A three-dimensional (3-D) finite element model for stress analysis of pavements with ultrathin whitetopping (UTW) under critical loading conditions was developed. The 3-D model developed was used to analyze the UTW test pavement sections at the Ellaville Weigh Station in Florida, which had less than satisfactory performance. The poorly performing UTW sections at the Ellaville Weigh Station were found to have relatively higher maximum computed stresses under critical loading conditions, which appeared to explain their poor performance and high percentages of cracked slabs. The 3-D model developed was also used to perform a parametric analysis to determine the effects of asphalt thickness, asphalt modulus, concrete thickness, concrete modulus, base stiffness, subgrade stiffness, slab dimension, temperature differential in the concrete, and applied load on the maximum stresses in UTW pavements under typical Florida conditions.

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As part of a study sponsored by NCHRP, research was conducted to evaluate the variability of concrete materials data in the Long-Term Pavement Performance (LTPP) program. The following materials-related data were studied: ( a) compressive strength, ( b) flexural strength, ( c) split tensile strength, and ( d) modulus of elasticity. The variability was determined in terms of the standard deviation and coefficient of variability. The strength and stiffness data used came from the General Pavement Study (GPS) as well as the Specific Pavement Study (SPS) test sections. The analysis of data indicates that, in general, the LTPP program GPS test sections as well as the LTPP program SPS test sections exhibit characteristics of well-controlled construction projects with respect to the strength- and stiffness-related properties of concrete. The results of the analysis indicate that on well-controlled concrete pavement construction projects it would not be unreasonable to produce concrete that has a coefficient of variation of 15% or less for compressive strength, flexural strength, split tensile strength, and the modulus of elasticity. The findings from the analysis can be used to refine statistics-based quality assurance/quality control procedures for concrete acceptance and to define the measures of variability to be used in mechanistically based concrete design procedures.

To obtain a better understanding of ultrathin whitetopping (UTW) pavement behavior under traffic loading and environmental effects and to collect data for calibration and development of a mechanistic design procedure, a UTW test pavement was constructed, instrumented, and load tested. The UTW pavement test section is located at the Spirit of St. Louis Airport, a general aviation airport in Chesterfield, Missouri, and is designed to carry a light aircraft load of 56 kN. The results of analyses conducted on this test pavement and its performance to date are described. The UTW test section was constructed in February 1995 and consisted of six slabs with dimensions of 1.3 × 1.3 m and a design slab thickness of 89 mm. The load testing was conducted in May and September 1995. Load-induced strains, temperature distribution, and surface profiles were measured at different locations and at different times. Pavement core samples were also taken and subjected to laboratory testing. It was observed from the evaluation that ( a) there was very little vertical slab movement in spite of the temperature differential in the slabs, ( b) there was no apparent change in load-induced strains (stresses) with temperature changes, ( c) pavement exhibited high load transfer efficiencies across contraction joints, and ( d) an interface shear strength of 689 kPa was achieved by the commonly used technique for asphalt surface preparation, milling and cleaning. A recent performance review of this pavement also showed that it has performed extremely well after over 6 years in service. Of the 11620 m2 of UTW pavements (about 72,000 UTW panels), only 18 panels have cracked.

To provide accurate climatic data for pavements under the Long-Term Pavement Performance (LTPP) Program, a climatic database was developed in 1992 and subsequently revised and expanded in 1998. In the development of this database, up to five nearby weather stations were selected for each test site. Pertinent weather data for the selected weather stations were obtained from the U.S. National Climatic Data Center and the Canadian Climatic Center. With a 1/ R2 weighting scheme, site-specific climatic data were derived from the nearby weather station data. The derived data were referred to as “virtual”weather data. To evaluate the effect of environmental factors on pavement performance and design, automated weather stations (AWS) were installed at LTPP Specific Pavement Study Projects 1, 2, and 8 to collect on-site weather data. Since the virtual weather data were developed for all LTPP test sites and will be used for future pavement performance studies, it is essential that the derived virtual data be accurate and representative of the actual onsite climatic conditions. The availability of the AWS weather data has provided an opportunity to evaluate whether virtual weather data can be used to represent on-site weather conditions. Daily temperature data and monthly temperature and precipitation data were used in this experiment. On the basis of the comparisons made between the virtual and onsite measured (AWS) data, it appears that climatic data derived from nearby weather stations using the 1/R2 weighting scheme estimate the actual weather data reasonably well and thus can be used to represent on-site weather conditions in pavement research and design.

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The results of a laboratory testing program carried out to investigate the effect of coarse aggregate types on the elastic modulus of typical pavement concretes are presented. The elastic modulus was determined in both flexure and compression using static and dynamic means. Three different mixes, made using three different aggregates, were compared. The water-cement ratio was kept at 0.53 throughout the test program. The results showed that within the tested range, the aggregate type significantly affected the studied properties of concrete. Calera aggregate (a dense limestone) with its rough-textured surface and angular shape produced a concrete with higher strength and stiffness than those of concretes made with Brooksville aggregate (a porous limestone) and river gravel. In addition, the measured dynamic modulus in compression was significantly different from that in flexure. Also, in flexure, the dynamic modulus was higher than the static modulus by an average of 23 percent, whereas in compression, the dynamic modulus appeared to be in the same range as the static modulus. The change in frequency from 1 to 7 Hz did not have a significant influence on the dynamic modulus.