In-situ cold recycling method is to mill and crush the pavement mixture on the original pavement with a high-power pavement milling mixer, then add stabilizer, cement, water (or emulsified asphalt) and aggregate for in-situ mixing at the same time, mix in-situ with a pavement mixer, and finally roll forming. In-situ cold recycling technology is generally suitable for the renovation of asphalt pavement of highway below the first grade with serious diseases, and the pavement after cold recycling generally needs a certain thickness of asphalt overlay.

The advantages of in-situ cold recycling technology are: the original pavement materials can be recycled in situ, which saves the transportation cost of materials; Low energy consumption and little pollution in the construction process; Wide application range. Disadvantages are: the construction quality is difficult to control; Asphalt pavement is generally needed, and the economy of recycling is not obvious.

The key technology of on-site cold recycling is the uniform mixing technology of the added binder (such as emulsified asphalt, foamed asphalt and cement) and the old mixture, and the milling and crushing technology of other old asphalt mixtures is also very important.

Second, the on-site thermal regeneration method

1. Hot-in-place recycling is a process of repairing damaged pavement in situ, which softens the pavement by heating and scoops up pavement garbage. Then mix with asphalt binder, and sometimes you may need to add some new aggregate. Then the recycled materials are re-paved on the original road surface.

2. The advantage of on-site thermal regeneration technology is that the construction speed is fast, and the original pavement materials can be recycled on the spot, saving the material transfer cost.

3. The disadvantage is that the regeneration depth is usually 2.5 ~ 6 cm, which is difficult to go deep; The gradation adjustment of the original pavement materials is limited, and it is difficult to remove the old materials that are not suitable for recycling; The quality stability and durability of recycled pavement are weakened.

4. The heating and remelting technology of hot recycled old asphalt mixture on site, as well as the uniform remixing technology of newly added asphalt and recycled agent with the old mixture are key issues, and the working performance of heating equipment and mixing and paving equipment should be fully considered in the construction process.

5. According to the different pavement damage and the different requirements for the quality grade of repaired pavement, there are three main construction technologies for the application of geothermal regeneration technology.

(1) plastic regeneration method

① Plastic recycling method is suitable for recycling 2 ~ 3 cm surface layer. After the old asphalt pavement is heated to 60 ~ 180℃ by a heater, the pavement is loosened by a recycling machine, and the loosened materials are collected in the mixing tank of the recycling machine. At the same time, add an appropriate amount of asphalt recycling agent into the mixing tank, re-pave the evenly stirred recycled mixture on the road surface, and roll it with a roller.

② It is suitable for repairing pavement with micro cracks, worn layer and small damaged area. After repair, it can eliminate the slight rutting and cracking of the original pavement, restore the smoothness of the pavement and improve the pavement performance.

(2) Reconstruction and regeneration method

(1) is suitable for the regeneration of 4 ~ 6 cm pavement, that is, two heaters are used to heat the old asphalt pavement. The first heating surface temperature can reach 160 ~ 180℃, and the second heating surface temperature will reach 180 ~ 250℃. After twice heating, the asphalt material of the old pavement is softened and then loosened by the main engine of the recycling machine. Collect loose materials in the mixing tank of the main machine of the recycling machine, and add an appropriate amount of asphalt regenerant to stir. Spread the evenly stirred recycled mixture on the pavement as the lower layer of the pavement, and lay a new layer of asphalt mixture on it as the wear layer, thus forming a pavement with brand-new materials. Finally, it is formed by rolling with a roller. The working speed of regenerator is generally 1 ~ 3m/min.

(2) This method is suitable for the maintenance and renovation of severely damaged pavements (such as large-area potholes) and the upgrading of old roads. After repair, a brand-new pavement with the same performance as the new road will be formed. However, this method will increase the elevation of the original pavement, so the number of repeated regeneration of pavement will be limited to some extent.

(3) There are generally two technological methods for rebuilding and recycling:

Method 1: heating → recycling of old materials (scarifying, adding regenerant, stirring, etc.). ) → paving and molding → crushing.

Method 2: heating → recycling old materials (scarifying, adding regenerant, stirring, etc.). ) → paving and molding → covering new surface technology.

④ The basic process flow of these two processes is as follows:

1) heat to soften the pavement.

2) Milling and scarifying the road surface

3) mixing and molding

4) Covering new faces

(3) Mixed regeneration method

The mixed regeneration method is suitable for the regeneration of 4 ~ 6 cm pavement. The method is to use two heaters to heat the old asphalt pavement in stages, and the heating method is basically the same as the resurfacing regeneration method. Milling by the main machine of the recycling machine, and uniformly mixing the milled materials, new asphalt mixture and recycling agent in the mixer of the main machine of the recycling machine to form a new high-quality asphalt mixture. Then spread on the road surface by the main engine or the paving device of the asphalt paver, and roll it with a roller. The process flow is basically the same as paving regeneration method, and the working speed of the regeneration machine is generally 1 ~ 3m/min.

6. To sum up, no matter what kind of in-situ recycling process, the damaged pavement must be sampled and analyzed in advance; Then choose the corresponding construction technology and method, formulate specific construction scheme, and determine the nature and proportion of materials to be added.

Third, the factory mixed hot recycling method

1. Plant-mixed hot recycling method is to dig the old asphalt pavement and transport it back to the mixing station, and then concentrate on crushing it. According to the quality requirements of different grades of pavement, mix design is carried out to determine the addition ratio of old asphalt mixture, and the recycled agent, new asphalt material and new aggregate are re-mixed into new mixture in a blender according to a certain proportion, so as to obtain excellent recycled asphalt concrete and pave recycled asphalt pavement. Recycled asphalt mixture can be used to pave various grades of asphalt pavement or maintain old roads.

2. With this method, the excavated base course and even the subgrade of some road sections can be reinforced conveniently and effectively, and the asphalt layer can be resurfaced according to the different technical requirements of the lower layer, the middle layer and the upper layer (wearing layer), so as to determine the addition ratio of the old asphalt recycled materials, just like a new road.

3. The advantage of plant-mixed hot recycling technology is that the recycling process is easy to control and the performance of recycled asphalt mixture is ideal. If proper mix design and strict quality control measures are adopted, recycled pavement has the same or similar road performance and durability as ordinary asphalt pavement.

4. The disadvantage is the high cost of regeneration.

5. The key technology of plant-mixed hot recycling is to solve the problems of heating and remelting asphalt in old asphalt mixture and accurate measurement of old asphalt mixture.

Typical example

According to the different pavement damage and different requirements for the quality grade of repaired pavement, the construction technology of geothermal regeneration technology mainly includes ().

A. Plastic recycling method B. Surface reconstruction recycling method

C. Mixed regeneration method D. Broken regeneration method

E. indirect regeneration method

Answer ABC

This topic analyzes and investigates the regeneration of old asphalt pavement. In-situ thermal regeneration includes plastic regeneration, surface regeneration and mixed regeneration. See textbook P79.

Can't be used as the old asphalt concrete pavement cold recycling adhesive is ().

A. emulsified asphalt

B. cement

C. lime

D. foamed asphalt

Answer c

This topic analyzes and investigates the regeneration of old asphalt pavement. The key technology of on-site cold recycling is to add adhesive (such as emulsified asphalt, foamed asphalt and cement) and mix the old mixture evenly. See textbook P79.