Annual Energy Outlook 2008 With Projections to 2030

INTROdu CTION Warm mix asphalt (WMA) has been gaining acceptance across the United States and Canada in recent years. A large number of state departments of transportation (DOTs) have hosted WMA demonstrations to determine if WMA should be allowed for state-funded paving projects. These demonstrations have shown that WMA is constructible and can reduce fuel usage and emissions associated with hot mix asphalt (HMA) production. However, many of these demonstrations were conducted with only one or two WMA technologies. Now there are over 25 commercially available WMA technologies in the United States. Most states do not approve a WMA technology for use on state-maintained roads without a welldocumented demonstration project. The WMA technology suppliers that were not part of these early demonstration projects often are required to organize a demonstration on their own to gain approval for state paving projects. A standard evaluation program for con

NAtioNAl CooperAtive HigHwAy reseArCH progrAm

Application of the convergence-confinement method of tunnel design to rock masses that satisfy the hoek-brown failure criterion

A. Federal Highway Administration

Aseismic design of underground structures

An improved closed-form solution is developed for calculating tunnel support thrusts, moments, and displacements. The solution directly models the interaction of an elastic, circular support with an elastic, isotropic, infinite ground mass. The major improvements in this solution over other solutions in the literature are: (1)A revised formulation of the compressibility ratio; and (2)the incorporation of the correct excavation unloading conditions for mined tunnels. The sensitivity of the tunnel support loads to variations in the relative support stiffness, support cross section, Poisson's ratio, and initial lateral stress ratio is demonstrated using the revised solution; these results are also compared to those from two other solutions in the literature. Discrepancies of up to 100% are found in the support forces calculated from the different solutions.

Simplified analysis for tunnel supports

Various models have been developed over the past several decades to predict the dynamic modulus ∣ E* ∣ of hot-mix asphalt (HMA) based on regression analysis of laboratory measurements. The models most widely used in the asphalt community today are the Witczak 1999 and 2006 predictive models. Although the overall predictive accuracies for these existing models as reported by their developers are quite high, the models generally tend to overemphasize the influence of temperature and understate the influence of other mixture characteristics. Model accuracy also tends to fall off at the low and high temperature extremes. Recently, researchers at Iowa State Univ. have developed a novel approach for predicting HMA ∣ E* ∣ using an artificial neural network (ANN) methodology. This paper discusses the accuracy and robustness of the various predictive models (Witczak 1999 and 2006 and ANN-based models) for estimating the HMA ∣ E* ∣ inputs needed for the new mechanistic-empirical pavement design guide. The ANN-based...

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1037&context=ccee_pubs

Accuracy of Predictive Models for Dynamic Modulus of Hot-Mix Asphalt

A comprehensive constitutive model for asphalt concrete was calibrated that included viscoelasticity, viscoplasticity, and irreversible microstructural damage in unconfined compression. Three different types of laboratory tests were designed and performed to calibrate each of these response components. Small-strain dynamic modulus tests were used to calibrate the undamaged linear viscoelastic properties. Cyclic creep and recovery tests to failure were performed to calibrate the viscoplastic properties. Constant-rate-of-strain tests to failure were used to calibrate the damage behavior. These tests were performed at a wide range of temperatures, loading rates, and stress levels. Upon calibration of each individual response, the model was validated by predicting the results of other constant-rate-of-strain tests at temperatures and strain rates different from those used in the calibrations. The predictions for these different conditions indicate that the comprehensive model can realistically simulate a wide range of asphalt concrete behavior.

Viscoelastic, Viscoplastic, and Damage Modeling of Asphalt Concrete in Unconfined Compression

Geotechnical Aspects of Pavements

Base reinforcement in pavement systems using geosynthetics has been found under certain conditions to provide improved performance. Current design methods for flexible pavements reinforced with a geosynthetic in the unbound aggregate base layer are largely empirical methods based on a limited set of design conditions over which test sections have been constructed. These design methods have been limited in use due to the fact that the methods are not part of a nationally recognized pavement design procedure, the methods are limited to the design conditions in the test sections from which the method was calibrated, and the design methods are often times proprietary and pertain to a single geosynthetic product. The first U.S. nationally recognized mechanistic-empirical design guide for flexible pavements is currently under development and review (NCHRP Project 1-37A, NCHRP 2003). The purpose of this project was to develop design methods for geosynthetic reinforced flexible pavements that are compatible with the methods being developed in NCHRP Project 1-37A. The methods developed in this project, while compatible with the NCHRP 1-37A Design Guide, are sufficiently general so as to allow the incorporation of these methods into other mechanistic-empirical design methods. The design components addressed in this project include material and damage models for the different layers of the pavement cross section, incorporation of reinforcement into a finite element response model, and the development of response model modules that account for fundamental mechanisms of reinforcement. Mechanistic material models are required for all components of the pavement cross section included in the finite element response model. Material models from the NCHRP 1-37A Design Guide for the asphalt concrete, and the unbound aggregate and subgrade layers are used in this study. Additional material models for the unbound aggregate layer are also examined. Material models for components associated with the reinforcement are developed in this project. These include a material model for the reinforcement itself, and an interface shear interaction model for the reinforcement-aggregate and reinforcement-subgrade interaction surfaces. Along with these material models, testing methods providing parameters for use in the material models have been examined and preliminarily evaluated. These testing methods include tension tests for evaluating non linear direction dependent elastic constants for the reinforcement and cyclic pullout tests for evaluating a stress dependent interface shear resilient modulus. These tests have been devised to provide parameters pertinent to small strain and displacement conditions present in pavement applications.

Charles W. Schwartz

Papers

Simplified analysis for tunnel supports

Accuracy of Predictive Models for Dynamic Modulus of Hot-Mix Asphalt

Viscoelastic, Viscoplastic, and Damage Modeling of Asphalt Concrete in Unconfined Compression

Geotechnical Aspects of Pavements

Development of design methods for geosynthetic reinforced flexible pavements