** modified asphalt pavement
SBR modified asphalt is based on the original matrix asphalt of ah-90, adding 3% butadiene rubber. Compared with the original asphalt, the modified asphalt has a higher viscosity and a higher softening point, and the durability and high temperature stability of the asphalt pavement are obviously improved under the favorable design mix ratio and construction conditions.
1. SBR modified asphalt mixture test.
1.1 raw material requirements
1.1.1 Coarse aggregate
Used in the surface of the modified asphalt mixture coarse aggregate, appropriate USES gravel or broken gravel, its particle size specification and quality requirements shall be in accordance with the provisions of the "technical specification for construction of highway asphalt pavement: (1) coarse aggregate should be clean, dry, no weathering, no harmful impurities, and has a certain hardness and strength. The coarse aggregate should have a good particle shape, and when the gravel is used for highway and first-grade highway, it should be broken by large gravel, and at least two more crushing surface should be used. For anti-skid surface coarse aggregate, hard rock (neutral or base igneous rock) should be selected. Due to the great difference in adhesion between hard rock and asphalt, the adhesion of coarse aggregate and asphalt should not be less than 4. It is suggested to use hard rock chips for the low content of 3mm ~ 5mm stone cuttings, and this part has a certain effect on the formation of inlay structure of asphalt mixture.
1.1.2 Fine aggregate
The fine aggregate includes artificial sand and natural sand. Artificial sand should be used as fine aggregate for asphalt pavement surface layer. Fine aggregate should be clean, dry, no weathering, no impurities, and suitable granules should be matched. Hot mix - intensive mixture, natural sand content should not exceed 20%.
1.1.3 Filling material
The filler used for modified asphalt mixture shall be clean and dry, and its technical specifications shall meet the technical requirements stipulated in the technical specification for road asphalt pavement. It is advisable to use strong base rock, limestone, magmatic rock and other hydrophobic stone materials to be finely ground. It is not recommended to use the mixture in the mixture to produce the powder. When the plastic index is less than 4, the amount of recycled powder should not exceed 1/4 of the total amount of the mineral powder.
1.2 The technical requirements of SBR modified asphalt.
1.3 attention problems of SBR modified asphalt test.
(1) Sampling of test samples. The modified asphalt used in the construction process must be inspected. Sample must be uniform and representative. For each sample, it should be heated to fill the required test mode once, and should not be used for repeated heating. Test pouring mold temperature must be above 170 ℃, and the sample before pouring mold and mixture preparation, must fully stir well.
(2) When making softening point test, the sample must be according to the test procedures after heated to a sufficient flow, casting sample rings, are not allowed to use other ways to fill ring sample, otherwise the test result error is very large.
2. Mix design.
Modified asphalt mixture ratio design, which should be followed in "technical specification for construction of highway asphalt pavement of hot mix asphalt mixture proportioning design target, production design and production validation of mix proportions three phases, in order to determine mineral aggregate gradation and the optimum asphalt content.
2.1 on the Richter scale
The grading selection principle should be adopted for the design level of asphalt mixture proportioning. The size of the sieve hole under the AC- 20-i type mixture 4.75mm shall be taken to the lower limit to achieve compaction and inlay.
Powder than 2.2
The amount of mineral powder has great influence on the volume index and usability of asphalt mixture. The content of the mixture gradation less than 0.075mm must consider the dust part contained in the coarse aggregate. It is required that the content of mineral powder should not exceed the content of bitumen, which is less than 0.075mm and the ratio between the content of asphalt and that of asphalt is between 1 and 1.2.
2.3 Technical indicators of mixed materials.
To effectively improve the performance of asphalt pavement surface layer asphalt mixture for secrete water conditions on one hand, on the other hand, to prevent super dense phenomenon, therefore, need further on asphalt mixture volume index.
2.4 precautions
In the design process of modified asphalt mixture, the following problems should be noticed:
(1) The mixing and compaction temperature of the mixture shall be determined according to the technical specification of the modified asphalt pavement and the viscosity-temperature relationship curve of asphalt cement. The mixing and beating temperature should be consistent with the mixing temperature and the ground rolling temperature of the mixing plant. According to the conditions in the test and construction, the recommended temperature is as follows:
Test and construction temperature of modified asphalt.
| Stage | temperature control |
| Mixing temperature | ≥170℃ |
| Initial pressure temperature | ≥160℃ |
| After pressure temperature | ≥140℃ |
| Pressure temperature | ≥120℃ |
(2) To ensure the uniformity of the bituminous samples when sampling, the preparation of samples and mixtures should be carried out after mixing and mixing.
(3) The determination of the volume index of the mixed material should be unified, and the method of table dry method should be adopted for the determination of the density of the test pieces of the mixed asphalt mixture. (4) the water stability of asphalt mixture should also conform to the requirements of the following two indicators, we cannot meet the requirements when the antis tripping measures should be taken: (1) using the asphalt mixture Marshall stability test method for determining the 48 h after flooding, the residual stability should not be less than 80%. The ratio of splitting strength measured by the method of "asphalt mixture freezing-thawing test" should not be less than 80%.
3. Construction of SBR modified asphalt mixture.
3.1 Technical requirements for transportation.
SBR modified asphalt in factory loading temperature must be kept between 160 ℃ ~ 165 ℃, and shipped to the temperature of the mixture mixing plant should not be below 160 ℃. Transport vehicles should be transported to designated locations as soon as possible.
3.2 Technical requirements for the storage of asphalt mixtures.
SBR modified asphalt storage temperature should be kept at about 160 ℃, if the temperature is lower than the required storage temperature, due to the large of SBR modified asphalt viscosity, leading to asphalt tank tubing road congestion, finally can only production of repair. Bituminous hot mixing plant should minimize the storage of SBR modified asphalt, so that it can be used as it is used. It should be saved in time, and it should not be stored for too long. Most is horizontal, asphalt mixing plant storage tanks to guarantee the uniformity of SBR modified asphalt, shall be installed on the top of the tank agitator, or use the tank with agitator, blender once every 3 h mixing, the mixing time for every 20 min.
3.3 Technical requirements for pumping.
SBR modified asphalt transportation, storage temperature, the demand is higher, when the production mix require pump to pump asphalt to mixture in the mixer, due to the asphalt pump with a filter easily by certain material blocked filter mesh, which affect the pumping capacity of asphalt, recommend the use of large mesh filter (9.5 mm) above, at the same time strengthening the asphalt pipeline heat preservation measures, in order to prevent the pipeline of SBR modified asphalt temperature lower block pipeline.
3.4 Technical requirements for mixing and transportation.
In order to ensure the quality of asphalt mixture is more stable and the asphalt dosage is more accurate, it is advisable to mix and mix with the gap type mixer. Because of SBR modified asphalt mixture construction high temperature requirement, suggest the mixing temperature control at 170 ℃. Mixing must be uniform, only the SBR modified asphalt modifier completely dispersed in the asphalt, can give full play to its effectiveness, for dense with mixture, should do after mixing the mixture of uniform, fine and coarse material separation and grey, the phenomenon of cluster into pieces. The transport vehicle must be covered with a cover or other insulating material to prevent the binding surface from hardening.
3.5 Technical requirements for the stall.
The SBR modified asphalt mixture should be continuously constructed during the paving, so as to reduce the stopping of the paver and the roller, and reduce the horizontal seam as much as possible, so as to improve the flatness of the surface layer. The surface layer should be used to maintain the same height of the sleigh with the same height. Since SBR modified asphalt has a large viscosity and strong adhesion force, the spreading speed should be controlled at 2m/min, and it can be spread slowly, evenly and continuously, without changing speed or stopping at random. Improve the paving process of preloading compactness, SBR - II - B modified asphalt mixture under high temperature condition is mainly rely on embedded squeeze effect of coarse aggregate, can be appropriately increase rammer vibrating frequency, reduce residual compaction coefficient, the early pressure traces of tiny, also further ensure the final pavement roughness.
3.6 Technical requirements for RCC.
For dense matches mixture, the suitable rolling temperature is 140 ℃ ~ 160 ℃, its final rolling surface temperature is not lower than 90 ℃. The compaction process of SBR modified asphalt mixture is based on the following principles:
According to the "follow up, slow pressure, high frequency, low amplitude" of the eight - word policy. The roller must be followed by the paver, only under high temperature conditions to achieve a better effect. The compaction speed is controlled at 4km/h ~ 5km/h. Closed when vibration rolling speed is balanced, decay, the direction to gradually change, no twist curved to walk, for each rolling start or finish a little twist roll rolling, to eliminate rolling wheel track joint. Never allow a new asphalt mixture to be turned, turned around, left and right moving position, sudden braking or parking rest.
4. The conclusion
Compared with petroleum pitch, SBR modified asphalt has many characteristics such as high viscosity and large softening point, and its durability and high temperature stability have also been improved significantly. With the further promotion of SBR modified asphalt, it will play an important role in highway construction.
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