Amar Raghavendra

Instrumentation and Accelerated Testing on Louisiana Flexible Pavements

Three flexible pavement test sections were constructed at the Louisiana Pavement Research Facility on December, 2004. Each section had a similar 50-mm thick Superpave wearing course but with various base and subbase layers. One objective of this study was to instrument and measure responses under accelerated loading on each test section with (a) multi-depth deflectometers (MDD) at six vertical locations, and (b) pressure cells on the top of subbase and subgrade. The field instrumentation data and Falling Weight Deflectometer (FWD) deflection data were collected at every 8,500 and 25,000 load repetitions, respectively. The preliminary pavement responses under wheel loading were estimated from the multi-layer elastic analysis program, ELSYM5. this paper reported (1) the instrumentation used in this study, (2) preliminary pavement performance results, (3) comparison of deflections measured from MDD and FWD, and (4) comparison of pavement responses between the measured and the predicted.

Evaluating Effects of Volumetric and Mechanistic Test Variability on Predicted Performance of Asphalt Pavement: Applying the Mechanistic–Empirical Pavement Design Guide

The objective of this study is to evaluate, with the Mechanistic–Empirical Pavement Design Guide (MEPDG), the effects of volumetric and mechanistic variability on predicted performance of asphalt pavements. In addition, the effect of volumetric variability on predicted mechanistic properties of asphalt mixtures, as determined with the Fonseca–Witczak predictive model, was quantified with the use of a Monte Carlo simulation. Data collected from NCHRP Project 9–48, Field Versus Laboratory Volumetric and Mechanical Properties, were used to quantify the variability in volumetric and mechanistic properties. The effects of mechanistic variability on the design outcomes were evaluated with a sensitivity analysis of the MEPDG. According to the results, the average coefficient of variation (CV) in the dynamic complex modulus calculated from the Fonseca–Witczak model was 8.1%, which was less than the CV of 13.9% determined from the dynamic modulus test data presented in NCHRP Project 9–48. Predicted pavement distresses from the MEPDG indicated that a variability level in the dynamic complex modulus of 10% or less resulted in a change in the predicted level of performance of 10% or less. In contrast, variability in the dynamic modulus of 20% changed the design life of the pavement structures by up to 42% and the design hot-mix asphalt thickness by as much as 19%.

Laboratory and Construction Evaluation of Warm-Mix Asphalt

AbstractWarm mix asphalt (WMA) describes various technologies that allow asphalt mixtures to be produced at lower temperatures as compared with hot mix asphalt (HMA). WMA technologies also offer improvements in workability, cost, and environmental sustainability, such as reduced fuel usage, greenhouse gas emissions, and wear and tear at plants, while enhancing worker health and safety conditions. The objective of this study was to quantify the laboratory performance of field-produced mixtures that utilize WMA technologies and to evaluate the influence of lowering the production temperature on the mixture properties in the field. To achieve this objective, three field projects across Louisiana were selected to provide eight mixtures for the evaluation of WMA technologies. Plant-produced mixtures were sampled and the laboratory performance of WMA mixtures and conventional HMA was evaluated. Further, the characteristics of WMA mixtures were compared with conventional HMA mixtures during production and constr...

Levels of Variability in Volumetric and Mechanical Properties of Asphalt Mixtures

AbstractThe objective of this study was to quantify the levels and sources of variability in the measurements of volumetric and mechanical properties of dense-graded asphalt mixtures on the basis of existing test data from state agencies and contractors. To achieve this objective, data were collected from state DOTs and research agencies, and a statistical analysis was conducted on a per-state basis to provide an overall quantification of the levels of variability for the different volumetric and mechanical properties. A meta-analysis based on the collected data was conducted to identify sources of variability for volumetric and mechanical properties. According to the results of the analysis, levels of variability for a wide range of volumetric and mechanical properties were quantified. Levels of variability were comparable for various state DOTs located in different climatic regions. It was determined that results obtained by the state and contractor were statistically equivalent for the majority of the ...

Dynamic Modulus of Asphalt Mixtures: Evaluation of Effects on Pavement Performance Prediction

Mix properties that deviate appreciably from the design properties during the production and construction of asphalt mixtures can lead to premature pavement distress or even failure. The objective of this study was to quantify the differences in the dynamic modulus of specimens prepared during design, production, and construction of dense-graded asphalt pavements and their effects on pavement performance prediction. For the achievement of this objective, Superpave® mixtures were collected from Iowa, Florida, Virginia, Michigan, South Dakota, Louisiana, Minnesota, and Wisconsin during design [laboratory-mixed and laboratory-compacted (LL)], production [plant-produced and laboratory-compacted (PL)], and construction [plant-produced and field-compacted (PF) specimens]. The nominal maximum aggregate size was kept constant at 12.5 mm. An indirect tension dynamic complex modulus (IDT |E*|) was measured for the three specimen types (i.e., LL, PL, and PF). Results showed that laboratory-compacted and field-compacted specimens exhibited large and significant differences. This finding was attributed to differences in the compaction effort and procedure between the field and the laboratory. Results of the AASHTOWare Pavement ME Design showed that the use of dynamic moduli obtained from different specimen types would result in significant differences in pavement performance prediction. This research was part of NCHRP Project 9-48, Field Versus Laboratory Volumetrics and Mechanical Properties.

Evaluation of various Hamburg wheel-tracking devices and AASHTO T 324 specification for rutting testing of asphalt mixtures

The Hamburg Wheel Tracking (HWT) laboratory test uses loaded wheel(s) to apply a moving load on asphalt mixture specimens to simulate traffic loading on asphalt pavements. Given that different machines with various degrees of compliance with the current AASHTO T 324 requirements are used by highway agencies, this study aimed to assess the capabilities of commercially available and representative HWT equipment, and to evaluate different analysis and reporting methods for rutting and stripping performance assessment. After performing a comprehensive evaluation of devices from different vendors, considerable discrepancies on equipment capabilities and configurations were identified. The machines did not meet all the requirements set forth in AASHTO T 324 including those for the wheel position waveform, the temperature range, and the reporting parameters. Evaluation of existing analysis methods revealed significant inconsistencies among different methods and deficiencies in the specification. Recommended modifications to the machines and test method were provided.

Hamburg Wheel-Track Test Equipment Requirements and Improvements to AASHTO T 324

In this study, a comprehensive experimental program was conducted to evaluate the capability of five commercially available Hamburg Wheel Tracking (HWT) equipment as well as their ability to accurately measure, control, and maintain the desired test conditions as specified in AASHTO T 324. Based on the results of this study, researchers were tasked to provide proposed revisions with commentary to AASHTO T 324 to enable the use of a performance type specification for Hamburg test equipment. Modifications are proposed to address equipment capabilities, components, or design feature in order to ensure proper testing and accurate, reproducible results. Proposed modifications are discussed in this report to ensure repeatable measurements and that the results from different manufacturers are comparable. These modifications include change to temperature measurement and range, impression measurement system, data collection, and data analysis and reporting. In addition to the proposed modifications to the AASHTO T 324 specifications, the vendors may need to modify their equipment to meet the new specification requirements.

Laboratory-Measured Dynamic Modulus and Predicted Performance of Asphalt Mixtures: Effects of Specimen Orientation

The dynamic modulus testing of asphalt mixtures is typically conducted by using a specimen 100 mm in diameter and 150 mm tall loaded along its primary axis (axial mode). This specimen orientation can present problems when as-built pavement layers, which are seldom constructed in 150-mm lifts, are evaluated. For this issue to be addressed, dynamic modulus testing in the indirect tension (IDT) loading mode was proposed. The objective of this study was to evaluate the influence of loading mode (axial versus IDT) on the measured dynamic modulus and the effects of the measured difference on pavement performance prediction. For the achievement of these objectives, Superpave® mixtures were collected from Florida, Iowa, Louisiana, Michigan, Minnesota, South Dakota, Virginia, and Wisconsin and were evaluated for the effects of loading mode. Results of the experimental program showed that statistical differences exist between IDT and uniaxial dynamic modulus values measured at different temperatures and frequencies. When the precision of the dynamic modulus test was considered, differences attributable to the loading mode (IDT versus axial) were observed for measurements conducted at all temperatures, with the dynamic moduli measured in the axial loading mode being stiffer than the dynamic moduli measured in the IDT loading mode. Results also showed that performance prediction was significantly affected by the loading mode. Predicted rutting and fatigue cracking in the asphalt layer were the most influenced distresses. Correlation factors were developed to correlate one set of dynamic moduli to the moduli measured in a different loading mode.

DESIGN, CONSTRUCTION, AND ANALYSIS OF PAVEMENTS USING ACCELERATED LOADING FACILITY

The Louisiana Transportation Research Center has recently completed the construction of a full-scale pavement test facility using the accelerated loading facility (ALF) machine. This facility contains nine pavement test sections, 12-m (38-ft) long and 3.66-m (12-ft) wide that are loaded by the ALF machine with loads ranging from 34.71 to 111.25 kN (7,800 to 25,000 lbf) on a dual-tire assembly. The advantage of this testing facility is its ability to cause a pavement to fail in a short period of time. In addition, the data acquisition methods and instrumentation used in this testing facility allow researchers to obtain reliable and representative performance data. The first test section has been loaded to failure and a preliminary analysis of the data is completed. VESYS 3A-M, a microcomputer version of the VESYS series, has been selected for the analysis due to its ability to predict damage and its flexibility. The analysis consists of the primary response analysis to determine strains, stresses, and deflection of the pavement and damage-prediction modeling that includes rutting, fatigue cracking, and roughness. The analysis was conducted by comparing the data obtained from field with that predicted by VESYS 3A-M. The performance data obtained from the field include fatigue cracking, rutting, and roughness. The analysis showed that VESYS 3A-M outputs are in good agreement with those obtained from the field.