| An in-depth study of factors and causes of punchout distress is presented. The study is based on a review of CRC pavement behavior under contraction restraint that encompassed several structural response models including two numerical models developed for CRC pavement structural response analysis. Each model was categorized according to different assumptions with regard to the bond stress distribution. Slab bending analysis models were also discussed in terms of transverse and longitudinal bending stresses under load. One of the models, the ILLI-SLAB program, was found to be versatile and provide accurate results. Other comparisons were also made with the structural response models on the basis of crack width, steel stresses, and concrete stresses. Distinct differences were noted between the TTICRCP model and the models which assume a uniformly distributed bond stress.;Causes of punchout distress were investigated by punchout surveys conducted under this study of in service pavements. Various phases of the punchout distress were noted. Field data was also obtained from a coring program, a non-destructive testing program, and a pavement instrumentation program. All the collected data was summarized from which an account of a progressive mechanism of punchout distress was developed. Subbase erosion was found to be the primary cause of the punchout distress.;Current design procedures were reviewed in light of the punchout study and several deficiencies noted. Failure modes representing various stages of punchout distress were formulated based on the punchout investigation. The failure modes provide a basis for thickness design in light of the punchout mechanism.;Major findings from this study include: (1) fundamental cause of punchout distress is attributed to loss of subbase or non-uniform support, (2) loss of load transfer (which is primarily due to crack spalling) occurs as a part of the mechanism leading to the development of the punchout, and (3) large variability is associated with the cracking behavior of CRC pavement which is influenced by the intrinsic material properties of the concrete and by the environmental conditions. |
