The support that the base and embankment or subgrade provide to a portland cement concrete pavement was found to have a very significant effect on the performance of the pavement. "Support" broadly includes stiffness of all underlying layers (base, embankment (select materials), existing subgrade, bedrock), uniformity of support along the project, seasonal variation in support, frictional resistance between the slab and base, drainability of pavement sections, erosion of the base or subgrade, and temperature curling and moisture warping of the slab (loss of support). The k-value (modulus of subgrade reaction) that is appropriate for design is defined as that on top of the finished subgrade or embankment and is an "elastic" k-value. Three categories of methods for determining an elastic k-value for use in concrete pavement design are now available with guidelines: correlation methods, deflection testing and backcalculation methods, and plate testing methods. The base layer is more realistically modelled as a structural component of the pavement system, rather than through the composite k-value (top of base) approach. The incorporation of these and other findings into the AASHTO design procedure for concrete pavements required a major revision of the main design model to improve the characterisation of support and its relationship to performance. The recommended procedure can now more realistically consider several design and climatic variables. A three-dimensional (3-D) finite element model for concrete pavements was developed to analyse accurately the many complex and interacting factors which influence the support provided to a concrete pavement. Concepts for improvement of support conditions for mechanistic design were developed. (A)
Samenvatting