* Modified Asphalt
SBR -II modified asphalt is one of the most widely used rubber modified asphalt. compared with ordinary asphalt, its softening point and low temperature ductility are greatly improved. it has better low temperature cracking resistance, high temperature stability and aging resistance under the influence of natural climate, thus prolonging the service life of pavement.
I. selection of matrix asphalt and its production process
1. selection of base asphalt.The base asphalt shall be road petroleum asphalt, the asphalt surface of high-speed and first-class roads or some important projects. when modified asphalt is used, the base asphalt shall be petroleum asphalt conforming to the current " technical requirements for heavy traffic road petroleum asphalt".
2. relevant requirements for outsourced base asphalt.For purchased base asphalt, the regular manufacturer shall be selected. the product specification shall be attached to indicate the product name, code, transportation and storage conditions, factory certification and test report.
II. performance of SBR -II modified asphalt and mixture
1. technical requirements for high temperature stability of SBR - II modified asphalt mixture.The modified asphalt mixture used for the asphalt surface of expressways and first-class highways shall be tested for high temperature stability, low temperature cracking resistance and water stability according to the requirements of the technical specification for highway asphalt pavement construction. the dynamic stability of the newly mixed modified asphalt mixture, which is mainly aimed at improving the high temperature rutting resistance, shall be determined according to the rutting test method of asphalt mixture.
2. technical requirements for low temperature stability of SBR -II modified asphalt mixture.The failure strain of the low temperature bending test determined by the asphalt mixture bending test method for the modified asphalt mixture used in expressways and first-class highways with the main purpose of improving the low temperature cracking resistance conforms to the construction technical specification.
3. water stability of SBR -II modified asphalt mixture.The water stability of SBR -II modified asphalt mixture shall meet the following two indexes, and anti-stripping agent measures shall be adopted if it fails to meet the requirements.
( 1 ) the 48h immersion Marshall residual stability test determined by the asphalt mixture Marshall stability test method shall not be less than 80 %.
( 2 ) the splitting strength ratio determined by the " freeze-thaw splitting test of asphalt mixture" method should not be less than 80 %.
III. analysis of routine test results of SBR - II modified asphalt
1. analysis of test results of SBR -IIi modified asphalt.The author used SBR -II modified asphalt in the highway project of the first contract section of ta cheng - e min on line s221. the structural layer of this project is two layers. the asphalt is made of Jinshi brand SBR - II modified asphalt produced by Xinjiang Jinshi real estate company. the main test indexes are shown in table 2.
From the above test results, it can be seen that the modified asphalt of Jinshi brand SBR - II conforms to the technical requirements in the technical specification for construction of highway modified asphalt pavement and has a low temperature ductility of more than 150 cm at 5 ℃ and shows good low temperature performance. various indicators of the residue after evaporation show good thermal stability and are suitable for large-scale use.
2. Marshall test results analysis of SBR - II modified asphalt mixture.The mix proportion design of the modified asphalt mixture is carried out according to the required steps. firstly, the mineral material composition is determined. secondly, the optimum oil-stone ratio is determined. finally, the trial mix and trial spread is carried out. the stability test is carried out according to the " highway engineering asphalt and asphalt mixture test regulations". the test in construction is also carried out according to this method. the Marshall stability test of the asphalt mixture reflects the strength of the modified asphalt. its various indexes meet the specification requirements, which shows that the mixture has good gradation and road performance.
IV. on-site inspection of SBR - II modified asphalt pavement
1. pavement deflection.With the improvement of the construction quality, the inspection of rebound index will be an important index to control the construction quality. pavement deflection is an index to evaluate the overall bearing capacity of the pavement, which not only reflects the overall strength and rigidity of the asphalt concrete pavement, but also has some internal connection with the usage state of the pavement.The rebound deflection of the modified asphalt test road is measured by Beckman beam. the representative deflection value of the main SBR - II modified asphalt road section is 22.9 ( 0.01 mm ) and the representative deflection value of the ramp ordinary asphalt road surface is 28.7 ( 0.01 mm ). the test results show that the carrying capacity of the SBR - II modified asphalt road surface is higher than that of the ordinary asphalt road surface.
2. road friction coefficient.The road friction coefficient is an important index to evaluate the road surface anti-skid performance. if the road surface anti-skid performance is insufficient, the braking distance of the car will be lengthened. when the car is running at high speed, the emergency steering or braking is prone to vehicle sliding accidents, especially in rainy days, which will have adverse effects on traffic safety. the factors affecting the friction coefficient mainly include the drainage capacity of the road surface structure, the properties of mineral aggregate, the quality of asphalt and the amount of asphalt used.The average friction coefficient of the main line of SBR - II modified asphalt pavement is 62.3 bpn after testing. at the same time, we tested the average friction coefficient of the turn road section is 54.6 bpn, thus it can be seen that the friction coefficient of SBR - II modified asphalt pavement is greater than that of ordinary asphalt pavement, which shows that the anti-skid performance of the modified asphalt pavement is better than that of ordinary asphalt pavement.
3. pavement seepage coefficient.The permeability of asphalt pavement has become an indirect indicator that reflects the gradation composition of asphalt mixture. if the entire asphalt pavement is permeable, the surface will penetrate into the base layer or subgrade, greatly reducing the bearing capacity of the pavement and easily causing water encroachment to occur rapidly.Research and practice show that there is a great relationship between the pavement water permeability coefficient and the void ratio. usually the residual void ratio is large, the greater the pavement water permeability coefficient is, the more serious the pavement water permeability is. through practice comparison, the water permeability coefficient of SBR - II modified asphalt pavement is smaller than that of ordinary asphalt pavement, which shows that the modified asphalt pavement has good waterproof performance.Through comparative analysis, it is proved that the road performance of SBR - II modified asphalt section is better than that of ordinary asphalt section.Greatly improves the strength of the asphalt pavement and the anti-water damage performance.
V. application prospect of SBR - II modified asphalt
Due to the large temperature difference between day and night, hot summer and severe winter weather in Xinjiang, the quality of road asphalt has higher requirements in highway construction.In addition, the massive paving of Xinjiang's high-grade highways also requires asphalt products with superior road performance.However, Xinjiang's asphalt production enterprises can only produce heavy traffic road asphalt with good performance from Karamay refinery. its output is limited, especially during the summer construction season, which cannot meet the current demand of highway construction. therefore, when constructing roads in high temperature and severe cold regions and special sections of high-grade roads, modifying ordinary asphalt is an effective way to improve the performance of asphalt pavement and make up for the insufficient output of heavy traffic asphalt.
Based on the research results of " application research of road modified asphalt in Xinjiang" by Xinjiang traffic research institute and related materials used by foreign countries for modified asphalt mixture, a large number of indoor, outdoor and experimental road observation and analysis show that modified asphalt has excellent durability. asphalt concrete pavement paved with modified asphalt can prolong service life, and the economic benefits brought about by the reduction of maintenance cost and the social benefits caused by avoiding the delay of normal operation due to maintenance are very large. therefore, the research and popularization of SBR modified asphalt can further improve the service quality of Xinjiang road asphalt and provide high-performance pavement for highway construction.
VI. concluding remarks
To sum up, SBR modified asphalt has the characteristics of lower price, stable performance, difficult segregation and more obvious improvement of low temperature cracking resistance among all kinds of modified asphalt.Due to its relatively high viscosity, it can be used to pave not only the conventional asphalt pavement but also the thin layer cover and waterproof layer under the drainage pavement, which has a very broad application prospect.
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