Hilde Soenen

The Morphology of Bitumen-SBS Blends by UV Microscopy: An Evaluation of Preparation Methods

ABSTRACT The morphology of bitumen-SBS blends is studied using Epi-Fluorescence microscopy. Morphology is defined as the partition of polymer-rich and bitumen-rich phases. Existing sample preparation methods for microscopy on bitumen are compared and the obtained morphologies are shown. In a second part, differences in morphology are related to differences in rheological behavior. The morphological properties strongly depend on the temperature, where a sample is taken, upon the cooling rate and upon isothermal annealing periods. During isothermal storage the morphology can undergo major changes. The so-called bulk morphology, which is obtained from a freeze-fractured surface, is different from the morphology seen on the surface which has been in contact with air or with silicon.

The multiple stress creep-recovery test: a detailed analysis of repeatability and reproducibility

The multiple stress creep-recovery (MSCR) test was recently introduced to evaluate bituminous binders at high service temperatures, in particular to evaluate the stress or loading resistance. This test allows classifying binders at the high-performance graded temperature, according to the traffic loading, starting from standard, to heavy, very heavy and extreme traffic loading. It is the intention that this test includes nonlinear binder properties. In this study, five laboratories have participated in a round robin test to evaluate the repeatability and reproducibility of the parameters derived from the MSCR test. Nine different binders were evaluated, including unmodified, slightly and highly modified binders. The MSCR tests were conducted at 50°C, and each laboratory performed testing five times under repeatability conditions. The test results were analysed according to ISO 5725 and observations and reasons for deviating test results are discussed in detail.

Asphalt Production at Reduced Temperatures using Zeolites and the Impact on Asphalt Performance

ABSTRACT The potential benefits of producing and paving asphalt at lower temperatures are beyond discussion. There is already a lot of know-how on various techniques for producing warm mix asphalt, but there is insufficient data available about the impact of these techniques on the final performance characteristics of the asphalt. Nynas and BRRC are working together on a research project, to study the most important and promising warm mix techniques on laboratory and field scale. These techniques are: the use of foamed bitumen, the addition of waxes to the bitumen and the addition of zeolites to the mixture. The present paper focuses on the last technique. The performance of warm asphalt mixtures produced with different types and quantities of zeolites is compared to the performance of a reference hot mix asphalt. Several aspects have been studied: compactability, permanent deformation, water sensitivity and low temperature cracking. Small scale field trials were made to validate the findings of the laboratory research.

Oxidation of bitumen: molecular characterization and influence on rheological properties

Rheological properties such as stiffness, elasticity, and viscosity are crucial parameters for the use of bitumen as a construction material. In bitumen oxidation studies, the increased viscosity has often been related to an increase in polar interactions from oxygen-containing compounds, like carbonyl groups. In this study, bitumen was subjected to two oxidation processes, aging and air blowing. Aging was performed using the rolling thin film oven test (RTFOT) and the pressure aging vessel (PAV), whereas air blowing was conducted in a laboratory unit. This investigation gives more insights in the changes observed during oxidation and highlights the differences between aging and air blowing. Moreover, the oxidation tests provide bitumen samples of increasing viscosity, which are used to evaluate relations between molecular and viscoelastic characteristics. As a comparison, the changes observed in harder bitumen samples prepared by a continued distillation are also included. As expected, the evolution of rheological properties with oxidation time is very similar in the PAV and in the air-blowing unit, although the timescales are very different. Fourier transform infrared spectroscopy (FT-IR) and acidity measurements reveal clear differences in the formation of oxygen-containing functional groups depending on the oxidation process. UV–visible spectroscopy shows that during aging as well as during air blowing, larger conjugated aromatic compounds are formed. These findings suggest that the formation of polyaromatic compounds may be the main contributor to the increase in elasticity and viscosity during oxidation.

Material characteristics of long lasting asphalt pavements

ABSTRACT Based on a catalogue of test roads in Denmark, four long lasting test sections constructed in the early 80s were selected for field sampling and extensive laboratory study. This paper focuses on characterizing the bituminous materials used in the test sections. First, asphalt cores were investigated in a non-destructive way using X-ray tomography and indirect tensile stiffness test. The field samples were further analyzed with respect to binder content, air void content, and aggregate gradation. To characterize recovered binders, both chemical and rheological tests were applied. It was found that the long lasting test sections consisted of thick asphalt layers of low air void contents. The wearing courses contained relatively high binder content except for one with a binder content of slightly below 6%. For all the test sections, no propagated cracks were observed. In achieving a long pavement lifetime, aging of bitumen was indicated as one of the key factors. Field aging of bitumen was strongly dependent on the air voids of asphalt mix. In the test sections of low air voids (< 3% at the time of field sampling), extremely slow bitumen aging was observed. The study also shows that field aged bitumens differ significantly in chemical compositions, and the aging- induced stiffing effect tends to correlate with carbonyl compounds and molecular weight, but not with sulfoxides.

Differential Scanning Calorimetry Applied to Bitumen: Results of the RILEM NBM TG1 Round Robin Test

The application of Differential Scanning Calorimetry (DSC) has been proven useful in characterizing bituminous binders, distillates and crude oils. In this paper, results of the round robin test, organized by the Rilem TC 231 Nanotechnology-based Bituminous Materials (NBM) TG1 group are reported. The purpose is to investigate the repeatability and reproducibility of standard DSC measurements when applied to bituminous binders. In the full test program of the Rilem NBM group, DSC measurements are further compared to observations made in atomic force microscopy (AFM), AFM measurements are reported in a separate paper. Seven laboratories have participated in this round robin test. Four bituminous binders were investigated, containing various amounts of natural or added wax. The test program consisted of a well-defined isothermal annealing procedure, followed by a first heating and cooling scan, and afterwards followed by a second heating scan. At this stage, the data, as they were reported by the different participants, were compared. For the glass transition (Tg), mid temperatures, can be defined with a reasonable reproducibility, which improves if natural wax is not present. Regarding melting and crystallization, the shape of the melting curve is highly dependent on the thermal history of the samples. Peak temperatures of melting and crystallization phenomena were reported with a good reproducibility, while the reproducibility of melting enthalpies (or surface area’s under the melting and crystallization signals) was not satisfactory. Different reasons for this and recommendations for improving the results are discussed in the paper.

An empirical constitutive model for complex glass-forming liquids using bitumen as a model material

While extensive research efforts have been devoted to understand the dynamics of chemically and structurally simple glass-forming liquids (SGFLs), the viscoelasticity of chemically and structurally complex glass-forming liquids (CGFLs) has received only little attention. This study explores the rheological properties of CGFLs in the vicinity of the glass transition. Bitumen is selected as the model material for CGFLs due to its extremely complex chemical composition and microstructure, fast physical aging and thermorheological simplicity, and abundant availability. A comprehensive rheological analysis reveals a significant broadening of the glass transition dynamics in bitumen as compared to SGFLs. In particular, the relaxation time spectrum of bitumen is characterized by a broad distribution of long relaxation modes. This observation leads to the development of a new constitutive equation, named the broadened power-law spectrum model. In this model, the wide distribution of long relaxation times is described by a power-law with positive exponent and a stretched exponential cut-off, with parameter β serving as a measure of the broadness of the distribution. This characteristic shape of the bitumen spectrum is attributed to the heterogeneous freezing of different molecular components of bitumen, i.e., to the coexistence of liquid and glassy micro-phases. Furthermore, as this type of heterogeneous glass transition behavior can be considered as a general feature of complex glass-forming systems, the broadened power-law spectrum model is expected to be valid for all types of CGFLs. Examples of the applicability of this model in various complex glass-forming systems are given.

Rheological Testing of Bitumen at Low Temperatures with 4-mm DSR

To measure bitumen low temperature rheological properties, a new test protocol using a dynamic shear rheometer with 4 mm parallel plates (or called 4-mm DSR) has been proposed in the US. In this paper, a series of experiments including different procedures of sample preparation were carried out to evaluate the 4-mm DSR. Comparison was made with the bending beam rheometer (BBR). The results obtained show that the 4-mm DSR can perform rheological tests at very low temperatures (down below −30 °C). With this new geometry, very little amount of sample is required, making it particularly suitable for study of field aging. There are correlations between complex modulus measured by the 4-mm DSR and creep stiffness by BBR, between phase angle and m-value, as well as between the limiting temperatures determined by the two test methods. With BBR data at 60 s loading time, higher correlation coefficients were observed at lower DSR frequencies or at a frequency corresponding to the 60 s loading time. The correlations seem also to be affected negatively by the waxes of bitumen, probably due to large differences in sample sizes that cause different thermal histories in DSR and BBR, making wax crystallization or physical hardening and its effect on rheology very different. In addition, common DSR with 8-mm plates can be applied to certain low temperatures, depending on instrument compliance and binder stiffness.

Bitumen/Aggregate Affinity—Rilem Round Robin Test on Rolling Bottle Test

Pavement durability is often linked with water damage either through raveling or loss of integrity, especially considering asphalt materials. A large number of tests exist to address the water sensitivity and affinity between aggregates and asphalt binder. In Rilem TC 237 SIB, TG1 looked at the common test methods used to evaluate the adhesion or affinity of asphalt binder to aggregate surfaces. One of the main purposes was to run a Round Robin Test to evaluate the reproducibility and repeatability of these test methods and to give recommendations for improvement. Three asphalt binders were selected, two unmodified and a polymer modified binder and four aggregate types with different mineralogy. This paper presents the first results obtained for the rolling bottle test. The influence of aggregate type is higher than that of the asphalt binder. While there are some potential trends after 24 h comparing the different combinations of aggregate and binder, there is still a lot of variability in the absolute results. The underlining reasons are not yet clearly identified.

Field experience of cold mix asphalt during 15 years

In the days of concern about high energy consumption and global warming, all sectors of our society are scrutinised for potential savings of energy. One potential area for energy saving in the road construction sector is to make asphalt without heating the aggregates which is the current practice when making hot mix asphalt. Bitumen emulsions have been used to make cold mix asphalt, but uncertainties about the quality of the constructions have limited a wider use. Twenty years ago, an extensive development took place to improve cold mix asphalt to make it more sustainable. In the current paper, the development of an improved technology for the manufacture of cold asphalts using emulsions is described. The technique was used to produce a number of test roads to demonstrate performance. Several of the roads have now been in service for more than 15 years. The roads have been evaluated by sampling and analysis. It is shown that the roads have sustained excellently throughout the years and an evaluation of binders recovered from the roads show remarkably little ageing in spite of high void content of the asphalt.