Browsing by Author "Winter, H. Henning"
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Item Characterization of physical aging by time-resolved rheometry: fundamentals and application to bituminous binders(Springer Verlag, 2018-11-01) Laukkanen, Olli Ville; Winter, H. Henning; Seppälä, Jukka; Department of Chemical and Metallurgical Engineering; Polymer technology; University of MassachusettsPhysical aging is a ubiquitous phenomenon in glassy materials and it is reflected, for example, in the time evolution of rheological properties under isothermal conditions. In this paper, time-resolved rheometry (TRR) is used to characterize this time-dependent rheological behavior. The fundamentals of TRR are briefly reviewed, and its advantages over the traditional Struik’s physical aging test protocol are discussed. In the experimental section, the TRR technique is applied to study physical aging in bituminous binders. Small-diameter parallel plate (SDPP) rheometry is employed to perform cyclic frequency sweep (CFS) experiments over extended periods of time (from one to 8.6 days). The results verify that the mutation of rheological properties is relatively slow during physical aging (mutation number N′mu << 1), thus allowing rheological measurements on a quasi-stable sample. The effects of temperature, crystallinity, and styrene-butadiene-styrene (SBS) polymer modification on the physical aging of bitumen are evaluated. The time-aging time superposition is found to be valid both for unmodified and for polymer-modified bitumen. Vertical shifts are necessary, in addition to horizontal time-aging time shifts, to generate smooth master curves for highly SBS-modified bitumen.Item The dynamic fragility and apparent activation energy of bitumens as expressed by a modified Kaelble equation(Elsevier, 2018-11-01) Laukkanen, Olli Ville; Winter, H. Henning; Department of Chemical and Metallurgical Engineering; University of MassachusettsThe temperature dependence of the dynamics of glass-forming liquids can be characterized by the dynamic fragility (m) and apparent activation energy (Ea) at the glass transition temperature Tg. In this study, we derive analytical expressions that allow the calculation of these parameters from a modified Kaelble equation which divides the temperature dependence into two regimes above and below a characteristic temperature Td. Special emphasis is given to the analysis of the Td parameter that can be considered as the rheological glass transition temperature. Rheological characterization is performed on twenty-seven bitumens originating from various crude oil sources and refining processes. Their dynamic fragilities and apparent activation energies are calculated at the calorimetric Tg and at Td. Bitumen can be classified as a strong glass-forming liquid, dynamic fragilities varying in the range of m(Tg) = 26 … 52 for the individual bitumen samples. The results indicate that m(Tg) and Ea(Tg) are linearly correlated with Tg, and these Tg-dependences are unusually strong in comparison to other classes of glass-forming liquids. However, dynamic fragilities and apparent activation energies evaluated at Td are nearly independent of the type of bitumen and show only a weak dependence on Td.Item An empirical constitutive model for complex glass-forming liquids using bitumen as a model material(Springer Verlag, 2018) Laukkanen, Olli-Ville; Winter, H. Henning; Soenen, Hilde; Seppälä, Jukka; Department of Chemical and Metallurgical Engineering; Polymer technology; University of Massachusetts Amherst; Nynas NVWhile 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.Item From simple to complex glass-forming liquids: broadening of the glass transition as studied by shear rheology(Det Nordiske Reologiselskab, 2017) Laukkanen, Olli-Ville; Winter, H. Henning; Soenen, Hilde; Seppälä, Jukka; Department of Chemical and Metallurgical Engineering; University of Massachusetts Amherst; Nynas NVItem Low-temperature rheological and morphological characterization of SBS modified bitumen(ELSEVIER SCI LTD, 2018-08-10) Laukkanen, Olli Ville; Soenen, Hilde; Winter, H. Henning; Seppälä, Jukka; Department of Chemical and Metallurgical Engineering; Polymer technology; Nynas NV; University of MassachusettsPolymer modification is widely used to improve the engineering properties of bitumen, the most commonly used polymer modifier being styrene-butadiene-styrene (SBS) block copolymer. Although extensive studies have been performed on polymer modified bitumen (PMB), no reliable data is currently available on the effect of polymer modification on the dynamic rheological properties at low temperatures. In this study, we focus on the rheology of SBS modified bitumen near and below the glass transition temperature (Tg) using the 4-mm DSR technique. In addition, fluorescence microscopy and temperature-modulated differential scanning calorimetry are used to study the phase behavior and interactions in the SBS-bitumen blends. At high SBS concentrations, thermorheological complexity is observed in the investigated temperature range, attributable to the formation of a continuous SBS-rich network structure. In the case of compatible SBS-bitumen blends, a linear correlation is established between the flexural creep stiffness measured by bending beam rheometry (BBR) and the complex shear modulus measured by 4-mm DSR. Deviations from this linear trend are shown to result from the macro-phase separation induced by the poor compatibility of SBS and bitumen.Item Low-temperature rheology of bitumen and its relationship with chemical and thermal properties(2015-05-18) Laukkanen, Olli-Ville; Winter, H. Henning; Blomberg, Timo; Insinööritieteiden korkeakoulu; Pellinen, TerhiThe thermal cracking performance of asphalt pavements is largely governed by the properties of the bituminous binder, and thus the low-temperature rheological characterization of bitumen is of great importance. Recently, a novel testing technique has been developed for the measurement of the low-temperature rheological properties of bituminous materials. This testing technique, commonly referred to as the 4-mm DSR, uses a 4-mm parallel plate geometry on a dynamic shear rheometer (DSR) with radial instrument compliance corrections. However, very little data produced by using the 4-mm DSR technique is currently available in the literature. The primary objective of this study was to examine the low-temperature rheological characteristics of various unmodified bitumens by using the 4-mm DSR technique. In addition, the correlations of the chemical and thermal properties with the low-temperature rheology of bitumen were investigated. The secondary purpose of this thesis was to study physical aging in bitumen. The 4-mm DSR technique was used to test twenty-seven bitumen samples originating from various crude oil sources and refineries. The chemical properties of the bitumens were described in terms of their molecular weight properties, as measured by gel permeation chromatography (GPC), and aromatic properties, as measured by ultraviolet-visible spectroscopy (UV-vis), infrared spectroscopy (FT-IR) and refractive index (RI) techniques. The thermal properties of the studied bitumens, including the glass transition temperatures (Tg), were determined by differential scanning calorimetry (DSC). Both horizontal and vertical shifts were needed to produce smooth master curves in the vicinity of Tg. The temperature dependence of horizontal shift factors was shown to accurately follow the Kaelble-WLF equation in the temperature range of Tg-30 K to Tg+115 K. The calculated relaxation time spectra H(tau) evidenced a transition from small-scale molecular to large-scale cooperative relaxation processes when bitumen was cooled below its Tg. It was shown that the low-temperature rheological properties of bitumen can be fairly accurately predicted from the molecular weight and aromatic properties. Physical aging in bitumen was successfully analyzed by means of time-aging time superposition, and, based on the limited data available, equilibrium is attained in approximately 2-3 days at Tg. However, additional studies are needed to properly assess the effect of physical aging on the low-temperature rheological properties of various bitumens.Item New approach for modeling polymer modified bitumens as polymer solutions: power-law scaling of rheological constants(Det Nordiske Reologiselskab, 2017) Laukkanen, Olli-Ville; Winter, H. Henning; Soenen, Hilde; Seppälä, Jukka; Department of Chemical and Metallurgical Engineering; University of Massachusetts Amherst; Nynas NVItem Strain accumulation in bituminous binders under repeated creep-recovery loading predicted from small-amplitude oscillatory shear (SAOS) experiments(Springer Netherlands, 2018) Laukkanen, Olli-Ville; Winter, H. Henning; Department of Chemical and Metallurgical Engineering; University of Massachusetts AmherstThe creep-recovery (CR) test starts out with a period of shearing at constant stress (creep) and is followed by a period of zero-shear stress where some of the accumulated shear strain gets reversed. Linear viscoelasticity (LVE) allows one to predict the strain response to repeated creep-recovery (RCR) loading from measured small-amplitude oscillatory shear (SAOS) data. Only the relaxation and retardation time spectra of a material need to be known and these can be determined from SAOS data. In an application of the Boltzmann superposition principle (BSP), the strain response to RCR loading can be obtained as a linear superposition of the strain response to many single creep-recovery tests. SAOS and RCR data were collected for several unmodified and modified bituminous binders, and the measured and predicted RCR responses were compared. Generally good agreement was found between the measured and predicted strain accumulation under RCR loading. However, in the case of modified binders, the strain accumulation was slightly overestimated (≤20% relative error) due to the insufficient SAOS information at long relaxation times. Our analysis also demonstrates that the evolution in the strain response under RCR loading, caused by incomplete recovery, can be reasonably well predicted by the presented methodology. It was also shown that the outlined modeling framework can be used, as a first approximation, to estimate the rutting resistance of bituminous binders by predicting the values of the Multiple Stress Creep Recovery (MSCR) test parameters.Item Systematic broadening of the viscoelastic and calorimetric glass transitions in complex glass-forming liquids(Elsevier, 2018-03) Laukkanen, Olli-Ville; Winter, H. Henning; Soenen, Hilde; Seppälä, Jukka; Department of Chemical and Metallurgical Engineering; University of Massachusetts Amherst; Nynas NVIn this experimental study, we explore the broadening of the glass transition in chemically and structurally complex glass-forming liquids (CGFLs) by means of thermal and rheological characterization techniques. Petroleum fluids with different levels of chemical and structural complexity are used as model materials. Thermal characterization by temperature-modulated differential scanning calorimetry (TMDSC) reveals a systematic increase in the width of the glass transition region ΔT g with increasing chemical and structural complexity. The broadening of the glass transition is also strongly reflected in the linear viscoelastic properties that are measured by small-diameter parallel plate rheometry. Most notably, this is observed as the broadening of the relaxation time spectrum at long times. The recently proposed broadened power-law spectrum model is used to describe the constitutive behavior of the investigated petroleum fluids. In this model, the stretching parameter β serves as a quantitative measure of the spectral broadening. A strong power-law correlation is found between ΔT g and β, manifesting a relationship between the broadness of the calorimetric and viscoelastic glass transition in CGFLs.
