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Slab-support interaction has long been established as an important consideration in the design and construction of concrete pavements for streets, highways, and airfields. With the current interest in design features such as open-graded permeable bases, unbonded concrete overlays, and whitetopping pavements, the need for an accurate and standard means for characterizing this behavior is evident. With respect to conventional concrete pavements, previous studies have concluded that excessive restraint between the slab and the support layers of a pavement structure can lead to pavement distresses that are ultimately detrimental to the performance of the pavement. These studies have indicated that undesirable restraint characteristics typically are caused by improper subbase design or construction. The consequences of underestimating or neglecting the support restraint characteristics have been shown to result in uncontrolled slab cracking, excessive joint movements, and underdesigned reinforcement. However, in some cases a high degree of slab-support restraint is desired, such as for whitetopping pavements, especially ultrathin whitetopping. Recent developments in characterizing and modeling axial slabsupport restraint characteristics of concrete pavements are presented. Test procedures that have been developed to accurately assess the level of axial slab-support restraint present are identified, as are future enhancements to characterization and modeling of this phenomenon.It is well understood that proper design of concrete pavements requires careful consideration of a wide variety of inputs. Beyond prudent traffic loading predictions, the design engineer must also consider the many influences of environmental loads on a pavement design. Both the diurnal cycle of ambient thermal influence and changing moisture conditions contribute to the cyclical rise and fall of stresses in a pavement. These effects are especially pronounced during the first 72 h after construction because of the dynamic nature of the hydration processes. Tools such as the FHWA HIPERPAV system have been able to demonstrate the importance of this phenomenon (1). AASHTO has also recognized the importance of including these measures in proper pavement design (2).Stresses in a concrete pavement result from the expansion and contraction of the pavement combined with the restraint characteristics caused by, among other factors, the interaction of the support layers beneath the pavement. The level of restraint plays a key role in determining the performance of a concrete pavement. The need for accurate characterization of the axial support restraint when designing and constructing concrete pavements is described here. Both the theoretical and practical aspects of this problem are examined.It should be noted that another important aspect of restraint in a concrete pavement is the restraint of the curling and warping action. However, because of the need for brevity, that topic is not covered here. A complete analysis should consider stresses due to both ...

A portland cement concrete pavement (PCCP) moisture model and associated program are developed for enhancing the FHWA HIPERPAV software predictions. This model predicts PCCP moisture transport and moisture loss to the environment due to drying and self-desiccation. The former is simulated in terms of Fick's second law; the second part is based on Oh and Cha's model. The one-dimensional Crank–Nicolson finite difference method is used to build the mathematical algorithm for solution. FORTRAN coding is developed to program this computational procedure and incorporate the moisture model into the HIPERPAV software. The moisture model has been partially validated with other researchers’ experimental data. Results showed reasonable agreement between predictions and measurements. A sensitivity analysis shows that parameters such as the diffusivity coefficient, surface emissivity, and curing method affect moisture variations, especially at positions close to the surface and the bottom of the slab. Future research will focus on simulations of PCCP critical stresses and distresses with this enhanced moisture model.

HIPERPAV (high-performance paving) is a concrete paving software product developed jointly by FHWA and The Transtec Group, Inc., and is intended to serve as a tool in the proper selection and control of the factors affecting concrete pavement behavior at early ages. Adequate selection and control of these factors will ensure good performance throughout the design life of the pavement. Praised by industry, agencies, and academia, HIPERPAV is the first software tool of its kind to provide real control over concrete pavement design and construction. With HIPERPAV, materials, pavement design, and construction operations can now successfully be integrated into one easy-to-use Windows based software package. This integration captures all aspects of a concrete pavement construction project and provides a real systems approach to analysis of the first 72 h after construction. With a true systems approach, the development of stresses and strength in concrete pavement can be assessed during these critical first 72 h to maximize quality, increase long-term performance, boost productivity, and optimize pavement options. A brief history of the development, validation, and implementation of the HIPERPAV software to date is presented.

Systematic, well-designed research provides the most effective approach to the solution of many problems facing highway administrators and engineers. Often, highway problems are of local interest and can best be studied by highway departments individually or in cooperation with their state universities and others. However, the accelerating growth of highway transportation develops increasingly complex problems of wide interest to highway authorities. These problems are best studied through a coordinated program of cooperative research. In recognition of these needs, the highway administrators of the American Association of State Highway and Transportation Officials initiated in 1962 an objective national highway research program employing modern scientific techniques. This program is supported on a continuing basis by funds from participating member states of the Association and it receives the full cooperation and support of the Federal Highway Administration, United States Department of Transportation. The Transportation Research Board of the National Academies was requested by the Association to administer the research program because of the Board's recognized objectivity and understanding of modern research practices. The Board is uniquely suited for this purpose as it maintains an extensive committee structure from which authorities on any highway transportation subject may be drawn; it possesses avenues of communications and cooperation with federal, state, and local governmental agencies, universities, and industry; its relationship to the National Research Council is an insurance of objectivity; it maintains a full-time research correlation staff of specialists in highway transportation matters to bring the findings of research directly to those who are in a position to use them. The program is developed on the basis of research needs identified by chief administrators of the highway and transportation departments and by committees of AASHTO. Each year, specific areas of research needs to be included in the program are proposed to the National Research Council and the Board by the American Association of State Highway and Transportation Officials. Research projects to fulfill these needs are defined by the Board, and qualified research agencies are selected from those that have submitted proposals. Administration and surveillance of research contracts are the responsibilities of the National Research Council and the Transportation Research Board. The needs for highway research are many, and the National Cooperative Highway Research Program can make significant contributions to the solution of highway transportation problems of mutual concern to many responsible groups. The program, however, is intended to complement rather than to substitute for or duplicate other highway research programs.