First, the rubber asphalt stress absorption layer Sammy
The reflection cracks in K6 1+589-K7 1+902 Baijiahei section of Beijing-Zhuhai Expressway are serious, and there is a transverse crack every 5- 10. In order to solve the cracks reflected by cement pavement slab joints in Baijiahei section, a rubber asphalt stress absorption layer SAMI was laid on the pavement in 2009.
1, application materials and technical indicators
(1) Base asphalt: No.70 road petroleum asphalt is adopted, and all technical indexes meet the requirements of technical specifications after testing.
(2) Rubber asphalt: waste tire rubber powder is 40 mesh bias tire rubber powder ground and crushed at normal temperature, and the rubber powder mixing ratio in the test section is 22%, which is processed on site by wet mixing batch process.
2. Sami construction technology of rubber asphalt stress absorption layer
(1) Clean the lower bearing layer before construction. Before spreading rubber asphalt, arrange construction personnel to clean the construction working face with portable hair dryer to ensure that the working face is clean and dry.
(2) Spreading rubber asphalt: Use a special asphalt spreader with heating, heat preservation and stirring functions to spread rubber asphalt. During paving, the paver keeps running at a constant speed, the designed paving amount is about 2.0 ~ 2.4 kg/m2, and the paving temperature is controlled within the range of 180~ 190℃. In the pavement treatment project of Guangzhou-Zhuhai section of Beijing-Zhuhai Expressway, the overlay thickness is only 3cm. In actual construction, some places are flooded due to the large amount of paving. In this case, it is more appropriate to change the paving quantity to 1.8 ~ 2.0 kg/m2.
(3) After the rubber asphalt is spread, the ready-mixed macadam is spread in time, and the spreading amount is 60-70% of the area coverage, and the macadam specification is 6- 1 1 mm single-particle ready-mixed macadam, and the spreading amount is controlled at 10kg/m2.
(4) After paving the macadam, follow the macadam paving vehicle with a heavy rubber-tyred roller 1 ~ 2 times in time, and prohibit the traffic, and arrange paving the asphalt mixture as soon as possible.
3. Quality control of SAMI construction of rubber asphalt stress absorption layer
(1) In order to ensure that the paving quantity of rubber asphalt and ready-mixed macadam meets the requirements, tests should be conducted before construction, and the paving quantity of equipment should be adjusted.
(2) When the asphalt distributor starts, if the asphalt quantity is uneven or the asphalt is sprayed into blocks, asphalt paper can be used to cover the starting section to protect the working face. When the amount of asphalt in asphalt distributor is small, uneven distribution and leakage will occur. When the asphalt distributor is short of asphalt, stop the construction and continue the construction after filling it with asphalt.
(3) In the process of construction, assign special personnel to follow behind the distributor. When asphalt caking is found, it should be removed in time. When gravel is found to overlap and spread, excess gravel should be removed.
Second, the stress absorption layer of high elastic modified asphalt
With the rapid growth of expressway traffic volume of Humen Bridge, serious longitudinal and transverse reflection cracks appear on asphalt pavement in subgrade section. In order to solve the reflection cracks on the pavement, in 2006, a 2.5cm high elastic modified asphalt stress absorption layer SAWFTL was added to the pavement maintenance, and then it was covered. The application mechanism of SAWFTL, a stress absorbing layer of high elasticity modified asphalt, is to absorb and disperse stress and prevent cracks from reflecting to the surface layer, which can not only prevent cracks from reflecting at the base, but also prevent rainwater from infiltrating into the base and prolong the service life of asphalt pavement.
1, application materials and mix design
The cementing material of stress absorption layer is SBS modified asphalt, a special polymer produced by Guangzhou Lu Xiang Company, which has high high temperature viscosity and low temperature ductility, good high temperature stability and low temperature fatigue resistance. The aggregate mainly adopts diabase machine-made sand, stone chips and Yunfu limestone powder from Shenzhen Furong Stone Field, and the technical indexes of each aggregate meet the requirements of the specification. In the target mixture ratio, machine-made sand accounts for 66%, stone chips account for 26% and mineral powder accounts for 8%. After secondary screening and hot bin sampling, the production mix ratio was finally determined as follows: 1# hot bin 55%, 2# hot bin 4 1%, mineral powder 4%, and the optimal oil-stone ratio was 9.0.
2. Mixing the mixture of stress absorption layer
Fine aggregate less than 2.36mm in aggregate accounts for about 70% ~ 80% of aggregate, so it is difficult to mix. The content of mineral powder in stone chips is very high, so it is necessary to remove some dust by increasing the air intake. Because of the existence of a large number of fine aggregates, the screening efficiency of the powder screen in the vibrating screen is greatly reduced, and the corresponding screen hole of 2.36mm should be 3.5 mm, otherwise, the excessive channeling rate will make the mixture gradation difficult to stabilize. Dry mixing time is 10S, wet mixing time is 50 ~ 55s, and mixing temperature is 175 ~ 180℃, which shall not exceed 190℃.
3. Laying and rolling of stress absorbing layer
Before paving the stress absorption layer, a layer of 1.2kg/m2 hot asphalt adhesive layer should be sprinkled, and 3 ~ 5 mm ready-mixed macadam should be sprinkled on it before paving the stress absorption layer. Stress absorption paving should ensure uniform thickness. Rolling should follow the principle of "following closely, slowly pressing, high frequency and low amplitude", and pay special attention to the selection of roller tonnage. According to the site construction, Ingersoll Rand DD 1 10 steel wheel roller was used for rolling in the test section, and the wheel sticking was very serious. After analyzing the reasons, use the small-tonnage CC2 1 1 steel roller immediately. Therefore, it is advisable to roll 1 ~ 2 times with a small tonnage steel wheel roller of 8 ~ 10 ton, and then roll 2 ~ 3 times with a rigid wheel roller of 10 ~ 16 ton. Rubber rollers are not allowed. In addition, because the stress absorption layer is very thin, the paving and rolling temperature must be well controlled. The paving temperature should be controlled around 165℃, the initial pressure temperature should be around 160℃, the rolling work should be completed around 90℃, and the traffic can be liberated only when the temperature is lower than 50℃.
4. Quality management
The average thickness of (1) stress absorption layer is 2.5cm, which should be controlled within the range of (2.5±0.5)cm. (2) The stress absorption layer should be compacted by rotating method, with rotational moulding pressure of 600Kpa, compaction times of 50 times, void ratio of 0.5% ~ 2.5%, VMA≥ 19% and VFA index of 85% ~ 98%. (3) Because the porosity of the stress absorption layer is very small, the moisture on the compacted subgrade cannot be discharged after evaporation, and some small air pockets may be formed, which should be punctured. (4) The compaction density is (97 2)% of the maximum theoretical density. After compaction, the porosity is controlled at 65438 0% ~ 5%.
Three. Concluding remarks
As a preventive measure of asphalt pavement cracks, stress absorption layer has been widely used in various expressways in recent years. The paper has the properties of delaying the generation of reflective cracks and waterproof. In 2006, SAWFTL, a high elastic stress absorbing layer of modified asphalt, was built on the base section of the east approach road of Humen Bridge Expressway, with a cumulative half width of 5.5km. Federation of Trade Unions of Saudi Arabia, 2007-2008; The stress absorption layer of high elastic modified asphalt was laid on the base of the west approach road of Humen Bridge Expressway. In 2009, a two-way rubber asphalt stress absorption layer with a length of 10km was built in Guangzhu section of Beijing-Zhuhai Expressway. Through the successful implementation of these test sections, it is believed that the stress absorption layer will be widely used in the prevention and treatment of reflective cracks in asphalt pavement in Guangdong Province.
For more information about bidding for projects/services/procurement, and to improve the winning rate, please click on the bottom of official website Customer Service for free consultation: /#/bid.