SGC Tests for Influence of Material Composition on Compaction Characteristic of Asphalt Mixtures
Compaction characteristic of the surface layer asphalt mixture (13-type gradation mixture) was studied using Superpave gyratory compactor (SGC) simulative compaction tests. Based on analysis of densification curve of gyratory compaction, influence rules of the contents of mineral aggregates of all sizes and asphalt on compaction characteristic of asphalt mixtures were obtained. SGC Tests show that, for the mixture with a bigger content of asphalt, its density increases faster, that there is an optimal amount of fine aggregates for optimal compaction and that an appropriate amount of mineral powder will improve workability of mixtures, but overmuch mineral powder will make mixtures dry and hard. Conclusions based on SGC tests can provide basis for how to adjust material composition for improving compaction performance of asphalt mixtures, and for the designed asphalt mixture, its compaction performance can be predicted through these conclusions, which also contributes to the choice of compaction schemes.
THE SUPERPAVE MIX DESIGN MANUAL FOR NEW CONSTRUCTION AND OVERLAYS
The Superpave mix design system is a comprehensive method of designing paving mixes tailored to the unique performance requirements dictated by the traffic, environment (climate), and structural section at a particular pavement site. It facilitates selecting and combining asphalt binder, aggregate, and any necessary modifier to achieve the required level of pavement performance. This laboratory manual presents Superpave mix design system in a complete, step-by-step format. It is intended for engineers and technicians in public and private organizations to use when designing paving mixes for all classes of highways, from farm-to-market roads to urban freeways. An essential companion to this manual is "The Superpave Mix Design System Manual of Specifications, Test Methods and Practices." The Superpave software program--"The Superpave Specification, Mix Design and Support Program"--and its users manual are also necessary to take full advantage of the mix design system.
Effect of Flat and Elongated Coarse Aggregate on Characteristics of Gyratory Compacted Samples
The effect of various levels of flat and elongated (F&E) particles on the gyratory compaction characteristics in a standard bituminous mixture was examined. Compaction characteristics involve the effect of F&E particles on the void development in the gyratory compactor as well as the break-down characteristics. F&E particles could also affect the performance characteristics of the compacted mixtures. F&E particles in typical Illinois surface mixtures were examined. Two coarse aggregate sources, a dolomite and crushed gravel, were used. A cubical mixture was prepared in which all particles had an F&E ratio < 3:1 and baseline compaction characteristics were established. Coarse aggregates were individually measured to produce aggregate particles with measured F&E ratios < 3:1, between 3:1 and 5:1, and > 5:1. The coarse aggregates in the cubical gradation were replaced with various percentages of the same-sized aggregate with F&E ratios in the 3:1 and 5:1 range. These mixtures were compacted and the volumetric and gyratory characteristics were compared. Solvent extractions and binder ignition samples were obtained to indicate the relative breakdown in aggregates achieved with the different percentages of the F&E particles. The testing indicates the changes produced when different percentages of F&E particles are introduced into a mixture. When combined with performance testing, these data will provide a valid base upon which to recommend levels of allowable F&E particles in an asphalt mixture.