With the development of society, people's requirements for driving comfort and understanding of engineering quality have changed greatly. It is urgent to improve the grade and smoothness of pavement, and the engineering quality is more concerned by the society, so higher requirements are put forward for pavement construction technology, construction level and construction quality.
1, reasonable selection of engineering materials
1. 1 asphalt materials For incoming asphalt, the shipment quantity, date of shipment and test report shall be strictly checked, and sampling inspection shall be conducted at the same time. The inspection items include penetration, softening point, ductility, wax content and density.
1.2 The preparation of mineral aggregate should meet the following requirements: mainly check whether the technical standards such as stone grade, saturated compressive strength, wear rate, crushing value and adhesion between stone and asphalt meet the requirements, and should meet the requirements of hardness, cleanliness, dryness, no weathering, no impurities, water content less than 3%, mud content less than 1% and particle shape similar to cube and polygon. The quality of sand should be hard, clean, dry, free from weathering and impurities, with appropriate particle composition and soil content less than 3%.
2, construction equipment preparation
2. 1 Mixing equipment Intermittent asphalt concrete mixer should be used for mixing equipment, which can screen the aggregate twice, with accurate and stable measurement and high equipment integrity rate. The mixing building should have automatic recording equipment, which can show the dosage of asphalt and various mineral materials and the mixing temperature during mixing.
2.2 transport equipment transport equipment should use a dump truck with a clean metal floor, and organic substances should not be stuck in the car trough. The transport capacity of transport vehicles should be greater than the mixing capacity or paving speed to ensure continuous paving.
2.3 Paving and compaction equipment Paver shall have the functions of automatic leveling and high-precision vibration tamping. The screed should also be able to heat and spread automatically within the lane width according to the specified typical cross section and thickness as shown in the drawings. The paver should be equipped with automatic control device of leveling plate, and sensors are installed on both sides. The elevation and smoothness can be controlled by reference lines and datum points, and the ideal vertical and horizontal slopes can be paved. Compaction equipment shall be equipped with vibratory roller, tire roller and static roller, and shall be compacted according to reasonable compaction technology.
3. Composition design of asphalt macadam mixture
3. 1 Design asphalt macadam mixture with target mixture ratio, which consists of coarse aggregate, fine aggregate, mineral powder and asphalt. Components should be classified according to particle size and have good gradation. And should be as close as possible to the grading range and the middle value. According to the test regulations and simulated production, 6 different asphalt dosage ranges of 0.5% were mixed with mineral aggregate in the laboratory. The density, stability and flow value of the specimen are determined by Marshall test, and the porosity and asphalt saturation are calculated to determine the optimal asphalt content. This work is a reflection of technology and experience, and should be operated by a skilled test engineer to ensure that the test method is correct and the results are reliable. If necessary, parallel tests should be conducted. With mineral aggregate gradation and asphalt content as the target mixture ratio.
3.2 In the design of production mix ratio, all the screened materials entering the mixer's cold and hot silos must be re-sampled and screened and adjusted, so that all the materials in production can meet the requirements of target mix ratio, and the material mix ratio of each hot silo is determined for use in the mixer control room. At the same time, the cold bin and the feeding bin are repeatedly adjusted to achieve the feeding balance, and Marshall test is carried out to determine the optimal asphalt content of the production mixture ratio.
3.3 Verification of production ratio The mixer uses the production ratio to conduct trial mixing and paving test section, and uses the mixed asphalt mixture and the core samples drilled on the road to conduct Marshall test, mineral screening and asphalt dosage inspection, so as to determine the standard mixture ratio for production, which is the basis for production control and the standard for quality inspection. During the construction, it shall not be changed at will to ensure that all indicators meet the requirements and the standard deviation is as small as possible. At the same time, the following contents should be determined in the test to provide various data for large-scale construction.
Reasonable machinery, machinery quantity and combination mode; The feeding speed, mixing amount and mixing temperature of the mixer; Paving temperature and speed, rolling sequence, temperature, speed and times; Determine the loose laying coefficient and joint method; Verify the asphalt mixture ratio.
4, asphalt mixture mixing
4. 1 coarse and fine aggregates should be piled up and fed by classification, and aggregates of various specifications, mineral powder and asphalt must be mixed according to the required proportion.
4.2 Intermittent mixer shall ensure uniform feeding, continuous metering and less loss of mineral powder.
4.3 The heating ex-factory temperature of various materials and asphalt mixture shall comply with the provisions in the table below.
4.4 The mixing time of the mixture should be such that all particles of the aggregate can be evenly wrapped with binder, and the asphalt mixture after mixing should be uniform without ashing, separation of coarse and fine materials and caking. It is suggested that the dry mixing time should be no less than 5S, and the mixing time for each pot should be 30S-50S. All overheated or carbonized and foamed mixtures should be discarded.
5. Asphalt mixture transportation
5. 1 When loading materials from the mixer to the truck, the truck should be moved for each barrel of mixture to reduce the segregation of coarse and fine aggregates.
5.2 When the transportation time exceeds half an hour or the weather temperature is lower than 10℃, the material carrier shall be covered with tarpaulin.
5.3 In the process of continuous paving, the truck should stop in front of the paver 10-30cm, and shall not hit the paver. During unloading, the truck should be placed in neutral position and pushed forward by the paver.
6. Laying of mixture
6. 1 Before paving the mixture, the lower bearing layer must be inspected. The lower bearing layer should be dry and clean without any loose stones, dust and impurities. Before the surface layer is laid, the smoothness of the bottom layer should be tested, especially at the bridge head and joints. Those that fail to meet the smoothness requirements should be treated.
6.2 The paving of asphalt mixture shall not be carried out in rainy days, when water accumulates on the road surface and the average temperature is lower than 10℃.
6.3 Paver must maintain the continuity of paving and drive at a constant speed. It is not allowed to change the speed or stop halfway to ensure uniform mixing.
6.4 The operation of the paver should not make the mixture accumulate on both sides of the receiving hopper, and any mixture cooled below the specified temperature should be removed.
6.5 In order to ensure the elevation and smoothness of asphalt pavement, the paving thickness of the lower layer adopts the elevation control method guided by steel wires on both sides, and the elevation of steel wire vertices on the skeleton is strictly measured. The upper layer adopts the "sliding" paving thickness control mode with the same height difference, because it combines the automatic adjustment of paving thickness on the paver, which not only ensures the design elevation and paving thickness, but also improves the smoothness of the paving layer.
7. Compaction of the mixture
7. 1 Compaction is divided into three stages: initial compaction, secondary compaction and final compaction. The roller should run at a uniform speed, and the roller speed should meet the requirements in the table below.
7.2 Rolling shall be carried out when the temperature is high after paving. In general, the initial pressure and temperature should not be lower than 130℃. The higher the temperature, the easier it is to improve the smoothness and compactness of pavement. The initial pressure should be carried out at a low speed to avoid pushing the hot material and cracking it.
7.3 In order to improve the smoothness of road surface and ensure good compaction effect, double steel roller is used for initial compaction, and the paving layer should be stabilized first. Tire roller for recompression, in the rolling process, the structural layer is compacted due to the kneading effect of tires on the paving layer mixture, which is the main stage of structural layer forming; Final pressing is carried out with a steel wheel roller, so that the wheel tracks on the surface of the spreading layer are eliminated and finally rolled and formed.
7.4 In the rolling process, the rolling overlap is 1/2 wheel width. In order to ensure the smoothness of the surface layer, it is forbidden to brake and stop the roller back and forth, so as to avoid paving the paving layer. The positions of the two ends should retreat and move forward with the rolling section.
8. Joint processing
8. 1 Longitudinal joints shall be continuous and parallel, and shall be hot joints. Two pavers are used for paving, and echelon paving is used, and the minimum spacing between pavers is kept at about 15m; When using paver, the travel of paver should be strictly controlled, so that the length of longitudinal joint can always meet the requirements of hot joint.
8.2 The mixture on the longitudinal joints shall be rolled by the static steel wheel roller behind the paver. Rolling shall be continued until the joint is smooth and dense.
8.3 The dislocation between the upper and lower layers of longitudinal joints shall be at least 15cm.
8.4 Transverse joints shall be at right angles to the paving direction, and oblique joints are strictly prohibited. The transverse joints between adjacent horizontal planes and adjacent strokes shall be staggered by at least 1m and have vertical edges. Before paving in the next trip, an appropriate amount of viscous asphalt should be painted at the end of the last trip, and the height of the whole board should be set to leave appropriate reserves for rolling.
9. Treatment of Surface Smoothness The surface smoothness of paving layer is an important symbol of asphalt pavement quality. In order to make the paving layer uniform, the following technical measures can be taken according to experience during construction.
9. 1 Adjust the mineral aggregate gradation appropriately. Within the allowable range of the specification, the particle amount between the maximum particle size dmax and Dmax/2 should be increased appropriately, and the percentage of particles below dmax/2 should be close to the median value of the specification.
9.2 Adjust the screw feeder of asphalt paver to the best state, so that the height of asphalt mixture in the screw feeder submerges 2/3 of the screw diameter, and adjust the distance between the front edge of screed and the screw of the feeder to the middle position.
9.3 In the process of loading the mixture, the hopper moves back and forth, so as to avoid forming a conical pile and separating coarse and fine particles.
9.4 Pay attention to the operation procedures of paver hopper to reduce the segregation of coarse and fine materials. The hopper of the paver shall be received when the scraper is not exposed and there is still hot material with a thickness of about 10cm, and when the material carrier just exits. And when the two wings of the hopper just return to the original position, the next car will also start unloading.
10, conclusion
Asphalt mixture surface is the key of the whole project, which must be paid great attention to during construction, and fully prepared from the aspects of equipment selection, technical preparation, construction technology and guarantee measures, which is the key to ensure the quality of the project. Therefore, in the process of construction, we must resolutely control the following aspects:
1. Mixing, transportation, paving and compaction equipment shall be sufficient and have good performance.
2. The raw materials must meet the requirements, and the feeding point must be strictly controlled. Ensure the accurate mixture ratio of asphalt mixture.
3. The surface should strictly control the elevation, thickness and smoothness.
4. The construction compaction degree should be tracked and detected on site.
5. Before laying the surface layer, the smoothness of the bottom layer should be tested, especially at the bridge head and joints. Anyone who can't meet the requirements of ride comfort or has obvious feeling during driving should be treated until the requirements are met.
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