Effects of morphological characteristics of aggregate particles on the mechanical behavior of bituminous paving mixtures
Introduction
In order to improve the performance, durability, safety, and efficiency of asphalt mixtures, the Strategic Highway Research Program (SHRP), established in 1987, proposed the Superpave system in 1993. Superpave included a set of significant advancements in the methodologies used to classify asphalt binders and to design asphalt mixtures. In addition, the Superpave system also defined the so-called consensus and source properties of aggregate particles.
The four consensus properties identified by SHRP researchers as key characteristics directly related to the performance behavior of the mixtures were coarse- and fine-aggregate angularity, amount of flat and elongated particles in coarse aggregates, and sand equivalency of fine aggregates. The criteria specified for these properties are generally function of the traffic volume expected in the area where the flexible pavement will be built. On the other hand, the characterization of source properties is considered optional and the corresponding limiting criteria are specified based on the experience of the local transportation agencies to account for the regional geological differences.
Several research efforts have demonstrated reasonable to good correlations between the consensus properties of aggregates specified by the SHRP and the overall mechanical behavior of asphalt mixtures [1], [2], [3], [4], [5], [6], [7]. However, in the last years, researchers have criticized some of these tests [6], [8], [9], [10], [11], [12], [13], which are often considered to be subjective and/or based on indirect measurements and to produce results that are a function of the skills of the operator. Some testing procedures, such as the one specified for the determination of the coarse aggregate angularity, can also be tedious and time-consuming.
Considering the relevance of aggregates and the corresponding effects of their properties on the overall behavior of asphalt mixtures and on the costs related to the production and maintenance of flexible pavements, the study of alternative methodologies that are able to characterize aggregates properties in more objective and representative manners becomes a very important task. In that sense, several researchers have adopted protocols to identify aggregate morphological properties based on image analysis techniques, including VDG-40 Videograder, Computer Particle Analyzer, Micromeritics OptiSizer PSDA, VideoImaging System (VIS), Buffalo Wire Works PSSDA, Camsizer, Wipshape, University of Illinois Aggregate Image Analyzer (UIAIA), Aggregate Imaging System (AIMS). Masad et al. [8] compared several of these image analysis systems and identified AIMS as the most promising equipment as it allows a comprehensive, objective, and direct analysis of shape, angularity, and texture based on two-dimensional and three-dimensional images of aggregate particles.
This study evaluates the effects of morphological properties of aggregate particles on the overall mechanical behavior of asphalt mixtures. For that, properties of two aggregates with distinct morphological characteristics, i.e., round river gravel and crushed gneiss, were first characterized based on the specifications of the Superpave system. Alternatively, aggregate morphological characteristics were also determined using the second generation of the modern image analysis system AIMS (i.e., Aggregate Imaging Measurement System 2: AIMS 2). To further identify the effects of the different morphological properties of aggregates on the overall performance behavior of asphalt mixtures, six mixtures comprising different amounts of gravel and crushed gneiss were designed based on Superpave mix design specifications, and their performance behavior was compared to the morphological characteristics of their aggregate skeleton.
Specific objectives of this paper are:
- •
To characterize aggregate particles with distinct morphological properties based on Superpave specifications and using the image analysis system AIMS 2.
- •
To characterize the mechanical behavior of asphalt mixtures containing different amounts of gravel and crushed gneiss. For that, three primary mixture characteristics are evaluated: stiffness, permanent deformation, and cracking.
- •
To identify correlations between the morphological properties of the aggregates evaluated and the mechanical behavior of the corresponding asphalt mixtures.
Section snippets
Materials and mix design
One PG 70-16 S binder obtained from a refinery in Rio de Janeiro, Brazil, and two types of aggregates, i.e., gravel from the state of Pará, Brazil, and crushed gneiss from Rio de Janeiro were used in this study.
Six mixtures with the same aggregate gradation were designed based on Superpave specifications. The first mixture contained crushed gneiss with cubic particles. The second mixture was composed of gravel and natural sand. The use of natural sand as the fine part of gradations containing
Aggregate properties
Table 3 presents results of the different combinations of aggregates evaluated in this study based on conventional testing procedures. It can be observed that both crushed gneisses presented higher specific gravities, but were less absorptive than the gravel.
The crushed gneisses also presented higher values for both FAA and CAA than the gravel, as expected. All combinations of fine aggregates presented FAA values above 45%, which is the minimum FAA specified by Superpave for the traffic level
Summary and conclusions
This paper evaluated the effects of morphological properties of aggregates on the mechanical behavior of asphalt mixtures. Three different aggregates, i.e., two crushed gneisses with different shapes and one gravel, were used in the composition of six Superpave asphalt mixtures. Several aggregate properties were characterized based on Superpave procedures for typical aggregate consensus properties. Additionally, morphological aggregate characteristics were also determined in a modern image
Acknowledgements
The authors are grateful for the financial support received from the Carlos Chagas Filho Foundation for Research Support of the State of Rio de Janeiro (FAPERJ, Brazil) and from the National Council for Scientific and Technological Development (CNPq, Brazil).
References (36)
- et al.
Aggregate Tests Related to Asphalt Concrete Pavement Performance in Pavements. NCHRP Report 405
(1998) - et al.
Identification of aggregate role in performance of Superpave mixtures employing accelerated testing facility
ASTM Spec. Tech. Publ.
(2001) - et al.
Aggregate Properties and the Performance of Superpave-Designed Hot Mix Asphalt. NCHRP Report 539
(2005) - et al.
Aggregate Tests for Hot-mix Asphalt Mixtures Used in Pavements. NCHRP Report 557
(2006) - et al.
Effect of coarse aggregate morphology on permanent deformation behavior of hot mix asphalt
J. Transp. Eng.
(2006) - et al.
Sensitivity of HMA Performance to Aggregate Shape Measured Using Conventional and Image Analysis Methods. TTI Report 0-1707-5
(2006) - et al.
Experimental testing and finite-element modeling to evaluate the effects of aggregate angularity on bituminous mixture performance
J. Mater. Civ. Eng.
(2012) - et al.
Test Methods for Characterizing Aggregate Shape, Texture, and Angularity. NCHRP Report 555
(2007) - et al.
Caracterização de agregados convencionais e alternativos utilizando técnicas de processamento digital de imagens
Monogr. CBUT
(2009) - et al.
Avaliação do processo de produção de agregados por medio da utilização do processamento digital de imagens
Associação de Pesquisa e Ensino em Transportes-ANPET
(2011)
Evaluation of polishing and degradation resistance of natural aggregates and steel slag using AIMS
Effects of Aggregate Angularity on Mix Design Characteristics and Pavement Performance. Report No. MPM-10
Comprehensive evaluation of AIMS texture, angularity, and dimension measurements
J. Mater. Civ. Eng.
Standard Specification for Superpave Volumetric Mix Design
The Difficult Nature of Minimum VMA: A Historical Perspective
The Effect of Voids in Mineral Aggregate (VMA) on Hot Mix Asphalt Pavements. Report MN/RC-2000-13
VMA as a design parameter in hot-mix asphalt
Factors that affect the voids in the mineral aggregate of hot-mix asphalt
Cited by (57)
Characterization and evaluation of coarse aggregate wearing morphology on mechanical properties of asphalt mixture
2023, Construction and Building MaterialsQuantitative characterization of aggregates and their chemical constituents in terms of acid and alkaline indicators
2023, Case Studies in Construction MaterialsDiscrete element analysis of the effect of aggregate morphology on the flowability of self-compacting concrete
2023, Case Studies in Construction MaterialsUtilization of inferior quality aggregates in asphalt mixes: A systematic review
2022, Journal of Traffic and Transportation Engineering (English Edition)Effect of aggregate morphology characteristics on the voidage of aggregate loose packing based on 3D discrete element method
2022, Construction and Building Materials