Hilde Soenen

Bio: Hilde Soenen is an academic researcher from University of Antwerp. The author has contributed to research in topics: Dynamic shear rheometer & Glass transition. The author has an hindex of 6, co-authored 9 publications receiving 196 citations.

Creep-recovery behavior of bituminous binders and its relation to asphalt mixture rutting

Abstract: Rutting is one of the main distress modes of asphalt pavements, especially after prolonged warm periods, and thus a great deal of research has been focused on the development of a rheological parameter that would address the rutting susceptibility of both unmodified and modified bituminous binders. In this study the Multiple Stress Creep Recovery (MSCR) test method is used to investigate the creep-recovery behavior of various bituminous binders and its relation to asphalt mixture rutting. Frequency sweep and MSCR tests were conducted on three unmodified and six elastomer and/or wax modified binders, and the resulting data were used to calculate the values of various binder rutting parameters. These binders were also used to manufacture asphalt slabs for mixture rutting simulations in the LPC wheel tracking device. It was found that the non-recoverable creep compliance parameter (J nr3200) and the accumulated strain at the end of the MSCR test (γ acc) correlate very strongly with each other and that they both have a superior capability of predicting asphalt mixture rutting compared to other rheological binder rutting indicators. An effort was made to explain the manifested nonlinear viscoelastic properties of the modified binders with their expected microstructural characteristics. The use of the MSCR test in the rutting characterization of bituminous binders is highly recommended based on the results of this research.

Oxidation of bitumen: molecular characterization and influence on rheological properties

Abstract: 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.

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

Abstract: 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.

Investigation of bitumen low temperature properties using a dynamic shear rheometer with 4 mm parallel plates

Abstract: This paper investigates the low temperature rheological properties of bitumen using a dynamic shear rheometer with 4 mm parallel plates (4-mm DSR). Different procedures of sample preparation were tested and evaluated. For comparison, low temperature measurements were also carried out using a bending beam rheometer (BBR). Test results show that the 4-mm DSR can perform rheological measurements at very low temperatures (down below −30 °C). With this geometry, very little amount of bitumen sample is required. There are certain statistical correlations between complex modulus measured by 4-mm DSR and creep stiffness by BBR, and also between phase angle and m-value. With the 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. For the limiting temperatures, a statistical correlation was found in LST between the two test methods; however, there was very weak or no correlation in LmT. The presence of waxes in bitumen seems to have a negative effect on the correlations between the 4-mm DSR and BBR. This is probably due to differences in thermal histories caused by the large differences in sample size between BBR and DSR tests. In addition, DSR with 8-mm plates can be applied to certain low temperatures, depending on instrument compliance and stiffness of the binder to be tested.

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

Abstract: 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.