Bitumin kylmälämpötilareologia ja sen yhteys kemiallisiin ja termisiin ominaisuuksiin

The 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.Asfalttipäällysteen pakkashalkeilu on suuressa määrin riippuvaista bitumisen sideaineen ominaisuuksista, ja siksi bitumin reologinen karakterisointi alhaisissa lämpötiloissa on erittäin tärkeää. Äskettäin bitumin reologisten kylmälämpötilaominaisuuksien mittaamiseen on kehitetty uudenlainen mittaustekniikka. Tässä niin kutsutussa 4-mm DSR -mittaustekniikassa dynaaminen leikkausreometri (DSR) on varustettu 4 mm:n levy-levy-geometrialla, ja mittaustulokset korjataan säteittäisen laitekomplianssin suhteen. Tähän mennessä on julkaistu kuitenkin vain hyvin rajallinen määrä 4-mm DSR -tekniikalla tuotettua dataa. Tämän työn ensisijainen tavoite oli tutkia modifioimattomien bitumien reologisia kylmälämpötilaominaisuuksia 4-mm DSR -tekniikalla. Lisäksi tutkittiin kylmälämpötilaominaisuuksien yhteyttä bitumin kemiallisiin ja termisiin ominaisuuksiin. Työn toissijainen tavoite oli tutkia bitumin fysikaalista vanhenemista. Tutkimusta varten kerättiin 27 bituminäytettä, jotka olivat peräisin useista raakaöljylähteistä ja öljynjalostamoista, ja näiden näytteiden ominaisuuksia tutkittiin 4-mm DSR -tekniikalla. Bitumien kemiallisia ominaisuuksia kuvattiin geelisuodatuskromatografialla (GPC) mitattujen molekyylipaino-ominaisuuksien avulla, sekä ultravioletti-näkyvän valon spektroskopialla (UV-vis), infrapunaspektroskopialla (FT-IR) ja taitekerroinmittauksilla (RI) määritettyjen aromaattisten ominaisuuksien avulla. Bitumien termisiä ominaisuuksia, mukaan lukien niiden lasisiirtymälämpötiloja (Tg), tutkittiin differentiaalisen pyyhkäisykalorimetrian (DSC) avulla. Sekä vaaka- että pystysuuntaisten siirtojen käyttö oli tarpeen kunnollisten master-käyrien aikaansaamiseksi Tg:n läheisyydessä. Vaakasiirtokertoimien lämpötilariippuvuuden huomattiin noudattavan tarkasti Kaelble-WLF-yhtälöä lämpötila-alueella Tg-30 K … Tg+115 K. Lasketut relaksaatioaikaspektrit H(tau) osoittivat siirtymän pienen mittakaavan molekulaarisista relaksaatioprosesseista suuremman mittakaavan relaksaatioprosesseihin tapahtuvan jäähdytettäessä bitumi sen Tg:n alapuolelle. Bitumin reologiset kylmälämpötilaominaisuudet pystyttiin ennustamaan melko tarkasti molekyylipaino- ja aromaattisten ominaisuuksien perusteella. Bitumin fysikaalista vanhenemista analysoitiin onnistuneesti aika-vanhenemisaika-superposition avulla, ja tämän tutkimuksen rajallisten mittaustulosten perusteella kestää noin 2-3 päivää ennen kuin tasapainotila fysikaalisen vanhenemisen suhteen saavutetaan Tg:ssa. Lisätutkimukset ovat kuitenkin tarpeen, jotta fysikaalisen vanhenemisen vaikutusta eri bitumien reologisiin kylmälämpötilaominaisuuksiin voitaisiin kunnolla arvioida

Durability of Ring-Road II asphalt pavement - Phase I report on forensic analysis of Ring-Road II pavement distresses

This report presents findings from prematurely failed pavement of Ring-Road II (Kehä II) in Espoo, Finland. The road had excessive potholes, cracking, raveling and stripping only five years after construction. Core samples taken for this study revealed also that pavement layers were partially separated due to the lack of bonding. Research focus was to determine the causes of Stone Mastic Asphalt surface layer failure. Documentation of mix design, construction and material quality analysis, prior to and after construction, was compared to the samples collected from the road. Traditional quality assessment of the pavement by means of binder content and aggregate gradation analysis, air voids content, Indirect Tensile Strength and Stiffness, as well as binder tests including Penetration, Ring and Ball Softening Point and rheological characterization by Dynamic Shear Rheometer (DSR) were performed. Discrepancy was found in filler composition and additional analysis was made by applying standard analytical procedure of hydrochloric acid solubility. The findings were confirmed by means of Thermogravimetral Analysis (TGA), X-Ray Diffraction (XRD), and Scanning Electron Microscopy (SEM), supported by BET-adsorption surface area measurements. The investigation revealed presence of fly ash that was apparently used for extending limestone filler during construction. It can be concluded that the main reason for the pavement failure was due to this substitution and the consequent problems that followed in the construction and thereafter in the pavement performance

Controlled Monofunctionalization of Molecular Spherical Nucleic Acids on a Buckminster Fullerene Core

An azide-functionalized 12-armed Buckminster fullerene has been monosubstituted in organic media with a substoichiometric amount of cyclooctyne-modified oligonucleo-tides. Exposing the intermediate products then to the same reaction (i. e., strain-promoted alkyne-azide cycloaddition, SPAAC) with an excess of slightly different oligonucleotide constituents in an aqueous medium yields molecularly defined monofunctionalized spherical nucleic acids (SNAs). This procedure offers a controlled synthesis scheme in which one oligonucleotide arm can be functionalized with labels or other conjugate groups (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid, DOTA, and Alexa-488 demonstrated), whereas the rest of the 11 arms can be left unmodified or modified by other conjugate groups in order to decorate the SNAs' outer sphere. Extra attention has been paid to the homogeneity and authenticity of the C60-azide scaffold used for the assembly of full-armed SNAs

Small-diameter parallel plate rheometry: a simple technique for measuring rheological properties of glass-forming liquids in shear

The rheological characterization of glass-forming liquids is challenging due to their extreme temperature dependence and high stiffness at low temperatures. This study focuses on the special precautions that need to be taken to accommodate high sample stiffness and torsional instrument compliance in shear rheological experiments. The measurement errors due to the instrument compliance can be avoided by employing small-diameter parallel plate (SDPP) rheometry in combination of numerical instrument compliance corrections. Measurements of that type demonstrate that accurate and reliable rheological data can be obtained by SDPP rheometry despite unusually small diameter-to-gap (d/h) ratios. Specimen preparation for SDPP requires special attention, but then experiments show excellent repeatability. Advantages and some current applications of SDPP rheometry are briefly reviewed. SDPP rheometry is seen as a simple and versatile way to measure rheological properties of glass-forming liquids especially near their glass transition temperature.Peer reviewe

Rheological characterization of wax modified bituminous binders:Effect of specimen preparation and thermal history

The use of synthetic waxes in bitumen modification has recently become increasingly popular due to its potential as warm mix additive and its ability to improve the performance of asphalt binders and mixtures. This paper explores the challenges encountered in the rheological characterization of wax modified bituminous binders. A dynamic shear rheometer (DSR) is used to measure viscoelastic properties of wax modified binders, and the influence of specimen preparation is evaluated. The viscoelastic properties of wax modified binders were found to be highly sensitive to the loading method and thermal history of the test specimens. Furthermore, deviations in the rheological behavior of different test specimens were attributed to the stress-sensitive crystalline network structure of the wax additive. Based on the findings of this research, it is clear that more specific guidelines for the rheological testing of wax modified binders need to be developed in order to improve test repeatability and reproducibility and in order to better predict the performance of wax modified asphalt pavements.</p

Strain accumulation in bituminous binders under repeated creep-recovery loading predicted from small-amplitude oscillatory shear (SAOS) experiments

The 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.Peer reviewe

The dynamic fragility and apparent activation energy of bitumens as expressed by a modified Kaelble equation

The 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.</p

The dynamic fragility and apparent activation energy of bitumens as expressed by a modified Kaelble equation

The 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.Peer reviewe

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.</p