Tongyan Pan

Aggregate Morphology Affecting Resilient Behavior of Unbound Granular Materials

The resilient modulus (MR) defines the nonlinear elastic response of pavement geomaterials, such as the unbound aggregate base-subbase materials, under repeated traffic loading. The resilient behavior of unbound aggregate layers is affected by the stress states experienced because of wheel loading and physical properties of aggregate materials. Among the physical properties, the influence of aggregate morphology on the resilient behavior of base-subbase materials is not yet well understood because of a lack of quantitative measurements of shape, angularity, and surface texture characteristics of aggregate particles. This paper focuses on investigating the influence of aggregate angularity and surface texture properties on the resilient behavior of unbound granular materials expressed by a nonlinear, stress-dependent resilient response model. With an image analysis approach, two important aggregate morphological indices [the angularity index (AI) and the surface texture index (ST)] were defined to quantify...

Effect of Coarse Aggregate Morphology on the Resilient Modulus of Hot-Mix Asphalt

The resilient modulus measured in the indirect tensile mode according to ASTM D 4123 reflects effectively the elastic properties of asphalt mixtures under repeated load. The coarse aggregate morphology quantified by angularity and surface texture properties affects resilient modulus of asphalt mixes; however, the relationship is not yet well understood because of the lack of quantitative measurement of coarse aggregate morphology. This paper presents findings of a laboratory study aimed at investigating the effects of the material properties of the major component on the resilient modulus of asphalt mixes, with the coarse aggregate morphology considered as the principal factor. With modulus tests performed at a temperature of 25°C, using coarse aggregates with more irregular morphologies substantially improved the resilient modulus of asphalt mixtures. An imaging-based angularity index was found to be more closely related to the resilient modulus than an imaging-based surface texture index, as indicated b...

Quantification of Coarse Aggregate Surface Texture Using Image Analysis

Aggregate surface texture affects the performance of pavement and railroad track structural layers, such as the unbound aggregate base/ballast, asphalt concrete, and Portland cement concrete. A quantitative surface texture (ST) index is defined in this paper based on image analysis to measure the irregularities on the surface of coarse aggregate particles in the extent that is not characterized by the commonly used large-scale morphological descriptors, such as flatness, elongation, and angularity. Using an image analysis approach referred to as erosion and dilation, the new ST index quantifies the coarse aggregate surface irregularities at the pixel level. Samples of natural gravel and crushed aggregate were used in establishing a realistic range for the ST index independent of particle size. The effectiveness and practical applicability of the defined ST index in characterizing aggregate surface texture were evaluated by measuring surface irregularities or texture of commonly used coarse aggregate materials.