Materials and Construction

Characterization of Particle Shape Distribution of Construction Aggregates

There are huge research needs in the construction aggregate community to better understand the aggregate shape effect on the construction materials such as paving concrete, and to develop a systematic metrics for shape characteristics to optimize the mechanical performances of the aggregate-based materials. The current guidelines and standard specifications for use of construction aggregates (such as ACI 211, ASTM C33, C136 and D75) define the required nominal particle sizes and their distribution typically plotted in terms of the retained and/or passing percentage by weight on a linear or semi-log graph. The significance of the aggregate shape effect also has been well recognized in the construction materials community; however, there is no well-defined metrics/standards to describe the particle shape distribution (unlike the size distribution). This lack of a systematic protocol to quantitatively characterize the range and proportions (i.e., distribution) of particle shapes has significantly hindered to achieve enhanced predictive capabilities in the mechanical properties of cement-based and paving materials. For example, a research team of Western New England University tested two different groups of concrete cylinders, where aggregates used in both specimens strictly met the standard specifications, and all the properties were closely comparable to each other (e.g. the size distribution of the aggregates was same) except the shape: Aggregate A had a shape spectrum with relatively high angularities, while Aggregate B were more circular and rounded. A set of lab experiments showed strengths of the specimens are significantly different. However, the current specifications classify those aggregates equally acceptable. Therefore, a systematic way that can quantify the particle shape distribution needs to be developed to better design / estimate the performances of aggregate-based construction materials. The research will be able to use newly developed techniques to quickly characterize the shapes of different aggregates and investigate the effects on the mechanical properties of the construction materials.

Last Edited by Seung Jae Lee

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Idea No. 142