Uncompacted Void Content of Fine Aggregate as Quality Indicator of Materials Used in Superpave Mixtures

Abstract

The uncompacted void content of fine aggregate, or fine aggregate angularity (FAA), was introduced in the Superpave mixture design system to screen smooth or rounded fine aggregates that may result in mixtures with low rutting resistance. The assumption is that fine aggregates with lower FAA values have lower shear strength (internal friction) and lower resistance to rutting. Continued implementation and evaluation of the Superpave system has led to numerous questions regarding the validity of this assumption and of the use of the FAA test in general. Nine fine aggregates were used to evaluate the FAA test and to determine whether it was a reliable indicator of fine aggregate shear strength. FAA tests were performed using three gradations and the three standard test methods (A, B, and C). Microscopic analysis was conducted to obtain independent visual measures of angularity and texture. Direct shear tests were performed at four confining stresses to determine shear strength parameters. Results indicated that FAA values were related to visual measures of texture and angularity. However, although FAA value contributed to shear strength, it appeared that other factors such as toughness, gradation, and packing characteristics of the fine aggregate overshadow its effect. For the fine aggregates tested, the FAA test rejected aggregates with high shear strength and accepted aggregates with low shear strength. It was concluded that FAA values alone may not be adequate to assess shear resistance of fine aggregate. Direct shear strength may be a better parameter, but additional work is required to evaluate its validity and feasibility.

Fatigue life evaluation of asphalt mixtures containing natural river sands and designed by bailey method

“…Most of these studies had inconsistent results, where the evaluation of the inclusion of natural sand was arbitrarily or without following a systematic procedure, and percentages of natural sands included in the mix were relatively high. This can be seen in a number of studies including [4,5,6,7,8,9,10]. The results of the aforementioned studies lack consistency since not much consideration was given to aggregates particles shapes, packing, and gradations.…”

Comparing Fine Aggregate Angularity with Aggregate and Hot-Mix Asphalt Performance Tests

“…Cubical-shaped particles, for example, even with 100% fractured faces, have been found not to be able to meet the FAA requirement for heavy-volume traffic even though good field performance has been observed. Additional field studies have also shown that even when the fine aggregates met the minimum FAA values, poor field performance had occurred (3)(4)(5). Therefore, further work may be needed to validate, possibly refine the use of the FAA test as a means of screening different fine aggregates for their use in HMA, provide a surrogate test method to screen fine aggregates for use in HMA, or all functions.…”

Correlation of Fine Aggregate Imaging Shape Indices with Asphalt Mixture Performance

“…Several studies have demonstrated the significant effect of fine aggregate shape properties on the mixture stability and its capability to resist rutting (e.g., 2-4). However, recent findings show that the FAA values of aggregates do not correlate well with the performance of mixtures in which they are used (5,6). These findings emphasize the importance of developing new procedures for quantifying fine aggregate shape properties based on the fundamental understanding of the different elements that make up aggregate shape.…”