Gabriele Tebaldi

Microstructural Characterization of Asphalt Mixtures Containing Recycled Asphalt Materials

AbstractMost studies addressing the use of recycled asphalt materials in asphalt paving mixtures are based on experimental tests and performance evaluation. Investigating the effect of adding recycled materials to the microstructure of asphalt mixtures has received little consideration. For example, higher-order microstructural information can be used in place of simple volumetric information as input in micromechanical models that can more accurately predict the effective properties of asphalt mixtures. In this paper, the influence of adding three different recycled materials, reclaimed asphalt pavement (RAP), manufacturer waste scrap shingles (MWSS), and tear-off scrap shingles (TOSS), on the microstructural distribution of the aggregate phase is investigated using digitally processed images of asphalt mixtures and numerical evaluations of two- and three-point correlation functions. No significant variations are found among the gradation curves, and minimal differences were observed for two- and three-p...

Synthesis of standards and procedures for specimen preparation and in-field evaluation of cold-recycled asphalt mixtures

The use of recycled asphalt (RA) materials in pavement rehabilitation processes is continuously increasing as recycling techniques, such as cold recycling (CR), are being utilised in increasing magnitude and greater awareness for use of recycled materials and consideration of sustainable practices is becoming common in the construction industry. The focus of this paper is on developing a state of the art and state of the practice summary of processes used for classification of RA as well as the curing and specimen preparation practices for cold-recycled asphalt mixtures. A variety of topics were explored through an exhaustive literature search, these include RA production methods, definition of RA materials, stockpiling practices, industrial operations, specimen curing and preparation practices and in-field evaluation of cold-recycled rehabilitation. This paper was developed through efforts of CR task group (TG6) of RILEM Technical Committee on Testing and Characterization of Sustainable Innovative Bituminous Materials and Systems (TC-237 SIB).

Effects of interface condition characteristics on open-graded friction course top-down cracking performance

Top-down cracking is a distress mode that is of particular concern for pavements with Open-Graded Friction Course (OGFC) because open-graded mixture has considerably lower resistance to fracture (lower fracture energy limit and lower resistance to damage) than dense-graded mixture. This particular cracking phenomenon initiates on the pavement surface and propagates downward; so because the OGFC layer is thin, cracking performance relies on the properties and characteristics of three components near the pavement surface: OGFC, underlying structural layer, and the interface between. For this reason, to increase the durability of pavements surfaced with OGFC, it is significant to ensure a quality fracture resistant bond between OGFC and the structural layer. This research investigated top-down cracking performance of OGFC with different tack coats using a newly developed composite specimen interface cracking (CSIC) test. In addition, X-ray computed tomography (CT) was employed to analyze the interface characteristics between OGFC and dense-graded HMA. HMA fracture mechanics was employed to quantify the effect of polymer modified asphalt emulsion (PMAE) on pavement top-down cracking resistance enhancement. Results clearly indicated that PMAE-created bonded interface conditions greatly increased pavement top-down cracking resistance as compared with conventional tack coat.

Strain Localization and Damage Distribution in SBS Polymer Modified Asphalt Mixtures

ABSTRACT A laboratory investigation was conducted to estimate the macroscopic cracking response of Styrene Butadiene Styrene (SBS) polymer modified asphalt mixtures by analyzing the localized strain distribution within the material microstructure. Five asphalt mixtures composed by the same aggregate gradation but different SBS modified asphalt binders were produced in the laboratory. An in-house developed Digital Image Correlation (DIC)-based system was employed to obtain 2D full-field strain maps of the specimens during tensile loading. Strain distributions were observed from three different test configurations, namely the Indirect Tensile Test (IDT), the Semi-Circular Bending (SCB) test and the Three-Point Bending (3PB) test. The cracking performances of the mixtures were evaluated using a visco-elastic fracture mechanics-based model entitled HMA Fracture Mechanics. The results clearly show the beneficial effect of SBS polymer modifier in redistributing the stress within the mastic.

Micromechanical Analyses for Measurement and Prediction of Hot-Mix Asphalt Fracture Energy

A verification of fracture energy density is presented as a fundamental fracture threshold in hot-mix asphalt. Fracture energy density was evaluated with the semicircular bending (SCB) test. Experimental analyses were enhanced by a digital image correlation system capable of providing a dense and accurate displacement-strain field of composite materials at the microstructural level and suitable for describing the cracking behavior of materials at crack initiation. The resulting fracture behavior in the SCB was predicted with a displacement discontinuity method to explicitly model the microstructure of asphalt mixtures and to predict their fracture energy density. The input parameters for the displacement discontinuity micromechanical model of the SCB were obtained from the Superpave® indirect tensile test. The predicted crack initiation and crack propagation patterns are consistent with observed cracking behavior. The results also imply that fracture in mixtures can be modeled effectively with a micromech...

The effect of polymer modification on hot mix asphalt fracture at tensile loading conditions

A laboratory investigation was conducted to evaluate the effect of both cross-linked and linear styrene–butadiene–styrene (SBS) modifiers on the cracking resistance of hot mix asphalt (HMA) mixtures. Five types of asphalt mixtures composed by the same aggregate gradation but different asphalt binders were produced in the laboratory. The cracking performances of the mixtures were evaluated using a viscoelastic fracture mechanics-based model entitled ‘HMA Fracture Mechanics’. Crack localisation and crack growth were investigated performing the indirect tensile test and the semi-circular bending test. A digital image correlation system capable of providing full-field strain maps was applied. The results show the benefit of SBS modifiers to the mixtures cracking resistance in terms of reduced rate of damage accumulation and increased tensile limits to failure. Finally, significant damage and first fracture have shown to be strongly more localised in modified specimens than in the unmodified one.

Characterisation of asphalt mixture cracking behaviour using the three-point bending beam test

The use of a three-point bending beam (3PB) test was investigated to characterise hot mix asphalt (HMA) cracking behaviour. Fundamental HMA fracture properties, identified as tensile strength and fracture energy density at first fracture, were determined for six different asphalt mixtures (two natural and four SBS polymer modified) applying the HMA Fracture Mechanics framework. Full-field strain maps obtained from an in-house developed digital image correlation-based method were observed to better understand the crack initiation and propagation mechanisms in the 3PB specimen. The resulting fracture behaviour was predicted using a displacement discontinuity boundary element method to model the microstructure of the six asphalt mixtures and to predict their fracture properties. Both numerical and experimental results indicate that the fracture mechanism of asphalt mixtures can be properly described from 3PB test results when appropriate interpretation models are used.

Influence of Mixture Properties on Fracture Mechanisms in Asphalt Mixtures

ABSTRACT This paper reports a research study aimed at providing insight into key mechanisms and mixture properties that influence fracture in asphalt concrete. The experimental analysis was based on the Hot Mix Asphalt (HMA) Fracture Mechanics visco-elastic crack growth law. HMA cracking mechanism was investigated using multiple laboratory test configurations on both unmodified and polymer modified mixtures. A Digital Image Correlation (DIC) was employed to more accurately capture localized or non-uniform stress distributions in asphalt mixtures and as a tool for detecting first fracture. Crack initiation and crack growth were predicted effectively using a Displacement Discontinuity (DD) boundary element method.

Effect of Freeze—Thaw Cycles on Mechanical Behavior of Lime-Stabilized Soil

AbstractLime stabilization of clay soils is becoming, if not already, one of the most used construction techniques for road embankments and for subbase stabilization. In warm countries, lime stabilization is used without any problems; but in cold countries, some concerns are still present in relation to behavior of lime-stabilized soils at low temperatures, particularly in conditions of freezing and thawing. The research in this paper presents the results of an experimental campaign made on a typical Italian clay soil stabilized with lime. The research studies the evolution of mechanical performances of lime-stabilized soil under the effect of freeze and thaw cycles and after a series of several freezes and thaws. The results of the research clearly show that lime-stabilized soils can have proper mechanical performances after freeze and thaw cycles. In particular, the test campaign shows that lime-stabilized soils have decreased resistance after freeze and thaw cycles and that they almost fully recover th...

The flexural strength of asphalt mixtures using the bending beam rheometer

University of Minnesota M.S. thesis. December 2010. Major: Civil engineering. Advisor: Dr. Mihai O. Marasteanu. 1 computer file (PDF); iv, 66 pages.