Pavement Performance Study Research Articles

Using graphical models to interpret pavement condition data

Most of the multiple linear regressions developed in pavement performance studies have one response variable and one block of several explanatory variables. In this paper, graphical chain models are used to develop blocks of several possibly interacting responses with each block containing several interacting variables. The graphical chain model provides easy interpretation of conditional independence structure within the blocks. This ultimately provides an idea about association and dependence of different pavement condition variables. An example was presented using data from the Highway maintenance and Design Model (HDM).

A LTPP study with a new device for vertical deformation measurements

On the occasion of rehabilitating the heavily travelled Swiss motorway A1 between Zürich and Bern with SMA, a long-term pavement performance study was initiated in 1998, combining permanent in situ measurements, periodic inspections and selected laboratory tests on pavement samples. An in situ measurement station was installed to record traffic loads, vertical deformations and temperatures within the cross section of the pavement. This paper presents the traffic loads and the deformation response under traffic as well as the development of pavement conditions between 1998 and 2001 according to evenness, skid resistance and FWD measurements. Temperatures within the pavement's cross section are compared to other motorway sections with different pavement structures.

Selecting Preventive Maintenance Treatments in Texas

Although the cost-effectiveness of preventive maintenance (PM) treatments for pavement is important, literature addressing this issue is limited. Even under the well-controlled FHWA long-term pavement performance (LTPP) study, incomplete data and sections exist. Criteria for selecting PM treatments often conflict and have to be compromised. The multiple criteria decision-making (MCDM) method is one of numerous approaches available for resolving variations of results. The technique for order preference by similarity to ideal solution (TOPSIS), an MCDM method, was used to analyze successfully all 14 specific pavement study (SPS)-3 sites in Texas. The distress score (DS), international roughness index (IRI), and treatment costs were used as criteria to determine the cost-effectiveness of various PM treatments (thin overlay, slurry seal, crack seal, and chip seal). With TOPSIS, the cost-effectiveness of these treatments can be quantified, with variations caused by subjective judgment thus minimized. When all criteria were considered, the most and least cost-effective methods were chip seal and slurry seal, respectively. When cost was not considered, the most and least effective methods were chip seal and crack seal, respectively. The chip seals performed the best. Chip seals had the most forgiving qualities of all the methods, and they yielded no reflection of the cracking that preceded the treatment applications. The evaluation based on TOPSIS provides a viable option for engineers determining the best PM treatments for pavement in need of maintenance.

Selecting Preventive Maintenance Treatments in Texas: Using the Technique for Order Preference by Similarity to the Ideal Solution for Specific Pavement Study-3 Sites

Although the cost-effectiveness of preventive maintenance (PM) treatments for pavement is important, literature addressing this issue is limited. Even under the well-controlled FHWA long-term pavement performance (LTPP) study, incomplete data and sections exist. Criteria for selecting PM treatments often conflict and have to be compromised. The multiple criteria decision-making (MCDM) method is one of numerous approaches available for resolving variations of results. The technique for order preference by similarity to ideal solution (TOPSIS), an MCDM method, was used to analyze successfully all 14 specific pavement study (SPS)-3 sites in Texas. The distress score (DS), international roughness index (IRI), and treatment costs were used as criteria to determine the cost-effectiveness of various PM treatments (thin overlay, slurry seal, crack seal, and chip seal). With TOPSIS, the cost-effectiveness of these treatments can be quantified, with variations caused by subjective judgment thus minimized. When all ...

Development of Canadian asphalt pavement deterioration models to benchmark performance

The Canadian Long Term Pavement Performance (C-LTPP) study, initiated in 1989, involves 65 sections located at 24 sites constructed with various asphalt overlay rehabilitation treatments. This study investigates the impacts of the various alternative rehabilitation treatments on pavement roughness progression. A series of models are developed for predicting the rate of pavement deterioration occurring for the first 8 years of service. The models examine both within-site factors and between-site factors. Site location is found to be the primary influence on the rate of pavement deterioration. Overlay thickness and the amount of cracking prior to rehabilitation are also determined to influence pavement deterioration at a strong statistical level. Models are provided for benchmarking the performance of pavements across Canada, for comparison with individual project designs, and for estimating the performance of designs with different overlay thickness.Key words: Canadian Long Term Pavement Performance program, roughness, pavement deterioration, site effects, asphalt overlays, benchmark, univariate analysis.

Performance of Rigid Pavement Rehabilitation Treatments in the Long-Term Pavement Performance SPS-6 Experiment

The results of a study conducted to assess the relative performance of different jointed rigid pavement rehabilitation treatments, including the influence of pretreatment condition and other factors, are presented. The data used in the study were drawn from the Long-Term Pavement Performance Studies' Specific Pavement Study (SPS) SPS-6 and General Pavement Study (GPS) GPS-7B experiments. The rehabilitation treatments used in the SPS-6 experiment were minimal and intensive nonoverlay repair, 4-in. asphalt overlays with minimal and intensive preoverlay preparation, 4-in. overlays with sawed and sealed joints, and 4- and 8-in. asphalt overlays of cracked and seated concrete slabs. Overall, the rigid pavement rehabilitation treatments in the SPS-6 experiment could be ranked from most to least effective in the following order: 8-in. overlay of cracked or broken and seated pavement, 4-in. overlay (of either intact or cracked or broken and seated pavement, with or without sawing and sealing of joints and with either minimal or intensive preoverlay repair), concrete pavement restoration with diamond grinding, and concrete pavement restoration without diamond grinding. Concrete pavement restoration with diamond grinding yielded an initial posttreatment international roughness index (IRI) of 1.05 m/km, on average, whereas restoration without diamond grinding yielded no benefit in IRI and in fact tended to leave the pavement rougher than before. In the long term, both restoration and overlay treatments reduced long-term roughness, rutting, and cracking levels compared with those on the control sections, but the conditions of the restored test sections are approaching those of the control sections faster than those of the overlay sections.

Performance of Flexible Pavement Rehabilitation Treatments in the Long-Term Pavement Performance SPS-5 Experiment

The results of a study conducted to assess the relative performance of different flexible pavement rehabilitation treatments, including the influence of pretreatment condition and other factors, are presented. The data used in the study were drawn from the Long-Term Pavement Performance Studies' Specific Pavement Study (SPS) SPS-5 and General Pavement Study (GPS) GPS-6B experiments. The rehabilitation treatments used in the SPS-5 experiment are 2- and 5-in. overlays with virgin or recycled asphalt concrete mixes with or without preoverlay milling. Overlay thickness and preoverlay roughness levels were the two factors that most influenced the performance of the asphalt overlays of asphalt pavements in the SPS-5 experiment with respect to roughness, rutting, and fatigue cracking. Over the long term, the 5-in. overlays outperformed the 2-in. overlays with respect to roughness, rutting, and fatigue cracking. Overlay mix type (virgin versus recycled) and preoverlay preparation (with or without milling) had slight and inconsistent effects. The average initial postoverlay international roughness index of an asphalt overlay of an asphalt pavement was found to be 0.98 m/km. The data show a slight but statistically significant tendency for asphalt pavements overlaid when they were rougher to have more initial roughness after overlay than asphalt pavements overlaid when they were smoother. The data show that, on average, about 6 mm of rutting develops in the first year or so after placement of an asphalt overlay of an asphalt pavement. This is presumably due to compaction of the mix by traffic and appears to be independent of the overlay thickness, mix type, preoverlay preparation, and preoverlay rutting level.

Performance of Flexible Pavement Maintenance Treatments in the Long-Term Pavement Performance SPS-3 Experiment

A study was conducted to assess the relative performance of different flexible pavement maintenance treatments, including the influence of pretreatment condition and other factors. The data used in the study were drawn from the Long-Term Pavement Performance Studies' Specific Pavement Studies (SPS) SPS-3 experiment. The maintenance treatments used in the SPS-3 experiment are thin overlays, slurry seals, crack seals, and chip seals. The initial and long-term effects of the maintenance treatments on international roughness index (IRI), rutting, and cracking were analyzed, as were the influences of time, truck traffic, pretreatment condition, and climate. Thin overlays were found to be the most effective of the treatments studied, followed by chip seals and slurry seals. Crack sealing did not demonstrate any beneficial initial or long-term effect with respect to IRI, rutting, or cracking.

Evaluation of subgrade and climatic zone influences on pavement performance in the Canadian Strategic Highway Program's (C-SHRP) Long-Term Pavement Performance (LTPP) study

Sixty-five sections in 24 provincial test sites received pavement rehabilitation comprising of various thicknesses of asphalt overlays, as part of the Canadian Long-Term Pavement Performance (C-LTPP) study, which was initiated in 1989. This paper describes the impacts of the various alternative rehabilitation treatments on pavement performance in terms of roughness progression under comparative climatic, subgrade soil, and traffic loading conditions. Some findings from this study include (i) in wet, high-freeze zones, thinner overlays show a higher rate of roughness progression than thicker overlays, regardless of subgrade type; (ii) in dry, high-freeze zones, roughness progression for medium and thick overlays is relatively small; (iii) in wet, low-freeze zones, thinner overlays combined with fine subgrade soils show the highest rate of roughness progression; and (iv) traffic, in terms of equivalent single axle loads (ESALs), seemed to have a limited effect on all of the above; this was attributed largely to the fact that all of the traffic essentially fell into one level, where 200 000 ESALs per year was designated as the boundary between low and high traffic levels. The methodology developed in this paper provides valuable insight into how subgrade and climatic factors influence pavement performance and can be applied to performance trend analysis of other pavements with similar climatic, subgrade, and traffic loading conditions.Key words: subgrade type, climatic zones, pavement roughness, international roughness index (IRI), Long-Term Pavement Performance (LTPP).

Overlay Performance in Canadian Strategic Highway Research Program’s Long-Term Pavement Performance Study

The Canadian Long-Term Pavement Performance (C-LTPP) study, initiated in 1989, involves 65 sections in the 24 provincial sites that received rehabilitation comprising various thicknesses of asphalt overlays. The effects of the various alternative rehabilitation treatments on pavement performance in terms of roughness progression under comparative traffic loading, climate, and subgrade soil conditions are described. Roughness trends are the main subject of the C-LTPP study. Progression of roughness for thin overlays (30 to 60 mm) is significantly higher on a national basis than for medium (60 to 100 mm) and thick (100 to 185 mm) overlays. Factor effects, including climatic zone, subgrade type, and traffic level were also evaluated. Some findings are that ( a) in wet, high-freeze zones, thinner overlays show a higher rate of roughness progression than thicker overlays, regardless of subgrade type; ( b) in dry, high-freeze zones, roughness progression for medium and thick overlays is relatively small; ( c) in wet, low-freeze zones, thinner overlays combined with a fine subgrade show the highest rate of roughness progression; ( d) traffic in terms of equivalent single-axle loads (ESALs) appeared to have a limited effect for all the preceding factors—this was attributed largely to all the traffic essentially falling into one level and to the designation of 200,000 ESALs per year as the boundary between low and high traffic levels. In conclusion, the C-LTPP experiment has provided valuable information on roughness trends after only 8 years of observations. The methodology developed in this study for pavement roughness evaluation can be applied to performance trends analysis of other measured LTPP data.

Seasonal variation in material properties of a flexible pavement

Seasonal variation of temperature and moisture causes considerable changes in the load-carrying capacity of pavements in geographical areas subjected to extreme freeze/thaw conditions. The Seasonal Monitoring Program (SMP) of the Long Term Pavement Performance (LTPP) study of the Federal Highway Administration (FHWA) monitors seasonal variations in Falling Weight Deflectometer (FWD) deflections, air temperature, rainfall, soil temperature, moisture content, and soil electrical resistance at numerous sites across North America. This study relates changes in pavement load carrying capacity represented by the pavement layer resilient moduli to selected environmental factors for a test pavement site in southwestern Manitoba. The significant environmental parameters causing seasonal variation in pavement layer resilient moduli are identified as the surface temperature for the asphalt layer and the thawing index for base and subgrade layers. The resilient moduli of various pavement layers show a substantial decrease in magnitude with increasing values of respective environmental parameter. The present model can be used for preliminary verification of empirical pavement design and rehabilitation practices currently in use to account for seasonal variations. Key words: asphalt, backcalculation, falling weight deflectometer, freezing, pavements, moisture, resilient moduli, seasonal variation, thawing, temperature.

Seasonal variation in material properties of a flexible pavement

Seasonal variation of temperature and moisture causes considerable changes in the load-carrying capacity of pavements in geographical areas subjected to extreme freeze/thaw conditions. The Seasonal Monitoring Program (SMP) of the Long Term Pavement Performance (LTPP) study of the Federal Highway Administration (FHWA) monitors sea- sonal variations in Falling Weight Deflectometer (FWD) deflections, air temperature, rainfall, soil temperature, moisture content, and soil electrical resistance at numerous sites across North America. This study relates changes in pavement load carrying capacity represented by the pavement layer resilient moduli to selected environmental factors for a test pavement site in southwestern Manitoba. The significant environmental parameters causing seasonal variation in pave- ment layer resilient moduli are identified as the surface temperature for the asphalt layer and the thawing index for base and subgrade layers. The resilient moduli of various pavement layers show a substantial decrease in magnitude with increasing values of respective environmental parameter. The present model can be used for preliminary verifica- tion of empirical pavement design and rehabilitation practices currently in use to account for seasonal variations.

It’s 10 o’Clock: Do You Know Where Your Sensors Are?

More than 400 falling weight deflectometer (FWD) devices are presently in use throughout the world, and deflection reading accuracy is very important. Deflections are measured in microns, or hundredths of a mil, and even very small errors in the deflection readings can have a profound effect on the results of backcalculation. One question that has somehow escaped scrutiny is the one alluded to in the title to this paper—exactly where along the deflection basin are the FWD deflection sensors positioned? This is an extremely important issue for proper definition of the deflection basin as a function of distance from the center of the loading plate. A review of the FWD load-deflection data in the Long Term Pavement Performance (LTPP) study found that in at least 7 percent of some 4 million lines of FWD deflection data in the National Information Management System (NIMS) database, the sensors were not positioned as reported. This problem is not limited to LTPP and NIMS, and it occurs all too frequently on FWDs everywhere. How sensor positioning errors influence backcalculated moduli, even if all other facets of the FWD data are 100 percent correct, is described. Examples of the errors found in NIMS are also presented—real-life illustrations of what can go wrong and how much influence these errors can have on pavement analysis. A method of scanning for sensor positioning errors without carrying out backcalculation is presented. By use of the suggested transform, sensor positioning errors are clearly evident when suspect data are compared with correct data along the same, or other, pavement sections.

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.

Utilization of Industrial Wastes in Low-Volume Roads

In recent years, applications of marginal materials, also called nontraditional (either natural or waste products), have been considered in road construction with great interest in many industrialized and developing countries. The use of nontraditional materials in road making is based on technical, economic, and ecological criteria. The lack of traditional road materials and the protection of the environment make it imperative to investigate marginal materials carefully. India has a large network of steel plants located in different parts of the country and many more are planned for the near future. Several million metric tons of iron and steel are produced in these plants. However, along with production of iron and steel, huge quantities of solid wastes like blast furnace slag and steel slag as well as other wastes such as flue dust, blast furnace sludge, and refractories are also being produced in these plants. The iron ores in India, although rich in iron content, are high in alumina content also and as such the volume of slag generated is very high. Normally production of 1 metric ton (1 Mg) of steel generates 1 Mg of solid waste. Although the steel industry slags have their own unique properties and are exploitable for road works, they have never been put to use on Indian roads because of a lack of scientific studies conducted on these materials, nonavailability of proper design and construction standards on them, and the absence of data about the long-term behavior of these materials. In the absence other outlets, these solid wastes have occupied several acres of land around plants throughout the country. Keeping in mind the need for bulk use of these solid wastes in India, it was thought expedient to test these materials and to develop specifications to enhance the use of slags in road making, in which higher economic returns may be possible. Exhaustive and detailed laboratory investigations have been carried out at the Central Road Research Institute, New Delhi, India, to develop suitable specifications for construction of low-volume roads. Based on laboratory investigation results, specifications were developed for construction of low-volume roads in different parts of the country. While specifications were being formulated, attempts were made to maximize use of solid wastes in different layers of the road pavement. Postconstruction pavement performance studies have clearly indicated that these waste materials can be used for construction of low-volume roads with twofold benefits: ( a) it will help clear valuable land of huge dumps of slags, and ( b) it will also help preserve the natural reserves of aggregates, thus protecting the environment.

Engineering Application of Washington State’s Pavement Management System

Previous investigation into the Washington State Department of Transportation’s (WSDOT) Pavement Management System (WSPMS) revealed pavement sections on the state route system that were outperforming or underperforming other pavement sections constructed of similar materials and subjected to similar traffic and environmental conditions. Reasons were not clear. The WSPMS was used to identify superior and inferior candidate pavements for further investigation. All state route pavements were stratified into 18 distinct analysis groups, and population statistics were generated for each group providing WSDOT with a snapshot of the current “state of the state route system” and providing the basis for selecting candidate pavements. The five performance measures considered included: age of the surface course, a distress-based pavement structural condition score, annual design-lane equivalent single axle loads, roughness (in terms of International Roughness Index), and rutting. Results of the analysis suggest that WSDOT is properly designing layer thicknesses at appropriate reliability levels. Also, in 6 of 10 analysis group comparisons, inferior pavements were actually thicker than superior pavements. Both findings suggest that thickness design factors are not the primary cause of inferior performance in Washington State; construction, material and site specific factors are likely the cause. Additionally, in an international effort to exchange information on pavement performance and construction practices, highlights of a comparative study of pavement performance with South Africa’s Gauteng Department of Transportation are presented.

Precision and Bias of Data from Film

An objective of the Long-Term Pavement Performance study is the development of improved pavement design procedures. This objective depends on performance data being collected on present in-service pavements. The primary pavement distress data collection was done by recording 35mm film images at intervals since 1988. Five rounds of images have been collected. The accuracy and repeatability of distress data collection was of concern. The effort to assess the quality of distress data resulting from analysis of 35mm pavement images is reported. A set of 12 pavement sections, including asphalt surface, jointed and continuously reinforced concrete, was digitized three times by 10 operators with various skill levels at intervals of several weeks between passes. The distress analysis was done by using four semiautomated computerized workstations to view a projected image of the pavement on a digitizing tablet with the operator using a cursor to input distress type, severity, and location. A data summary and plot were output from the software. The results of each digitizing pass were used to evaluate the repeatability of the operators, and grouped data were used to evaluate accuracy.

Axle Load Distribution Characterization for Mechanistic Pavement Design

Proper consideration of traffic loading in pavement design requires knowledge of the full axle load distribution by the main axle types, including single, tandem, and tridem axles. Although the equivalent single axle load (ESAL) concept has been used since the 1960s for empirical pavement design, the new mechanistic-based pavement design procedures under development by various agencies most likely will require the use of the axle load distribution. Procedures and models for converting average daily traffic into ESALs and axle load distribution are presented, as are the relevant issues on the characterization of the full axle load distributions for single, tandem, and tridem axles for use in mechanistic-based pavement design. Weigh-in-motion data from the North Central Region of the Long-Term Pavement Performance study database were used to develop the models for predicting axle load distribution.