Showing papers by "Karim Chatti published in 2006"

Effect of Heavy Multiple Axle Trucks on Flexible Pavement Damage Using In-Service Pavement Performance Data

Abstract: Truck axle configurations and weights have changed significantly since the AASHO road study was conducted in the late 1950s and early 1960s. Emerging concerns about the effects of new axle configurations on pavement damage, which is unaccounted for in the AASHTO procedure, have prompted several researchers to investigate the impacts of different axle and truck configurations on pavement performance. However, there is still a need to strengthen the mechanistic findings using field data. In this paper, actual in-service traffic and pavement performance data for flexible pavements in the state of Michigan are considered. Monitored truck traffic data for different truck configurations are used to identify their relative damaging effects on flexible pavements in terms of cracking, rutting, and roughness. The analysis included simple, multiple, and stepwise regression. The results indicated that trucks with multiple axles (tridem or more) appear to produce more rutting damage than those with only single and tandem axles. On the other hand, trucks with single and tandem axles tend to cause more cracking. Pavement roughness results did not show enough evidence to draw a firm conclusion.

Backcalculation of Permanent Deformation Parameters Using Time Series Rut Data from In-Service Pavements

Abstract: Time series of rut data from 109 in-service pavement sections in the Long-Term Pavement Performance (LTPP) Special Pavement Study-1 (SPS-1) experiment were used to predict the permanent deformation parameters for the VESYS mechanistic-empirical rut model. This was accomplished by matching the rut performance curves versus time being matched for each section with a commercially available iterative solver. To ensure uniqueness of each section's permanent deformation parameters (PDPs), the transverse surface profiles were used to match the most likely contributions by layer according to the criteria proposed in the NCHRP Report 468. On average, the contribution to the total surface rutting from the various pavement layers was as follows: 57% from the asphalt concrete layer, 27% from the base layer, and 16% from the subgrade. These results confirmed that the contribution to the total rutting from asphalt concrete and base layers is important and needs to be included in any mechanistic-empirical design procedure.

Dynamic Backcalculation of Pavement Layer Parameters Using Frequency and Time Domain Methods

Abstract: In this paper, results from backcalculation of flexible pavement layer parameters based on dynamic interpretation of FWD deflection time histories using frequency and timedomain solutions are presented. The frequency-domain solution uses real and imaginary deflection basins as the measured quantities, while the time-domain solution uses either the peak deflections and corresponding time lags or traces of the deflection time histories as the measured quantities to be matched by the backcalculation procedure. Numerical examples show that the dynamic solutions are able to backcalculate layer moduli, damping and thicknesses accurately from synthetically generated FWD data. However, results using measured FWD test data indicate that dynamic backcalculation of layer parameters using field data presents some challenges. The frequency-domain method can lead to large errors if the measured FWD records are truncated before the motions fully decay in time. The time-domain methods when simultaneously backcalculating layer moduli and thicknesses produce mixed results. Convergence is not insured when using peak deflections and corresponding time lags. However, when matching traces of sensor time histories, the SVD method enabled very good convergence and the backcalculation of the AC layer thickness in addition to the layer moduli and damping even when using field measured data.

Effects of Design and Site Factors on Roughness of Flexible Pavements in the LTPP SPS-1 Experiment

Abstract: Although considerable mechanist-empirical research exists on the factors affecting flexible pavement roughness, it is limited in scope because of inadequate field validation and the complex interactions of structural and site factors. This paper presents the results of a study on the relative influence of design and site factors on roughness of in-service flexible pavements. The data form the SPS-1 experiment of the LTPP program were used in this study to investigate the effects of hot mix asphalt (HMA) surface layer thickness, base type, base thickness, and drainage on roughness of flexible pavements constructed in different site conditions (subgrade type and climate). Since this is the first comprehensive study of SPS-1 experimental data, a thorough methodology involving mean comparisons and multivariate ANOVA was adopted for data analyses. Among the design factors, base type was found to have the most significant effect on roughness. The best performance was shown by pavement sections with asphalt-treated bases. Drainage when combined with base type, also plays an important role in inhibiting roughness, while base thickness has only secondary effects. In addition, climatic conditions were found to have considerable influence. Pavement sections in the wet-freeze zone exhibited levels of roughness. Also, in general, pavements built on fine grained soils have shown the worst roughness levels. While most of the findings from this study support the existing understanding of factors affecting roughness, important interactions between design and site factors were identified and provide new insights for achieving better long-term pavement performance.

Effect of Design and Site Factors on Long-Term Performance of Flexible Pavements in SPS-1 Experiment

Abstract: Results are presented from a study to evaluate the relative influence of design and site factors on the performance of in-service flexible pavements. The data are from the SPS-1 experiment of the Long-Term Performance Pavement (LTPP) program. This experiment was designed to investigate the effects of HMA surface layer thickness, base type, base thickness, and drainage on the performance of new flexible pavements constructed in different site conditions (subgrade type and climate). Base type was found to be the most critical design factor affecting fatigue cracking, roughness (IRI), and longitudinal cracking (wheel path). The best performance was shown by pavement sections with asphalt treated bases (ATB). This effect should be interpreted in light of the fact that an ATB effectively means a thicker HMA layer. Drainage and base type, when combined, also play an important role in improving performance, especially in terms of fatigue and longitudinal cracking. Base thickness has only secondary effects on performance, mainly in the case of roughness and rutting. In addition, climatic conditions were found to have a significant effect on flexible pavement performance. Longitudinal cracking (wheel path) and transverse cracking seem to be associated with a wet-freeze environment, while longitudinal cracking (non-wheel path) seems to be dominant in a freeze climate. In general, pavements built on fine-grained soils have shown the worst performance, especially in terms of roughness. Although most of the findings from this study support the existing understanding of pavement performance, they also provide an overview of the interactions between design and site factors and new insights for achieving better long-term pavement performance.

Network-level evaluation of specific pavement study-2 experiment: Using a long-term pavement performance database

Abstract: The research described here was conducted as a part of NCHRP Project 20-50 (10&16), LTPP (Long-Term Pavement Performance) Data Analysis: Influence of Design and Construction Features on the Response and Performance of New Flexible and Rigid Pavements The relative effects of various design and site factors on the performance of jointed plain concrete (JPC) pavements are presented The data used in this study were primarily drawn from Release 17 of DataPave The Specific Pavement Study (SPS) 2 experiment was designed to investigate the effects of portland cement concrete (PCC) slab thickness, base type, drainage, PCC flexural strength, and slab width on the performance of JPC pavements On the basis of the statistical analysis of 167 test sections, ranging in age from 5 to 12 years, it was concluded that base type was the most critical design factor affecting performance in terms of cracking and roughness as measured by the international roughness index Pavement sections with a permeable asphalt-treated base and in-pavement drainage performed better than those with a dense-graded aggregate base or a lean concrete base PCC slab thickness also played an important role in improving the cracking performance of the pavements PCC flexural strength and slab width have only marginal effects on performance at this time

Effect of Design and Site Factors on Structural Rutting ofFlexible Pavements in the LTPP SPS-1 Experiment (With Discussion)

Abstract: The research described herein was conducted as a part of NCHRP Project 20-50 (10/16), LTPP Data Analysis: Influence of Design and Construction Features on the Response and Performance of New Flexible and Rigid Pavements. While there is considerable research on factors affecting flexible pavement rutting, they are limited in scope because of lack of field validation and no consideration for interactions of structural and site factors. This research addresses the relative influence of design and site factors on structural rutting of in-service flexible pavements. The data from the SPS-1 experiment of the LTPP program were used. This experiment was designed to investigate the effects of asphalt surface layer thickness, base type, base thickness, and drainage on performance of flexible pavements constructed in different site conditions (subgrade type and climate). Since there has been no comprehensive study of the SPS-1 experimental data, a thorough methodology involving analysis of variance (ANOVA), logistic regression and discriminant analysis was developed. Although most of the findings from the analysis of the SPS-1 experiment data support the existing understanding of pavement rutting performance, the results from this study provide an outline of the interactions between design and site factors. The results showed that while pavement structural and asphalt mix designs are crucial, pavement construction quality plays a vital role in achieving better rutting performance for flexible pavements. This was clearly apparent in the SPS-1 experiment where 56 out of 212 sections had construction-related problems leading to premature rutting failures. Among the sections that did not show premature rutting, the effects of design and site factors on structural rutting were marginal. This is mainly due to the fact that these sections are still fairly young. In general, pavements built on fine-grained soils have shown more rutting. Also, sections in warmer climates have shown slightly more rutting. Also, in general, regardless of site conditions, providing a thicker surface layer or an asphalt treated base layer will improve the structural rutting performance provided the materials are handled appropriately in design and during construction. Performance will be further enhanced if in-pavement drainage is provided, especially when the pavement structure is to be constructed on fine-grained soils. Also, analysis of transverse surface profiles showed that most of the rutting in the test sections is confined to the upper layers of the pavement structure. Therefore, using the mechanistic-empirical prediction models that incorporate the contribution of each pavement layer to surface rutting is a better approach to characterize the rutting mechanism in flexible pavements.

Part 1: Rigid Pavements: Network-Level Evaluation of Specific Pavement Study-2 Experiment: Using a Long-Term Pavement Performance Database

Abstract: The research described here was conducted as a part of NCHRP Project 20-50 (10&16), LTPP (Long-Term Pavement Performance) Data Analysis: Influence of Design and Construction Features on the Response and Performance of New Flexible and Rigid Pavements. The relative effects of various design and site factors on the performance of jointed plain concrete (JPC) pavements are presented. The data used in this study were primarily drawn from Release 17 of DataPave. The Specific Pavement Study (SPS) 2 experiment was designed to investigate the effects of portland cement concrete (PCC) slab thickness, base type, drainage, PCC flexural strength, and slab width on the performance of JPC pavements. On the basis of the statistical analysis of 167 test sections, ranging in age from 5 to 12 years, it was concluded that base type was the most critical design factor affecting performance in terms of cracking and roughness as measured by the international roughness index. Pavement sections with a permeable asphalt-treated b...