Aggragate Particle Shape-Highway Systems

Effects of Particle Shape on Performance and Durability of Aggregates Used in Road Construction

This research is looking into the effects of particle shape, specifically the amount of flat particles, on the performance of unbound aggregate base in road construction. Unbound aggregate base primarily has two important roles in a road structure. The first one is to provide a stable platform for the asphalt layer with appropriate structural capacity. The second is to provide efficient drainage to minimize accumulation of excess water below the asphalt layer. The selected material for the base layer has to be durable to take the abrasion of the material during hauling and compaction. The effect of aggregate shape on the stability, permeability, and durability of unbound aggregate base is being investigated in an extensive laboratory investigation.

The experimental program for this research includes resilient modulus, permanent deformation, permeability, Los Angeles Abrasion, and Micro-Deval testing. This program is developed to quantify the effect of particle shape on the overall performance of an unbound aggregate base layer. Four different aggregates are included in this study including aggregates originated from Diabase, Hornfels, Limestone, and Slate.

From a comprehensive review of current United States transportation agencies unbound aggregate base specifications, it was found that there is a large variation in current limits set on the shape of aggregate particles. In a literature review conducted, previous studies have hinted that aggregate shape can affect unbound aggregate base, but has not defined the extent of that effect or suggested a limit on particle shape for unbound aggregate base. This research is looking at quantifying the effects of aggregate shape on unbound aggregate base. One of the practical implications of this study is to provide guidance in determining the allowable amount of flat aggregate particles in unbound aggregate mixtures.

For related publications see: Cook et al. (2017)