Enhancements to Punchout Prediction Model in Mechanistic–Empirical Pavement Design Guide Procedure

Abstract

The punchout prediction model for continuously reinforced concrete pavements (CRCP) from the Mechanistic–Empirical Pavement Design Guide, along with improvements to the procedure made since the software program was released in 2004 as a product of NCHRP Project 1-37A, is presented. The punchout prediction procedure is based on mechanistic principles for estimating top-down fatigue damage in the CRCP and on an empirical punchout prediction model calibrated to field data. The mechanistic structural evaluation includes models for estimating crack width, crack spacing, load transfer efficiency across transverse cracks, and fatigue damage accumulation based on Miner's hypothesis. The punchout prediction model was calibrated to data on field distress development obtained from CRCP sections nationwide. Most of the field sections were part of the long-term pavement performance (LTPP) experiment, and most of the materials, traffic, climate, and construction data were obtained from the LTPP database. Since 2004, NCHRP has made two main technical enhancements to the design software. The first addressed comments from an independent panel that performed a formal review under Project 1-40A. Second, a systematic error was discovered in the coefficient of thermal expansion test procedure for portland cement concrete, and appropriate corrections were made in the LTPP database. The punchout model was recalibrated to account for this error. The developed models show that the procedure makes reasonable crack spacing, crack width, and punchout predictions that match field observations. The models resulted in similar CRCP thickness designs before and after the coefficient of thermal expansion corrections were made, if the corresponding model calibration coefficients were used.