Hassan Baaj

Effect of binder characteristics on fatigue of asphalt pavement using an intrinsic damage approach

ABSTRACT This paper presents the results of an experimental campaign of fatigue tests carried on several asphalt concrete mixes. The main goal of this study is to evaluate the effect of binder characteristics on the fatigue resistance of mixes. The intrinsic damage approach developed at the “Département Génie Civil et Bâtiment” (DGCB) is used to determine the damage rate per loading cycle. The results of the study confirm the efficiency of this approach to evaluate the fatigue resistance of mixes and to quantify the effect of changing some mix characteristics on this resistance. This approach is briefly presented and the results of the tests are analyzed and compared.

Atomic force microscopy to investigate asphalt binders : a state-of-the-art review

Atomic force microscopy (AFM) is a non-destructive imaging tool, which is capable of qualitative and quantitative surface analysis with sub-nanometer resolution. Simultaneously with the topology at the micro-scale, AFM is capable of acquiring micro-mechanical information such as relative stiffness/Youngs modulus, stickiness/adhesion, hardness, energy loss and sample deformation quantitatively. This paper presents an extensive review on the applications of AFM to investigate different physiochemical properties and performances of asphalt binder. AFM techniques and principles, different sample preparation techniques and its effect on observed micro-structures, chemical origin, surface or bulk phenomenon and temperature sensitivity of these micro-structures are also discussed in this paper. All of the studies conducted on this topic clearly indicated that AFM can successfully be utilised as a tool to better understand how the surface morphology and its physicochemical properties are interlinked and related to the binder performances.

Coupling of oxidative ageing and moisture damage in asphalt mixtures

In this paper, a possible way to capture the combined effect of oxidative ageing and moisture damage on mixture performance has been proposed. The formulations that are needed for finite element (FE) modelling of oxygen and moisture diffusion process have been established. The proposed model should be able to link the in-time changes to the mastic as function of mixture morphology, ageing propensity and the moisture diffusion properties to the physical properties of the asphalt mixture due to the loss of adhesive and/or cohesive bonding. Such an FE model can help find the trends and relationships that can assist in the development of predictive pavement performance model. Also, from this, one can figure out the key parameters that are mainly responsible for ageing–moisture-induced premature damage of asphalt pavements.

Observation of asphalt binder microstructure with ESEM

The observation of asphalt binder with the environmental scanning electron microscope (ESEM) has shown the potential to observe asphalt binder microstructure and its evolution with binder aging. A procedure for the induction and identification of the microstructure in asphalt binder was established in this study and included sample preparation and observation parameters. A suitable heat‐sampling asphalt binder sample preparation method was determined for the test and several stainless steel and Teflon sample moulds developed, finding that stainless steel was the preferable material. The magnification and ESEM settings conducive to observing the 3D microstructure were determined through a number of observations to be 1000×, although other magnifications could be considered. Both straight run binder (PG 58‐28) and an air blown oxidised binder were analysed; their structures being compared for their relative size, abundance and other characteristics, showing a clear evolution in the fibril microstructure. The microstructure took longer to appear for the oxidised binder. It was confirmed that the fibril microstructure corresponded to actual characteristics in the asphalt binder. Additionally, a ‘bee’ micelle structure was found as a transitional structure in ESEM observation. The test methods in this study will be used for more comprehensive analysis of asphalt binder microstructure.

Observation of bitumen microstructure oxidation and blending with ESEM

There have been a several studies observing bitumen microstructure using the environmental scanning electron microscope (ESEM); however, these have been few and far between. Nevertheless, there have been findings that show microstructure under ESEM clearly evolving with bitumen ageing. The objective of this paper is to focus on sample conditioning, oxidation and blending. A conditioning procedure was produced and the effect of freezing (−18°C) on the bitumen microstructure for 19 h was examined. A straight-run PG 58-28 bitumen was sampled, with the same bitumen being oxidised using hot air. Additionally, these two bitumens were mixed at ratios of 25/75, 50/50 and 75/25. The microstructures were compared with ESEM observation for their relative density, organisation and fibril size, clearly showing an evolution in the microstructure with oxidation and with different blending ratios.

Innovative Design, Traffic Management, and Construction of Concrete Overlay Technology: Canadian Municipal Application

Concrete overlays have been used successfully by various agencies. Spragues Road is a two-lane rural highway in the regional municipality of Waterloo in southwestern Ontario, Canada. The highway was identified as a candidate for concrete overlay rehabilitation because of traffic considerations and long-term performance requirements. Before this rehabilitation method was implemented, however, many issues associated with the construction of a concrete overlay on a restricted-width, two-lane rural highway had to be resolved. These issues included facilitating safe and effective traffic management and maintaining resident access, along with other perceived concerns related to concrete construction. More specifically, the challenges included a 12.8-km detour, subsequent increased wrong-way traffic, and restricted resident access when the concrete was curing and when lane elevation differentials separated the travel lane from the residential properties. Throughout the course of the project, evolving traffic management practices addressed the wrong-way traffic and mindful planning maintained resident access. This paper presents a case study of the project’s issues and discusses how they were resolved in the field. The project was completed successfully; various lessons learned are presented. A major part of this success is related to the communications strategy and feedback loop during the project.

ESEM Microstructural and Physical Properties of Virgin and Laboratory Aged Bitumen

The physical and microstructural properties of four straight run asphalt binders were examined and compared in virgin state and in after short term aging (RTFOT) and long-term (PAV) laboratory aging. RTFOT aging was conducted at 123, 143 and 163 °C. Physical testing parameters included penetration and softening point. Selected binders came from four different sources with same penetration grade. They all showed an increase in stiffness with aging, and RTFOT temperatures. The microstructural evolution of the binder was examined by Environmental Scanning Electron Microscopy (ESEM) on aged binders at 123 and 163 °C. The physical transformation corresponded to an evolution in the binders’ ‘fibril’ microstructure under ESEM as a result of electron beam exposure, with the microstructure getting denser with PAV aging. The asphalt binders showed varied ESEM ‘fingerprints’ and aged in different ways. The ESEM properties generally showed to evolve with the physical properties, although this was not the case for all of the binders due to their unique aging characteristics.

The use of compressible packing model and modified asphalt binders in high-modulus asphalt mix design

High-modulus asphalt mix, Enrobé à Module Élevé (EME) in French, is a type of HMA representing high modulus or stiffness. Traditionally, EME mixes are fabricated with straight-run hard grade asphalt cement which has poor performance at lower temperatures and is very susceptible to low-temperature cracking in cold regions. The main objective of this study is therefore developing a new approach to EME mix design that contributes to good performance at high, medium and low temperatures. EME mixes have a dense structure. In this regard, Compressible Packing Model (CPM) was used to optimise the packing degree of EME mixes for two different mix types based on nominal maximum aggregate size (EME 12.5 and EME 19). In addition, three types of modified asphalt binders, namely: PG 88-28, PG 82-28 and PG 58-28 plus 10% Elastomer additives were used in this study. Thermo-mechanical tests were conducted to evaluate the performance of EME mixes in terms of stiffness, rutting, fatigue and low-temperature cracking. Obtained results showed that the developed mixes had acceptable performance at all levels, and that the mixes could satisfactorily perform at lower temperatures.

Comparison of Short Term Laboratory Ageing on Virgin and Recovered Binder from HMA/WMA Mixtures

Oxidative ageing strongly affects asphalt mixture behavior. The Rolling Thin Film Oven Test (RTFOT) is currently used to simulate within a laboratory environment the binder short-term ageing, assuming that the mixture is produced at conventional Hot Mix Asphalt (HMA) temperatures (ca 160 °C). However, the introduction of Warm Mix Asphalts (WMAs), which are produced at lower temperatures than HMAs, could require adjustments in the short-term ageing simulation procedure as ageing is strongly influenced by the mixing and compaction temperatures. In this study, the physical properties of a straight-run bitumen, before ageing and after RTFOT ageing at two temperatures (123 °C and 163 °C), are compared to those of the same bitumen recovered from a HMA and a foamed WMA, both produced in laboratory. This comparison aims at determining the best RTFOT temperature for short-term ageing simulation for WMAs. To this end, all the binders were investigated through conventional (penetration value at 25 °C and softening point temperature) and rheological (frequency sweeps with dynamic shear rheometer) tests. Both conventional and rheological tests indicate that the WMA recovered binder is less aged than the binder aged at the standard conditioning temperature of 163 °C, whereas the HMA recovered binder is more aged than the artificially aged binder in the laboratory with RTFOT at 163 °C. These initial results support the idea that an appropriate ageing temperature for RTFOT short-term ageing simulation of WMA needs to be identified.

Protocol for the morphology analysis of SBS polymer modified bitumen images obtained by using fluorescent microscopy

ABSTRACT Fluorescent technique has been used to characterise the morphology of polymer modified bitumen for years. However, the main problem of this technique is a missing standardised protocol for image capture factors and processing algorithms (CF&PA). The purpose of this study was to find out the effects of CF&PA on morphology and set up a protocol for morphological analysis of SBS polymer-modified bitumen (PMB) using the fluorescent microscopy technique. In order to set up this protocol, fluorescent images were captured and processed with different CF&PA. Capture factors mainly include magnification, exposure time and storage format while processing algorithms include noise reduction, enhancement and segmentation. Morphological and parametric analysis indicated that all images must be captured under the same exposure time and should not be processed by white balance. Besides, four principles should be followed to determine the optimal magnification. As to the image storage format, JPEG 2000 was selected to retain the most details. The proper neighbourhood level was obtained from the particle number curve to realise noise reduction. Compared with other complicated segmentation algorithms, threshold methods are more suitable because of the typical two-phase characteristic of PMB. Because of potential change in detailed information of original images, enhancement was not recommended. Finally, the image capturing and processing steps and their levels were given based on the discussion above.