Improving the high temperature stability of modified emulsified asphalt is an important research topic in the field of emulsified asphalt. The high temperature stability of the modified emulsified asphalt was effectively improved by the composite modification method, and the modified emulsified asphalt products with high softening point were obtained.
SBS Modification |High softening point |Multiple modifications.
Modified emulsified asphalt has always been the key direction of the emulsified asphalt industry. The adhesive layer of China's highway and the micro-surface and ultra-thin wear layer of the maintenance market are the main application fields of modified emulsified asphalt.
Under the background of global warming and the increase of road load, the requirements for road modified asphalt and modified emulsified asphalt are gradually increasing, especially the softening point has received special attention, and the key projects in some areas even require the softening point to be higher than 70. Therefore, it has become the research direction to improve the modification effect and quality of modified emulsified asphalt and greatly improve the high-temperature stability.
1. Development and classification of modified emulsified asphalt
In China, road modified asphalt mainly includes SBS modification, SBR modification, epoxy modification, PE EVA modification, diatomaceous earth modification, polymer wax modification and other types. There is a big difference between SBS and SBR in the modification mechanism of asphalt. The soft section S of SBS gathers together to absorb the light oil in the asphalt and fully swells, and the hard section B connects the structure formed by the soft section to realize the role of bridging, and then form a spatial network system. The formation of this network system reduces the movement amplitude of the easily free components in the asphalt in the hot environment, thereby improving the high-temperature stability of the asphalt. The biggest difference between SBR and SBS is determined by the molecular structure of SBR, SBR cannot realize the construction of spatial network system in matrix asphalt, and the effect between asphalt components and SBR particles is only adsorption, so SBR is quite different from SBS in terms of high temperature stability. In the SEM images, the micromorphology of SBS-modified asphalt is sponge-like porous, while the micromorphology of SBR-modified asphalt is flocculent[1].
Therefore, there is a big difference between SBS modified asphalt and SBR when preparing modified emulsified asphalt. If the emulsion outlet temperature of SBR modified emulsified asphalt is lower than that of SBS, the production at atmospheric pressure will not lead to local boiling of emulsified asphalt and then gasification and demulsification. However, SBS modified asphalt needs to be specially formulated before emulsification to reduce the viscosity of the system, and then the outlet temperature is reduced through pressurization and heat exchanger cooling, and the continuity and stability of production are put forward. Therefore, the production of SBS modified emulsified asphalt must adopt high-power and high-precision colloid mill, with conditions such as back pressure control and large heat exchanger, and achieve stable production by strictly controlling the temperature and production indicators. SBS modified emulsified asphalt has high requirements for equipment, and the wear and tear of the equipment is also very large, if SBS modified emulsified asphalt is produced all year round, the grinding disc of the colloid mill will produce obvious wear [2]. Therefore, the production of SBS modified emulsified asphalt has always been a technical difficulty and focus in the field of emulsified asphalt.
2. Research on SBS modified emulsified asphalt
The research direction of modified emulsified asphalt is mainly focused on how to improve the SBS content and emulsion quality. In recent years, industry experts have proposed a variety of solutions, mainly including: 1) adding light component oil and surfactants to reduce the viscosity of modified asphalt; 2) Add water-based modifier; 3) Add two-component epoxy or polymer to improve high temperature stability. In this R&D project, a variety of modification technologies were used to compound the modification and emulsification of Zhenhai 70 asphalt commonly used in the market, and the satisfactory results were obtained.
Test conditions: The asphalt adopts Sinopec Zhenhai 70, the modifier adopts the linear SBS particles commonly used in the market, and the production equipment of the emulsified asphalt adopts a medium-sized indoor testing machine with a grinding time. The stone of the mixing test is made of Jiangsu basalt stone and 425 cement. Through the comparison of various methods such as epoxy modification, SBS modification, SBR modification and polyurethane modification and the combination of two different modifiers, it was finally determined that SBS and SBR modified emulsified asphalt were used for comparative study. Then, the performance of the modified emulsified asphalt with different modifier dosages was compared, focusing on the softening point, ductility and elastic recovery, and the test results are shown in Table 1, Table 2 and Figure 1. The results of the mixing test are shown in Table 3.
From the above test results, it can be seen that the softening point of SBS modified emulsified asphalt is greatly improved in the process of increasing the amount of modifier, and finally the softening point can be stably reached above 75, and the ductility and elastic recovery results will also be appropriately improved.
In terms of softening point and elastic recovery, the results of SBS modified emulsified asphalt are better than those of SBR.
The later mixing test also showed that the microsurface mixture of SBS-modified emulsified asphalt had excellent performance.
3. Conclusion
The following conclusions can be drawn from this study:
1) SBS modified emulsified asphalt can stably obtain the index of high softening point, and the elastic recovery and ductility can also be improved. In the asphalt industry, high softening points have always been the focus of attention of peers.
2) Too high softening point will cause the asphalt material to harden, which will affect the initial adhesion performance of the asphalt in the normal temperature construction, so special attention is required.
3) On the basis of this test, it is necessary to further supplement the pull-out test of various modified types to obtain the modified emulsified asphalt with balanced improvement of softening point, pull-out strength and adhesion.
End of full text. First published in Petroleum Asphalt in December 2021. About author:MA Weimin, male, graduated from the Department of Road Communication, Tongji University in 1994, and has been engaged in the research of road asphalt materials for a long time. Now he is the technical director of Jiehe Tianlong Chemical.