Multi-scale characterization of the effect of wax on intermolecular interactions in asphalt binder

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Despite the merits of using polyphosphoric acid (PPA) in modification of bitumen, its desirable stiffening effect on bitumen is totally composition-dependent. While asphaltenes and resins are correctly introduced as the immediate components affected by PPA, our laboratory rheological investigations show that bitumen's wax content could be a potential interference for PPA's modification function. As evidenced by the complex viscosity test, PPA is very effective in low-wax bitumen, but its effect on high-wax bitumen is quite negligible. In a high-wax medium, the trend of interaction energy improvement with the number of wax chains suggests that the crystalline networks of wax can interfere in interactions of PPA with either asphaltene or resin through concealing interaction sites of asphaltene and resin. This in turn leads to the reduction of their accessible active sites for interacting with PPA. To study the working mechanism of PPA on bitumen constituents, the density functional theory (DFT) approach and energy decomposition analysis (EDA) were performed on the pairs of PPA−asphaltene, PPA−resin, and PPA−wax molecules. In the case of the PPA−asphaltene interaction, EDA shows clear contributions of electrostatic, orbital, and dispersion forces. In the resin fraction, the strong interactions between basic sites of the resin molecules and PPA lead to the formation of ion-pair compounds stabilized through oppositely charged ions held together via Coulombic attraction. The formation of these new entities, which are often nonsoluble in heptane, can further explain the decrease of resin content after PPA modification. The reduction of resin is followed by an increase in the content of asphaltene with a smaller molecular weight in n-heptane precipitates, which is in line with our experiments and that of other researchers.

Section: Resultsmentioning

confidence: 99%

Moderating Effects of Paraffin Wax on Interactions between Polyphosphoric Acid and Bitumen Constituents

Mousavi

Fini

2019

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“…Paraffin wax has been used as a softener and to improve the workability of asphalt . The term “wax” usually refers to a material that is a white solid at an ambient temperature and melts at a higher temperature to form a low-viscosity liquid .…”

Section: Introductionmentioning

confidence: 99%

“…Paraffin waxes include n -paraffins ( n -alkanes), isoparaffins, and cycloparaffins. Paraffin waxes crystallize, and their melting points are in the range of 50–70 °C; their melting points are reduced to 20–30 °C when blended with bitumen. , Microcrystalline waxes are aliphatic hydrocarbon with a considerable amount of isoparaffins and cycloparaffins. Microcrystalline waxes have a less notable melting point and a high average molecular weight …”

Section: Introductionmentioning

confidence: 99%

Effects of Wax-Impregnated Nanozeolites on Bitumen’s Thermomechanical Properties

Samieadel

Chen

Ciota

et al. 2020

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This study presents a new carrier for wax-based additives used in bitumen; the new carrier alleviates wax crystallization while improving bitumen’s cohesion, adhesion, and elastic properties. The abovementioned wax carrier is a newly developed nanozeolite, which is impregnated with paraffin wax to form a hybrid additive referred to as Winz. Bitumen containing Winz showed an improved resistance to low-temperature cracking, which can be attributed to reduced wax crystallization when wax dispersed via nanozeolite. In addition, nanozeolite was found to adsorb acidic compounds of bitumen upon its release of wax. Our molecular modeling showed that while wax interacts with nanozeolite in the absence of acid, upon introduction of acid, wax molecules are replaced by acid molecules on the nanozeolite surface. Adsorption of acids to the nanozeolite surface was also evidenced in the significant change of shear-thinning behavior of bitumen doped with Winz when bitumen was exposed to water. Hydrolysis of acidic compounds at the surface of nanozeolite caused a 42% reduction in the shear-thinning rate (going from 3.25 to 1.89) after water conditioning. This in turn shows that bitumen acids were adsorbed to Winz and detracted from the interface of bitumen with stones. Therefore, Winz can be a promising candidate to promote sustainability by enhancing the durability of bituminous composites via reducing bitumen’s wax crystallization and bitumen’s acid accumulation at the stone interface. The study outcomes provide insights to synthesize multifunctional carriers for bitumen’s wax-based additives to enhance their dispersion and effectiveness.

“…It should be noted that paraffin wax is a component of several warm-mix additives, recycling agents, and rejuvenators. Use of a warm mix has been effective in reducing the environmental impact of pavement construction by lowering the mixing and compaction temperatures and extending the construction season. − The increased use of warm mix in the asphalt industry leads to increased use of wax-based additives, which are components of many commercial warm-mix additives. In addition, during oxidative aging of asphalt binder, the more reactive components of asphalt such as asphaltene and resin react with oxygen, but saturates such as paraffin wax remain intact due to their low reactivity.…”

Section: Introductionmentioning

confidence: 99%

“…10 Increases in nanoaggregates and overall asphaltene content are characteristics of an oxidized asphalt binder. 23−25 The presence of wax in most virgin asphalt binder has shown a preventive effect on the aggregation of asphaltene molecules, with a consequent decrease in the viscosity and stiffness of the asphalt binder 6,26 at high temperature. The results of the latter study provide insight into the effect of wax on virgin asphalt binder, as is the case when wax-based warm-mix additives are used in virgin asphalt binder.…”

Section: ■ Introductionmentioning

confidence: 99%

Examining the Implications of Wax-Based Additives on the Sustainability of Construction Practices: Multiscale Characterization of Wax-Doped Aged Asphalt Binder

Samieadel

Høgsaa

Fini

2018

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Paraffin wax is a component of many additives and rejuvenators commonly used in the asphalt industry to promote sustainability by facilitating recycling and/or reducing mixing and compaction temperatures during pavement construction. However, the effect of wax-based additives on asphalt molecules and consequently on asphalt binder’s performance characteristics has not been thoroughly understood. This paper uses a combination of a computational approach and an experimental approach to study the properties of aged asphalt binder specimens in the presence of paraffin wax. Differential scanning calorimetry showed that the introduction of paraffin wax to aged asphalt significantly reduces the glass transition temperature of the aged asphalt, with 10% wax-doped aged asphalt having a glass transition temperature 9 °C lower than the control asphalt. The above observations can be attributed to a plausible role of straight alkane chains of wax in disturbing the clusters of asphaltenes and increasing asphaltene mobility. The increase in asphaltene mobility is also reflected in the rheology of wax-doped aged asphalt; its percent recovery in the presence of 10% wax is reduced by 50% compared to the control. The results of molecular dynamics simulations revealed how paraffin wax molecules change the aggregation pattern of aged asphalt binder, as evidenced by the reduced formation of nanoaggregates in oxidized asphaltene in the presence of wax molecules. The reduced formation of nanoaggregates is described as a three-step mechanism: the attraction of wax molecules to nanoaggregates of oxidized asphaltene; the penetration of wax molecules to self-assembled asphaltene stacks; and disturbances in the formation of parallel oxidized asphaltene stacks. The results show the average aggregation number is reduced after adding paraffin wax molecules to an equilibrated system of oxidized asphaltene molecules. Furthermore, the radial distribution function confirms that, after the addition of paraffin wax molecules, the formation of parallel stacks of oxidized asphaltene is less likely. Thermogravimetric analysis shows that the addition of wax to aged asphalt binder increases the onset temperature of degradation; an increase of 25 °C is recorded when the wax dosage increases from 0% to 10%. The overall thermal stability of asphalt binder is reduced, as evidenced by lower residual mass in samples with higher wax content. In addition, the difference in critical cracking temperatures (determined based on the stiffness and the stress relaxation capability of the asphalt binder) increases as the wax content increases. This in turn indicates that the cracking properties of wax-doped binder are controlled mainly by the stiffness rather than by the stress relaxation capability; the control of cracking properties by stiffness could be attributed to the formation of a lamellar structure in wax-doped aged asphalt binder, causing a significant increase in stiffness. A molecular-level understanding of wax–asphaltene interaction helps explain how the per...