The American Society for Testing and Materials (ASTM) is an independent organization devoted to the development of standards.

American Society for Testing and Materials

The Environmental Protection Agency (EPA) provides access to information on a variety of topics related to the environment and strives to inform citizens of health risks. The EPA also has an extensive library network that consists of 26 libraries throughout the United States, which provide access to a plethora of information to EPA employees, scientists, and researchers. The EPA implemented a reorganization project to digitize their materials so they would be more accessible to a wider range of users, but this plan was drastically accelerated when the EPA was threatened with a budget cut. It chose to close and reduce the hours and services of some of their libraries. As a result, the agency was accused of denying users the “right to know” by making information unavailable, not providing an adequate strategic plan, and discarding vital materials. This case study explores the background of the digitization project, the practices implemented, and the critiques of the project.

/pdf/the-environmental-protection-agency-3gx4opzrjm.pdf

The Environmental Protection Agency

Artificial neural networks (ANNs) constitute a class of flexible nonlinear models designed to mimic biological neural systems. In this entry, we introduce ANN using familiar econometric terminology and provide an overview of ANN modeling approach and its implementation methods. † Correspondence: Chung-Ming Kuan, Institute of Economics, Academia Sinica, 128 Academia Road, Sec. 2, Taipei 115, Taiwan; ckuan@econ.sinica.edu.tw. †† I would like to express my sincere gratitude to the editor, Professor Steven Durlauf, for his patience and constructive comments on early drafts of this entry. I also thank Shih-Hsun Hsu and Yu-Lieh Huang for very helpful suggestions. The remaining errors are all mine.

Artificial neural networks

Highway Capacity Manual改訂の動向--テイラ-教授の講演より

Dynamics of structures

Pavement Life Cycle Assessment Framework

This study uses full-scale accelerated testing to provide new insight into the effectiveness of geogrids on the performance of low-volume flexible pavements. Although several previous studies reported that geogrids improve pavement performance by enhancing its structural capacity and reducing distress potential, this study goes further to quantify the effectiveness of geogrids, specify the mechanism of the reinforcement they provide and identify the optimum placement of geogrid in low-volume flexible pavements. Full-scale, low-volume flexible pavement sections were constructed on weak subgrade (California bearing ratio = 4%) and heavily instrumented with 170 sensors. The pavement was divided into three cells with each cell having three sections. The granular base and hot-mix asphalt layer thicknesses varied, and each cell had at least one control and one geogrid-reinforced pavement section. The instruments were embedded to measure stress, strain, deflection, moisture, pore-water pressure and temperature a...

Geogrid mechanism in low-volume flexible pavements: accelerated testing of full-scale heavily instrumented pavement sections

This paper demonstrates that the finite-difference time-domain (FDTD) method can be used to accurately simulate ground-penetrating radar (GPR) wave and its interaction with pavement having different densities and moisture conditions. The FDTD simulation described in this paper is part of the research efforts into the application of GPR on monitoring the density of asphalt pavement during compaction. The challenge is to separate the effect of density increase from the effect of the increase in surface moisture content on GPR signals. The first part of this paper describes the procedure for finding an equivalent excitation function used in simulation that can generate a GPR signal that matches the real signal. Discrete wavelet transform (DWT) was applied to denoise the signal. It was found that the equivalent excitation source and the DWT technique provided an accurate match between the simulation signal and real GPR signal in both the time domain and frequency domain. The second part of this paper demonstrates the application of FDTD simulation in investigating GPR responses on pavements with different densities and surface moisture content. The simulation successfully revealed the “frequency selective” feature of the effect of surface moisture content on GPR signals. Laboratory experiments were also conducted, and the results verified the findings in FDTD simulations. The FDTD simulation was shown to be an effective and efficient tool for studying the interaction of GPR waves with pavement. An accurate modeling of the signal and its propagation provided meaningful insights as well as the possibility for developing practical data-processing techniques.

Calibration of FDTD Simulation of GPR Signal for Asphalt Pavement Compaction Monitoring

According to a 1999 Federal Highway Administration statistic, the U.S. has around 8.2 million lane-miles of roadways that need to be maintained and rehabilitated periodically. Therefore, in order to reduce rehabilitation costs, pavement engineers need to optimize the rehabilitation procedure, which is achieved by accurately knowing the existing pavement layer thicknesses and localization of subsurface defects. Currently, the majority of departments of transportation (DOTs) rely on coring as a means to estimate pavement thicknesses, instead of using other nondestructive techniques, such as Ground Penetrating Radar (GPR). The use of GPR as a nondestructive pavement assessment tool is limited mainly due to the difficulty of GPR data interpretation, which requires experienced operators. Therefore, GPR results are usually subjective and inaccurate. Moreover, GPR data interpretation is very time-consuming because of the huge amount of data collected during a survey and the lack of reliable GPR data-interpretation software. This research effort attempts to overcome these problems by developing new GPR data analysis techniques that allow thickness estimation and subsurface defect detection from GPR data without operator intervention. The data analysis techniques are based on an accurate modeling of the propagation of the GPR electromagnetic waves through the pavement dielectric materials while traveling from the GPR transmitter to the receiver. Image-processing techniques are also applied to detect layer boundaries and subsurface defects. The developed data analysis techniques were validated utilizing data collected from an experimental pavement system: the Virginia Smart Road. The layer thickness error achieved by the developed system was around 3%. The conditions needed to achieve reliable and accurate results from GPR testing were also established.

Development of data analysis algorithms for interpretation of ground-penetrating radar data

A three-dimensional finite element model was developed to investigate the fracture behavior of a hot-mix asphalt (HMA) overlay on a jointed concrete pavement (JCP). Moving vehicular loads were applied to the HMA overlay on top of a joint to develop reflective cracking. A bilinear cohesive zone model (CZM) was inserted in the HMA overlay right over the joint. An interface constitutive model was implemented to specify interfacial behaviors between HMA-concrete layers. This study primarily examined the effects of interface bonding conditions on reflective cracking. The local and global behaviors of reflective cracking were investigated under various interface conditions regarding interfacial stiffness and bonding strength. Reflective cracking potential is quantified with representative fracture area (RFA), which represents a fractured area in the cross section of the HMA overlay. As a result, the fractured area increases significantly as the interface bonding strength becomes lower. On the contrary,...

Imad L. Al-Qadi

Papers

Pavement Life Cycle Assessment Framework

Geogrid mechanism in low-volume flexible pavements: accelerated testing of full-scale heavily instrumented pavement sections

Calibration of FDTD Simulation of GPR Signal for Asphalt Pavement Compaction Monitoring

Development of data analysis algorithms for interpretation of ground-penetrating radar data

Effects of Interface Conditions on Reflective Cracking Development in Hot-Mix Asphalt Overlays