This paper addresses the use of traffic speed deflection devices for the structural evaluation of pavements at the network-level. At the heart of the decision making process is the pavement management system (PMS), which provides condition indices or scores for each pavement segment in the network. Current PMS are driven by distress and ride quality as key pavement condition indicators. Both merit emphasis within the PMS process, but another important indicator to making rational pavement investment decisions is the structural adequacy, which is most often determined based on deflection testing.
The interpretation and use of deflection measurements on the prepared surfaces of the various pavement layers during construction are examined. Measurements were obtained from four asphalt concrete pavement test sections, two with unbound aggregate base and two with bituminous-treated base over an untreated aggregate base. Deflection basin measurements using a falling weight deflectometer were performed on the prepared surfaces of the subgrade, base layers, and asphalt concrete layers. The elastic moduli of each layer were computed using the EVERCALC backcalculation program. The primary finding from this investigation is that deflection measurements on the subgrade and base layers during construction can be used to control construction uniformity and provide checks on mechanistic-based pavement design assumptions. Also, subgrade uniformity has a profound impact on the entire pavement structure and subgrade variations affect total deflections and computed layer moduli of all successive layers. The backcalculated modulus is directly related to the stress state in the layer. For unbound aggregate bases, the backcalculated elastic modulus decreases with a decrease in the bulk stress, and for fine-grained subgrade soil, the backcalculated elastic modulus increased with a decrease in the deviator stress. As expected, a higher and more variable root-mean-square basin fit error value was obtained for measurements on unbound material as compared with measurements on bound material surfaces.
TRB 2012 Annual MeetingPaper revised from original submittal.Rada, Perera, Prabhakar and Wiser 1. ABSTRACTRide quality and structural adequacy are key pavement performance indicators. The relationship between these two indicators has been a topic of frequent and continuing discussion in the pavement community, but to date an accepted and widely used relationship has not been identified. The objective of this project was to identify and verify the relationship between these two performance indicators, if any, using the LTPP pavement performance data. This was done in an effort to improve the evaluation and use of pavement condition data in pavement rehabilitation and design decisions. More specifically, the project was intended to develop and document a mechanism to include both ride and structural adequacy values within the context of current network-level PMS practices for highway agency implementation to ensure smooth pavements that are also structurally adequate. Towards the accomplishment of the project objective, two major activities were carried out: (1) a literature search to gather, review and synthesize available information on relating ride quality and structural adequacy, and (2) a review and assessment of data from the LTPP program to determine if such a relationship exists. This paper details those two activities as well as their major findings, observations and conclusions; a viable relationship could not be identified.TRB 2012 Annual Meeting Paper revised from original submittal.Rada, Perera, Prabhakar and Wiser 2 .
The use of manual survey methods within the Long-Term Pavement Performance (LTPP) program for the collection of distress data has drastically increased both in intensity and in coverage over the past couple of years. Because these surveys are conducted by individual raters whose biases can lead to variability between raters, it was hypothesized that distress data variability existed and that it could potentially be quite large. Thus, the purpose of the presented study was to quantify manual distress data variability, with special emphasis on the bias and precision of the data. Results from seven LTPP program distress rater accreditation workshops conducted during the period from 1992 to 1995 were used as the only source of data. On the basis of analyses of these data, both the apparent bias and the precision for the common distress type-severity level combinations were quantified. It was also concluded from this study that individual rater variability for any given distress type-severity level combination is typically large and increases as the distress quantity increases; however, when all distress type-severity level combinations are viewed in terms of a single composite number such as the pavement condition index value, there is excellent agreement between the individual raters, the group mean, and the ground truth value, and individual rater variability is also quite small. Because LTPP program distress data are to be used in the development of pavement performance prediction models, improvements in variability are highly desirable to ensure that they serve their intended purpose. Recognizing that the LTPP program distress raters are experienced individuals, such improvements are not envisioned to come through additional training. It is the authors’ contention that the only way of achieving the desired improvement is through the conduct of group consensus surveys.
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