Presented are recommendations for high-performance concrete paving (HPCP) practice drawn from 20 years of design and monitoring of the performance of continuously reinforced concrete (CRC) pavements in Texas. Performance indicators used were crack spacing distribution, crack width, crack randomness, delamination spalling, and vertical distribution of tensile strength. Variables studied were aggregate type, aggregate blending, placement season, placement time of day, placement above 32°C (90°F), use of crack initiators, use of skewed transverse steel, evaporation rate, percent steel reinforcement, and steel bar diameter. The variables studied are ranked in the order they affected performance, to identify which are significant and can be controlled in the design and construction phases. The focus is on the most recent experimental pavements designed and built specifically to study HPCP in Texas—85 CRC test sections built at eight locations between 1986 and 1995 in the greater Houston area. Each project consisted of 8 to 22 experimental sections of slightly different design. These sections were closely controlled and monitored during construction, and periodic condition surveys continue to be conducted. The recommendations offered are especially useful under adverse conditions, such as hot weather placement of portland cement concrete using high thermal coefficient aggregates, or paving during periods of high surface evaporation. Critical temperatures and evaporation rates are specified; using weather stations, maturity meters, or other devices that indicate in situ temperatures and evaporation rates, dangerous conditions may be identified in time to take corrective measures and thus ensure adequate performance.
The dynamic stress response of concrete pavements subjected to moving tandem-axle loads of constant amplitude and harmonic and arbitrary variations was investigated. The concrete pavement was modeled using a plate of infinite extent on a viscoelastic foundation. Formulations were developed in the transformed field domain using ( a) a double Fourier transform in space and moving space for moving loads of constant amplitude and for the steady-state response to moving harmonic loads and ( b) a triple Fourier transform in time, space, and moving space for moving loads of arbitrary variation. The effects of viscous damping, velocity, load frequency, and phase between front- and rear-axle loads on the maximum stress and the stress distribution were analyzed. Without viscous damping, the effects of velocity and frequency, within practical ranges, on the stresses are negligible; however, with viscous damping, those effects are significant. Since materials used in various pavement layers possess damping characteristics, wheel load stresses can vary considerably because of velocity and load frequency. The increase in wheel load variations and corresponding concrete stresses can be significant if the roughness of the pavement surface is not controlled. The difference in the phase angles between front- and rear-axle loads can considerably increase the maximum stress; therefore, the use of tandem-axle loads and dynamic analyses is necessary to obtain the accurate stresses because the phase effect cannot be obtained with single-axle loads or static analyses.
As the number of vehicles on America’s roadways continues to grow at an unprecedented rate, pavements continue to deteriorate faster and require replacement. In urban and densely populated areas, however, pavement construction can cause traffic delays, thereby increasing user costs. A method for expediting pavement construction to reduce traffic delays and user costs is therefore needed. A feasible method for expediting construction of portland cement concrete pavements through the use of precast concrete panels is described. The main advantage of precast concrete panels is that they can be set in place and assembled quickly, allowing traffic back onto the pavement almost immediately. This allows pavement construction to be carried out in overnight or weekend operations, when traffic volumes are low, resulting in tremendous savings in user costs. The concept presented for precast concrete pavement should have the same, if not better, durability as conventional cast-in-place concrete pavements currently being constructed. Also, by incorporating prestressing, it is demonstrated that equivalent load repetitions and design life can be achieved with a significant reduction in pavement thickness over conventional pavements. Although the initial construction costs may be higher for precast pavements, the savings in user costs far outweigh any additional construction costs.
Continuously reinforced concrete pavement (CRCP) performance depends on, among other factors, the characteristics of early developing cracks caused by environmental loads. The primary objective is to evaluate effects of design, materials, and construction variables on the characteristics of cracks in CRCP when subjected to environmental loads. A mechanistic model is developed using finite element formulations. Concrete and longitudinal steel are discretized using the plane strain and the frame elements, respectively. Various bond stress and slip models between concrete and longitudinal steel and between concrete and the underlying layers are developed using the spring elements. The creep effect is also included using the effective modulus method. CRCP responses from the model vary depending on the concrete and steel bond-slip models. An accurate bond-slip model needs to be investigated further by experiments to increase the accuracy of the mechanistic model. Concrete creep has beneficial effects on CRCP responses. The thermal coefficient of concrete has significant effects on CRCP responses. Using concrete with a low thermal coefficient will improve CRCP performance. Longitudinal steel variables—the amount of steel, bar diameter, and steel location—are important design variables that influence CRCP behavior. For given environmental conditions, an optimum steel design can be developed using the model developed.
In 1998 eight test lanes of ultrathin whitetopping (UTW) were constructed over existing hot-mix asphalt (HMA) pavements at FHWA’s Accelerated Loading Facility (ALF) located at the Turner-Fairbank Highway Research Center in McLean, Virginia. Various combinations of thicknesses, joint spacings, fiber reinforcement, and types of HMA base were used. In spring 2000 the loading experiment of these pavements was completed, and the analysis of behavior and performance was begun. A summary of some of the pavement distresses observed at the ALF is presented, and hypothesized failure mechanisms are identified, providing an addition to the state of the knowledge with respect to the actual life cycle of UTW pavements.
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