Study on Low-Temperature Performance of Packed Waste Modified Pitch (I)

Foreword

As the most important material for highway construction, asphalt has always been valued. Due to the rapid growth of traffic caused by economic development, increase in vehicle axle load, large-scale vehicles, severe overload, and channelization of vehicles, the status quo of the highway has become increasingly unable to meet the needs. Ruts have become the most serious form of damage on asphalt. Damage to pavement water and temperature cracks in asphalt pavements in cold areas are also widespread [6]. Faced with this situation, road workers have to work hard on asphalt materials to dig potentials in order to get out of the woods. Since the 1990s, research on bituminous materials has entered an unprecedented boom.

As represented by the World Strategic Highway Research Project (SHRP) of the following day, all countries are recognizing the road performance of asphalt and researching and formulating asphalt standards that reflect road performance. The new SHRP asphalt standard, the new Canadian asphalt standard, and the European unified asphalt standard were all enacted [1]. In order to adapt to this situation, China has listed the “Study on the Performance of Road Asphalt and Asphalt Mixtures” as a national science and technology research topic during the “Eighth Five-Year Plan” period. Its main content is also proposed to meet China’s national conditions and adapt to asphalt and asphalt mixtures in different regions. Key technical indicators and technical requirements have now achieved initial results.

Nowadays asphalt quality and variety can no longer meet the higher requirements of asphalt pavement. Various asphalt modifiers and admixtures have emerged, and some noticeable new pavement structures have emerged. Almost one third of the provinces and cities in China have studied modified asphalt. The research on the modification technology of asphalt and asphalt mixture in China has a history of more than 20 years. It has achieved great practical value in many applications, especially the improvement of pavement performance. With the further development of road traffic in China, the demand for special high-grade pavements for epoxy resin modified asphalt materials has begun to increase, and the prospects for the asphalt modification industry are promising. At the same time, with the development of China's packaging industry and plastics industry, plastic packaging products have also caused pollution to the environment while benefiting people. At present, more than 60% of urban garbage is domestic garbage, and over 80% of domestic garbage is packaging waste. The "white pollution" formed by these wastes brings serious harm to the environment; in addition, it is accompanied by highways. With rapid development, construction technology of asphalt pavement has become one of the core technologies for highway construction. It has achieved considerable development and progress. However, there are many problems in asphalt concrete pavement, which has also aroused people's general attention. Modification has become a topic of global concern[2].

1 Introduction

1. 1 Research Status of Modified Asphalt

1.1.1 Classification and Development Trend of Modified Asphalt

Due to its good thermal plasticity, stickiness and viscoelasticity, petroleum asphalt has been used as road pavement material for more than 100 years, and will continue to be the basic material for road pavement in the future. Of the highways built in China, about 75% use asphalt concrete pavement. However, with the economic growth, the traffic volume has increased rapidly, the vehicle has become large-scale, the overload has been serious, and the vehicle canalization has put forward more stringent requirements for road paving materials, which has made the asphalt concrete pavement face a more severe test. Many road asphalt pavements cannot be adapted to the traffic volume soon. The early damages such as rutting, cracking, and pits have occurred. Many roads have had to repair the facades before the design deadline. In order to reduce this early damage, the method of adding an admixture to the bitumen proved to be effective [7]. After long-term research, people chose different modifiers for different modification purposes.

In a broad sense, the modified asphalt and modified asphalt mixture technologies adopted for different purposes can be summarized in Figure 1-1.

In a narrow sense, modified asphalt generally refers to polymer modified asphalt. The types of polymers used for modification are also numerous and generally fall into the following three categories:

(1) Rubber: Natural rubber (NR), styrene-butadiene rubber (S8R), chloroprene rubber (CR), butadiene rubber (BR), ethylene propylene rubber (EPDM), etc. There are SBR, CR, EPDM and so on. Such modifiers have excellent resistance to low temperature cracking and increase the adhesion of bitumen to stone.

(2) Rubber Plastics: Thermoplastic elastomers. Such as styrene-butadiene block copolymer (SBS), styrene-isoprene diblock copolymer (SIS), styrene-ethylene-butadiene-styrene copolymer (SEBS), polyester elasticity Body and so on. There have been practical effects of SBS. Such modifiers have increased flexibility, resistance to permanent deformation and good durability.

(3) Resins: Thermoplastic resins, such as polyethylene (PE), ethylene-vinyl acetate copolymer (EVA), random polypropylene (PP), polyvinyl chloride (PVC), polyamide, etc.; thermosetting resins, such as Epoxy resin (EP), phenolic resin, polyurethane resin, etc. There are EVA, PE, EP and so on. Such modifiers have a significant increase in stability at high temperatures, resulting in improved adhesion, shock and vibration resistance.

1.1.2 Key Technologies for Asphalt Modification

As a complex polymer hydrocarbon, bitumen exhibits typical elastic-viscoplastic behavior under certain temperature and load, and it will produce aging under high temperature and ultraviolet radiation. Therefore, the main purpose of adding the modifier is to improve the road performance of the asphalt mixture at high temperature, and improve the performance of anti-rutting, anti-fatigue, anti-aging and resistance to low temperature cracking. The key to asphalt modification is to solve the problem of compatibility between modifier and asphalt. The compatibility referred to in road engineering means that “the polymer modifier reacts with the fine particles and the matrix bitumen or evenly and stably disperses in the matrix bitumen without delamination, agglomeration, or segregation”. The compatibility of the modifier with the matrix asphalt mainly depends on the interfacial function between the two, the composition of the matrix asphalt and the polarity of the assembly, and the like. The stronger the polarity of the polymer, the more the molecular structure and the asphalt. Close to it, it is compatible with the matrix asphalt, size, molecular structure and other factors. As soon as possible, the modification effect is also better. Domestic research also shows that the polyolefin modifier has good compatibility with high saturation bitumen, while SBR, SBS, etc. have better compatibility with high aromatic matrix asphalt. After extensive research on SBS modifiers, FINA (Belgium has its own branches) found that the asphaltene content in the base asphalt has a great influence on the SBS modification effect. The higher the asphaltene content in the base asphalt, the more compatible it is. The better the sex. The United States chemist Brule even gave the composition ratio of the matrix bitumen with better compatibility [9], ie saturation: (fragrance + resin): asphaltene = (8-12%): (85-89 %): (1-5%). From these studies, we can see that the compatibility of the modifier with the asphalt is closely related to the components of the matrix asphalt. For the polymer modified asphalt, the compatibility of the asphalt and the polymer and the storage stability of the modified asphalt are the first problems to be solved. This has a guarantee of performance for the transportation and use of modified asphalt. The study discussed the mechanism, preparation process, and preparation of polymer SBS modified asphalt from the aspects of the properties of basic asphalt, high temperature performance of modified asphalt, and low temperature performance. It was necessary to add chemical modification to the preparation of polymer modified asphalt. In order to obtain a modified asphalt with good storage stability [18].

1.1.3 Modification Performance of Asphalt

One of the main functions of the modified asphalt is to improve the resistance to deformation of the asphalt mixture at high temperatures, but it has no adverse effect on the characteristics of the asphalt or asphalt mixture at other temperatures. Modified asphalt usually has the following characteristics:

(1) Excellent high temperature stability;

(2) Better low-temperature crack resistance and anti-reflection cracking capabilities;

(3) Enhanced adhesion and resistance to water damage;

(4) Has a long service life.

Different types of modifiers have different effects on the improvement of asphalt properties. In general, the penetration of asphalt modified by resin materials decreases, the softening point increases, and the ductility decreases. After modification of rubber materials, the penetration of bitumen will be reduced, while the ductility and softening point will increase; the thermoplastic elastomer material has a good two-way modification. As for the modification mechanism of asphalt, there is no definitive conclusion at present, summarizing the collected data and viewpoints:

(1) The best state of the blend of polymer and asphalt: the polymer is distributed uniformly in a continuous phase of the asphalt medium in a discrete phase state. This structure is similar to the dense structure in the gradation theory;

(2) Polymers will swell in asphalt;

(3) There is a critical value for the amount of polymer in asphalt (ie, the critical amount called by Collins, American scientist). When the critical content is reached, the polymer forms a stable and flexible network structure; when this exceeds this, When the value is changed, the phase change occurs in the modified system, and the polymer is converted from a discontinuous phase to a continuous phase, and the bitumen is converted from a continuous phase to a discontinuous phase; on the other hand, an excessively high amount of additive will greatly increase the modification cost and appear uneconomical. .

1.1.4 Domestically Modified Modified Asphalt Processing Method

At present, SBR, PE, EVA and SBS are widely used in China because of their good bidirectional modification performance (ie, the ability to simultaneously change the high-temperature and low-temperature properties of the base asphalt) in recent years. The quality level of several existing modified asphalts in China is basically the same as that of the modified asphalts with the same type of modifiers in the world. The difficulty in processing methods has become the main aspect of competition between domestic modified asphalt and similar international products. In this regard, there is a big gap between China and European and American countries. At present, at the time of production of modified asphalt at home and abroad, except for a very small proportion (such as SBR latex and finely ground rubber powder) that is directly mixed, most of the modifiers are not very compatible with road asphalt. High-speed shearing, colloidal grinding, mixing and other special processing methods must be adopted in order to evenly disperse the modifier in the mixture [12]. $Page break $

1.1.5 Manufacturing Process of Domestic Modified Asphalt

China's existing modified asphalt processing technology has few mature technologies that can form large-scale production, among which the more influential are Guochuang No.1 and Guochuang No.2 produced by Beijing Guochuang Modified Bitumen Co., Ltd. The process and the solvent production process developed by the Chongqing Institute of Transportation Science. The key to making modified asphalt is to grind the modifier and evenly disperse it in the asphalt colloid. Asphalt modification equipment generally includes seven sub-systems: asphalt admixture supply system, refining mixing system, heating and insulation system, control system, weighing weighing system, hydraulic station and finished product storage tank [5]. Colloid mill is the core of the entire modification equipment. It should be able to rotate at high speed and high pressure for a long time at high speed. It should also be able to control the homogenous particle size and peptizing effect of the material. Special equipment such as colloid mill type, high-speed shearing and other special equipment are already available in China. Among them, Beijing Guochuang Modified Bitumen Co., Ltd.'s refining-type modified bitumen equipment has passed the joint appraisal of the Ministry of Communications Technology Department and the Highway Division, and its performance has been achieved. The international advanced level, in addition to the Chongqing Transportation Research Institute, Xi'an Road Building Machinery Plant and other units have also developed the corresponding equipment, Henan Provincial Department of Transportation and other provincial highway departments have also imported the appropriate equipment from abroad.

1.2 Problems and Possible Countermeasures in the Research of Domestic Modified Asphalt

(1) There are many researches on modified asphalt in China, and many achievements have been made. However, the proportion actually applied to projects is much lower than that of European and American countries, and it is far from the level of scale application. In addition, the research work on modified asphalt in China is often completed independently by universities and scientific research institutes. It lacks large-scale system engineering such as the US Highway Strategy System (SHRP). The research is random and the supporting work is lagging behind. Due to the interests of various departments, the key technology for asphalt modification is often secret and unprovoked, which causes a huge waste of human and material resources to some extent.

(2) The compatibility of modified asphalt. Looking at most of the modified asphalt in China, no obvious chemical reaction occurs between the polymer and the matrix asphalt, and they are only physically linked by a weak interface. therefore