Design and Construction Guidelines for Composite Concrete Over Asphalt Pavements
I. Problem Statement:
Composite pavements consist of two or more pavement layers, having some degree of bond and shear strength at their interface. The pavement layers, which are mainly Portland cement concrete (PCC) and hot mix asphalt (HMA) layers, act as one unit in response to applied traffic loads and environmental effects. In recent years many composite pavements have been constructed in new and rehabilitation projects in the US and abroad, involving combinations of HMA on PCC, PCC on HMA or PCC on PCC layers. Since the topic is very broad, this problem statement will only pertain to composite pavements, which consist of PCC on HMA layers.
In new construction, composite PCC on HMA pavement include full depth concrete pavement on HMA base in new construction. In Rehabilitation projects, Whitetopping and unbonded PCC overlay can also qualify as composite pavements when some degree of bond is established by design or unintentionally between the PCC and HMA layers.
The performance of these composite pavements has been mixed varying from excellent to poor. Level of performance has often been attributed to design, material properties and construction issues including; thickness of concrete and HMA layers, stiffness of the pavement layers, degree of bond at the interface, concrete panel size, environmental effects (curling and warping of the concrete layer), condition of the HMA layer, and drainage.
There is a need for effective design and construction guidelines for composite pavements of concrete over asphalt layers. These guidelines should be based on better understanding of the effect of design, materials properties and construction parameter on the performance of the PCC/HMA composite pavements. An improved methodology for characterizing the bond condition in the field is also essential for proper design and construction the pavement. This effort should also serve as the first step in the development of an effective mechanistic design for long lasting composite pavements.
II. Research Objective:
The main objective of the proposed research is to develop design and construction guidelines for composite PCC-HMA pavements. This objective would be accomplished by evaluating the influence of design, material properties and construction on the performance of composite PCC-HMA pavements.
Specific objectives include:
1. Characterizing initial and long term bond at the interface between the layers,
2. Determining the optimum thickness ratios of the two layers, based on load and environmental conditions,
3. Characterizing the condition of the HMA layer
4. Optimizing Layer stiffness
5. Selecting optimum pavement panel size/joint spacing.
6. Determining Curling and warping potential of concrete panels.
7. Identifying drainage needs based on degree of initial bond and potential degradation of bond with time.
8. Incorporating the results into design and construction guidelines. Also, providing recommendations on where composite pavements are most effective.
III. Proposed Scope of Work
To accomplish objectives of this research, the following tasks are proposed as a minimum:
Conduct a literature search, and survey of states and industry on the use, design, material characteristics of layers, construction practices, and performance of composite pavements, which consist of PCC over HMA layers. Identify in-service pavement sections for detailed field evaluation.
Develop an effective test /methodology for characterizing bond strength between the
Based on results of Task 1 select test sections from existing pavements. The test sections would include combinations of layer thickness, degree of bond, different conditions of HMS layer, concrete panel sizes, layers’ modulii, and drainage conditions.
Perform condition survey and deflection tests on the field sections to determine load response characteristics of the various field sections. Identify critical, design, material and construction features. Also evaluate drainage conditions and any impact of presence or lack of drainage on pavement performance.
Construct and instrument a test section, which would include design features critical to the performance of the composite pavement. Measure pavement response to load and curling and warping effects. Perform deflection tests to determine stiffness characteristic of the pavement layers and system.
Develop and/ or evaluate existing computer models capable of analyzing and predicting pavement response to load and environmental effects. The computer programs should be capable of evaluating multiple combinations of layer thickness and stiffness, different degree of bond between the layers, different panel size, and various curling warping cases.
Develop design and construction guidelines for composite PCC/HMA pavements. These guidelines should also identify circumstances under which composite pavements are most effective.
IV. Funding and Time:
Recommended Funding: $400,000
Research Period: 36 months
V. Date and Submitted by:
Jamshid Armaghani, Ph.D., P.E.