CAM and SMA mixtures to delay reflective cracking on PCC pavements

• CAM and SMA have been used successfully to retard reflective cracking.
• The field performances of CAM and SMA overlays have been excellent as they have exceeded 8 years of life expectancy.
• The SMA overlays have been placed approximately 12 years ago and zero maintenance is needed.
• OT of exceeding 700 cycles should be used to ensure the CAM and SMA overlays will be able to retard the reflective cracking.

Reflective cracking potential in hot mix asphalt (HMA) overlays on Portland cement concrete (PCC) pavement depends on the condition of PCC pavement in terms of slab stability at discontinuities (cracks and joints) and asphalt material characteristics in terms of their ability to resist reflective cracking. To develop a more comprehensive HMA overlay on PCC pavement program that minimizes reflective cracking potential and thus improves HMA overlay performance, TxDOT employed evaluation tools for both continuous deflection measurement of PCC slabs and overlay mix material characteristics. Rolling Dynamic Deflectometers (RDD) evaluate deflections on pavement surface continuously, providing valuable information on the stability of concrete slabs and load transfer efficiencies at discontinuities such as cracks and joints. Overlay testers (OT) evaluate the capacity of asphalt mixtures to resist reflective cracking. Since the performance of HMA overlay on PCC pavement depends on the extent of reflective cracking, design criteria should be developed for both slab stability and asphalt material properties. To that end, RDD and OT were utilized for the evaluations of HMA overlay on PCC pavements in four projects in Texas: (1) IH20, (2) SH225, (3) SH12, and (4) US96, with the objective of developing design criteria. This paper documents the efforts made to evaluate the PCC pavement condition before overlay, overlay material properties, and long-term performance of the four sections. CAM and SMA mixtures have been used successfully to retard reflective cracking, as they have exceeded eight years of life expectancy. Threshold values were validated for slab stability and asphalt materials, and applied for the designs of three rehabilitation projects.