I. Mechanism of action
In-situ cold recycling technology refers to making full use of the existing old pavement materials (surface and base), adding additives (foamed asphalt, cement) and appropriate amount of water according to the new design requirements, continuously milling, crushing, mixing and paving the old asphalt pavement in natural environment, and then leveling, compacting and curing to form a new pavement base with satisfactory performance and quality.
Second, the case analysis
Handan county section of National Highway 309 is an important channel for Shanxi coal transportation to the east, and it is also the export of Handan city to the east. With the rapid increase of traffic volume, subgrade subsidence and frost boiling have occurred in some sections, which can no longer meet the driving requirements. According to this situation, in July, 2006, the Maintenance Department of Handan City overhauled and reconstructed the K785+100-K788+100 section of the highway, and adopted the cold recycling technology of the old asphalt pavement in the project.
1. Preparation before regeneration
(1) Clean and treat the original pavement. Before construction, the original pavement should be cleaned to avoid impurities mixing into the mixture and affecting the quality of cold recycled base. For frost boiling and subgrade subsidence, it is necessary to deal with them in advance.
(2) Determine the regeneration range. According to the width of the old pavement to be recycled, the working width of the recycling machine and the overlapping width of two adjacent roads, the number of recycling ranges is determined. The pavement width of National Highway 309 is 12m, the working width of each recycling machine is 2. 1m, the overlapping width of every two adjacent recycling layers is 12cm, and the number of recycling frames is 6.
2. Regeneration process
(1) Determine the length of the reclamation section. According to the initial setting and final setting time of additives, weather changes and the configuration of mechanical equipment, the length of primary regeneration section is determined. According to the principle that the length of each regeneration is 300 meters, we can construct two regeneration sections every day, with a total length of 600 meters and an equivalent area of 7200 square meters.
(2) the first crushing. When crushing, adjust the working width of the reclaimer according to the number of recycled frames, road width and overlapping width of two pieces, and add water slightly lower than the optimal water content for crushing. The first crushing depth is lower than the depth to be regenerated (1㎝~1.5 ㎝, (15 ㎝ ~14.5 ㎝) to avoid the second crushing.
(3) the second crushing. After the initial leveling of the first broken section, calculate the dosage per square meter according to the required dosage, and make a grid to determine the dosage. Then spread out the cement and additives on the one in front of the recycling machine and mix them evenly. The paving length depends on the speed of the recycling machine, generally 5- 10 meters away from the recycling machine to ensure the normal work of the recycling machine. The regeneration depth should reach the required depth (16㎝) (deeper than the first time, 1- 1.5 ㎝), and the water content, depth and overlapping of two pictures should be observed by special personnel at any time during the regeneration process. When the regeneration reaches about half of the working length, a roller is used behind the regeneration machine to stabilize the regeneration layer at low speed, so that the recycled material can be initially compacted.
(4) forming and compacting. After a working section is completely regenerated and initially compacted, leveling should be carried out, which includes adjusting the horizontal and vertical slopes of the reclaimed layer and eliminating the wheel tracks of the reclaimed layer. After the completion of full-width regeneration, point leveling shall be carried out immediately, with one gray point every 20 meters in the longitudinal direction and five gray points in each cross section in the transverse direction. When the grader looks for it, someone will be assigned to look after the gray spots to avoid damage. If there is any damage, retest the grey spots in time until the whole section of the whole regeneration section is completely flat and reaches the required elevation and cross slope, and then roll it immediately. When rolling, use 16t vibratory roller for light vibration 1 time, then strong vibration for 2 times, and finally use 18t-2 1t three-wheel roller for static pressure for 2-3 times. During rolling, recycled materials should be watered at any time according to weather conditions and water content; During the rolling process, the roller shall not brake, stop or turn around at any time on the rolling section.
(4) Combined therapy. There will inevitably be work stoppage during the construction, and the joint treatment of the two constructions is very important, which should be dealt with seriously to avoid potential quality problems. When restarting after temporary shutdown, the whole regeneration device should retreat 1-2m to reach the regenerated materials, so as to ensure that all materials are treated after the start of construction. When the last operation section is compacted in real time, 3-5m shall be reserved for no rolling. When the next section is regenerated, it should be regenerated at the same time. During leveling, the grader should also walk 3-5 meters on the leveled road section and start leveling to ensure the smoothness of the joint.
keep fit
After the compaction of the reclamation layer is completed, sprinklers should be used for health preservation to prevent the surface of the reclamation layer from dehydration and dryness, and the number of sprinklers per day depends on the weather. During the whole curing period, the surface of the recycled layer should always be moist to avoid dryness or wetness. During the maintenance period, except the sprinkler, the traffic should be closed, and the maintenance period is 7 days.
To sum up, the application of cold recycling technology in the maintenance and reconstruction of old roads can greatly simplify the construction technology, save materials, shorten the construction period, be conducive to waste disposal and protect the environment, and have remarkable economic and social benefits.
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