Alvaro Guarin

Packing theory-based framework to evaluate permanent deformation of unbound granular materials

Permanent deformation of unbound granular materials plays an essential role in the long-term performance of a pavement structure. Stability of unbound granular materials is defined by the particle-to-particle contact of the system, the particle size distribution and the packing arrangement. This paper presents a gradation model based on packing theory to evaluate permanent deformation of unbound granular materials. The framework was evaluated by using 10 unbound granular materials from different countries. The disruption potential, which determines the ability of secondary structure (SS) to disrupt the primary structure (PS), is introduced. This study also identified the amount of PS and SS that may eventually be used as a design parameter for permanent deformation of unbound road layers. The evaluation of the model regarding permanent deformation behaviour of granular materials is found to compare favourably with experimental results.

Asphalt Internal Structure Characterization with X-Ray Computed Tomography and Digital Image Processing

In this paper, detailed study is carried out to develop a new workflow from image acquisition to numerical simulation for the asphalt concrete microstructures. High resolution computed tomography scanned images are acquired and the image quality is improved using digital image processing techniques. Nonuniform illumination is corrected by applying an illumination profile to correct the background and flat-fields in the image. Distance map based watershed segmentation are used to segment the phases and separate the aggregates. Quantitative analysis of the micro-structure is used to determine the phase volumetric relationship and aggregates characteristics. The result of the quantitative analysis showed a very high level of reliability. Finite Element simulations were carried out with the developed micro-mechanical meshes to capture the strength and deformation mechanisms of the asphalt concrete micro-structure. From the micro-mechanical investigation the load transfer chains, higher strength characteristics and high stress localization at the mastic interface between adjacent aggregates was shown.

Disruption factor of asphalt mixtures

Typically, aggregate gradation is selected to meet Superpave mix design specification; however, many Superpave mixtures have exhibited deficient field performance. The porosity of the dominant aggregate size range (DASR), which is the primary structural network of aggregates, has been extensively validated as a tool to evaluate coarse aggregate structure of laboratory and field asphalt mixtures. Mixtures identified by the system as having poor or marginal gradations resulted in poor rutting resistance. This study focused on how asphalt mixture performance is affected by changes in interstitial component (IC), which is the material between DASR particles. Laboratory testing clearly showed that IC characteristics may have a significant effect on rutting and cracking performance of mixtures. The disruption factor (DF) was developed to evaluate the potential of IC aggregates to disrupt the DASR structure. DF satisfactorily distinguished poor performing mixtures; therefore, it may eventually be used in combination with DASR porosity as a design parameter for rutting and cracking resistant asphalt mixtures.

Packing theory-based framework for evaluating resilient modulus of unbound granular materials

Enhancing the quality of granular layers is fundamental to optimise the structural performance of the pavements. The objective of this study is to investigate whether previously developed packing theory-based aggregate parameters can evaluate the resilient modulus of unbound granular materials. In this study, 19 differently graded unbound granular materials from two countries (USA and Sweden) were evaluated. This study validated both porosity of primary structure (PS) and contact points per particle (coordination number) as key parameters for evaluating the resilient modulus of unbound granular materials. This study showed that decreasing the PS porosity – higher coordination number – calculated based on the proposed gradation model, yields higher resilient modulus. Good correlation was observed between the proposed packing parameters and resilient modulus of several types of aggregates. The packing theory-based framework successfully recognised granular materials that exhibited poor performance in terms of resilient modulus.

Laboratory Evaluation for Rutting Performance Based on the DASR Porosity of Asphalt Mixture

ABSTRACT Researchhas shown that gradation characteristics determine whether the aggregate structure in asphalt mixture results in good performance. A recent study indicated that large enough aggregates should engage dominantly to form an aggregate structure that can resist deformation; also, a new approach identified the porosity of the Dominant Aggregate Size Range (DASR) as the key parameter that determines whether or not a particular gradation results in a suitable aggregate structure. This paper presents a laboratory experiment to evaluate the DASR porosity in terms of its ability to identify unsuitable aggregate structures. Eight dense-graded Superpave mixtures were designed using two aggregate types (limestone and granite). For each aggregate type, mixtures with varying DASR porosity were produced and tested to evaluate laboratory rutting resistance. Test results indicated that the new approach successfully separated mixtures according to their observed laboratory rutting performance, indicating that DASR porosity can serve as an effective parameter to evaluate aggregate structure.

A comprehensive review on self-healing of asphalt materials: Mechanism, model, characterization and enhancement

Self-healing has great potential to extend the service life of asphalt pavement, and this capability has been regarded as an important strategy when designing a sustainable infrastructure. This review presents a comprehensive summary of the state-of-the-art investigations concerning the self-healing mechanism, model, characterization and enhancement, ranging from asphalt to asphalt pavement. Firstly, the self-healing phenomenon as a general concept in asphalt materials is analyzed including its definition and the differences among self-healing and some viscoelastic responses. Additionally, the development of self-healing in asphalt pavement design is introduced. Next, four kinds of possible self-healing mechanism and corresponding models are presented. It is pointed out that the continuum thermodynamic model, considering the whole process from damage initiation to healing recovery, can be a promising study field. Further, a set of self-healing multiscale characterization methods from microscale to macroscale as well as computational simulation scale, are summed up. Thereinto, the computational simulation shows great potential in simulating the self-healing behavior of asphalt materials from mechanical and molecular level. Moreover, the factors influencing self-healing capability are discussed, but the action mechanisms of some factors remain unclear and need to be investigated. Finally, two extrinsic self-healing technologies, induction heating and capsule healing, are recommended as preventive maintenance applications in asphalt pavement. In future, more effective energy-based healing systems or novel material-based healing systems are expected to be developed towards designing sustainable long-life asphalt pavement.

Introducing a new method for studying the field compaction

The flow of particles during compaction may have a prominent influence on the difference of field and laboratory results as recently demonstrated by the authors with their newly developed compaction flow test (CFT). This test with a simple compaction simulator was used for studying the flow behaviour and rearrangement of particles for mixtures with different structures and thicknesses. However, validating the CFT results for practical purposes requires field measurements that provide more insight into the compaction process and eventually allowing to adjust the CFT for further use as an evaluating in-site tool. This study presents a new method for conducting such measurements during field compaction. In this method, some representative particles are tracked inside asphalt specimens and the accuracy of the results is examined by X-ray computed tomography. The results of the feasibility tests show that this method has potential for further use in the field and for building up a comprehensive basis of knowledge on field compaction towards closing the gap between the field and laboratory results.