Aramis Lopez

STATISTICAL ANALYSES OF TEMPERATURE AND MOISTURE EFFECTS ON PAVEMENT STRUCTURAL PROPERTIES BASED ON SEASONAL MONITORING DATA

In light of the data collected under the Seasonal Monitoring Program of the Long-Term Pavement Performance Program, the relationship between climatic factors and pavement structural properties is investigated. Using deflection data collected at a seasonal site over the course of 1 year, layer elastic moduli are backcalculated. The correlations between pavement structural properties (represented by layer elastic moduli) and climatic factors (represented by pavement temperature and moisture conditions) are studied using a series of statistical analyses. Bivariate analysis is used to evaluate linear association between pairs of variables. Principal components analysis is used to identify principal constructs of the system. Multiple regression is used to calibrate linear models. Numerical optimization is used to calibrate nonlinear models that correlate backcalculated layer moduli to pavement temperature. The latter models are then used to derive a temperature correction algorithm of backcalculated asphalt co...

ANALYSIS OF METHODS USED IN TIME DOMAIN REFLECTOMETRY RESPONSE

Time domain reflectometry (TDR) is a new technique that can be used to measure indirectly the in situ volumetric moisture content of soil. A growing body of research has been conducted in providing a variety of prediction equations to estimate the volumetric moisture content using the dielectric constant calculated from the apparent length obtained from the TDR reader. However, limited research has been conducted to determine which of several available procedures should be used to obtain the apparent length of the TDR response to be used in calculating the dielectric constant. As a result, evaluating which procedure yields the most accurate assessment of the volumetric moisture content of soils is the object of this paper. There are five known methods of analyzing the apparent length of TDR responses. They are the method of tangents, method of peaks, method of diverging lines, alternate method of tangents, and the Campbell scientific method. Twenty-eight soil samples, from the FHWA seasonal monitoring program, were obtained throughout the United States and Canada and used in a laboratory study. Three levels of moisture and five levels of compaction were initially planned for use with each soil sample. A total of 361 data points were eventually obtained and used to analyze each method. The method of tangents proved the most accurate method of estimating the volumetric moisture content. Current studies are ongoing to provide improved multiple regression models to estimate the volumetric moisture content on highway soils.

THEORETICAL EVALUATION OF POISSON'S RATIO AND ELASTIC MODULUS USING INDIRECT TENSILE TEST WITH EMPHASIS ON BITUMINOUS MIXTURES

The theoretical fundamentals used in evaluating Poissons ratio and elastic modulus of materials using the indirect diametral tensile test are evaluated. With the current state of practice (ASTM D4123), the material properties are evaluated by the two-dimensional stress equations for a circular element supporting short-strip loading along the vertical diameter. Because of the inability of these equations to study misalignment of the specimen, the planar solution is analyzed. The analysis of the above two approaches indicates that the material properties predicted are relatively insensitive to specimen size and misalignment. However, the influence of aggregate inclusions in the vertical plane may cause significant propagation of errors in the vertical measurements outside the central half-radius that significantly affects the value of the predicted Poissons ratio. The influence of aggregate inclusions in the horizontal plane does not appear to be a significant factor contributing in the horizontal displacement variations. Thus, determination of the elastic modulus from horizontal displacements alone has great potential in providing consistent, reasonable results with an assumed Poissons ratio. In addition, a means of estimating the magnitude of the displacements and the required sensitivity of the measuring devices based upon expected Poissons ratio and gauge length is presented. Finally, test control parameters based upon the ratio of vertical to horizontal deformations have been developed to check if the material being tested is within the elastic range as the test progresses.

Accuracy of Weather Data in Long-Term Pavement Performance Program Database

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.

Implementation of Startup Procedures in the Laboratory

This paper describes how, as part of the Federal Highway Administration’s (FHWA) Long-Term Pavement Performance Program (LTPP) Materials Characterization effort, a quality control/quality assurance (QC/QA) procedure was developed in order to verify the proficiency of laboratory equipment and personnel in performing resilient modulus testing. This effort is documented in the FHWA RD-96-176 report, “Resilient Modulus of Unbound Materials (LTPP Protocol P46) Laboratory Startup and Quality Control Procedure”. Since the issuance of that report in 1997 a great deal of experience has been gathered in using the procedure. This paper provides an outline for the procedure, the rationale behind the procedure and also documents recent changes that have been developed. The paper also discusses issues to look for when implementing the startup procedure. A brief list of issues that have been found by using the procedure is presented in the conclusion of the paper.

Resilient Modulus Testing of Unbound Materials: LTPP’s Learning Experience

This paper describes how resilient modulus is a key data element for characterizing unbound pavement materials within the Long Term Pavement Performance (LTPP) program. Although the test has been around for nearly three decades, its implementation within the program has been a challenge. A suitable test protocol was not available when the program began in 1987. It was incorrectly assumed in the early years that equipment manufactured for the test would work as intended. It was also incorrectly assumed that properly operating equipment and knowledgeable personnel imply good data. This paper has been prepared to share LTPP’s experience over the past 14 years in achieving repeatable, high-quality resilient modulus data. Specific issues addressed in this paper include the test protocol, laboratory startup and quality control procedures, quality control and quality assurance processes, and comprehensive guidelines contained in an easy-to-use interactive CD-ROM.