Slab-Base Interface Friction Evaluation for Continuously Reinforced Concrete Pavement

The frictional characteristics at the slab-base interface are known to contribute to the development of the cracking pattern in continuously reinforced concrete pavement (CRCP) and also to its long-term performance. The backcalculation of the effective slab thickness from falling weight deflectometer (FWD) data can provide an efficient method for evaluating the degree of slab-base friction in CRCP. A direct method for the assessment of slab-base interface friction coefficient using FWD data is presented, which extends a simplified friction model for jointed concrete pavements and evaluates for several base types, effect on friction coefficient over time, and temperature dependency. One field project containing either microsurfacing or an asphalt concrete interlayer on top of a cement-treated base (CTB) enhanced the frictional resistance as measured by a greater effective thickness and increased coefficient of friction. Temperature impacted the backcalculated coefficient of friction when asphalt was present. The backcalculation process was also applied to assess the slab-base interface condition over time for an interstate CRCP test section with a mix-in-place CTB. For this project, the CRCP and CTB interface had a relatively low coefficient of friction but demonstrated stable friction and excellent performance in terms of smoothness and punchouts over the 11-year testing period.