After years of operation, a highway in Guizhou Province has rutting, cracks, pits and grooves, which need urgent maintenance. The relevant departments decided to repair some sections (thickness: 10mm) with micro-surfacing technology, so as to explore and accumulate the methods and experiences of micro-surfacing technology in the early disease treatment of asphalt pavement in our province and provide more economical and effective methods for pavement maintenance.

Keywords micro-surfacing technology; Treatment of early diseases of asphalt pavement

I. Micro-surfacing Office

Micro-surfacing is an advanced form of emulsified asphalt slurry overlay, which is suitable for preventive maintenance of heavy traffic roads, early repair of light rutting of roads and anti-sliding wear layer of new roads. Micro-surfacing is a thin-layer structure with high skid resistance and durability, which uses special mechanical equipment to mix polymer (modified) emulsified asphalt, coarse and fine aggregate, filler, water and additives into slurry mixture according to the designed mixture ratio, and spreads it on the original road surface without rolling.

Polymer modified emulsified asphalt is polymer modified emulsified asphalt. The modified emulsified asphalt of this line is BCR, and its softening point is greater than or equal to 53℃.

Second, the micro-surfacing treatment of the original pavement before construction

1. The structural strength of the original pavement must meet the requirements, otherwise it should be reinforced by renovating or even replacing the subgrade in advance.

2. For the local structural damage of the original pavement, asphalt repair must be selected on the basis of analyzing the causes of the disease, and then micro-surfacing should be carried out.

3. The cracks on the original pavement must be filled up in advance, otherwise the cracks with a width greater than 5 mm on the original pavement will be reflected on the pavement after opening to traffic.

4. The rut with a depth of 25~40mm should be filled many times first; Rutting with depth of 15~25 mm is treated by rutting filling box alone, and local rutting with depth less than 15 mm can be directly covered by micro-surfacing.

5. Before the micro-surfacing construction, the markings on the original road surface shall be planed, and the road surface dregs shall be blown clean by a blower, and the oily road surface shall be thoroughly cleaned.

Third, the construction control points

1. Aggregate and mineral aggregate gradation

There must be a certain amount of coarse materials in aggregate to play the role of skeleton. If the coarse aggregate is too small, the embedding force between coarse aggregate and fine aggregate will decrease, resulting in the decrease of strength and high temperature stability. It is also necessary to add a proper amount of fine materials to the aggregate to ensure the compactness, cohesiveness, durability and workability of the slurry. Sand equivalent index should also be strictly controlled. Low sand equivalent means that the clay content in aggregate is high, which will make it difficult to attach stones and emulsion, and the formed pavement will produce fine cracks. The gradation of mineral aggregate is usually medium or coarse (JTGF40/ MS- 2 or MS-3). In this micro-surfacing construction, hard, rough and wear-resistant basalt is used as coarse aggregate (4.75-9.5mm) according to the road conditions and the requirements of the owner, and its gradation meets the requirements of coarse aggregate of asphalt mixture. Fine aggregate adopts limestone (0-4.75mm), and its gradation meets the requirements of fine aggregate of asphalt mixture. MS-3 mineral aggregate gradation in JTGF40 specification is synthesized, and the mineral aggregate gradation is shown in the following figure. And strictly control the sand equivalent index of machine-made mountain sand (sand equivalent is not less than 65%). The thickness of the formed pavement structure is about10 mm.

2. Modified emulsified asphalt

Modified emulsified asphalt According to the conditions and requirements of expressway pavement, we choose BCR modified emulsified asphalt, which is mainly characterized by improving high-temperature stability, improving adhesion with aggregate, improving pavement peeling resistance, and having good toughness and viscotoughness. The technical indexes of modified emulsified asphalt meet the requirements in the table below. Technical requirements for micro-surfacing emulsified asphalt:

3. filler -P. 032.5 cement is used as the filler of the mixture.

4. Water-it must not contain harmful soluble salts, substances that can cause chemical reactions and other pollutants, just ordinary drinking water.

5. Mix proportion-The mix proportion design of micro-surfacing mixture was issued by Koch Asphalt Material Co., Ltd., an authoritative asphalt supplier in China.

6. Micro-surfacing construction process inspection requirements (micro-surfacing construction process inspection)

Four, the main advantages of the project construction

Short construction period, convenient construction, few construction personnel and fast construction speed. The continuous micro surfacing paver can work continuously under good material supply and weather conditions. 300-400t micro-surfacing mixture can be paved in 1 day, which is equivalent to a standard driveway with a length of 6.4 -8.5Km. It can be formed and opened to traffic in 0.5-2 hours after construction, with fast opening time, short construction period and long construction season.

Anti-wear and anti-skid performance The friction coefficient of micro-surfacing seal coat is large, which can improve the anti-skid ability of pavement. In the weather with poor natural meteorological conditions, improve the driving safety of expressway.

Waterproof function, micro-surfacing has a good sealing effect, forming a dense waterproof layer on the road surface, which can effectively prevent rainwater from infiltrating into the lower layer of the road surface. Because its thin structure is used on the bridge deck, the bridge deck will not increase too much weight and will not affect the drainage, thus preventing the bridge deck from being damaged by water.

In order to reduce the cost, firstly, compared with asphalt concrete overlay, micro-surfacing overlay has thinner structural thickness and lower corresponding cost; Secondly, due to the pre-maintenance function of micro-surfacing, the micro-surfacing seal coat can be laid 3-4 times during the service life of the pavement, which can improve the service life of the pavement and reduce the maintenance cost of the road.

Energy-saving and environmental protection, compared with hot-mixed asphalt mixture, it works at room temperature, reduces energy consumption and meets environmental protection requirements. Micro-surfacing can be applied to two different pavements, asphalt and cement concrete (spraying oil is needed to spread micro-surfacing on cement pavement).

Verb (abbreviation of verb) conclusion

The driving practice of this expressway shows that the pavement after micro-surfacing construction has good effect, excellent rutting repair function, firm bonding with the original pavement and less peeling phenomenon. Compared with other pavement construction and maintenance measures, micro-surfacing technology has the advantages of fast and convenient construction, greatly shortening the open traffic time, saving energy and low cost, and is a road maintenance method with perfect functions. Therefore, micro-surfacing technology has a broad application prospect because of its excellent performance and remarkable social and economic benefits.

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