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.
Effect of Fine Aggregate Angularity on Compaction and Shearing Resistance of Asphalt Mixtures
The effect of fine aggregate angularity (FAA) on the densification characteristics of asphalt mixtures was evaluated with the Superpave® gyratory compactor (SGC). Aggregates from three different sources used in production of Superpave mixtures in Wisconsin were studied. From each source, a fine gradation and a coarse-shaped gradation were included. To vary the FAA values of the fine aggregates, the proportions of the manufactured sand to the natural sand from each source were varied and the same overall gradations were maintained. A range of FAA values between 40 and 48 for the sources was achieved. All other mixture variables were kept constant, and the mixtures were compacted in an SGC equipped with a special device called a gyratory load plate assembly to measure the densification and the shear force required for compaction of each mixture. Densification data were analyzed to estimate the effect of the FAA on densification to 92% of theoretical maximum density (Gmm), which is assumed to represent resistance of the mixture to construction compaction, and to densification above 92% Gmm, which is assumed to represent mixture resistance to traffic. Results indicate a consistent trend of higher resistance to compaction with higher FAA values. Mixtures with higher FAA require higher compaction effort, as measured by densification rate and shear force required for gyrating. Resistance to densification above 92% Gmm, which is assumed to represent traffic, shows inconsistent trends. For one source of aggregates, the increase in FAA resulted in less resistance to densification and shear distortion above 92% Gmm. Results indicate that the sensitivity of mixture response variables to change in FAA values is highly dependent on the source of the aggregates and on gradation. Therefore, it is recommended that mixture design be based on limits of densification characteristics instead of a target FAA value for all mixture types.
Bevel RIE application to reduce defectivity in copper BEOL processing
Bevel etch used during wafer fabrication for semiconductor devices is discussed. In this case, the bevel etch process was utilized in middle of the line processing (MOL) to reduce back end of line (BEOL) defectivity. Tungsten and titanium nitride films, from the formation of contacts to the transistors, extend into the bevel region of the wafer and have been shown to initiate arcing. This can spread foreign material defects on the front side of the wafer in various BEOL post processing steps including subsequent reactive ion etching, SEM metrology and film depositions. The bevel etch tool confines a plasma etch to the outer edge of the front side of the wafer (which can be individually adjusted) and can remove dielectric, organic and Ti/TiN/W films using a fluorine based chemistry.