Waheed Uddin

Determining Hardness and Elastic Modulus of Asphalt by Nanoindentation

Nanoindentation is a relatively new technique which has been used to measure nanomechanical properties of surface layers of bulk materials and of thin films. In this study, micromechanical properties such as hardness and Young’s modulus of asphalt binders and asphalt concrete are determined by nanoindentation experiments. Indentation tests are conducted on a base binder and two polymer-modified performance grade (PG) binders such as PG-70-22 and PG76-28. In addition, two Superpave asphalt mixes such as SP-B and SP-III are designed using these PG binders, and the corresponding mixes are compacted to prepare asphalt concrete. Aggregate, matrix (Materials Passing No. 4 sieve) and mastic (Materials Passing No. 200 sieve) phases of each asphalt concrete sample are indented using both Berkovich and Spherical indenters. In nanoindentation, an indenter penetrates into asphalt material and the load (milli-Newton) and the depth (nanometers) of indentation are recorded continuously. Indentation load versus displacem...

Infrastructure Inventory and Condition Assessment Using Airborne Laser Terrain Mapping and Digital Photography

The combination of airborne laser and digital camera technologies can be used as a cost-effective and efficient means of digital mapping for civil and environmental applications. A framework for the use of these remote-sensing technologies in conjunction with Global Positioning System (GPS) receivers for digital mapping of infrastructure projects is presented. An example of the benefit of airborne laser terrain mapping combined with differential positioning with a GPS is low-altitude, high-speed laser scanning of up to 81 km2 (20,000 acres) per day, which achieves an accuracy of 10 cm with reduced operating constraints, such as cloud and vegetation cover, traffic and usage, and time of day. The three-dimensional digital coordinate data are directly loaded into terrain mapping and computer-aided design software. This leads to efficient and error-free data processing and map generation. Conventional topographic surveys are slow, and aerial photogrammetry is limited by operating constraints and time-consuming data processing and interpretation. Examples of recent applications of the system for diverse projects like pipeline networks, power transmission lines, railroad tracks, and freeway interchanges are presented.

3D-FE Simulation Study of Structural Response Analysis for Pavement-Subgrade Systems Subjected to Dynamic Loads

This paper presents the results of a comprehensive simulation study that investigated the effects of infinite elements in pavement models, eigenvalue analysis, and damping. The results provide useful insight into pavement structural responses. This is not possible from traditional static linear elastic analysis and two dimensional-finite element models developed for pavement analysis and design. A three dimensional finite element half model of an asphalt highway pavement-subgrade system was created with optimum size and boundary conditions. The model was used for simulations of the load-time history of a falling weight deflectometer impact test. The half model was validated by the results of the Greens function and showed the limitation of the use of infinite elements for pavement models. The fundamental natural frequency of 8 Hz for the an asphalt highway pavement was determined by the eigenvalue analysis using the implicit finite element code. The results of a parametric study are presented to evaluate the effects of both system damping and Rayleigh damping on pavement deflection response and back-calculated modulus values.

3D-FE Modeling and Simulation of Airfield Pavements Subjected to FWD Impact Load Pulse and Wheel Loads

The purpose of this paper is to discuss and compare the results of an analysis done with a three dimensional-finite element dynamic and another done with a two dimensional-finite element-dynamic analysis for the thick and string pavement section. Nondestructive structural evaluation of existing airfield pavements by deflection testing is used to assess the load carrying capacity and strengthening design for future aircraft operations. The current back calculation programs analyze the deflection data and calculate in situ Youngs modulus values based on linear elastic structural response analysis for static loading. Advanced three dimensional finite element dynamic analysis is used in this study to simulate airfield pavements subjected to nondestructive test load pulses. This study validates the in situ modulus values of a thick and strong airfield pavement section backcalculated from static analysis.

In Situ Material Properties from Dynamic Deflection Equipment

Dynamic deflection equipment presents a very practical and cost-effective approach for nondestructive testing and evaluation of pavement-subgrade systems. The in situ Youngs moduli are calculated by the inverse application of layered elastic theory to the measured dynamic deflection data. This paper discusses some of the fallacies associated with this iterative approach. The calculated moduli are user dependent and nonunique if the user inputs the initial set of moduli to start iteratives. A proven methodology to ensure uniqueness of the moduli is the generation of seed moduli as the function of measured deflections and radial distances of the sensors. The FPEDD1 (for pavements with asphalt concrete surfacings) and RPEDD1 (for rigid pavements) computer program incorporate this methodology. The predictive equations used to generate seed moduli are based on numerous layered theory solutions and are therefore applicable to any region and soil condition. This paper describes the approaches used in these programs to estimate nonlinear moduli for granular layers and subgrade soil, and considers rock layers. Examples are presented for in situ material properties from dynamic deflection data measured on a variety of pavement-subgrade systems. It is shown that an appropriate analysis technique yields comparable pavement moduli from the dynamic deflection data measured by vibratory or impulse loading equipment.

Airborne Laser Survey Specifications and Quality Management Protocols for Airport Obstruction Surveys

Airport obstruction surveys are conducted to identify obstacles (objects penetrating obstruction identification surfaces that may pose a hazard to air navigation) and to provide critical data for the safety of aircraft and passengers. The current practice of airborne light detection and ranging (LIDAR) technology for airport obstruction surveys is presented. Obstruction survey requirements and current federal standards related to airport airspace analysis and the airport-geographical information system (GIS) program are reviewed. The accuracy of airborne LIDAR surveys and obstruction analysis has been established in previous field studies conducted by the National Geodetic Survey (NGS). Commercial obstruction surveys have been conducted on many airports in North America with LIDAR configurations and survey specifications recommended by NGS. In most cases, LIDAR survey data can be collected efficiently during the day as well as at night. LIDAR point cloud and intensity data are used to identify obstacles for the entire survey area through computationally efficient office computer algorithms and complementary use of photogrammetry. In contrast, traditional photogrammetry-only methods are limited to identifying obstacles at discrete locations because of laborintensive data processing. In addition, LIDAR data can be processed into GIS shape files for seamless integration into an electronic airport layout plan. Multiuse of LIDAR data for both canopy and bare ground enables the generation of accurate digital elevation models, contours for engineering design, and planimetrics for GIS mapping. Mission planning, ground point spacing and density, and other key parameters considered in the latest sample LIDAR survey specifications published as ACRP Research Results Digest 10 are discussed.

An overview of GPR applications for evaluation of pavement thickness and cracking

Pavement asset management requires accurate and rapid measurement of asphalt layer thickness for reliable backcalculation of modulus values of pavement layers from nondestructive deflection tests. Also needed are measurements of layer delamination, surface cracking, and other distresses. Top-down cracking in the longitudinal wheel path of thick asphalt highway pavement is a major distress problem. The objective of this paper is to evaluate several nondestructive testing technologies that can be operated at highway speed to assess asphalt thickness and surface cracking depth. This paper presents key findings of an extensive literature review of GPR equipment and data interpretation methodologies. The study supports that nondestructive GPR technology has evolved over the last three decades to measure pavement layer thickness and delamination accurately, which is more cost-effective than extracting cores. The study did not find a field technology that can operate at highway speeds for mapping pavement surface cracking and its penetration depth. However, GPR remote sensing has the potential to map the penetration depth of top-down cracking from the surface through asphalt layer thickness.

Application of Remote Sensing Tunable Laser Technology for Measuring Transportation Related Air Pollution

This paper presents initial results of the air quality analysis project that is focused on remote sensing laser measurements of air pollutants and air quality impact of transportation systems. Tunable laser remote sensing technology is being used over a distance of several hundred meters for measuring Nitrogen Dioxide and Ozone related to transportation. The laser is tuned between ultraviolet, visible, near infrared, and thermal infrared spectral regions. The difference in the absorption of light at these different wavelengths is used to determine concentration of air pollutants. The absorption band of Nitrogen Dioxide lies in the visible part of the electromagnetic spectrum. It absorbs blue color of sky, resulting in brown color smog. The laser measurement results of Nitrogen Dioxide concentration, measured near Mississippi Highway 6 in Oxford, showed nearly 25 times more concentration at 10 AM (daytime) compared to the measurement at 11 PM (nighttime) when the traffic was minimal. Higher Nitrogen Dioxide concentration is also associated with higher air temperature in the daytime measurement.

Pavement Construction Effects on Subgrade Resilient Modulus and Validation by 3D-FE Simulation

ABSTRACT This study investigates the changes shown by the in situ resilient modulus of compacted subgrade resulting from the construction of lime treated subgrade, base, and asphalt pavement layers. In situ modulus values are backcalculated from traditional static linear elastic layered analysis of peak deflection data of falling weight deflectometer nondestructive impact tests. Sensors 2 through 6 are more appropriate for analysis of the deflection data collected on compacted subgrade surfaces because of abnormally high sensor 1 deflections, which are above the sensor accuracy range. The data from a dynamic cone penetrometer, a destructive test, are related to layering in the subgrade soil and the modulus of each soil layer. The modulus results from both field tests agree reasonably well with the average laboratory resilient modulus values of the bottom subgrade layer for 12 selected pavement construction sites in Mississippi. Effects from the construction of top pavement layers on the subgrade modulus values are evaluated using side-by-side testing by field methods conducted over the summer, winter, spring, and following summer season. The subgrade modulus values backcalculated from the deflection tests conducted on the top constructed asphalt layer is 176% higher than the modulus for the compacted subgrade only. The nonlinear subgrade modulus calculated after full pavement construction is within 6% of the average laboratory modulus, which validates the nonlinear correction procedure of shear strain based equivalent linear analysis. The asphalt paved section is simulated by three dimensional-finite element dynamic analysis to validate the backcalculated modulus values.

Pavement Materials Property Databases for Pavement Management Applications

Pavement layer structure and layer material property data play a key role in the development of pavement performance models, pavement design and analysis procedures, diagnostic evaluation of premature pavement deterioration, and selection of cost-effective maintenance/rehabilitation alternatives. This paper describes system design considerations for the end user interface and analysis requirements related to pavement material property database management. Case studies of material database development and implementation include the long-term pavement performance (LTPP) studies of the Strategic Highway Research Program, network-level pavement management applications on the state level, and a recent United Nations highway maintenance management project. Reference is made to the steps taken to ensure quality assurance, database integrity, and database security. Relational database tools provide an excellent facility for system development that should consider a number of key identifiers. The most important property data are the historical material data of all layers at the time of construction. For pavement management applications, the scope and data categories are limited and dictated by the end users and economic considerations.