Determining Representative Volume Elements of Asphalt Concrete Mixtures without Damage

Abstract

This study presents a simple method to define the representative volume elements (RVEs) of asphalt concrete mixtures without damage. Three currently used asphalt concrete mixtures (two dense-graded Superpave® mixtures with different nominal maximum aggregate sizes of 9.5 and 12.5 mm and one stone matrix asphalt mixture with a nominal maximum aggregate size of 19.0 mm) were selected and evaluated. To address the significant heterogeneity of asphalt concrete mixtures properly in defining RVEs, several geometrical factors, such as area fraction, gradation, orientation, and the distribution of aggregate particles in asphalt concrete mixtures, were all considered together by using two-dimensional images of actual asphalt concrete inner structures produced by digital-image processing. Geometrically defined RVEs were then supported by finite element simulations to check whether effective nondamage material properties obtained from the RVEs, such as the linear viscoelastic dynamic modulus, were representative of the corresponding bulk asphalt concrete mixture. Analysis results indicated that typical dense-graded Superpave asphalt concrete mixtures can be characterized by their effective non-damage properties with an approximate RVE size of 50 mm. However, the properties of stone matrix asphalt mixtures, which contain larger aggregates, should be measured on a larger scale for improved accuracy. Findings from this study were generally consistent with results of other studies performed on the basis of extensive laboratory tests, which implies that the simple geometrical–numerical method here can be a potentially efficient approach to define the RVEs of asphalt mixtures with much less time and effort.

Geometrical Evaluation and Experimental Verification to Determine Representative Volume Elements of Heterogeneous Asphalt Mixtures

“…Thus, there is a need to investigate the aggregate size distribution (i.e., gradation) in a mixture in order to monitor the existence of any particular concentration of specific particle sizes. In an attempt to account for the particle size distribution, Kim et al [19] used gradation curves obtained from the image analysis of each TRVE, and the curves were then compared with the maximum density line to calculate the area, representing the density of each gradation curve, between the two curves. This process was attempted to quantify the gradation characteristics as a number for more efficient comparison among TRVE sections.…”

“…The outcomes from the previous study [19] need further validation for a more conclusive finding. Toward this end, the 12.5 mm NMAS mixture was selected for this study as a typical and the most representative dense-graded Superpave mixture used today.…”

“…In other words, the averaged characteristics (mechanical or geometrical) in an RVE should be statistically homogeneous so that the bulk sample characteristics and the RVE characteristics are the same. To determine the RVEs of asphalt concrete mixtures when any additional heterogeneities due to structural damage, such as cracking, is not related, Kim et al [19] used the virgin inner structure image of mixtures to perform various geometrical analyses. Analyses results indicated that mixture heterogeneity is primarily due to the initial configuration of the aggregate particles, which further indicates that spatial homogeneity of the RVEs can be reasonably identified by investigating the statistical homogeneity of various geometric factors, such as area fraction, gradation, orientation, and the distribution of aggregate particles in asphalt concrete mixtures.…”

“…Recently, Kim et al [19] attempted the geometricalnumerical approach based on the two-dimensional image processing for determining asphalt mixture RVEs. They investigated spatial heterogeneity of mixtures by addressing statistical homogeneity of several geometrical factors such as volume fraction, gradation, orientation, and the spatial distribution of aggregate particles in three different mixtures (i.e., 9.5, 12.5, and 19.0 mm nominal maximum aggregate size (NMAS)) through two-dimensional, actual images of asphalt mixture inner structures.…”

“…In order to determine its proper RVE dimension, two parallel approaches were conducted; geometrical analysis of mixture heterogeneity using two-dimensional actual images of asphalt concrete inner structures and experimental evaluation by performing uniaxial tensile tests of asphalt concrete mixtures incorporated with digital image correlation (DIC). The geometrical analysis is the same approach presented in the previous study [19], but a total of ten specimens were analyzed for this study to reach a better gener- ality. For the experimental evaluation, uniaxial tensile tests of two asphalt concrete cylinder specimens (75 mm diameter and 140 mm high) were conducted with the use of high-resolution chargecoupled device (CCD) digital cameras and photogrammetric principles to measure the strain tensor on the specimen during loading.…”