With the rapid growth of highway asphalt pavement mileage, the pressure of highway maintenance department's management and maintenance tasks is increasing. How to take correct and reasonable maintenance measures to maintain asphalt pavement, ensure the maintenance quality of asphalt pavement, reduce maintenance costs, save maintenance costs and improve the investment benefit of funds has become an important research topic for highway maintenance departments. The following is an analysis of the early diseases of highway asphalt pavement and how to take preventive measures.
2. Cause analysis of early diseases of highway asphalt pavement.
The early diseases of highway asphalt pavement mainly include cracks, pits and other diseases.
2. 1 crack
Cracks are mainly caused by defects such as pavement structure, pavement material, subbase and subgrade filling strength.
The main reason for transverse cracks is that the highway pavement base mostly adopts semi-rigid structure design with high strength and high density. Although the strength is high, the deformation is small and the overall performance is good, the temperature difference expansion and contraction of the pavement is very obvious, which is easy to cause transverse reflection cracks. When the grading control of pavement materials is not strict, and the water content, dust content and needle aggregate content in the mixture exceed the standard, transverse cracks are easy to occur under the shear impact of vehicle load, vehicle speed change (acceleration and braking) and wheel load alternation after opening to traffic.
The main reason for longitudinal cracks is that the compaction degree of subgrade in high fill section is not enough. Uneven settlement occurs under the self-weight of subgrade soil and vehicle load, and the subgrade slips, especially the semi-excavated and semi-filled subgrade filling part, which is not compacted tightly, and uneven settlement occurs under the self-weight of subgrade soil and vehicle load. The widening of the old road improves the pavement section, and the insufficient strength of the widened subgrade is also one of the reasons for the longitudinal cracks.
2.2 Pits and subsidence
After cracks and reticular cracks appear, the pavement gradually loosens to form cracks and falls off, and is taken away by the running wheels, forming pits and grooves. Subsidence is a disease caused by lax control of some construction sections, inadequate subgrade compaction and repeated traffic loads. According to the investigation, at present, the early diseases of highway asphalt pavement are mainly water damage pits and subsidence, and the damage mainly occurs in rainy season, especially in rainy and rainstorm seasons; The carriageway is more serious than the overtaking lane: the braking water in the downhill lane is more serious than that in the uphill lane. The place where the water disaster occurs is generally in the part with poor drainage, and the pavement seepage is serious. Digging the surface of the road shows that there is water at the grass-roots level; Generally, there are small reticular cracks in the damaged parts of pavement. Preliminary analysis of the main reasons are:
A there is no drainage system in the structural layer of this road section, resulting in long-term water accumulation on the surface.
B. Ultra-high drainage of curved road section is through the opening of central separation zone, so that road water is discharged from high road surface to low road surface. Water often stays on the road surface, especially around the central separation zone, resulting in water accumulation on the road surface.
C. Heavy vehicles frequently brake on downhill sections, brake pads are constantly sprayed with water to cool, and a large amount of braking water continuously flows to the road surface, especially for overloaded vehicles. On the road with heavy traffic, even on sunny days, the downhill road is wet, and the asphalt pavement is in a wet state for a long time, which aggravates the damage of the asphalt pavement and leads to pits.
D. With the action of driving and the invasion of natural conditions (wind, rain, snow, sunshine), the pavement is bare and white, and the asphalt pavement is aging. With the extension of time, the asphalt in the pavement gradually becomes brittle, the anti-stripping ability gradually weakens, the adhesion between aggregates in the pavement weakens, the surface particles become loose, and gradually separate from the original pavement, forming pits and grooves.
E. the asphalt-aggregate ratio and gradation do not meet the requirements. During pavement construction, the amount of asphalt in asphalt mixture is small, and white aggregate appears, which leads to weak adhesion between particles and easy separation of particles from the pavement under the action of vehicles, resulting in early pavement damage. Gradation does not meet the requirements, too much coarse aggregate leads to the asphalt mixture is not dense, water sealing is not strong, and pavement water is immersed in the pavement. Too much fine aggregate and insufficient pavement strength will cause waves and ruts under the action of vehicles.
F uneven mixing or segregation of pavement stabilized base materials leads to uneven strength of pavement base, uneven settlement under the action of vehicles for a long time, and cracks and damage of pavement due to accumulated water.
G local (or edge) of pavement base is not dense, and its strength does not meet the requirements. Rutting is formed under the repeated action of vehicle load, and the lane is more obvious than overtaking, especially the lane is more serious. At present, most of the pits and grooves in asphalt pavement are repaired afterwards, but the effect is not ideal and the durability is poor. There are also thermal repair methods (such as thermal regeneration), which are inefficient and have poor economic benefits. None of the above traditional methods can fundamentally solve the problem of early damage of asphalt pavement.
3, early disease treatment measures
The treatment of early diseases of asphalt pavement mainly focuses on preventive maintenance. Preventive maintenance refers to taking forward-looking and predictable countermeasures and practical maintenance measures before the minor diseases of asphalt pavement are destroyed, so as to find and deal with pavement diseases and disease factors first, prevent the development of diseases, maximize the service life of roads and improve the efficiency of maintenance funds. The premise of preventive maintenance is that the strength of pavement base is sufficient, and its essence is to take corresponding technical measures for corresponding diseases of pavement at an appropriate time. Its core is to emphasize the initiative, planning and rationality of maintenance. Its purpose is to achieve the best maintenance cost-effectiveness. According to different early diseases and highway grades, different preventive maintenance measures can be taken:
3. 1 joint filling and sealing
The purpose of joint filling and sealing is to prevent surface water from entering the cracks. Joint filling and sealing are suitable for dealing with relatively stable inactive cracks and cracks that develop under temperature and vehicle load.
3. 1. 1 joint filling: due to the semi-rigid base asphalt pavement structure, there are different degrees of reflection cracks on the pavement. In order to prevent cracks from expanding under the action of rain, reflection cracks should be filled in time. At present, the commonly used joint filling methods in China are: common hot asphalt joint filling, SBR modified emulsified asphalt joint filling, pavement crack sealant joint repairing and grouting joint repairing.
3. 1.2 "pressure joint belt" sealing: cracks are one of the common early diseases of asphalt pavement, and most of the early cracks in roads are transverse cracks and longitudinal cracks. It is a good measure to treat cracks in asphalt pavement by using "seam pressing belt", which plays a very important role in prolonging the service life of pavement. In 2005, the "Kuidao" seam-pressing belt was used in the preventive maintenance of K48+000-K50+000 section of Yan (Jin)-Shui (Fu) expressway. After more than two years of use, the observation effect was good. It can be pasted directly along the crack without any input of mechanical equipment, without changing the original structure of the crack, and the traffic can be opened immediately after the construction is completed.
3. 1.3 fiberglass-polyester paving mat: In order to effectively eradicate the influence of reflective cracks at the base on the tensile stress of the pavement, the pavement is milled and planed at the road section with disease at the base but good strength, and hot asphalt is sprayed on the surface of the base, then fiberglass-polyester paving mat is paved, and then an asphalt surface layer is paved on it. In the maintenance of K2+000 ~ K6+000 section of Wei (Xin) Xu (Yong) secondary highway, the practice proves that the effect is good.
3.2 Repair of pits and grooves
Due to the lax local quality control in the construction of oil pavement base, local cracks will gradually form loose and potholes. In view of local damage such as potholes and looseness, the commonly used repair methods are: hot repair method, in-place hot regeneration method, hot mix cold repair method and cold mix cold repair method.
3.2. 1 When the pavement base structure is not deformed and the strength is sufficient, the hot repair method was often used in the past. The usual practice is to remove all the old asphalt mixture from the damaged area and then fill it with new hot asphalt mixture. This method can ensure the quality of repair, but a large number of old asphalt mixtures are abandoned, resulting in great waste of resources and environmental pollution. In order to avoid the waste of resources, many road sections have carried out research on waste recycling, recycling the waste asphalt mixture and stacking it centrally. After reaching a certain amount, asphalt regeneration mixing technology should be adopted for regeneration. The development and application of cold patching materials are carried out in some sections, and the pavement is repaired with a mixture composed of cold patching additives, diluents (diesel oil), asphalt and aggregates. Some ordinary road sections also bought "in-situ geothermal recovery machinery" to repair the pavement.
3.2.2 When the structural strength of the pavement base is insufficient or the road section has been damaged, the damaged pavement base should be removed to the base and leveled. According to the pit and groove area, different compaction machines (roller or impact rammer, plate rammer) are used for compaction. According to the thickness of the original base, the paving height of the second and third layers of water-stabilized macadam is determined to be consistent with the original base, and the layered compacted stone meets the compaction requirements, and the water-stabilized base is cured for 7 days. After spraying the adhesive layer oil, lay the oil surface.
3.3 Road table (seal coat) treatment
In the process of pavement maintenance and production, in addition to the standardized repair of pits and grooves, the road sections with many pits and grooves and serious water damage are treated with pavement seal. Common pavement sealing measures include: fog seal, slurry seal, crushed stone seal, asphalt surface treatment, scraping oil seal and so on.
3.3. 1 fog seal coat: Many diseases of asphalt pavement are caused by water infiltration, so it is very necessary to effectively prevent water from entering the pavement, and fog seal coat technology is a very direct, effective and economical preventive maintenance measure. Fog seal coat is a thin layer of high-permeability polymer modified emulsified asphalt sprayed on the asphalt surface to form a tight waterproof layer to seal the pavement, which has the functions of waterproofing and seepage prevention, protecting the pavement, minimizing water damage to the pavement, increasing the cohesive force between pavement aggregates, reducing the aging problem of surface asphalt caused by air and water infiltration, prolonging the service life of the pavement and improving the appearance.
3.3.2 Slurry seal coat: After the asphalt pavement is used, the pavement base is basically in a stable state. However, with the increase of service life, pavement diseases such as oxidation, fatigue cracking and potholes began to appear to varying degrees. Slurry seal coat is a kind of seal coat composed of well-graded aggregate (composed of fine sand and mineral powder) and emulsified asphalt, which is evenly sprayed on the road surface by a special sprayer. It has waterproof, anti-slip and wear-resistant properties, which can prolong the service life of pavement. Slurry seal coat has certain requirements for the original pavement conditions, requiring that the original pavement base must have sufficient strength and rigidity, and the construction surface should be smooth and free from potholes and other diseases. Therefore, in order to achieve good results of slurry seal coat, pavement diseases must be treated in advance, and rutting repair can be carried out on the sections with deep rutting first. Preventive maintenance measures of slurry seal will also make the old pavement look brand-new.
3.3.3 Synchronous macadam seal coat: Due to the bonding between cement and stone, the paved seal coat has good crack resistance, which reduces the cracks on the pavement and has a certain repairing effect on the cracks on the original pavement. The rough surface of synchronous macadam seal coat improves the anti-sliding performance of the original pavement and improves the use function and service level of highway pavement. At the same time, it can save the cost of materials and equipment, reduce the engineering cost and improve the work efficiency. Due to the high precision of synchronous macadam sealing equipment, the labor intensity is greatly reduced. After the construction is completed, it can be opened to traffic within 2 hours, which shortens the time of closed traffic and improves the transportation efficiency of the highway.
3.3.4 Asphalt pavement: Asphalt pavement is a kind of thin-layer pavement not more than 3cm, which is composed of asphalt and fine gravel in proportion. Asphalt pavement has the advantages of thin pavement, low cost, simple construction and good driving performance, and has become the main pavement treatment measure to improve the driving quality and traffic capacity of low-grade highways. There are two common construction methods for asphalt pavement: paving method and mixing method. Paving method is a kind of asphalt pavement construction method, in which oil is poured in layers on the pavement base, fine gravel aggregate is paved in layers, and the asphalt pavement is formed by rolling. The characteristic of layered paving method is layered construction, and there are two-layer method and three-layer method commonly used. Mixing method is to spread a thin layer of hot-mixed asphalt mixture on the old pavement, and its thickness is generally19-38 mm. If the original pavement has potholes and other diseases, the potholes and other diseases should be treated first.
3.3.5 Scraping oil seal layer: Scrape a layer of hot asphalt on the original pavement surface with a special scraper, scrape the hot asphalt into cracks and crevices, and then evenly spread a layer of fine aggregate. Finally, the fine aggregate is pressed into asphalt by roller, and the aggregate is controlled between 0. 1-5 mm, which has the functions of sealing the pavement, preventing the pavement from cracking and loosening, delaying the aging of the pavement and improving the skid resistance of the pavement. Scraping oil seal layer is suitable for preventive maintenance of low-grade roads.
4. Concluding remarks
In a word, the preventive maintenance of asphalt pavement is essentially a predictive, forward-looking, proactive and reasonable maintenance measure. It does not consider whether the road surface is damaged. Maintenance managers should always check the sections they manage, and correctly and reasonably choose different preventive maintenance technical measures for timely maintenance according to the actual situation in the use of asphalt pavement, so as to ensure the quality of pavement, prolong the service life of pavement and improve the efficiency of capital use.
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