1 Introduction?
Due to the increase of traffic volume and the aggravation of vehicles, the quality requirements of asphalt pavement are getting higher and higher. Ordinary petroleum asphalt is easy to crack at low temperature and soften at high temperature. Under the repeated action of traffic load, it is easy to produce rutting, displacement and boiling, and its performance can no longer meet the needs. It is one of the advanced technologies at home and abroad to use modified asphalt to solve the problems of high and low temperature resistance, skid resistance, durability and large bearing capacity of pavement. ?
Since 1873 first published the patent of asphalt rubber in Britain, modified asphalt has formed many brands. Modified asphalt refers to adding modifiers such as rubber, resin, polymer and rubber powder. , or slightly oxidized asphalt, thus improving the performance of asphalt. The pavement paved with it has good durability and wear resistance, does not soften at high temperature and does not crack at low temperature. Regarding the selection of asphalt modifiers, due to the different climatic conditions and processing equipment in different regions, the preparation of modified asphalt is also diversified, and its modification effect is closely related to the variety of modifiers. There are many kinds of modifiers, and modifiers used for road modification are generally divided into rubber, resin and thermoplastic rubber. Therefore, when using modified asphalt, the corresponding modifiers should be selected according to different construction environment, economy and construction technology, so as to effectively improve its application efficiency in expressway and meet the traffic demand. ?
2. What factors affect the application of modified asphalt?
At present, the research on modified asphalt in China has a history of more than 20 years, and many technical achievements have been made, and the technical specifications for modified asphalt pavement construction have been promulgated. As far as the domestic application research status is concerned, the advantages of modified asphalt in road performance have been deeply understood and widely recognized. However, most modified asphalts, whether produced at home or imported from abroad, have their unique functions. When using, we should pay attention to the following factors that affect the popularization and application:
(1) The construction temperature of modified asphalt is higher than that of ordinary asphalt 10℃-20℃, which increases the construction difficulty in the process of mixing, paving and rolling, thus increasing the direct construction cost. Moreover, because the construction temperature of ordinary asphalt is already very high, the aging phenomenon of asphalt is aggravated after the temperature rises. ?
(2) Processing and producing modified asphalt requires special mechanical equipment, which increases the difficulty of use and the corresponding cost. ?
(3) The price of imported modified asphalt is generally higher, which is generally more than 50% higher than that of ordinary asphalt. ?
(4) The modified asphalt, whether produced in China or imported from abroad, will segregate or agglomerate if it is stored for too long. ?
3 The application of several common modified asphalt?
3. 1 SBS modified asphalt?
SBS modifier is styrene-butadiene-styrene block copolymer. Its biggest feature is that it can improve the high and low temperature performance of asphalt at the same time, with good elastic recovery performance and strong aging resistance. ?
3. 1. 1 mixed design?
The mixture ratio design of modified asphalt should follow the three stages of hot mix asphalt mixture ratio design in Technical Specification for Highway Asphalt Pavement Construction: target mixture ratio, production mixture ratio and trial mixing and trial paving, and determine the mineral aggregate gradation and the optimum amount of modified asphalt. The following measures can improve the performance of modified asphalt to a certain extent and give full play to its effectiveness. For example, the mixing and compaction temperature of the mixture should be determined according to the technical specifications for the construction of modified asphalt pavement and the viscosity-temperature relationship curve of asphalt binder, and the mixing and compaction temperature in the indoor mix design should be consistent with the mixing temperature of the mixing plant and the on-site rolling temperature; The measurement of volume index of mixture should be unified, and the temperature of dense graded asphalt mixture specimen should be measured by vacuum method. In the 48h immersion Marshall stability test determined by asphalt mixture Marshall stability test method, the residual stability should not be less than 80%. ?
3. 1.2 SBS modified asphalt construction?
(1) Comprehensively examine and approve the metering and temperature control of mixing equipment to ensure the accuracy of weighing and temperature of aggregates, fillers and asphalt. Among them, temperature control includes the control of aggregate heating temperature, asphalt heating temperature, mixture mixing temperature and outlet temperature. ?
(2) Determine the compaction process. The recommended rolling temperature range is120℃-150℃; The rolling process combination is as follows: rolling, DD 130 or DD 1 10 vibration and compression adopt low secondary high frequency (the relative value measured by nuclear densitometer will not increase); Roller overlap should be greater than 20 cm; ; Final pressure: DD 130 or DD 1 10 static pressure for one cycle; If wheel tracks are found, the final pressure can be carried out again, and the final pressure should be completed above 90℃. It is forbidden to scroll in the range of 105℃- 1 15℃. ?
(3) For asphalt pavement mixture, the field compaction effect should be controlled by two-way porosity and compactness. Compaction is controlled by 93% of theoretical density and 97% of Marshall density. The maximum theoretical density required for void ratio calculation is subject to daily measurement, and the test is conducted according to the maximum relative density test of asphalt pavement mixture (vacuum method). ?
3.2 MAC modified asphalt?
3.2. 1 MAC asphalt introduction?
MAC modified asphalt is the abbreviation of multi-grade asphalt, which is a new type of modified asphalt imported from the United States. MAC modified asphalt was developed and produced by Harley Asphalt Material Company in the United States on 1987, and it was used in Arizona, Texas and Indiana in the United States, with good results. China introduced this technology in 1998, and it was first applied on some expressways in Shandong, and gradually popularized. ?
3.2.2 What are the characteristics of MAC modified asphalt?
MAC modified asphalt has good aging resistance, good stability through chemical modification, no segregation after storage for half a year at room temperature, no need to add any stabilizer, no sulfur, and no harm to human body, so it is an environmental protection product. MAC also has good rutting resistance and water (oil) damage resistance. Because of its high viscosity at high temperature, it is easy to form a thick asphalt film without leakage, which can effectively prevent moisture intrusion, improve the adhesion between asphalt and aggregate, increase the cohesive force, and play a role in resisting water damage. ?
3.2.3 Application of MAC modified asphalt?
Compared with ordinary asphalt, MAC modified asphalt has obvious elasticity. After the coring test, the mixture has high density and obviously reduced porosity, which can be used in the upper layer of expressway, such as Rizhao-Zhuyuan section in Shandong Province, and the modified asphalt has achieved good results. See table 1 for Marshall technical requirements of asphalt mixture. At the same time, MAC modified asphalt is often used in road network reconstruction and maintenance projects. Pay attention to temperature control when using. The temperature of MAC asphalt is higher than that of ordinary asphalt 10℃-20℃. In particular, the final rolling temperature should be controlled at 1 10℃, and "high temperature, strong vibration and fast compaction" should be adhered to. For example, Shandong expressways are mostly 2cm-3cm thick. ?
3.3 Waste rubber powder modified asphalt?
3.3. 1 What are the characteristics of waste rubber powder modified asphalt?
The addition of rubber powder has great influence on the overall performance of asphalt. First of all, through the study of Carcia-Morales, the modified asphalt has strong ability to bear vehicle load and good adaptability. Secondly, through the research of Zhang Liping, the modified asphalt has good water damage resistance, high temperature stability and low temperature crack resistance. For example, adding tire rubber powder to asphalt, Navarro F.J and others found that on the one hand, it can improve the high-temperature linear viscoelastic modulus and viscosity of asphalt pavement. In the temperature range of 50℃- 163℃, the viscosity increases with the increase of rubber powder particles, which is obviously higher than that of unmodified asphalt under corresponding conditions; On the other hand, the low-temperature storage modulus and loss modulus are reduced, which makes the asphalt binder more flexible in a specific temperature range. Thirdly, through the study of Chipps J. F, it is found that modified asphalt has the best aging performance, slow hardening speed and low oxidation speed; Palit S.K and other studies also found that rubber powder modified asphalt mixture improved fatigue and permanent deformation performance, and had lower temperature sensitivity and better water damage resistance. ?
3.3.2 Application of waste rubber powder modified asphalt?
Waste rubber powder has been used as an additive for hot asphalt in the United States for many years. 200 1 the United States has a relatively complete construction specification for road waste rubber powder modified asphalt. Since the late 1960s, China has carried out research on rubber powder modified asphalt, which is used for building waterproofing and roads. 2 1 century, waste rubber powder modified asphalt has been widely used in asphalt concrete pavement in China. Up to now, about 17 provinces and cities in China have set up test sections, and relevant highway engineering companies in Beijing, Jiangsu, Tianjin and other places have also formulated better construction specifications. With the development of industry, the problem of black pollution is becoming more and more serious, and the utilization of waste is paid more and more attention. Rubber powder modified asphalt can solve the above problems at the same time, and the rational use of rubber powder to prepare road asphalt with good performance will be gradually popularized and applied. ?
3.4 epoxy asphalt?
In 1960s, Shell Petroleum Asphalt Company developed epoxy asphalt for the first time and applied it in different environments all over the world, which fully demonstrated the excellent road performance of this product. In the past 40 years, the varieties of epoxy asphalt have emerged one after another, and its research and application have become increasingly extensive. Epoxy asphalt has excellent rutting resistance at high temperature, crack resistance at low temperature, durability and fatigue resistance, and is widely used in orthotropic steel bridge deck pavement and super heavy traffic roads. ?
Domestic SBS modified asphalt is often used as matrix asphalt for epoxy asphalt, and Japanese epoxy resin is used. Epoxy resin consists of two parts: main agent and curing agent. See Table 2 for technical indicators. ?
4 conclusion?
In addition to the above kinds of modified asphalt, natural rock asphalt modified asphalt, Tahe heavy oil modified asphalt, SBR modified asphalt and composite modified asphalt are commonly used. Compared with ordinary asphalt, the durability, waterproofness, high and low temperature stability and rutting resistance are improved to varying degrees. ?
Many changes have taken place in modern highways and roads: the traffic flow and driving frequency have increased sharply, the axle load of freight cars has increased continuously, and one-way driving with separate lanes has been widely implemented, which requires further improvement of the anti-fluidity of pavement, that is, the ability to resist rutting at high temperature; Improve flexibility and elasticity, that is, crack resistance at low temperature; Improve wear resistance and prolong service life. In order to meet the above demanding requirements, people began to pay attention to the modification of petroleum asphalt. The variety and preparation technology of modified asphalt depend on the type and dosage of modifier and the composition and performance of matrix asphalt (original asphalt). In view of the increasing variety of modified asphalt, we should be familiar with their performance, application and production efficiency. , and strive to save costs while ensuring the improvement of road quality, so as to effectively improve the application level of different types of modified asphalt in expressways. ?
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