With the development of the national economy, China's road transport has shown a situation of large flows and heavy loads. Therefore, the technical performance of a large number of early-built highways is far from being able to meet the needs of the modern situation. As far as the current situation in Hebei Province is concerned, most of the provincial highways and county-level local roads were built before the 1980s. These highways have low technical grades, poor carrying capacity, and have been severely damaged, and urgently need technical renovation.

     In terms of old asphalt pavement reconstruction, Handan City, Langfang City, and Shijiazhuang City, Hebei Province have introduced in-situ cold-recycling equipment for asphalt pavement, and conducted large-scale construction attempts, all of which have achieved good economic and social benefits. Practice has proved that it is scientific and feasible to use in-situ cold-recycling construction technology to retrofit old asphalt pavements in accordance with the current status of highways in our province.

 

    1. Construction principle of cold-in-place regeneration Cold-in-place regeneration of asphalt pavement is not what people usually understand is to restore the damaged asphalt pavement to its original state, but to mix and mix the old surface layer and some base layers together. Afterwards, it was converted into a new base layer (or sub-base layer). Strictly speaking, this process should be called in-situ reuse of old asphalt pavement materials. The working principle of pavement cold regeneration in situ is based on the original old road pavement and in accordance with new design requirements, the appropriate amount of aggregate, cement, lime, fly ash, emulsified asphalt, foamed asphalt and Water and other external materials, using in-situ Road cold recycler equipment, is actually a large-scale stable soil road mixer.) At natural and normal temperature, the old pavement (pavement and part of the base) is continuously milled, crushed, Adding materials, mixing, paving, etc., followed by screeding and rolling, finally build a special graded road base (or sub-base).

    2. Scope and advantages of in-situ Road cold recycler As the in-situ Road cold recycler construction changes the surface and base of the original road into a new road base (or subbase), the surface of the new road must be at least elevated at this level Paving has begun on the basis of road construction. Moreover, in the reconstruction of high-standard roads, sometimes the regeneration layer is used as the base layer, and base materials such as fly ash and gravel are added on top of this. This makes the road surface after the transformation far higher. Much higher than the original elevation of the pavement, the design structure of the pavement at the structures along the road will change accordingly. If this method is used in urban road construction, the original drainage system will also be affected. Therefore, it is not suitable to use this method for roads with stricter elevation restrictions.

    Although the applicable range of in-situ Road cold recycler is limited by the elevation of the road surface, in the vast majority of general road reconstructions, compared with traditional construction methods, it still has many advantages.

    (1) Simple process As the original old pavement materials are all used in situ, a series of tasks such as excavation, transportation, and backfilling have been omitted, which greatly simplified the construction process.

    (2) Lower cost Some foreign construction materials show that compared with traditional construction methods, because the old road materials can be fully used, the cost can be reduced by 20% to 46% with the difference in the thickness of the regeneration layer. The deeper the thickness, the more the cost is reduced. At present, there is not much data summarized in this area in China, but from the results of the quota measurement performed by our province on the construction method, it is certain that this process can reduce the engineering cost.

    (3) Improve the road grade As the construction method strengthens the foundation's bearing capacity # If the new design grading is reasonable, the strength of the regeneration layer can reach (13-15Mpa), which fundamentally guarantees the improvement of road grade. This advantage is particularly important for the reconstruction of low-grade roads.

    (4) High production efficiency In-situ cold regeneration is carried out under natural conditions. Except for some severe pits that require simple pretreatment, the remaining pavements do not require any treatment. Coupled with the one-time construction characteristics, the operating time is fully used, so the production efficiency is greatly improved. During the construction of the water-stabilized roadbed lime ash and gravel, after our field measurement, a WR2300L regeneration machine, in the organization Under reasonable circumstances, each worktable shift can regenerate more than 4000 square meters of pavement.

    (5) Protect the environment and resources. Because the old materials can be fully used in situ, the mining of new materials is reduced, and there is no problem of the transportation of old materials and the random disposal of waste materials. The construction process is free of dust and exhaust pollution, which saves resources. Protects the environment, so some people call it "green" construction technology!

    (6) No interruption to traffic construction Because the cold-in-place regeneration process is simple, "the construction equipment put into the site is very insensitive to traffic disturbances! Therefore, it can be" half-opened "and" half-construction "in the case of less traffic!

    3. Common construction schemes

    According to the difference between the original road structure and the new design scheme, a variety of construction schemes can be combined by cold-in-place regeneration! In fact, the working principles of the various construction schemes are the same, the difference is that the method of adding materials is different That's it! But as far as the road structure in northern China is concerned, it is the most commonly used scheme for Road cold recycler in situ on asphalt pavements with cement as an additive!

    When using cement for cold regeneration in situ, the external additive is mainly cement. The usual amount of cement is 2% -5% by weight. If the amount of cement is too much, it is easy to make the recycled layer brittle. In order to obtain a good compaction effect, an appropriate amount of water must be added at the same time. There are two ways to add cement! One is to manually spread the cement on the road surface that needs to be recycled by using manual or special machinery. At this time, the method of adding water is to transport water from the shift through the microcomputer control system equipped on the regeneration machine. The vehicle is transported to the mixing tank of the recycling machine. Another method is to use a cement slurry mixing and conveying truck to mix the cement and water to be added into the cement slurry, and then transfer it to the recycling machine through the control system on the recycling machine. In the mixing bin.

     Each of the above two methods has advantages and disadvantages. The pre-spreading cement method has a simple process, but it is easy to produce dust during the construction process. However, this method has a great advantage in that it is very convenient in controlling the dosage. In the construction, the regeneration machine needs to divide into several working strokes to complete the entire pavement milling in one operation section, and the final rolling of the regeneration layer can not be carried out until all the construction procedures of the entire operation section are completed. The time interval between the milled road surface and the post-milled road surface to the final rolling is very different. In hot or dry climates, with the delay of time, the water content of the first milled road surface evaporates more. Then the milled pavement evaporates less.

     If the amount of water added in advance is the same, the moisture content of each part of the road will be different when the roller is finally rolled. The only way to resolve this contradiction is to adjust the amount of water added in the construction sequence. Based on construction experience, add more water first and less water later. Because the pre-spread cement method separates grey water, it will not affect the amount of cement when adjusting the amount of water added. Adopting cement slurry input method can eliminate dust pollution during construction and "reduce construction pollution", but it is more difficult to adjust water consumption alone.

 

6. Evaluation of construction costs

Since the Handan Municipal Transport Bureau of Hebei Province introduced the first Road cold recycler machine in the country in 1998, so far, nearly 10 similar equipment have been introduced nationwide, with three in our province alone. As this process is still new in China, many related contents need to be further explored and summarized. In order to have a more reasonable evaluation of the economic cost of Road cold recycler construction, the highway engineering quota station of Hebei Province carried out a follow-up measurement of the Road cold recycler construction site belonging to the Shijiazhuang Highway Division in August 2002 from the perspective of the quota. The evaluation is as follows

    (1) Overview of the old road

    This section of the highway was built in the 1980s and belongs to the third-grade highway standard. The width of the pavement is 7.5M, the surface layer is 3cm thick, and the base layer is a lime soil structure. After years of heavy truck rolling, the road surface was seriously damaged.

    (2) Transformation plan

    Cement Road cold recycler in situ, designed milling depth is 15cm, actual milling depth is 18cm, cement addition is 3m, and the reclaimed layer is used as the base layer, and then the fly ash is added on top of it The base course is then paved with asphalt concrete.

    (3) Process flow

    Individual severe pits and pulping are pre-treated by hand: manually spread cement on the road that needs regeneration construction; the reclaimer performs milling and mixing; the water carrier follows the regenerator to supply water to the mixing tank. The vibratory roller is used for voltage stabilization; the elevation is measured manually; the grader is used for leveling; the vibratory roller is used for rolling; the static roller is used for final rolling.

    (4) Mechanical equipment

See Table 1 for the invested machinery and equipment.

    (5) Staffing

    The total number of various personnel put into construction is 28.

    (6) Material consumption

    Based on the 5% cement consumption, the average cement consumption is 17.1kg / m2, and the average water consumption of the entire project is 1.1kg / m2. The total amount of the two materials is 5.75 yuan.

    (7) Production quota

Through field measurements and calculations, the project's output quota is 3,920 square meters per day (8 hours).

    (8) Economic cost evaluation

Economic cost consists of three parts: labor, materials and machinery.

Labor cost 16.57 * 28 = 463.96 yuan

Material part cost 5.75 yuan

The cost of the mechanical part is 34,049.80 yuan.

It follows that the approximate cost of regenerating 1 square meter of pavement (18cm deep) is (463.96 + 34049.80) /3920+5.75=14.55 yuan.

    The charging standard in the above calculation is for reference only. It cannot be used as a standard quota. A dedicated in-situ Road cold recycler equipment has a large power reserve coefficient. If the actual milling depth during construction is less than or appropriately larger than that in the above example, Depth. Generally speaking, the construction speed does not change much but the amount of materials used changes. Therefore, the construction cost of cold-in-place recycling is relatively stable.

 

 

Conclusion:

 

The in-situ Road cold recycler construction method is not unfamiliar to northern China. It is stable with road mixing and the soil construction method is basically the same. The main difference is that the external materials have changed. The stable soil construction has a single addition material, while the Road cold recycler construction adds The types of materials are more extensive. For asphalt pavement, in-situ cold-recycling construction, the main work should be the study of the formula of added materials. For different old road structures, according to the road standards to be upgraded, it is rich in resources, low in price, and effective. Obviously, the reinforced materials that are easy to construct make this technology constantly perfect to achieve greater comprehensive benefits.

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