Showing papers in "Road Materials and Pavement Design in 2006"

A mathematical-based master-curve construction method applied to complex modulus of bituminous materials

Abstract: This paper gives a mathematical-based procedure in order to construct master-curves from complex-modulus measurements. The method is based on the Kramers-Kronig relations linking modulus and phase angle of a complex function. Three pure bitumens, one polymer-modified-binder and two mixtures are chosen to validate the possible use of this methodology and apply it. Assumptions which are needed to apply this procedure, are verified on complex-modulus data measured from these materials. Hence, master-curves can be built without introducing error from manual adjustement. The method seems to be suitable for binders and mixtures as soon as their behaviour is in agreement with the time-temperature equivalency principle. In conclusion, some interpretations of the WLF constants are given.

A Dissipated Energy Approach to Fatigue Evaluation

Abstract: The fatigue behaviour of bituminous binders and/or bitumen-filler mastics has been postulated as having a strong correlation with the fatigue behaviour of asphalt mixtures. The binder is one of the major factors controlling fatigue of the asphalt mixture and is considered as the leading media of energy dissipation. It is verified in this paper that the application of the Ratio of Dissipated Energy Change (RDEC) approach in terms of the fatigue characteristics of bituminous binders and mastics produces a unique energy parameter, known as the Plateau Value (PV), similar to the PV previously identified for asphalt mixtures. The relationship between PV and fatigue life (Nf) is found to be unique for asphalt mixtures and binders (mastics). This suggests the RDEC approach is a fundamental approach for fatigue analysis of HMA. Furthermore, the two PV-Nf curves for asphalt mixtures and binders are strongly related, which provides a new way to explain mixture fatigue behaviour from a binder's rheological ...

A comparison between beam and semi-circular bending fracture tests for asphalt

Abstract: Mode I and mixed-mode I-II fracture properties of two bituminous mixtures, a Stone Mastic Asphalt and a Dense Bitumen Macadam, have been determined by means of three-point bending tests on notched specimens. Two specimen geometries, namely single-edge notched beam and semi-circular bending, have been used in the study. Comparisons have been made based on two fracture parameters, the stress intensity factor and the fracture energy. Experimental results have shown that for mode I there is good agreement between the stress intensity factors obtained from the two specimen geometries. Moreover, both geometries have been found suitable to study mixed-mode fracture of bituminous materials.

Why do we Need to Change G*/Sinδ and How?

Abstract: In the United States, a number of State Highway Agencies claim that the Superpave specification has some critical gaps, most of them related to the performance characterization of modified bitumens (D'Angelo, 2002). Recognizing this fact AASHTO sponsored project NCHRP 9–10 and in 2001 NCHRP 459 (Bahia et al., 2001a) report was published. The report offered a revised system for testing and evaluating asphalt bitumens based on damage behavior. A scheme to conduct bitumen rutting tests that would allow a more direct qualification of bitumens for specific climate and traffic conditions was presented. The proposal, however, was only conceptual and lacked the details required for implementation, such as specific criteria and limits. This paper addresses the implementation of NCHRP 9–10 for bitumen rutting resistance. It reviews why G*/sinδ has to be changed for a new parameter, called viscous component of the creep stiffness Gv. It is shown how a mechanistic system based on damage behavior can be trans...

Investigation of low temperature cracking in asphalt mixtures by acoustic emission

Abstract: This paper investigates the use of acoustic emission (AE) to characterize microstructural phenomena and the corresponding macroscopic behavior during the low temperature fracture of asphalt mixtures. An acoustic emission system with eight channels of recording was used to monitor the failure process during testing at low temperature using the semi circular bend (SCB) configuration in three Superpave mixtures used at MnROAD facility. Algorithms to automatically detect the relative arrival time of the AE signal and to locate the AE source were developed. The analysis of the accumulated AE events illustrated the relationship between the micro damage and macroscopic behavior at different loading levels. The damage level under certain loading conditions was evaluated and preliminary results showed that the load level corresponding to the localization played a critical role in the damage process of the material. As a first step, the fracture energy of asphalt concrete specimen was related to the accumu...

The structure of asphaltenes in bitumen

Abstract: The definition of asphaltenes and some of its chemical properties like polarity and molecular weight is discussed, based on available knowledge. A critical examination of the currently common claim that asphaltenes is dispersed in bitumen in the shape of micelles is made. It is concluded that it is not likely that any micelles exist in bitumen. An alternative model, a thermodynamic solubility model is suggested. As a support for the solubility model, the Hansen solubility parameter is used to describe the solubility properties of bitumen, asphaltenes and maltenes. In the solubility model bitumen is considered to be a mixture of million of different molecules which is kept in solution by its mutual solubility. A continuum of different polarities and molecular weights are necessary for complete stability. The model predicts that if certain fractions are removed from bitumen the stability may be lost resulting in formation of precipitate and phase separations. The usefulness of the model is illustra...

Shear Fatigue Behaviour of Tack Coats in Pavements

Abstract: For many years, pavement engineers use mechanistic design methods that are based on algorithms to compute stresses, strains and displacements in a flexible pavement structure, or in a multi-layered structure in general. Most of these methods assume, to ease the modelling of the structure and the computation process, that the layers are fully bonded or completely unbounded to each other. Moreover, determining the effectiveness of the bonding between two layers is difficult since there is no standard test procedure to assess it. Hence, proper modelling of the interface bonding condition will represent an important finding in understanding the real behaviour of road structures, and will lead to reduce maintenance and rehabilitation costs. Asphalt emulsion is commonly used, as tack coat, to ensure the bond between two pavement layers. This study deals with an experimental characterization of interfaces shear fatigue behaviour through laboratory tests. A testing device for determining the shear fatigu...

Microstructure-based identification of bitumen performance

Abstract: Motivated by recent progress in both experimentation and the micromechanical description of the behavior of multi-composed materials, a multiscale model for asphalt is currently developed at the Christian Doppler laboratory for “Performance-Based Optimization of Flexible Pavements” at Vienna University of Technology. This model allows us to relate macroscopically observable asphalt properties to finer-scale information. Since the mechanical properties of asphalt and the influence of environmental conditions (temperature, aging) originate from the binder properties, a proper characterization of bitumen is essential for the predictive capability of the anticipated multiscale model. In this paper, the characterization of bitumen, comprising the bitumen chemistry, its microstructure, and its viscoelastic properties, is presented for two types of bitumen (standard and polymer-modified bitumen) considering the unaged and aged state. The obtained results provide new insight into the durability behavior ...

Influence of water on resilient properties of coarse granular materials

Abstract: The objective of this work was to investigate influence of water on resilient properties of a coarse (maximum particle size 90 mm) granular material using various gradings. Triaxial testing, using large-size samples (diameter 500 mm and height 1000 mm) and constant confining pressures, was performed at varying water content up to practically full saturation. Time Domain Reflectometry (TDR) was used to monitor transient in-sample water contents. Evaluation comprised resilient modulus and Poisson ratio in terms of total stresses, although the results were also discussed in the context of effective stresses. The coarsest grading experienced only a small reduction in resilient modulus when brought close to saturation, while specimens with an increased amount of fines and more even distribution responded with a substantial loss of resilient modulus upon increased water content. It also appeared that, as water content increased, the specimens became more dilative (increase in Poisson ratio).

Evaluation of field aging effects on asphalt binder properties

Abstract: The oxidative aging that takes place in the asphalt binders used in the construction of asphalt pavements significantly affects the performance of the pavements during their service life. In this paper two issues that still generate a lot of debate in the research community are investigated: how far aging penetrates inside the asphalt layer and how reasonable laboratory aging tests simulate the aging occurring in the field. Cores were obtained from three cells at MnROAD facility and the binders were extracted and recovered from 25 mm slices cut along the depth of the cores. The properties of the recovered binders as well as the properties of the original binders aged in laboratory conditions were investigated, using standard testing procedures part of the current specifications as well as additional test methods. The results indicated differences in aging effects with location inside the asphalt layer and significant differences between the recovered and the laboratory aged binders.

Influence of Crumb Rubber and Digestion Time on the Asphalt Rubber Binders

Abstract: The behavior of asphalt binders modified with recycled crumb rubber depends on several factors, such as: rubber content and type, temperature and time employed during the digestion process. Some of these aspects are investigated in this paper by means of a series of tests performed on asphalt-rubber produced via the wet process. Crumb rubber manufactured by ambient grinding and cryogenic processes were used in this work. Reduction of penetration and sharp increase of viscosity, softening point and resilience were observed for increasing rubber contents. The results show that the Brookfield viscosity limits the crumb rubber content incorporated into straight binder, once it tends to become too high above a certain critical amount of incorporated rubber. The effect of digestion time on the viscosity of the modified binders depended in this research on the rubber content. For high rubber contents, there seems to exist a critical time after which viscosity tends to decrease for continuing digestion p...

Rheological characteristics of crumb rubber-modified asphalts with long-term aging

Abstract: SHRP asphalts AAD-1 (less-compatible) and ABD (more compatible) were mixed with crumb rubber and their rheological properties were studied as a function of long-term oxidative aging. Master curves were constructed by shifting the aging time-frequency data to assist in the interpretation. The results show that the stiffness effect of crumb rubber to asphalt AAD-1 is higher than to asphalt ABD. Addition of crumb rubber to both asphalts AAD-1 and ABD reduced viscosity build-up with aging. In addition, rubber modification dramatically increased the elasticity of both asphalts. It is possible that rubber modification will improve rutting resistance because of the increased viscosity and elasticity at high temperatures and improve thermal cracking and fatigue resistance by either decreasing viscosity or lowering viscosity build-up with aging at low temperatures.

Strength Behaviour of Geogrid Reinforced Shedi Soil Subgrade and Aggregate System

Abstract: Shedi soil (Lithomargic clay), a yellowish-white silty soil underlying lateritic soil, is densely deposited along Konkan belt of India. The strength behaviour of Shedi soil under varying moisture content is major problem for road construction projects in this region. In the present investigation, the subgrade is stabilized with geogrid, keeping the geogrid at different positions from top of subgrade, to locate its optimum position. The plate load tests were also conducted at soaked and unsoaked conditions for unreinforeced, reinforced (with Geogrid) subgrade with aggregate base course. An equation has been established based on load-deflection values recorded for subgrade of un-reinforced and reinforced with geogrid at different levels. The deflection values obtained from equation and from the laboratory investigation were compared. In the case of reinforced subgrade with aggregate base course, the theoretical deflection values were computed based on Burmister's theory and compared with laboratory...

Fracture mechanics and asphalt binders

Abstract: In this paper, the applicability of linear elastic, elastic plastic, and time-dependent (viscoelastic) fracture theories to asphalt binders at lower service temperatures is examined Linear elastic fracture mechanics was found to be applicable only at temperatures below the glass transition temperature Above the glass transition temperature, neither elastic nor elastic plastic fracture mechanics are applicable to asphalt binders because in this temperature regime they behave as time dependent viscoelastic materials and time-dependent fracture mechanics models must be used Fracture parameters from each of the theories provide a different low temperature ranking of asphalt binders than the PG specification used in the United States The authors conclude that, pending further development, the direct use of fracture mechanics parameters in a purchase specification is not realistic

Size effect regarding fatigue evaluation of asphalt mixtures

Abstract: Experimental results for fatigue tests on three size geometrically similar asphalt concrete specimen are presented. Effect on fatigue life is analyzed and compared to trends given by a fatigue damage model. This innovative laboratory campaign points out a size effect on fatigue assessment of asphalt mixture. In a second part, the application of a nonlocal fatigue damage model for asphalt mixtures is presented. A qualitative agreement is obtained between experimental results and non local damage fatigue predictions trends. This agreement validates the nonlocal modelling that allows to model the influence of the heterogeneous nature of the material on fatigue failure. Differences observed between laboratory data and model predictions may be attributed to viscoelasticity induced thermal softening which had to be quantified and coupled to damage in order to properly study these fatigue test data.

Surfactants in Aged Asphalt and Impact μ on Moisture Susceptibility of Laboratory-prepared Mixes

Abstract: Short-term aging (rolling thin-film oven test) of an asphalt binder resulted in the production of surfactants (surface-active compounds), while long-term aging (pressure aging vessel test) of asphalt binders resulted in the production of not only surfactants but also strong acids. The strong acids were identified as being sulfonic acids. It was proposed that the generation of surfactants and/or sulfonic acids in asphalt binder would promote moisture damage in asphalt-aggregate mixes. The surfactants could act as a detergent and emulsify components of the mix, and sulfonic acids could attack the aggregate surface, thus, disrupting the asphalt-aggregate interface. A model compound, p-dodecylbenzenesulfonic acid, which incorporates these two structural features, was used as a modifier in several different mixes. Briquets fabricated from the modified mixes were tested for moisture susceptibility using the freeze-thaw pedestal test. It was observed that those mixes, which were originally not susceptib...

Interpreting Dissipated Energy from Complex Modulus Data

Abstract: An asphalt mixture's ability to absorb energy without fracturing is directly related to cracking performance of asphalt pavement The dissipated energy per load cycle is commonly determined as the area of the hysteresis loop developed during cyclic loading of asphalt mixture However, it is unclear whether all dissipated energy determined in this manner is irreversible and associated with damage, or whether it is at least partially reversible and not fully associated with damage Therefore, this study was undertaken to evaluate the nature of the dissipated energy determined from the area of the hysteresis loop developed during cyclic loading of asphalt mixture Dissipated energies determined experimentally from cyclic load tests were compared to dissipated energies predicted using rheological parameters determined from static creep tests For a range of asphalt mixtures, the area of the hysteresis loop appeared to be strongly affected by the delayed elastic behavior of the mixture, even when cyclic response had reached steady-state conditions Therefore, it appears that the area of the hysteresis loop is not fully associated with damage and very probably overestimates the rate of dissipated energy and damage development during cyclic load testing of asphalt mixture Furthermore, it is generally not possible to reliably separate reversible from irreversible dissipated energy in the hysteresis loop using conventional complex modulus data Consequently, it is recommended that irreversible dissipated energy be determined using rheological parameters obtained from static creep test data The key is to have parameters in the rheological model that properly separate the elastic (immediate and delayed) from the viscous response, since only the viscous response is irreversible and contributes to damage

Rheology of thin asphalt films in contact with aggregate

Abstract: A specially designed shear viscometer fixture was built to investigate the physical properties of thin asphalt films between aggregate plates. Viscosities were measured using the specially designed fixture in an Instron instrument. The properties of thin asphalt films are not predictable from thick (1.0 mm) films on steel plates, which are used in the current Superpave® specification. Rheological properties of thin films (20 microns thick) of neat SHRP asphalt AAD-1, PAV-aged AAD-1 (20 hours at 100°C), and decanedicarboxylic acid-modified AAD-1 were determined at 25°C using the specially designed fixture. Atomic force microscopy (AFM) was applied to investigate the surface roughness profiles of different substrates including glass and aggregate plates. It was found that the roughness of the glass plate was only 20nm disparity in height, approximately one one-thousandth of the film thickness being studied. The AFM profiles of the polished aggregate plates used in the study showed that they had a s...

Dense graded hot mixes using asphalt-rubber binders with high rubber contents

Abstract: This paper shows the results of a study about the mechanical behavior of dense graded asphalt-rubber hot mixes prepared with two different types of asphalt-rubber binders. These asphalt-rubber binders were obtained with penetration grade asphalt (AC 50/70) mixed with 21% and 25% of crumb rubber in weight. The rubber was recycled from unserviceable tires using the ambient grinding process. Hot mixes made with the conventional binder AC 50/70 were also studied for comparison. The mechanical behavior of hot mixes was evaluated through laboratory tests for fatigue life, permanent deformation and indirect tensile strength. The results showed that asphalt-rubber hot mixes presented better mechanical behavior for fatigue life and permanent deformation than those obtained with the straight binder.

Dilation behaviour of asphalt mixtures

Abstract: An extensive experimental study of the dilation behaviour of asphalt mixtures was performed. The effect of mixture composition (volume fraction, gradation, shape and size of aggregate) and test conditions (loading/unloading, temperature and confinement pressure) of idealized asphalt mixtures of various volume fractions of aggregate was performed. The volume fraction and angularity of aggregate was found to play an important role on the dilation behaviour whereas the experimental conditions were found to have no effect on the dilation behaviour of asphalt mixtures. A generic DBM mixture was fabricated with two different volume fractions of bitumen. It was found that an increase in bitumen content decreases the dilation gradient. An analytical model proposed by Goddard and Didwania (1998) was successfully used to predict the dilation gradient for mixtures with sub-spherical aggregate, but failed to predict the dilation behaviour of specimens with angular aggregate.

Some material and construction aspects regarding in situ recycling of road pavements in South Africa

Abstract: In situ recycling as a pavement rehabilitation option in South Africa is becoming increasingly important. Use has been made of both bitumen (emulsion and foamed) and traditional chemical stabilizers (lime, cement, lime/slagment, etc). Very little detailed information regarding the effect of the in situ processing on the original material properties or the consistency of mixing and effectiveness of deep compaction has been reported. A project in which the shoulder and base of a national road were milled, mixed and replaced as a subbase with the addition of 2.5 per cent cement has recently been investigated. Testing of the material prior to and after recycling was carried out and the densities achieved after compaction were measured. This paper summarises the findings and conclusions from this project and highlights aspects that need better control during the in situ recycling operations.

Modulus Testing in Indirect Tension Mode

Abstract: In 2004, a new European standard (NF EN 12697-26), the object of which is the measurement of stiffness modulus, appeared. It includes five annexes corresponding to five different testing methods, in particular modulus testing in indirect tension (IDT) mode. Given that a typical asphalt layer thickness is about a few centimeters and that coring is the most effective method for obtaining specimens from actual pavements, the IDT testing of cores is bound to become very practical for routine use. Notwithstanding this fact, IDT testing is still of little use in French public and private sector laboratories and, moreover, little information is available in the technical literature concerning the comparison between stiffness modulus data obtained in uniaxial direct tension or tension-compression and in biaxial indirect tension. This paper provides rational understanding, based on principles of linear viscoelasticity in particular, of the moduli commonly used for structural evaluation of asphalt mixtures...

The Role of Temperature and Binder Type on the Fracture Resistance of Asphalt Mixtures at Low Temperatures

Abstract: In the past decade fracture mechanics concepts have been introduced to the study of the fracture behavior of asphalt mixtures One of the main goals was to obtain reliable fracture properties that could be used in the selection of crack resistant material and in the development of performance models This paper presents the results of an investigation of the low temperature properties of asphalt mixtures using a testing protocol and analyses based on the semi circular bend test The load, the load-line displacement, and the crack mouth opening displacement were recorded during the test and used to calculate the stiffness, the fracture toughness, and fracture energy of three asphalt mixtures used in three test sections at MnROAD facility The statistical analysis of the experimental data shows that both the fracture toughness and fracture energy are significantly affected by the type of asphalt binder used and the testing temperature For all three mixtures the fracture energy decreased as the tem

Characterization of Bituminous Mixtures for Numerical Modeling of Permanent Deformations

Abstract: Because of recent increase in traffic intensity and axle loads, the relevance of rutting due to permanent deformation of the bituminous layers has increased on road pavements. In fact, recent pavement performance studies indicate that rutting in the bituminous layers is a major deterioration mechanism in flexible pavements. Most of the models used for pavement design do not take this mechanism explicitly into account. One of the reasons for that is the difficulty to determine the parameters that describe the materials behaviour for use in advanced models. A simple laboratory test and interpretation methodology is necessary to evaluate its permanent deformation behaviour. Ideally, it should be able to simulate “in situ” conditions and the test specimen should be representative of the bituminous materials applied on the field. However, more “realistic” test methods involve more complex and expensive equipment together with high levels of technical expertise. This paper deals with the use of uniaxia...

Applications, Properties and Design of High Modulus Bituminous Mixtures

Abstract: High modulus bituminous mixtures (HMBM) have been used for almost two decades in several countries. This paper presents an overview of use of this kind of bituminous material, as well as a summary of its typical compositions and mechanical properties. The rehabilitation of a structural layer on the EN14 (Portuguese national highway 14) using HMBM has been adopted as a case study. The project workplan involved the laboratory design of the mixture by undertaking performance tests to observe the effectiveness of the mixture. Prismatic specimens were extracted from constructed trial sections and similar specimens have been produced in the laboratory. Repetitive four-point bending tests were performed on both specimens for several temperatures and loading conditions. This made it possible to determine their stiffness modulus, phase angle and fatigue resistance. In addition, cores and slabs taken from trial sections have been used to characterise the permanent deformation behaviour of HMBM in laborator...

Evaluation of Rutting Resistance of Double-layered Asphalt Mixes

Abstract: The wheel tracking test is one of the important methods to evaluate the high-temperature performance of asphalt mixes. In this paper, the rutting resistance of composite structures of surface/intermediate layers was studied by using both the Circular Road Track (CRT) test and the Hamburg Wheel Tracking Device (HWTD). Several performance indices, including the dynamic stability, rut depth, and deformation profiles, were evaluated and compared to determine the rutting resistance of several double-layered asphalt mixes. Several approaches to mitigate rutting in asphalt pavements were suggested by this study, such as use of modified binders in the intermediate layer, and addition of polyester fibers into Stone Mastic Asphalt (SMA). The HWTD test has the potential to replace existing Chinese wheel tracking test as a routine test procedure for determining the rutting resistance of asphalt mixes.

Damage evaluation in simple shear tests with and without stress reversal of asphalt concrete

Abstract: The paper presents a study of the effect of shear stress reversal on the development of damage in asphalt concrete. Prismatic specimens 50 x 80 x 220 mm were cut from field samples. Specimens were glued in the simple shear apparatus and tested under different shear stress conditions, with and without stress reversal in 20,000 load repetitions. The damage caused to the material was evaluated using two approaches: (1) Comparing the dynamic shear modulus before and after loading and (2) Analyzing the material response during rest period of each cycle and comparing it to the computed response of a linear undamaged visco-elastic model. It was found that (1) A substantial amount of damage is caused by shear loading and (2) More damage is caused when the shear stress is reversed than without reversal.

A viscoelastic displacement discontinuity method for analysis of pavements with cracks

Abstract: This paper presents a development of the displacement discontinuity boundary element method for modeling the linear viscoelastic behavior of asphalt mixtures and simulating crack propagation in asp ...

Sound Propagation above a Porous Road Surface by Boundary Element Method

Abstract: A numerical method for the prediction of sound pressure levels nearby roads has been developed and validated. It is based on an integral formulation of the acoustic problem and a numerical solution by Boundary Element Method (BEM). The advantage of such a method is that complex geometries and boundary conditions can be considered. A special care has been taken to integrate air/porous medium interface. This development was validated experimentally by a basic sound propagation case above a porous road surface. In a first part, the basics of sound propagation in the air and in a porous medium are presented. Then, the Boundary Element Method (BEM) model is described along with the specific developments to introduce porous road surface boundary conditions. Then, the validation case of porous road interface treatment in BEM is shown. Finally, the software was successfully applied to two different cases of complex geometries that illustrate the possible use of the model in road environment problems. One...