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1 CHAPTER 1 BACKGROUND 1.1 PROBLEM STATEMENT In jointed plain concrete pavements (JPCP) and continuously reinforced concrete pavements (CRCP), the concrete slab is placed on base and subbase layers. Among other requirements, the base layer of a concrete pavement serves as a construction platform for the concrete slab so that the pavers will have a stable platform on which to operate, provides uniform support for the concrete slab and prevents erosion of the pavement support. The base layer may consist of a wide variety of unbound, asphalt stabilized, cement stabilized, and other materials. The presence of the base layer affects the structural behavior and performance of the concrete pavement. The interaction of the concrete layer and base depends on construction factors, environmental conditions, slab and base material properties, loading factors, and other parameters. The American Association of State Highway and Transportation Officials (AASHTO) mechanistic-empirical (M-E) design procedure directly considers the effect of the base layer in the analysis and performance prediction of concrete pavements and overlays. However, the procedure incorporates oversimplified slab-base interface model allowing either a fully bonded or fully unbonded interface condition. While other pavement characteristics such as material properties, traffic loading, or temperature curling may vary on a monthly or hourly basis, the slab-base interface may vary only once in the pavement life. Thus, predictions from AASHTO M-E do not appear to adequately consider aspects of the interaction between the concrete slab and the underlying base layer. Pavement designs informed by these compromised performance predictions may be consequently under designed or over designed. The inability to account for slab-base interaction in design and analysis is therefore an important issue in pavement engineering. 1.2 RESEARCH SCOPE The objective of this research is to develop an M-E model (and associated software) to consider the interaction between the slab and base layer and its effect on pavement performance. The researchers reviewed available literature concerning laboratory and field efforts to characterize slab-base interaction. In-service and experimental pavement data were used to identify important factors surrounding slab-base interaction and pavement performance. The researchers also evaluated available models for slab-base interaction and pavement performance in JPCP and CRCP, including those of the AASHTO M-E procedure. Alternative models for the AASHTO M-E procedure were developed and validated. Finally, rudimentary software was created to allow the models to access existing AASHTO M-E design projects. In this way, the AASHTO M-E software can be used to predict performance given the alternative models for performance and slab-base interaction.
