ItemSensitivity Analysis of Flexible-Pavement Response and the AASHTO Design Guide to Properties of Unbound Layers. Summary(International Center for Aggregates Research, 2005) International Center for Aggregates Research"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." ItemLASS Incorporates the Third Dimension in Order to Improve the Accuracy of Rapid-Gradation Technology(International Center for Aggregates Research, 2004) International Center for Aggregates Research"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" ItemStructural Characteristics of Unbound Aggregate Bases for Mechanistic Design(International Center for Aggregates Research, 2001) International Center for Aggregates ResearchThe next AASHTO Guide for the Design of Pavement Structures will make extensive use of mechanistic-empirical design principles, and may result in pavement designs with different layer thicknesses than are currently common. ICAR Research developed new testing protocols and materials characterization models that properly characterize unbound granular materials. Now, for the first time a structural model accurately characterizes unbound aggregate bases for evaluation during design against other types of layers in flexible and rigid pavements. ItemIncreased Single-Lift Thicknesses For Unbound Aggregate Base Courses(International Center for Aggregates Research, 1998) International Center for Aggregates Research"State departments of transportation (DOTs) have used aggregate base courses for many years as an integral structural component of pavements. Specifications prescribe requirements for placement and compaction of aggregate bases in addition to quality requirements for the aggregates. Typically, specifications also limit the lift thickness of unbound aggregate bases. While advances have been made with regard to the capabilities of compaction equipment, lift thickness limits have generally remained unchanged, and this has raised the question of whether these specifications are too restrictive... The objective of this study was to evaluate the feasibility of compacting unbound aggregate base courses in thicker lifts than currently permitted by DOTs and to identify effective test methods that assess the quality of the final compacted base or subbase." ItemImplication of Aggregates in the Frictional Performance of Seal Coat Overlays(International Center for Aggregates Research, 1988) International Center for Aggregates ResearchTo investigate the effect of aggregate type on pavement friction, researchers used Texas as a test model and constructed 59 seal coat test sections 1,000 feet (304 m) long in the four climatic regions of the state. The environmental characteristics of these four regions included: wet and no freeze; wet and freeze-thaw cycling; dry and no freeze; and dry and freeze-thaw cycling. Researchers used many of the aggregate types that are common to each region, and economically available, in the design mixture for each seal coat section. ItemFrom 12 Months to 3 Months : ICAR Study Yields New Test for Alkali-Silica Reaction that Reduces Time Required(International Center for Aggregates Research, 2002) International Center for Aggregates ResearchICAR 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. ItemRole of Aggregate Characteristics in Resistance to Load in SMA(International Center for Aggregates Research, 2006) Gatchalian, Dennis; Masad, Eyad; Chowdhury, Arif; Little, Dallas N.Stone Matrix Asphalt (SMA) mixtures rely on stone-on-stone contacts among particles to resist applied forces, and permanent deformation. Aggregates in SMA should resist degradation (fracture and abrasion) under high stresses at the contact points. This study utilizes conventional as well as advanced imaging techniques to evaluate aggregate characteristics, and their resistance to degradation. Aggregates from different sources and types with various shape characteristics were used in this study. The Micro-Deval test was used to measure aggregate resistance to abrasion. The aggregate imaging system (AIMS) was used to examine the changes in aggregate characteristics caused by abrasion forces in the Micro-Deval. The resistance of aggregates to degradation in the SMA was evaluated through the analysis of aggregate gradation before and after compaction using conventional mechanical sieve analysis, and the nondestructive X-ray computed tomography (CT). The findings of this study lead to the development of an approach for the evaluation of aggregate resistance to degradation in SMA. This approach measures aggregate degradation in terms of abrasion, breakage, and loss of texture ItemEvaluation of Aggregate Characteristics Affecting Hot Mix Asphalt (HMA) Response(International Center for Aggregates Research, 2004) International Center for Aggregates ResearchAggregate 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. ItemEvaluation of Superpave Aggregate Specifications(International Center for Aggregates Research, 2002) International Center for Aggregates ResearchThe 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. ItemMeasuring Workability of High-Fines Concrete(International Center for Aggregates Research, 2005) International Center for Aggregates Research"The workability of fresh concrete has traditionally been evaluated with the slump test, which provides an inadequate indication of this important parameter... The need for a better test method for workability is well established within the concrete industry. ICAR researchers identified 61 existing workability test methods. Based on this literature search and on feedback from government, industry, and academia, criteria for an improved workability test device were developed. This research sought to identify an effective field test method for measuring the workability of concrete in general and of high-microfines concrete in particular. ICAR researchers first described key principles and trends in the measurement of workability and then described the 61 test methods."