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The viscoelastic properties of some binders change significantly with time at low temperatures. The
binder usually stiffens over an extended period of time, even if maintained at a constant temperature.
Therefore, the ability of the binder to relax the developed thermal stresses decreases with the time spent in
a cold environment. At a certain poin...
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... Modulated differential scanning calorimetry The changes in the glass transition temperature (T g ) of the bitumen were monitored to infer the change in the bitumen structure due to ageing (e.g. Masson and Polomark 2001;Kriz et al. 2007;Sá Da Costa et al. 2010;Wang et al. 2019a;Kaya et al. 2020). In this study, T g of the bitumen top coat of the unaged and aged BGMs was measured, using a TA Instruments Modulated Differential Scanning Calorimeter (MDSC250), equipped with a refrigerated cooling system (RCS120), according to the inflection method (ASTM E2602). ...
The degradation behaviour of a 4.8 mm thick elastomeric bituminous geomembrane (BGM) immersed in pH 0.5, 9.5, and 11.5 synthetic mining solutions is examined over 26 months at 22, 40, 55 and 70°C. The low pH solution simulates the leach solutions found in copper, nickel, and uranium heap leach pads while the two high pH solutions simulate the chemistry and pH found in gold and silver heap leaching facilities. The mechanical, rheological, and chemical properties are examined at different incubation times to assess the degradation in the BGM at different temperatures. It is shown that the degradation rates of all properties are faster in pH 11.5 and 9.5 than in pH 0.5. Additionally, the BGM started to exhibit degradation in its mechanical properties even with a slightly degraded bitumen coat in all the mining solutions at elevated temperatures. The time to nominal failure of the BGM is predicted at different field temperatures using Arrhenius modelling. Due to the relatively fast degradation in the mechanical properties of the BGM, especially at temperatures above 50 o C, the tensile strains in the BGM in the field should be limited so it can meet the required liner design life of heap leaching applications.
... In the asphalt research, the glass transition temperature (T g ) is typically used as an indicator of the degradation of bitumen when exposed to service conditions (Kaya et al., 2020;Mark et al., 2004;Puello et al., 2013;Yu et al., 2019). In amorphous or random network materials, T g refers to the energy needed to break and recreate covalent bonds (Ojovan 2008) that separates between the glass-like brittle behaviour below T g and the rubbery-like behaviour above T g (Aguiar-Moya et al., 2017;Kriz et al., 2007). Ageing can alter the thermal characteristics of polymer-modified bitumen, and hence its T g due to changes in the chemical structure of the bitumen (Kaya et al., 2020;Wang et al., 2019a). ...
The effect of elevated temperatures on the degradation of an elastomeric bituminous geomembrane (BGM) when exposed to air and deionized (DI) water at temperatures between 22 and 85 °C is investigated using immersion tests. The changes in the mechanical, chemical and rheological properties of the BGM are examined over approximately two years under different ageing conditions. It is shown that the BGM exhibited different degradation rates in its different components when exposed to elevated temperatures that are dependent on the incubation media. In air, the BGM exhibited thermo-oxidative degradation in the elastomeric bituminous coat that changed the bitumen glass transition temperature and increased its rigidity. Further degradation led to the brittleness of the bitumen coat before any degradation in the tensile and puncture strengths of the BGM. In contrast, exposure to DI water resulted in faster degradation of the mechanical properties of the BGM, while the bitumen coat exhibited substantially less degradation than in air. Arrhenius modelling is used to estimate the degradation times of the BGM at a range of field temperatures for both media.
... Rather than being the result of wax crystallization alone, wax develops a semi-crystalline structure (similar to semi-crystalline polymers) that inhibits the segmental motion of the molecules within the amorphous phase of the binder, creating a rigid and glassy medium that stiffens the binder. Further, the increased presence of semi-crystalline saturate materials creates an accelerating increase in glass transition temperature, allowing for the formation of a rigid amorphous phase at higher and higher temperatures [269]. The change in glass transition depending on crystallinity is presented in Fig. 24. ...
... Dependence of rate of change in Tg on wax content and enthalpy of melting[269]. ...
Wax in asphalt is an important factor that affects the life cycle cost of flexible pavements. Due to limitations in characterization methods for asphalt microstructure, deficiencies in our understanding of how wax affects physical and chemical properties of asphalt still exist today. However, thanks to the construction of carefully controlled pavement trials in support of the development of asphalt binder specifications, researchers now have a better understanding of long-term performance issues, and how waxes of various types influence these. Therefore, this article reviews early research on wax in asphalt as well as new insights obtained with modern characterization methods. The classification of wax in asphalt is discussed in relation to its chemical characterization by advanced spectroscopic methods. Physical characterization techniques of wax in asphalt are presented. Modern microscopy methods are shown to help researchers capture the detailed morphology of wax crystalline phases in asphalt. Wax content is one of the most important factors affecting asphalt performance yet its quantification by different methods can vary greatly. Therefore, the advantages and disadvantages of various methods are systematically reviewed here. Potential effects of wax on the different kinds of performance indices of asphalt and its mixtures are summarized. Shortcomings of the exsisting specifications are also discussed. Moreover, the current status of the use of wax-based, warm-mix additives in pavement engineering are analyzed. This paper provides a detailed review of the mechanisms by which waxes affect asphalt properties. It helps asphalt manufacturers to produce high-quality products and, last but not least, allows user agencies to avoid the use of inferior binders that lead to early and excessive cracking in the asphalt pavement.
... Thermal analysis technologies, such as differential scanning calorimetry (DSC) or modulated differential scanning calorimetry (MDSC) are essential methods for characterizing reversible aging properties of asphalt binders [40]. However, compared with the rheological method, it is very hard to implement DSC analysis practically. ...
The primary objective of this paper is to understand reversible aging properties of modified asphalt binders containing different percentages of coal liquefaction residue (CLR), which is a by-product of the coal liquefaction process. To fulfill this objective, regular performance grading test, extended bending beam rheometer test, and dynamic shear rheometer test were conducted to comprehensively evaluate the effect of CLR on base asphalt while reversible aging was also considered. The results showed that adding a certain percentage of CLR significantly increased the high-temperature performance grade of modified asphalt while the regular low-temperature performance grade kept constant. However, when the conditioning time prolonged, all the CLR modified asphalts in this study experienced severe hardening trend and the grade loss higher than 6 °C after 72 h conditioning time. From statistical analysis, it could be concluded that the grade loss had a significant change even just by adding 3% CLR in base asphalt binder. For all the CLR modified asphalt systems containing different percentages of CLR, significant differences in the grade loss between 24 and 72 h conditioning time occurred. However, no significant differences were observed when the conditioning time extended from 72 to 168 h.
... La T g alrededor de -25ºC corresponde al butadieno, mientras la T g alrededor de los 80ºC corresponde al estireno presente en el SBS. Las T g a temperaturas entre 20 y 40ºC han sido atribuidas a la interface butadieno-estireno [35]. La mezcla con un contenido de 15% p/p de SBS además de mostrar las Tg características del asfalto, muestra la Tg correspondiente al estireno presente en el SBS, lo que indica algún grado de interacción entre el asfalto y el SBS. ...
Bitumen is a black material composed of a mixture of various natural hydrocarbons. Bitumen has been commonly used in road paving and roofing applications thanks to its hydrophobic and adhesives properties. The production of Polymer Modified Bitumens (PMB) has allowed the development of materials with better performance in comparison to pure bitumen. This work presents the effect of addition of polymer to a Colombian bitumen from its morphological, rheological and thermal properties, in order to identify different modification levels. The polymers used as modifiers were polyethylene wax (CPE), styrene butadiene styrene (SBS) and crumb rubber (CR). They were added to bitumen in proportions between 3 to 15% w / w. Both neat bitumen and PMB were characterized by penetration and softening point. Thermal and rheological characteristics were analyzed by differential scanning calorimetry (DSC) and rotational rheometry, respectively. Changes in the morphology were measured by atomic force microscopy (AFM). The experimental results showed that the CPE mixtures had the most pronounced effect on the conventional properties, achieving a 75% reduction in penetration and a 250% increase in the softening point compared to neat bitumen. The results obtained by DSC allowed identifying three glass transition temperatures (Tg) in neat bitumen.Mixtures with SBS altered Tg, showing changes on the thermal characteristics of neat bitumen. Mixtures with CPE and SBS showed the highest values of G*. The results obtained by AFM help identifying three different phases in neat bitumen and its variation with the addition of different polymer modifiers, showing considerable structural changes that led to changes in the material properties at the macroscopic level.
... La T g alrededor de -25ºC corresponde al butadieno, mientras la T g alrededor de los 80ºC corresponde al estireno presente en el SBS. Las T g a temperaturas entre 20 y 40ºC han sido atribuidas a la interface butadieno-estireno [35]. La mezcla con un contenido de 15% p/p de SBS además de mostrar las Tg características del asfalto, muestra la Tg correspondiente al estireno presente en el SBS, lo que indica algún grado de interacción entre el asfalto y el SBS. ...
Resumen El asfalto es un material constituido por una mezcla de diversos hidrocarburos de origen natural cuyas buenas propiedades aglutinantes e hidrofóbicas lo han llevado a ser ampliamente utilizado en aplicaciones que van desde la impermeabilización hasta la fabricación de vías. Mundialmente, la técnica de adicionar polímeros al asfalto ha permitido obtener materiales que cumplen con prestaciones que un asfalto por si solo no resistiría. En este trabajo se presenta el efecto de la modificación polimérica de un asfalto de origen colombiano en sus características: morfológicas, reológicas y térmicas con el objeto de identificar diferentes niveles de modificación. Se utilizaron como polímeros modificadores: cera de polietileno (CPE), copolímero de estireno butadieno estireno (SBS) y caucho molido de llanta (CR), que fueron adicionados al asfalto en proporciones de 3 al 15 %p/p. Los asfaltos, tanto en estado crudo como modificados, fueron caracterizados mediante ensayos de penetración y punto de ablandamiento. Las características térmicas y reológicas se analizaron mediante calorimetría diferencial de barrido (DSC) y reometría rotacional. Los cambios en la morfología se analizaron mediante microscopía de fuerza atómica (AFM). Los resultados experimentales demostraron que las mezclas con la CPE tuvieron el efecto más acentuado sobre las propiedades convencionales logrando una disminución del 75% en la penetración y un aumento 250% en el punto de ablandamiento, con respecto al asfalto sin modificar. Los resultados obtenidos mediante DSC permitieron identificar tres temperaturas de transición vítreas (Tg) en el asfalto crudo que están relacionadas con sus componentes fundamentales. Las mezclas con SBS alteraron dichas Tg evidenciando la modificación de las características térmicas del asfalto crudo. Las mezclas con CPE y SBS presentaron los mayores valores de G *. Los resultados obtenidos mediante AFM, permitieron identificar tres fases diferentes en el asfalto crudo y su variación con la adición de los polímeros modificadores, evidenciando cambios estructurales considerables que conllevaron a cambios en las características y propiedades del material a nivel macro.-Palabras clave: Asfalto, bitumen, asfalto modificado con polímeros * Autor de correspondencia: teléfono: + 57 + 4 + 261 9500 ext. 9603, correo electrónico: eossa@eafit.edu.co (E. Ossa)
... Kriz successfully identified binders that are sensitive to time hardening at low temperatures by using modulated differential scanning calorimetry (MDSC). In such binders, several thermodynamic and morphology parameters are strongly time-dependent, suggesting that the viscoelastic properties change with time [15]. Garcl´a-Morales et al. deals with the viscous properties of recycled-polymer modified bitumens (PMBs) in a wide range of temperatures. ...
In order to improve the road performance of asphalt mixture, the phase behavior of asphalt mastic which is the most important component of asphalt mixture was studied. The glass transition temperature (Tg) and glass transition activation energy of asphalt mastic were obtained by the dynamic mechanics analysis (DMA) method, and the effect of fillers on the distribution of wax in asphalt was studied by the differential scanning calorimetry (DSC). The effect of fillers on temperature sensitivity of asphalt mastic was studied through Brookfield viscometer. The phase separation of asphalt mastic and the applicability of time temperature superposition principle (TTSP) on asphalt mastic were studied by van Gurp-Palmen (vGP) plot. The results show that the faster the load frequency is, the higher Tg is, and the addition of fillers can increase Tg and glass transition activation energy. The distribution of wax in asphalt is discrete, and fillers have little impact on it. The addition of fillers can improve the temperature sensitivity of asphalt mastic, and the effect order is as follows: granite > andesite > limestone. The TTSP is effective for virgin asphalt at any temperature because of its homogeneity, but it is not effective for modified asphalt when the temperature is higher than 45 °C because of its phase separation, and the addition of fillers can promote phase separation occur in modified asphalt.
... As a result of these benefits, MDSC is a powerful analytic tool which can provide information on the morphological and thermodynamic properties of a material. Of particular interest in this study is its ability to provide unique information on how asphalt properties evolve over time (Kriz et al., 2007). MDSC is also a fast and operator-insensitive method requiring only a small quantity of material, differentiating it from other testing methods, namely extended BBR testing. ...
... The transition from the rubbery to glassy state is accompanied by a sudden change in a variety of mechanical, optical and thermodynamic properties. The viscosity increases substantially (up to 10 13 Pa·s in magnitude) while the material develops a glossy appearance and becomes extremely brittle and rigid (Kriz et al., 2007). Thermodynamically, the transition is acknowledged as a stepwise drop in heat capacity which coincides with a loss in free volume (Ngai, 2004). ...
... There are a variety of variables which must be carefully chosen while developing a procedure for a MDSC experiment, the most significant of which include: the thermal history of the sample, rate of linear heating/cooling, modulation period, modulation amplitude, and the specific method of evaluation used (Kriz et al., 2007). Due to the kinetic nature of the glass transition, the measured temperature is reliant upon heating rate. ...
Low temperature cracking is a major cause of pavement failure, particularly in northern climates. Unfortunately, current asphalt cement test methods do not account for the effects of gradual physical hardening in the material during cold conditioning, and therefore cannot properly assess thermal cracking performance. Testing done using the extended Bending Beam Rheometer (BBR) protocol has been shown to provide much better results, but the method is considered to be lengthy for regular specification grading. In this study, Modulated Differential Scanning Calorimetry (MDSC) was investigated to determine if it could be used as a more practical alternative to extended BBR testing. Asphalts from an Ontario pavement trial were tested to see how their glass transition temperatures changed with conditioning. Although a direct comparison to extended BBR data was unsuccessful, a new value was discovered which was able to relate the MDSC results to performance in service.
... In asphalt literature, terms like 'reversible aging' [1], 'isothermal hardening' [2] and 'physical hardening' [9] are used to describe the overall change in the viscoelastic properties of asphalt that, perhaps, may originate not only from physical aging of the glassy state but also from intermolecular interactions and crystallinity. Some of the aspects of asphalt aging/hardening have been covered in our previous studies [10] [11] [12]. It was shown that, at low strains and at temperatures within the glass transition range, the creep or stress relaxation curves of amorphous polymers [4], and also of asphalt [11], have the same shape, irrespective of the previous storage time. ...
... An example of calorimetric signal is presented in Figure 3. The glass transition temperature was assigned to the half-height change in the reversible heat capacity upon heating [10]. The dependence of the glass transition temperature on the storage time and temperature is presented in Figure 4. ...
... The exothermic peak of cold crystallization diminishes with storage time as the crystalline phase approaches structural equilibrium. The time needed to complete the crystallization was calculated in our previous study to be no longer than several hours at −20°C [10]. Enthalpy relaxation and cold crystallization may eventually overlap. ...
At low temperatures, some asphalt binders are known to harden significantly with time. This process is commonly referred to as physical hardening; and, if neglected during testing, it may lead to overestimation of asphalt binder performance at low temperatures. Modulated differential scanning calorimetry (MDSC) and dynamic mechanical analysis (DMA) were employed to study the morphology, glass transition, enthalpy relaxation, crystallinity, and viscoelastic properties of two asphalt binders. The binders were subjected to isothermal storage at different temperatures within the glass transition range. The glass transition temperature and enthalpy relaxation linearly increased with the logarithm of storage time. The rate of change (slope) was dependent on storage temperature and was different for each binder. The hardening rate was calculated from rheological data, and similar trends in calorimetric data were observed. The thermo-reversibility of hardening was also studied.
The presented results indicate that the physical hardening of asphalt binders was predominantly caused by the physical aging of the glassy state (generally at temperatures below 10°C). The rate of hardening increased with decreasing temperature. By heating above the glass transition region (generally above 10°C), the effect of hardening was fully reversed in the amorphous binder, while in the semi-crystalline binder a negligible hardening was still observed at higher temperatures.
... The specific times needed to reach the equilibrium within the crystalline phase did not exceed 10 hours in asphalts. Calculation was provided in the previous study (22). The rate of physical aging in amorphous polymers is often determined from the slope in the enthalpy relaxation versus storage time plot. ...
... RAPh is a glassy amorphous phase stable at temperatures above the main glass transition and has been found to significantly affect the viscoelastic properties (stiffen) of semi-crystalline polymers, even at temperatures above g T (1,24,25,26). The presence of RAPh in semi-crystalline binders was first discussed in the previous studies (15,16,22). All the binders in this study had some degree of crystallinity; therefore, there should have been a certain amount of RAPh developing during the isothermal storage. ...
The effect of isothermal storage at −20°C on the glass transition temperature and enthalpy relaxation in five asphalt binders was determined by modulated differential scanning calorimetry. It was found that the glass transition temperature and enthalpy relaxation increased linearly with the logarithm of the storage time suggesting isothermal changes in asphalt properties. The rates of increase of the glass transition temperature increased linearly with the wax content. One asphalt binder was subjected to dynamic mechanical analysis; and, the data indicated a strong effect of physical aging on mechanical properties. The rate of physical aging, μ , was calculated, and the relation of μ to the amount of glassy domain was discussed. The effect of physical aging persisted even after heating 30 °C above the storage temperature. Based on the calorimetric and rheological evidence, the presence of a rigid amorphous phase
is considered. Characteristic relaxation times were found to increase with the isothermal storage time, indicating that the ability of the binder to relax stresses decreases under isothermal conditions with time.
