Interaction of asphalt and water between porous asphalt pavement voids with different aging stage and its significance to drainage

https://doi.org/10.1016/j.conbuildmat.2020.119085Get rights and content

Highlights

  • Content of asphaltene in asphalt has a favorable effect on interaction between asphalt and water.

  • The interaction process between asphalt and water is explained at molecular level.

  • The shape of wave crest in atomic map is closely related to the interaction energy between asphalt and water.

Abstract

Compared with traditional asphalt pavement, porous asphalt (PA) pavement has great advantages in terms of drainage, noise reduction, anti-skid and other functional behavior. More practices have proved that the PA pavement is an important development direction of asphalt pavement. The voids structure of PA pavement can quickly eliminate the precipitation on the pavement, which provides an important guarantee for driving safety in rainy days. However, with the increase of porosity, the contact area between the asphalt on the voids surface and the external environment also increases. Therefore, the aging stage of asphalt plays an important role in the realization of drainage function of PA. In this study, the molecular dynamics (MD) is used to simulate the contact state between water molecules and asphalt surface layer in PA. At the molecular level, the action mechanism between asphalt and water in different aging stages is explained, and the effect of aging on the action of asphalt and water is explored. On this basis, the changes of the interaction between different aged asphalt and water molecules were verified by drip observation (DO) and atomic force microscope (AFM). The results show that the interaction energy between asphalt and water in different aging stages is different. The longer the service life of PA pavement is, the more serious the asphalt aging, and the greater the interaction energy to water molecules is. In the case of large surface area of PA, the interaction between asphalt and water molecules in the aged asphalt can promote the interaction. That is adverse to drainage, thus causing more water retention in the PA structure at macro level. Under the comprehensive action of load, temperature and other factors, water damage of PA pavement structure is caused. The research results have certain theoretical and practical value for promoting the development of PA pavement.

Introduction

In order to improve and expand the road function, porous asphalt (PA) pavement has gradually become the research focus of road engineering. The PA is that its air voids is as high as 15–20% or even more than 20%, while the air voids of traditional asphalt pavement is only 3–6%. Due to the large voids, rainwater can infiltrate into the road surface and drain away from the connected pores in the road surface to the edge of the road surface (shown in Fig. 1). Therefore, the PA pavement drainage performance is an important index to achieve its pavement functionality, and it is also the object of many scholars’ research [1], [2], [3].

Early studies on PA were mostly limited to the relationship between asphalt performance and the characteristics of mixture gradation and drainage performance. For example, Ni Fu-jian et al.[4] tested the properties of PA made of three different kinds of asphalt. Mansour et al.[5] studied the influence of aggregate level paired PA performance, which can be changed by gradation optimization. Shirini et al.[6] evaluated the effect of crumb rubber (CR) on the performance of PA. These studies show the influence of various properties of asphalt and aggregates on PA and lay a foundation for the development and improvement of PA. However, these studies tend to focus on the composition of the foundation, the types of asphalt and aggregates are limited, and important drainage functions have not received much attention.

The internal porous structure is the main characteristic of PA, so the shape and distribution of the pores are of great significance to the drainage performance. With the development of technology, X-ray, image processing, computer simulation and so on are used in the observation and study of PA internal voids [7], [8], [9]. These research results established the relationship between the void of the mixture and the function, and the research on the porous asphalt pavement was further expanded. However, the main reason for the existence of voids is to achieve drainage performance. It is an obvious disadvantage to consider the form of voids without considering the contact between water and the surface asphalt of voids.

With the emergence and application of molecular simulation technology, the micro-technology has enriched the study of PA void drainage mechanism. Zhang Lei et al. [10] used molecular simulation technology to study the adsorption behavior of asphaltene. Guo Meng et al. [11], [12] conducted a lot of molecular simulation studies on the diffusion behavior of asphalt on the surface of mineral aggregates. In 2018, Pahlavan [13] studied the molecular simulation of aggregate oxidized asphalt and explored the MD evolution of asphalt. Wang Lan [14] studied the difference of molecular dynamics of asphalt modification before and after aging, which further enriched the application of MD in asphalt materials. The application of MD to the analysis of complex asphaltenes allows many macroscopic phenomena to be well explained at the nanoscale. These studies focused on the nature of the asphalt and did not introduce the effect of water molecules on the surface of the voids of the asphalt. However, this phenomenon is widespread in reality.

In conclusion, as far as I know, the molecular dynamics simulation between asphalt and water in the interstitial space of PA has not been studied so far. However, it is well known that when the PA interacts with the external environment, excluding precipitation is an important aspect. In addition, the asphalt on the void surface is easily aged, which will definitely affect the drainage. Therefore, the object of study is to explain the interaction principle at the molecular level by comparing the differences in the interaction between water and asphalt at different aging stages. The study provides a new research direction for the drainage of PA and has certain theoretical and practical value for the development of PA pavement.

Section snippets

Introduction to molecular dynamics simulation

Molecular dynamics (MD) is a method used to calculate the equilibrium and transfer properties of the first classical multibody system [15]. Choose a simulation system composed of N system particles and solve the newton motion equation of such a simulation system. The basic idea is to give the system an initial state, then run under the action of force field and collect system samples for statistical calculation.

Different from other macroscopic simulations, periodic boundary conditions (PBC) are

Interfacial energy

Interface energy, also known as interaction energy, is an important parameter for studying the interaction between two materials. The interface energy between different materials can be expressed in Fig. 10.

As shown in Fig. 10, when two different materials A and B are in contact at a specific temperature and pressure, the two materials have a coplanar C. At this point, the molecules at the contact surface of the two materials begin to move until the whole system reaches a stable state. In this

Laboratory validation of simulation results

In order to further verify the simulation results, 90# asphalt was taken to conduct the aging simulation test in the room. The aging temperature was 163 °C, and the aging time was divided into 0 h, 35 h and 75 h. The aged asphalt was observed by macroscopic dripping test and atomic force microscope, and the test results were shown in Table 6 and Fig. 16.

As can be seen from the dripping test results of asphalt at different aging stages (Table 6 and Fig. 16). With the increase of asphalt aging

Conclusions

  • (1)

    Asphalt aging occurs in PA at different use stages. The content of asphaltene is in direct proportion to the energy of asphalt-water interaction, which has a favorable effect on the interaction between asphalt and water, but is unfavorable to drainage. The saturated content and aromatic content are inversely proportional to the asphalt-water interaction, which is beneficial to the drainage of PA.

  • (2)

    The interaction energy difference between asphalt and water with different aging degrees is about

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

The authors gratefully appreciate the supports from the province key laboratory of road in Northeast Forestry University and the foundations for the project of National Natural Science Foundation of China (E080703) and the project of Heilongjiang Traffic and Transportation Department.

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