Field Experiences with RDD and Overlay Tester for Concrete Pavement Rehabilitation

Since reflective cracking is related to both the existing pavement condition and the overlay material, appropriate tools are needed to characterize both properties. The rolling dynamic deflectometer (RDD) was employed to measure the continuous deflection profiles that relate to vertical movements of the underlying joints and cracks. An overlay tester (OT) was utilized to characterize the asphalt mix’s ability to resist reflective cracking. The reported threshold values were employed in the study that include: (1) $W1–W3=6.5\mathrm{mils}$ for composite pavement with old asphalt concrete (AC) overlay; (2) $W1–W3=5.5\mathrm{mils}$ for exposed concrete pavement; and (3) 700 cycles of the OT were employed to evaluate six field rehabilitation projects (SH12, IH20, US96, SH73, SH225, and IH44). It was found that although there were severe transverse cracks and spalling on US96, all $W1–W3$ deflections were less than $5.5\mathrm{mils}$ , indicating low risk for reflective cracking. A stone-mastic asphalt (SMA) layer was placed 3 years ago and the performance is excellent. There are no visible cracks or distresses. The SMA was tested with the OT and exceeded 700 cycles (excellent property on resisting reflective cracking). For comparison, there were severe reflective cracks within 4 years on SH225 even with good underlying support and low vertical movements (all $W1–W3$ deflections less than $6.5\mathrm{mils}$ ) on the jointed concrete pavement (JCP). The reflective cracks were due to a stiff/brittle mix (with OT life of 2 cycles) used on top of the JCP. Dowel bar retrofit (DBR) and full depth repair did improve load transfer and lowered $W1–W3$ deflections on the SH73 project. After 10 years of service, those locations had minor cracks, as opposed to severe reflective cracks in sections without DBR or full depth repair. Based on the results obtained, the RDD, OT, and the three threshold values provide an objective evaluation that correlates to field performance data. It is strongly recommended that both tools be used for the rehabilitation of concrete pavement with an AC overlay to evaluate the potential for reflective cracking.