes suggesting that the subgrade in the westbound direction was saturated. Further, petrographic analysis indicated deicing chemicals contributed to corrosion of the dowel bars and deterioration of the concrete joints. This investigation demonstrates some advantages for using unbonded overlays as rehabilitation alternatives for existing concrete pavements.
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