Number Of Equivalent Single Axle Loads Research Articles

Accelerated Pavement Testing of Re-Recycled Cold Central Plant Recycled Asphalt Mixtures

Cold central plant recycled asphalt mixtures (CCPR) have been shown to provide a high-quality, economical, and environmentally conscious asphalt base mixture. Existing literature, however, does not indicate what would be an appropriate future rehabilitation method for a pavement that includes CCPR. Given the previously cited benefits of CCPR, it is logical to ask whether a CCPR can be re-recycled and, if so, how will it perform? This paper presents a study of a test section containing a re-recycled CCPR placed at the National Center for Asphalt Technology Test Track. CCPR from a Virginia Department of Transport study on the Test Track was recovered, re-recycled, and placed at 5-in. thick with a 2-in. asphalt concrete (AC) overlay. In preparing for a re-recycled CCPR layer, milling an existing CCPR layer resulted in a coarser gradation and lower indirect tensile strength values. Initially, the re-recycled CCPR test section did not perform well owing to moisture in the aggregate base present during construction of the re-recycled CCPR layer. It is suspected that this moisture negatively affected the curing of the re-recycled CCPR layer. Thus, the re-recycled CCPR layer was milled and re-recycled again (3rd generation re-recycled CCPR) and placed at 5-in. thick with a 2-in. AC overlay. The 3rd generation re-recycled CCPR performed well through 3 million equivalent single axle loads (ESALs), the same number of ESALs that resulted in fatigue cracking and rutting failures in the initial re-recycled CCPR.

Investigation of Factors Affecting the Intermediate-Temperature Cracking Resistance of In-Situ Asphalt Mixtures Based on Semi-Circular Bending Test

Cracking is one of the main distresses in asphalt pavement. At present, few studies have been conducted on the cracking performance of asphalt mixtures from the field due to the difficulty of sample collection. Therefore, this study aims to assess the cracking resistance of in-service asphalt pavement at intermediate temperature using a large number of field cores in Jiangsu province, China. A semi-circular bending (SCB) test at 25 °C was conducted on field-cored samples covering three asphalt layers from 16 in-service road sections that represent a combination of influencing factors, including air void, mixture type, service age, cumulative number of equivalent single-axle loads (ESALs), and overload rate. The flexibility index (FI) and tensile strength were calculated from the experimental data as cracking performance evaluation indices. According to the analysis of variance results, at the top layer, ESALs and service age had a strong influence on cracking resistance. The decline rate of FI became slower with increasing ESALs. The most rapid decline in crack resistance with service age occurred on medium-traffic-level sections that served for over 14 years. At the middle layer, the overload rate replaced service age as a significant factor for FI. At the bottom layer, the air void was the only significant factor affecting the cracking resistance. In general, as the depth of layer increased, the effect of traffic load and service age decreased, whereas the effect of material properties increased. In addition, the FI and tensile strength were more sensitive to traffic load and air void, respectively.

Methodological Framework for Truck-Factor Estimation Considering Vehicle–Pavement Interaction

AbstractTruck traffic is usually characterized by using truck factors (TFs). A TF converts a mixed truck traffic stream over the pavement design lifetime into a number of equivalent single-axle loads (ESALs). This conversion requires equivalent single-axle load factors (EALFs), which can either be empirical or theoretical. The mechanistic-empirical pavement design guide (MEPDG) considers axle load spectra and uses it to run the response model, considering implicitly theoretical EALFs. This paper presents a methodology for TF estimation based on theoretical EALFs calculated by using simulated axle loads, thus overcoming the unavailability of data to define axle load spectra. Once the EALFs are calculated for several simulations, TFs are established and regression models are defined to predict TFs. To reach this point, the study considered the two most common Portuguese truck configurations and pavement structures. The methodology development and application revealed its flexibility and upgradability. The r...

Accelerated performance testing of concrete pavement with short slabs

A new concept for designing concrete pavements by optimising the slab geometry in order to reduce the slab thickness as well as to minimise the mechanical load transfer devices has recently been proposed. Theoretically, the reduced slab size lowers the load and curling-induced tensile stresses and concomitantly a thinner concrete slab can be constructed. Full-scale test sections were constructed and tested under accelerated pavement loading conditions to validate this design concept hypothesis. The design and concrete material factors studied in this research were concrete thickness of 9, 15 or 20 cm; granular or asphalt concrete base layer; and plain or fibre-reinforced concrete (FRC). A methodology was presented to convert the channelised traffic loading to equivalent single axle loads (ESALs) so that comparisons could be made between the various test sections. The accelerated pavement testing showed that shorter slab sizes can sustain a significant number of overloads and greater number of ESALs before developing cracking relative to standard jointed concrete pavements. The most prevalent distress observed was corner cracking which occurred twice as much as longitudinal cracks, whereas only 3 out of 46 cracking distresses were transverse cracks. The 20 cm concrete slabs on granular base did not experience fatigue cracking for trafficking up to 51 million ESALs. The 15 cm concrete slabs on granular base began cracking on an average of 11 million ESALs. As expected, the concrete slabs on asphalt base resisted a significant larger number of ESALs relative to the same concrete thickness on granular base. The cracking performance of the 9 cm concrete slabs on granular base varied with the stiffness of the soil. For the 9 cm slab thickness, structural fibres provided a longer fatigue life and extended service life relative to the plain concrete slabs. Finally, the smaller slab sizes maintained a medium-to-high load transfer efficiency over the accelerated loading period for all slab thicknesses without the development of any faulting. As expected, these slab systems resulted in higher deflections, and, therefore, the granular base and subgrade layers as well as lateral drainage system must be designed and specified to reduce the rate of permanent deformation and minimise the possibility of support erosion.

Development of Roughness Prediction Models for Low-Volume Road Networks in Northeast Brazil

Roughness evaluation is the most effective way to diagnose pavement condition for design and decision making. The index most commonly used worldwide to indirectly describe the surface condition of asphalt pavements is the international roughness index (IRI). However, few studies have tried to predict the pavement performance of low-volume roads (LVRs) on the basis of the IRI, especially for LVRs in tropical regions. In an attempt to remedy that lack of knowledge, this paper presents IRI-based prediction models developed for asphalt pavement LVR networks in northeast Brazil. The following independent variables were considered to affect the IRI: Thornthwaite's aridity index, which describes local climate; the modified structural number, representing pavement bearing capacity; and the cumulative number of equivalent single-axle loads, representing the traffic applied to the pavements. A multiple regression analysis was carried out, and the results showed that the IRI increases exponentially over time. The analysis of the model parameters confirmed their significance, and the R-square values were 0.87 and 0.94, respectively, for low-volume roads with hot asphalt mixes and bituminous surface treatments. The hot-mix asphalt model was compared with that of the Highway Development and Management Model and with other models developed in research also sponsored by the World Bank. Because of regional differences (especially climate and materials), the models proposed in this paper provide a better estimation of roughness progression in LVRs of the northeast of Brazil.

Validation of Backcalculated Modulus Values from Falling Weight Deflectometer through Instrumentation on I-35 in Oklahoma

Several state departments of transportation evaluate the modulus of pavement layers from nondestructive deflection tests such as the falling weight deflectometer (FWD). Although the FWD is a widely used nondestructive testing device, it still does not fully represent the loading conditions generated by moving vehicular traffic. Therefore, the modulus values backcalculated from FWD data may be different from those values backcalculated from vehicular traffic loading data. A comparison is presented of modulus values backcalculated from FWD and strain gauge measurements collected on a 1,000-ft-long instrumented section of I-35 in central Oklahoma. The FWD data were captured at different temperatures with different loading configurations. Meanwhile, longitudinal and transverse strain data were captured from May 30, 2008, through October 28, 2009, over a wide range of middepth pavement temperatures (40°F to 110°F) under actual vehicular traffic loading. The influence of different backcalculated modulus values is demonstrated through the prediction of remaining life in terms of number of equivalent single-axle loads of the existing pavement. Also presented is a description of the testing program, data collection efforts, and subsequent analysis for the I-35 instrumented section. Overall, modulus values backcalculated from the FWD and from longitudinal strain gauges showed close agreement at temperatures above 50°F.