Composite pavements are pavement systems constructed with both portland cement concrete (PCC) and hot mix asphalt (HMA) pavement layers. Two types of composite pavements have been used in the past: HMA overlays of new or structurally sound existing PCC pavements (thermally insulated concrete pavements) and whitetoppings. Thermally insulated concrete pavements (TICPs) consist of a concrete pavement structure (jointed or continuously reinforced) covered by an asphalt layer during construction (before opening to traffic) or soon after construction to address ride quality or surface characteristic issues. TICPs combine the structural longevity of PCC pavements with the serviceability of HMA pavements. One of the perceived benefits of TICPs is the simplification of the PCC design and construction through a thinner PCC layer due to reduced stresses in the concrete from the insulating effects of the asphalt layer, simplified finishing and simplified joint formation techniques. There is a need for life cycle cost evaluation of TICPS and effective design and construction guidelines for applications where it has economic advantages. These guidelines should be based on a better understanding of the effects of design, materials and construction parameters on the performance of the TICPs. The research proposed in this pooled fund study aims to perform the life cycle cost comparison with alternative strategies and develop the required guidelines for mechanistic design and construction. The study will focus on the initial questions of life cycle analysis, the environmental/climatic effects on performance, pavement design (interaction of concrete and asphalt thicknesses), materials properties for the asphalt and concrete materials and design details such as joint spacing, dowels and joint support. This investigation will determine an initial set of pavement structures that provide the best performance with respect to performance, constructability and cost-efficiency. The investigation will use a review of the literature, extensive mechanistic analysis combined with measured field properties and available information from field and accelerated pavement testing performance to determine the optimized set of pavement structures. These structures will then be available for construction and determination of more detailed extensive field and accelerated pavement testing performance data as validation of the design process. Thin asphalt overlays of PCC pavements encompass many of the same ideas as TICPs and they will also be considered in this pooled fund study. The other type of composite pavement, concrete over asphalt, is often referred to as ¿whitetopping¿. Since behavior and design of this type of pavement will be the subject of another pooled fund study initiated by the Minnesota Department of Transportation, the scope of this study will include PCC over HMA composite pavements in the literature review only.

The main objective of the proposed research is to perform life cycle cost analysis comparisons and develop design and construction guidelines for TICPs (i.e. composite thin HMA overlays of new or structurally sound existing PCC pavements). The study also has the following secondary objectives: 1. Validation of the structural and climatic models of the Mechanistic-Empirical Pavement Design Guide (MEPDG) for asphalt overlays of concrete pavements. 2. Investigation of applicability of the MEPDG for design of TICPs. 3. Investigation of applicability of reflective cracking and asphalt rutting models developed in California. 4. Development of recommendations for feasibility analysis of newly constructed TICPs or thin overlays of the existing concrete pavements. These objectives will be accomplished by collecting field performance data and evaluating the influence of design, material properties and construction on the performance of TICPs. A portion of this project involves constructing new test sections at the Minnesota Road Research Facility (MnROAD) to study TICPs. The funding for initial construction of the test sections will be obtained separately from Mn/DOT and other partners.

Task 1: Development of Information on Composite Pavements The project team will assess the state of practice and knowledge for the design and construction of composite pavement systems. The review of the state of practice will focus on two main issues: summarizing design and construction guidelines and identifying test sections or field projects to determine performance histories. It will include the design and construction of AC overlays of old PCC pavements and new composite pavement systems. Task 2: Perform Initial Life-Cycle Analysis A life cycle analysis will be performed, taking into account agency and user costs as well as environmental and sustainability aspects. This analysis will compare several hypothetical TICPs and overlays with conventional asphalt and concrete pavements to determine economically viable solutions and relative environmental costs. Task 3: Enhanced Integrated Climatic Model (EICM) Validation and Analysis The research team will conduct extensive validation of the EICM. A sensitivity analysis will be conducted to ensure that the predicted temperature distributions are reasonable for a wide range of the input parameters that might be expected for composite pavements. This will be followed by an extensive analytical investigation of the effect of various TICPs designs on the reduction of PCC slab curling and joint movements due to presence of the HMA layer. Critical design, material and construction features will be identified. Task 4: Evaluation of Pavement Response Models The research team will use the information collected at the MnROAD test sections to evaluate and adapt available computer models capable of predicting pavement response to load and environmental effects. The responses of the MEPDG structural model, ISLAB2000, will be compared with the measured responses from the test sections. Task 5: Develop Design Guidelines The research team will develop guidelines for the design of composite pavements. To develop these guidelines, sensitivity analyses will be performed using MEPDG and CalME performance models. Task 6: Develop Construction Guidelines A group of experts in materials and construction will be convened to determine constructability of composite pavements. This panel will evaluate materials, methods, sequencing and value engineering. The use of CA4PRS pavement construction schedule estimating software for TICPs alternatives will be investigated. Task 7: Develop Synthesis The research team will prepare a synthesis as a stand-alone FHWA document. Task 8: Draft final report The research team will prepare a final report that contains the following: - A summary of experience to date based on the literature survey. - A detailed description of the environment, structural and performance model and their predictive capabilities. - A summary of the pavement designs considered, the expected performance based on the sensitivity analyses, expected construction schedule and approximate life cycle cost over a common analysis period. - Information addressing relevant issues to advise the participating state departments of transportation on possible changes in their design and construction specifications. Task 9: Prepare Final Report The research team will address the panel comments on the final report.

Mn/DOT along with other participating states are asked to contribute $20,000 per year for 5 years to fund the research proposed in this pooled fund study. The Minnesota Department of Transportation (as the lead agency) along with other partners will provide approximately $200,000 in construction funding outside of this pooled fund study to construct the pavement test sections at MnROAD for validating the design and construction guidelines for composite pavements and thin HMA overlays.