Gonzalo R Rada

Investigation of Backcalculated Moduli Using Deflections Obtained at Various Locations in a Pavement Structure

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.

Assessment of Long-Term Pavement Performance Program Manual Distress Data Variability: Bias and Precision

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.

Collecting and Interpreting Long-Term Pavement Performance Photographic Distress Data: Quality Control-Quality Assurance Processes

The Long-Term Pavement Performance (LTPP) program is making use of photographic technology to provide, first, detailed, distress-specific condition data for use in the development and validation of pavement performance models and, second, a permanent, objective, high-resolution record of pavement condition over the full length and width of the sections in the program. Because high-quality distress data are critical to the success of the LTPP program, numerous quality control-quality assurance (QC-QA) processes have been implemented over the life of the program. Those processes address data quality before the start of data collection, during data collection, during data interpretation, after data interpretation, and after the uploading of data to the LTPP database. Some of the processes are a direct result of advance planning, based on past experience, while others are the result of lessons learned in the course of the program. Some were implemented early in the program, while others were introduced well into the program. The Distress Identification Manual, distress rater accreditation workshops, time series review, database checks, data studies and analyses, and feedback reports are just a few of the elements that make up the full suite of QC-QA processes. A detailed summary of the QC-QA processes associated with the LTPP photographic distress data is presented.

Update of Long-Term Pavement Performance Manual Distress Data Variability: Bias and Precision

Pavement distress surveys based upon field interpretation and manual mapping and recording of the distress information on paper forms has been used in the Long-Term Pavement Performance (LTPP) program to collect important pavement condition and distress data. Although this manual method was used in the past as a backup to the 35-mm black and white photographic-based method, recently the use of manual distress survey methods has increased in intensity and coverage. To promote uniformity and consistency of distress data collection, one of the early LTPP efforts was to develop standard definitions, measurement procedures and data collection forms. Various quality control and quality assurance functions have also been implemented to provide for high quality data. However, despite these efforts, manual surveys are still based upon a single rater’s subjective classification of distresses present in the field. Recognizing that rater variability exists, a study was undertaken by FHWA to assess the level of variability between individual distress raters and to address the potential precision and bias. Results from nine LTPP distress rater-accreditation workshops conducted during the period of 1992 to 1996 were used as the source of data. Analyses of those data led to numerous observations and conclusions regarding the bias and precision of LTPP distress data. Because LTPP distress data are to be used in the development of pavement performance prediction models, it is believed that the level of variability found in this study should be reduced to increase its potential usage in the development of such models. A number of recommendations to improve the variability associated with manual distress surveys data are included.

Dynamic analyses of traffic speed deflection devices

Abstract Two traffic speed deflection devices (TSDDs) that measure surface deflections at posted traffic speeds (up to 80–96 kph) were evaluated through a recent Federal Highway Administration project that included field trials at the MnROAD facility. Four geophones were embedded near the pavement surface to measure surface deflections during field trials at each of three MnROAD cells. In addition, the MnROAD facility counted with numerous other sensors such as strain gauges to measure pavement responses and thermocouple trees to collect pavement temperature at various depths. For the implementation of TSDDs in any network-level pavement management system, it is important to utilise a proper analytical model that can accommodate moving load and viscoelastic properties of pavement layers in the simulation of TSDD measurements. The 3D-Move software was chosen for this purpose. The viscoelastic properties used for the asphalt concrete (AC) layer include dynamic modulus and damping coefficient as a function of frequency relevant to the temperature at the time of the MnROAD field trials. The field trials and available data represented realistic field case scenarios to validate once more 3D-Move specifically for TSDD measurements. The proposed dynamic analytical model provided a good match with a variety of independent pavement responses that included surface deflection bowls (measured using embedded geophone sensors) as well as horizontal strains at the bottom of the AC layers (measured using MnROAD sensors).

Assessment of Long-Term Pavement Performance Plan Wall Projection-Based Distress Data Variability

In the Long-Term Pavement Performance (LTPP) program, 35-mm, black and white, continuous-strip photographs are used as a permanent record of pavement distress development for archival purposes and to quantify the distress severity and extent for pavement performance analysis. The traditional method of interpreting distress from LTPP film utilizes a relatively small image projected onto a digitizing tablet. From quality control checks performed on the interpreted data, it was found that some low severity types of distress, identified from larger magnified images projected onto a wall or projection screen, could not be seen in the smaller image used for distress interpretation. The variability in distresses interpreted directly off of the large format, wall-image projection was assessed through analysis of interpretations performed on six asphalt concrete and six portland cement concrete pavement sections used in the LTPP distress rater accreditation workshops. The data set included distress ratings from eight individuals, four two-person rater teams, and an experienced rater team. Also available were distress ratings performed in the field by the experienced rater team, which are used as reference values which represent the best estimate of ground-truth. Statistical tests show that the film-interpreted distresses from individual raters exhibit much larger variability than those from the rating teams. The most significant contributor to this finding is outlier observations in which one of the individual raters had significantly different ratings than the rest of the group. The spread in the rating teams was much lower. The film interpreted distresses from the experienced group correlated very well with the field-derived reference values.

VARIABILITY OF FILM-DERIVED PAVEMENT DISTRESS DATA

ABSTRACT This paper presents the Findings of an effort undertaken by the Federal Highway Administration (FHWA) Long-Term Pavement Performance (LTPP) program to assess variability of distress data collected using a photographic method. The primary source of data used to characterize the film-derived distress data variability is the results of a distress survey conducted on 12 pavement test sections, including six asphalt concrete (AC) and six portland cement concrete (PCC) pavements. Distress surveys were performed by experts, individual raters, and two-person teams. A consensus survey on the pavements by a group of experts based on the photographic method was also conducted. Finally, a reference rating of the distress present on the same 12 test sections was performed using a consensus manual rating method by the same group of experts; data from these reference surveys were used as a surrogate of “ground-truth”. Based on the analyses of these data, variability of the film-derived distress data was evaluat...

Relating Ride Quality and Structural Adequacy for Pavement Rehabilitation and Management Decisions

Ride quality and structural adequacy are key pavement performance indicators. The relationship between these indicators has been a topic of frequent and continuing discussion in the pavement community, but an accepted and widely used relationship has not yet been identified. The objective of this study was to identify and verify the relationship between these two performance indicators, if any, with data from the Long-Term Pavement Performance Program. This study was meant to improve the evaluation and use of pavement condition data in pavement rehabilitation and design decisions. More specifically, it was intended to develop and document a mechanism to include values of both ride and structural adequacy within the context of current network-level pavement management system practices for highway agency implementation to ensure smooth pavements that are also structurally adequate. To accomplish the study objective, two major activities were carried out: a literature search to gather, review, and synthesize available information on relating ride quality and structural adequacy and a review and assessment of data from the Long-Term Pavement Performance Program to determine if such a relationship exists. These two activities—as well as their major findings, observations, and conclusions—are detailed; a viable relationship could not be identified.

Validation of Dynamic Simulation of Slow-Moving Surface Deflection Measurements

Recent studies have concluded that measured surface deflections can be used as a low-cost pavement monitoring and condition assessment tool to determine remaining structural life and pavement performance. Moving load devices are being used more often to measure continuous surface deflections. They are considered a faster alternative to falling weight deflectometer–based structural condition evaluation applications. The objective of the study was to compare the analytical dynamic simulation of slow-moving deflection measurements with field data. The surface pavement deflections and the pavement structural responses generated by the Euroconsult Curviametro loading at the Minnesota Department of Transportation’s MnROAD facility near Maplewood, Minnesota, were used in the evaluations. Four geophones were embedded near the pavement surface to measure surface deflections during field trials at each of three tested MnROAD cells. In addition, numerous other sensors, such as strain gauges and thermocouple trees, were available at the MnROAD facility. The 3D-Move program was used in the simulations because it can accommodate moving loads and the viscoelastic properties of pavement layers and produce continuous deflection basins. The viscoelastic properties of pavement layers were estimated on the basis of the actual temperatures at the time of the field trials and the appropriate loading frequency of the Curviametro. The proposed dynamic analytical model provided a good match with a variety of independent pavement responses, which included surface deflection basins (measured by embedded geophone sensors) as well as horizontal strains at the bottom of the asphalt concrete layers (measured by MnROAD sensors).

Evaluating Pavement Condition of the National Highway System

FHWA recently conducted a study to identify a means for evaluating the health of the Interstate highway system, with a specific focus on pavements and bridges. One important component of any statement of health is the condition of the pavement, which is the focus of this paper. Data on an 874-mi long corridor of I-90 were used to review the potential of a set of six metrics for evaluating pavement condition as good, fair, or poor across the Interstate network. The metrics reviewed included both functional and structural pavement condition. The study concluded that currently the international roughness index provides the most consistent method for evaluating ride quality. Other metrics, which use distress or structural condition to evaluate pavement, are not currently suitable as measures of nationwide condition and will require further work before they can be implemented for routine use.