72 research outputs found
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Sensitivity Analysis of Flexible-Pavement Response and the AASHTO Design Guide to Properties of Unbound Layers. Summary
"Unbound granular materials generally compose the base and subbase layers in road pavements. The granular materials distribute the load through aggregate contacts to a level sustainable by the subgrade. Pavement design and analysis often describe the base and subbase layers using the resilient modulus, which is the ratio of the dynamic-resilient stress to the dynamic-resilient strain. The resilient modulus represents a power function of the sum of the principal stresses. However, this model has serious limitations because it neglects shear strain's effect and it only works at low strain values in granular-materials characterization... The influence of using different response models (isotropic vs. anisotropic and linear vs. nonlinear) on the performance predictions of asphalt pavements needs further investigation. In addition, the sensitivity of the proposed AASHTO 2002 guide to unbound layers' properties needs urgent evaluation prior to the use of this guide in practice."Aggregates Foundation for Technology, Research, and Education (AFTRE); the National Stone, Sand, and Gravel Association; funds from The University of Texas at Austin and Texas A&M University; and contributions from the aggregates industryCivil, Architectural, and Environmental Engineerin
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User’s Manual for Finite Element Pavement Response Analysis Software TTI-PAVE
A finite element program was developed to calculate the responses of the pavement under traffic load. The finite element procedure and the code was originally derived by Owen and Hinton (1980) using elasto-plastic formulation. This software is developed to analyze an axisymmetric problem with material nonlinearity. Liu modified the program by developing a mesh generation algorithm, implementation of several constitutive models and non-symmetric solutions... Later in 2000 Park made another set of modification to the software to incorporate stress dependent Poisson ratio nonlinear analysis using load increments. Adu-Osie later modified the program to incorporate cross-anisotropy in the formulations. Adu-Osie implemented Uzan’s model presented in equation 1 instead of the nonlinear elasto-plastic model for pavement analysis.Aggregates Foundation for Technology, Research, and Education (AFTRE)Civil, Architectural, and Environmental Engineerin
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Alkali-Silica Reaction in Portland Cement Concrete
ICAR PROJECT 301, "Alkali-Silica Reaction in Portland Cement Concrete," headed by Dr. David W. Fowler at The University of Texas at Austin, succeeded in modifying ASTM C 1293 to yield comparable findings in [three] weeks that previously required twelve months or more. Furthermore, the second stage of the project identified several economical mitigation alternatives for aggregates that did prove reactive.Aggregates Foundation for Technology, Research, and Education (AFTRE); the National Stone, Sand, and Gravel Association; funds from The University of Texas at Austin and Texas A&M University; and contributions from the aggregates industry.Civil, Architectural, and Environmental Engineerin
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Status of By-Product Fines in the United States
"The objectives of the study were to identify the scope and diversity of marketing by-product fines; develop a technically and economically based protocol to identify potential uses; establish an advisory team to assist the industry in identifying and developing markets for fines; prepare guidelines for fines uses and recommendations for long-term objectives; and provide data to assist in a long-term marketing strategy for the industry. Following a review of pertinent literature and the organization of a Fines Expert Task Group, researchers developed a database to assist in quantifying the magnitude of the fines problem."Aggregates Foundation for Technology, Research, and Education (AFTRE)Civil, Architectural, and Environmental Engineerin
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Evaluation of Aggregate Characteristics Affecting Hot Mix Asphalt (HMA) Response
Aggregate shape properties are known to influence asphalt pavement performance. Angularity and texture govern the frictional properties and dilation of the aggregate structure. Aggregate texture plays a major role in influencing the adhesive bond between the aggregate and the binder, while aggregate form influences the anisotropic response of asphalt mixes... Aggregate shape properties are known to influence asphalt pavement performance. Angularity and texture govern the frictional properties and dilation of the aggregate structure. Aggregate texture plays a major role in influencing the adhesive bond between the aggregate and the binder, while aggregate form influences the anisotropic response of asphalt mixes.Aggregates Foundation for Technology, Research, and Education (AFTRE); the National Stone, Sand, and Gravel Association; funds from The University of Texas at Austin and Texas A&M University; and contributions from the aggregates industryCivil, Architectural, and Environmental Engineerin
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LASS Incorporates the Third Dimension in Order to Improve the Accuracy of Rapid-Gradation Technology
"Sophisticated asphalt designs, such as the Superpave specification, specify aggregate shape parameters like flatness and elongation ratios as an additional design variable. Conventional sieve analysis has drawbacks such as: poor efficiency and accuracy; labor intensiveness; time consumption; subjectivity; inability to measure shape parameters; and inability to measure irregularly shaped particles accurately. Although several rapid-gradation devices are currently on the market, their appropriateness and cost effectiveness for various applications in both the laboratory and in the field has yet to be determined. The research team evaluated five commercially available rapid gradations devices for accuracy and performance using fifteen aggregate test samples of various size, shape, and minerology. The project uses several methodologies in characterizing accuracy and studies two technologies in detail: digital-image analysis and laser profiling. The second part of the final project developed a laser scanning device for grading aggregates"Aggregates Foundation for Technology, Research, and Education (AFTRE); the National Stone, Sand, and Gravel Association; funds from The University of Texas at Austin and Texas A&M University; and contributions from the aggregates industry.Civil, Architectural, and Environmental Engineerin
The greenhouse gas emissions and mitigation options for materials used in UK construction
The UK construction industry faces the daunting task of replacing and extending a significant proportion of UK infrastructure, meeting a growing housing shortage and retrofitting millions of homes whilst achieving greenhouse gas (GHG) emission reductions compatible with the UK's legally binding target of an 80% reduction by 2050. This paper presents a detailed time series of embodied GHG emissions from the construction sector for 1997–2011. This data is used to demonstrate that strategies which focus solely on improving operational performance of buildings and the production efficiencies of domestic material producers will be insufficient to meet sector emission reduction targets. Reductions in the order of 80% will require a substantial decline in the use of materials with carbon-intensive supply chains. A variety of alternative materials, technologies and practices are available and the common barriers to their use are presented based upon an extensive literature survey. Key gaps in qualitative research, data and modelling approaches are also identified. Subsequent discussion highlights the lack of client and regulatory drivers for uptake of alternatives and the ineffective allocation of responsibility for emissions reduction within the industry. Only by addressing and overcoming all these challenges in combination can the construction sector achieve drastic emissions reduction
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Evaluation of Superpave Aggregate Specifications
The purpose of this study was to evaluate the restricted zone effect using four different aggregates: crushed granite, crushed limestone, crushed river gravel, and a mixture of crushed river gravel as coarse aggregate with naturals and fines. Each type of aggregate was used for mixture design of three hot-mix asphalt (HMA) gradings: above, through, and below the restricted zone.International Center for Aggregates Research is funded by the Aggregates Foundation for Technology, Research, and Education (AFTRE); the National Stone, Sand, and Gravel Association; funds from The University of Texas at Austin and Texas A&M University; and contributions from the aggregates industry.Civil, Architectural, and Environmental Engineerin
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