I. Overview of the Project
This project starts from Zhangyang Road Interchange in the north and ends at Huandongyi Avenue in the east, with a red line width of 100 meter. It is a first-class urban trunk road with 8 lanes in both directions and a total length of 2387 meters. The road structure is asphalt flexible pavement, and the structural layer consists of subgrade+15cm gravel cushion +40cm lime-fly ash macadam base+15cm three-layer asphalt concrete surface. The combination of surface course is as follows: the surface course is modified stone matrix asphalt (SMA-16) 4 cm; The middle course is 6 cm medium-grained modified asphalt concrete (LH-25); The bottom layer is 6 cm coarse-grained modified asphalt concrete (CLH-35); The lower seal layer is 1 cm.
Second, the difficulties in quality control of modified asphalt construction
1. The viscosity of modified asphalt mixture is high, and the construction temperature of each process is higher than that of ordinary asphalt mixture. The temperature drop during storage and transportation shall not exceed 10℃, and the distance between the production plant and the construction site is far. The traffic in Shanghai is busy and the climate changes greatly, so it is difficult to control the storage temperature of the mixture.
2. The quality of asphalt pavement construction is closely related to the performance of pavers, which have various models and different performances. How to choose construction machinery with good performance is the focus of engineering quality control.
3. When paving asphalt, it must be uniform and continuous, the quality of workers must be high, and the paving interface should be judged correctly.
III. Mixing and Construction of SMA Asphalt
1. Asphalt mixture mixing. Because the biggest difference between SMA and ordinary dense graded asphalt concrete is that SMA is discontinuous graded, and the coarse aggregate has a single particle size, a large amount, less fine aggregate and a large amount of mineral powder. Fine aggregate, including stone chips and sand, only needs about 15%, which brings many difficulties to the feeding and mixing of the mixture. Therefore, the hopper and silo should be rearranged, and the aggregate silo with particle size of 5 ~ 10 mm should be added to ensure the quantity of cold materials, while the quantity of fine aggregate is very small, and the door of cold silo is rarely opened. In the process of feeding, fine aggregate should be kept dry to ensure the smooth feeding of fine aggregate. The main belt sends the coarse ingredients into the rolling hole, and the aggregate is heated by the burner. Thermocouple detects the material temperature, and automatically adjusts the air-oil ratio of the burner to make the aggregate temperature reach 190℃ ~ 200℃. Hot materials enter the vibrating screen through the hoist, and the hot materials are screened into different hot bins according to the specification requirements of the target mixture ratio (the screen size can be changed as needed). The computer controls the sliding door of each hot bin to automatically mix and measure according to the input production ratio. Due to the single particle size of SMA coarse materials and less fine materials, hot materials may often be short of coarse silos (short of materials) and fine silos often overflow, so the control room operators cannot adjust the material quantity. Then add the lignin fiber into a stirring pot to dry mix with the aggregate, then add the stone powder and asphalt metered by computer, and finish the production of the finished product after mixing. The dry mixing time of SMA is 4 seconds to 5 seconds, and the wet mixing time is 30 seconds to 45 seconds.
Heating temperature control of various materials: asphalt heating temperature 160℃ ~ 165℃, field manufacturing temperature 165℃ ~ 170℃, maximum processing temperature 175℃, aggregate heating temperature1. The highest mixture temperature (waste temperature) is 195℃, the paving temperature is not lower than 160℃, the initial starting temperature is not lower than 150℃, the lowest recompression temperature is not lower than 130℃, and the final rolling temperature is not lower than 130℃.
2. transportation. Due to the high viscosity of asphalt mastic of SMA asphalt mixture, more oil-water mixture should be coated on the bottom of the carriage of transport vehicles. In order to prevent the mixture on the surface of transport vehicles from forming a hard shell, transport vehicles must be covered with tarpaulin during transportation, and the volume of vehicles should be appropriately increased.
3. pave the road. Asphalt must be spread slowly, evenly and continuously. In the process of paving, it is not allowed to change the speed or stop halfway at will. The paving speed should be determined according to the output of mixer, the supporting conditions of construction machinery and the thickness and width of paving layer. The paving speed is 3.5m/min.
4. Scroll. Rolling process is an important link in surface construction. The eight-character policy of rolling SMA is "following closely, rolling, high frequency and low amplitude", and the combination mode and rolling steps of roller are reasonably selected.
5. seams.
(1) longitudinal joint: according to the characteristics of this project, our unit adopts German ABG423 paver to spread asphalt mixture side by side. In this way, it can be paved into a whole picture at one time, and the longitudinal seam hot joint improves the smoothness of the road surface and beautifies the visual effect of the road surface.
(2) Transverse joint: The joint treatment of SMA pavement is more difficult than ordinary mixture. Therefore, when paving, baffles can be set at the edges, or the asphalt SMA layer can be cut after daily construction and before cooling, and the joints can be washed clean with water. Brush the sticky layer oil the next day, that is, spread a new mixture.
6.6 Problems easy to occur in construction. SMA asphalt mixture:
(1) Over-rolling: SMA pavement has a small degree of compaction due to the embedded aggregate, and it is easy to reach the degree of compaction. However, with the increase of rolling times, the aggregate keeps going down and the hoof fat floats up bit by bit, which leads to the decrease of structural depth. In the rolling process, special attention should be paid to keeping the surface texture at 1 ~ 1.5mm, so as to have a suitable texture depth.
(2) Oil stain: Oil stain on SMA pavement is also a common disease, which is caused by uneven mixing of SMA fibers. Therefore, when mixing, it is necessary to strictly control the number and time of fibers, extend the dry mixing time, and ensure uniform fiber mixing. Also pay attention to the fiber drying during storage to prevent the fiber from getting wet and caking.
(3) It is a common problem that the rolling temperature is not high enough. The rolling effect of SMA at 130℃ is very poor. Uneven rolling is easy to occur at low temperature. Rutting occurs due to insufficient rolling during driving.
Asphalt mastic is a kind of mastic asphalt composed of fiber stabilizer, slag and a small amount of fine aggregate in asphalt mixture, which is filled with discontinuous skeleton space of primary coarse aggregate and extruded to form a dense mesh structure mixture. SMA modified asphalt pavement and SMA are a new type of pavement. SMA modified asphalt mixture is very hard and has high strength after cooling. This paper takes the outer ring road (Pudong), the construction project of Central Avenue in Shanghai, as an example, to talk about how to carry out the construction of modified asphalt pavement and the control of SMA.
I. Project review
The project has a red plot with a road width of 100 m in the east section of Xuanxiang North Road Interchange to the east of Central Avenue, which is used as a class I main road of the city with 8 two-way lanes, with a total length of 2,387 meters. The roadway is in the form of flexible asphalt pavement, and the structural layer is subgrade+15 cm gravel +40 cm ash layer+15 cm three-layer asphalt concrete surface. The surface layer is composed of modified stone matrix asphalt (SMA-16) 4cm, flaky modified asphalt concrete (LH-25) 6cm, coarse-grained modified asphalt concrete (CLH-35) 6cm, and the bottom layer is sealed for 1cm.
Second, the modified asphalt construction quality control is difficult.
1. The viscosity of modified asphalt mixture is high, and the temperature during construction is higher than that of ordinary asphalt mixture. The temperature drop during storage and transportation shall not exceed 65438 00℃, and the distance from the manufacturing plant to the construction site is long. The traffic in Shanghai is busy and the climate changes greatly, so it is difficult to control the storage temperature of the mixture.
2. The performance of asphalt paver is closely related to the construction quality. There are many kinds of asphalt paver with uneven performance. How to choose construction machinery with good performance is the focus of engineering quality control.
3. When paving asphalt, it must be uniform and continuous. Workers must be of high quality and must be able to correctly judge the paving interface.
3. Mixing and construction of SMA asphalt
1. Asphalt mixture mixing. The biggest difference between Jimmy's SMA and ordinary asphalt concrete is that SMA is graded intermittently, and the coarse aggregate has a single particle size and a large number, while the fine aggregate has a small amount of slag. Fine aggregate, including stone chips and sand, is only about 65438 05% in total, which brings many difficulties to the mixing of mixture. Therefore, the hopper and silo are rearranged to increase the position of aggregate with a diameter of 5 to 10 mm, so as to ensure that the quantity of cold and fine aggregate is small, and the door of cold silo is rarely opened, so as to maintain the drying process of fine aggregate and ensure the smooth fine aggregate material. The main ingredients are sent to the rolling burner with thick material belt to heat the aggregate, and the feed temperature is detected by thermocouple and the specific air of the oil burner is automatically adjusted to make the aggregate temperature reach 190℃ ~ 200℃. The hot material enters the vibrating screen of the hoist, and the hot material reaches the specification ratio on the target, and is screened into different hot bins (the screen size can be changed as required). The computer-controlled bin Flamengo automatically produces mixed ingredients and measures according to the entry. Due to the small particle size of a single SMA coarse material and less small material, the hot material may not be collected in the conventional hopper (short of material), and the small hopper often overflows abnormally, so the control room operator cannot adjust the discharge amount. Then add lignin fiber, dry mix it with aggregate in a common mixing pot, add the ratio of powder to asphalt controlled by computer, and stir it, and it is expected to complete the finished product. The dry mixing time of SMA mixture is 4 seconds to 5 seconds, and the wet mixing time is 30 seconds to 45 seconds.
Heating temperature control of various materials: asphalt temperature 160℃ ~ 165℃, field production temperature 165℃ ~ 170℃, maximum processing temperature 175℃, aggregate heating temperature195℃. The discharge temperature of the mixture is 175℃ ~ 185℃, the highest temperature of the mixture (waste temperature) is 65448, the lowest temperature of recompression is not lower than 130℃, the end temperature of rolling is not lower than 130℃, and the starting temperature is not higher than 60℃.
2. transportation. Because the asphalt mastic in SMA asphalt mixture is sticky, and the oil-water mixture at the bottom of the carriage of the transport vehicle is coated more, in order to prevent the mixture on the surface of the transport vehicle from forming a hard shell, the transport vehicle should be covered with tarpaulin during transportation, and the volume of the carriage should be appropriately increased.
3. Paving machine. Asphalt must be slow, even if it is an uninterrupted paver. In the process of paving, it is not allowed to change the speed at will or stop halfway. The paving speed should be determined according to the production mixing, matching and paving thickness and width of construction machinery. The paving speed is 3.5m/min.
4.RCC。 Roller compacted concrete is an important link in the construction process. On the basis of the SMA eight-character principle of roller compacted concrete, the composition and rolling steps of roller are reasonably selected.
5. Joints.
(1) longitudinal joint: according to the engineering characteristics, our unit adopts a German ABG423 paver to pave side by side in the process of paving asphalt mixture. This method can longitudinally joint the whole paver to increase the smoothness of the road surface and beautify the visual effect of the road surface.
(2) Joints: The joint treatment of SMA pavement is more difficult than ordinary mixture. Therefore, a baffle can be set at the paving edge, or the SMA asphalt layer can be cut one day after the construction is completed before it is cooled, and the joints can be cleaned with clean water. The next day, paint the oil with viscosity, that is, the newly paved mixture.
6. Problems easily occurred in the construction of 6.SMA asphalt mixture:
(1) Rolling: Due to the aggregate embedded in SMA pavement, the degree of compaction is not enough, and it is easy to achieve. However, with the increase of rolling times, the aggregate continues to go down, and the sand glue floats up a little, resulting in the decrease of structural depth. During the rolling process, pay special attention to keep the surface structure at 1 to1.5mm, so as to have a proper structural depth.
(2) Oil stain: It is a common disease that oil stain appears on the pavement after SMA paving, which is caused by uneven mixing of SMA fibers. Therefore, when mixing, it is necessary to strictly control the number and running time of fibers and extend the dry mixing time to ensure uniform fiber mixing. We must pay attention to the dry fiber during storage to prevent the fiber from being exposed to moisture and entering the university.
(3) It is a common fault that the forming temperature of RCC is not high enough. SMA has poor effect on 130℃ RCC. It is not easy to form when it is rolled at low temperature. In the process of rutting in the driveway, due to insufficient rolling.
You can try this book Road and Bridge, an American magazine.
You can read some core journals in the industry, such as "China Highway Transportation and Mechanics", and you can also read the journals of various schools, such as Tongji University, Harbin Institute of Technology, Chang 'an University, or some teaching materials can also be used as reference.