A research study was conducted with the goal of determining the expected performance life of thin bonded concrete overlay of asphalt (BCOA) in California. Eleven thin BCOA sections were built and tested with the Heavy Vehicle Simulators (HVS) in Davis, California. The performance of the sections in the HVS testing provided insight into the mechanics of the thin BCOA structures and the effects the different rapid-strength concrete materials, traffic, jointing, and base factors on their performance, including testing in both very wet and very dry conditions. Overall, the performance of the thin BCOA sections in the HVS testing was excellent. The eleven sections resisted the predefined HVS loading without cracking. In five of the sections, that loading was equivalent to 6 million single-axle loads and included load levels more than twice the legal limit in California, channelized traffic at the shoulder edge of the slabs, and a continuous water supply that simulated flooded conditions. The main conclusion from this research study is that a well-designed, well-built thin bonded concrete overlay with half-lane width slabs placed on top of an asphalt base that is in fair to good condition can provide 20 years of good serviceability on most of California’s non-interstate roadways.

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A dynamic load test study was performed on instrumented asphalt and concrete pavement test sections at the Minnesota Road Research facility. Test variables included different types of vehicles (featuring various axle groupings, load levels, and tire pressures) operating at various speeds over different structural sections. Four flexible pavement sections were selected for inclusion, and the primary structural response measured was horizontal strain at the bottom of the asphalt layer. The test data suggest that the structural response of the four sections to varying loads was linear when other test parameters were held constant. The pavement sections also exhibited a pronounced viscoelastic behavior in response to changes in vehicle speed and load rate. This behavior was attributed mainly to the asphalt concrete layer. Changes in tire pressure did not significantly affect pavement behavior. The test data were used to validate a multilayer linear elastic pavement structural model. Sub-grade and base moduli inputs were back calculated from falling weight deflectometer data, and the asphalt modulus was determined experimentally from measured strain. This model adequately reproduced the strain distribution observed at the bottom of the asphalt layer under the passage of moving vehicles with certain limitations: the longitudinal strain asymmetry due to viscoelastic effects could not be reproduced, and the modulus of the asphalt layer had to be readjusted for temperature and vehicle speed. Also, it was not possible to calibrate or fit the model to observed longitudinal and transverse strains simultaneously because the pavement behaved more stiffly longitudinally than transversely.

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