Asphalt pavement has been widely used in urban roads and expressway trunk lines, and has become the largest advanced pavement in China. However, the damage of asphalt pavement shows many forms and characteristics. After summary and analysis, there are mainly the following common diseases.
First, common asphalt pavement diseases
1. Asphalt pavement cracks
After the asphalt pavement is completed, there will be various cracks. Initial cracks have little effect on the performance of asphalt pavement, but with the invasion of surface rain, the strength of pavement decreases, and under the action of a large number of traffic loads, asphalt pavement is structurally destroyed. There are various forms of cracks in asphalt pavement, which can be divided into three types: transverse cracks, longitudinal cracks and mesh cracks. The main factors affecting the cracks are: the variety and grade of asphalt, the composition of asphalt mixture, the thickness of surface layer, the shrinkage of base material, soil foundation and climate conditions.
2. Rutting of asphalt pavement
Rutting is the supplementary compaction of pavement structure layer and soil foundation under repeated driving loads, resulting in cumulative permanent deformation caused by lateral displacement of structure layer materials. The main factors affecting the rutting depth of asphalt pavement are the internal factors of asphalt pavement structure and asphalt concrete itself, as well as the external factors such as climate, traffic volume and traffic composition. The main reasons for rutting are as follows: (1) The asphalt mixture has too large asphalt-aggregate ratio; (2) excessive surface wear: (3) rainwater invades the asphalt concrete; (4) Because the base contains unstable interlayer, the pavement is pushed sideways, forming wavy ruts.
3. Loose asphalt pavement
Looseness is a pavement disease that directly affects driving safety. The whole road surface may be loose. It may also occur in some areas, but it is generally more serious in the wheel track area because of the driving action. The main reasons are: (1) uneven settlement of local subgrade and base causes pavement damage; (2) Gravel contains weathered particles, which will cause asphalt stripping after water enters; (3) With the increase of service time, the bonding performance of asphalt binder itself decreases, which promotes the asphalt wear in the contact part between the surface layer and the tire, resulting in the decrease of asphalt content and the loss of fine aggregate; (4) Mechanical damage or oil pollution.
4. Water damage of asphalt pavement
Under wet conditions, asphalt pavement is subjected to repeated actions of traffic load and temperature rise and fall. On the one hand, water gradually invades the interface between asphalt and aggregate, and at the same time, due to the action of hydrodynamic force. The asphalt film gradually peeled off from the surface of aggregate, resulting in the loss of adhesion between aggregates and pavement damage. The main causes of water damage of asphalt pavement are materials, design, construction, soil foundation and base, overloaded vehicles and so on.
5, frost heaving and frost boiling of asphalt pavement
Frost heaving and frost boiling of asphalt pavement mainly occurs in freeze-thaw period. Due to the invasion of water, the water stability of subgrade soil is poor, and the water on the upper layer of subgrade freezes, which leads to the cracking of pavement bulge. Road frost boiling is the comprehensive result of five main factors: water, soil quality, temperature, pavement and traffic load. Among them, water, soil and temperature constitute three natural factors of boiling, and it is impossible to form boiling without any one factor.
6. Settlement of asphalt pavement
Subsidence is the most common pavement deformation, which has the characteristics of large area and deep structure, and mainly appears at the junction of excavation section and filling and excavation. The main reasons are: (1) poor drainage of soil cutting, uneven settlement caused by over-wet genes under subgrade, and local settlement of pavement; (2) The pavement strength can't adapt to the increasing traffic volume, and it is easy to produce fatigue damage. (3) The strength of subgrade or base is insufficient or the strength of filling and digging subgrade is inconsistent. Under the action of vehicle load, the subgrade or base structure is damaged, causing subsidence. (4) Uneven settlement of the bridge deck causes settlement and dislocation with the bridge deck.
Second, the preventive measures of asphalt pavement cracks
1, preventive measures
In view of the causes of asphalt pavement diseases analyzed above, corresponding preventive measures are taken from five aspects: building materials, design, construction, maintenance and traffic management.
(1) in terms of materials
Reasonable determination of asphalt pavement structure, asphalt pavement cracks are mainly caused by low temperature shrinkage of asphalt pavement itself. Select high-quality asphalt with low stiffness, large ductility, poor temperature sensitivity and low wax content at low temperature, carefully select mineral aggregate, accurately grade mineral aggregate of asphalt surface, and rationally allocate asphalt mixture ratio. Preparing asphalt mixture with excellent performance, controlling asphalt content and ensuring excellent performance of asphalt mixture can effectively reduce cracks. In recent years, additives have been tried to improve the quality of asphalt pavement, mainly including the following categories: ① Anti-stripping agents, which belong to surfactants. Its function is to reduce the interfacial tension between asphalt and aggregate, so that the asphalt film is easy to adhere to the wet surface of aggregate and acid stone, and is not easy to be peeled off by water; It can also be used when asphalt needs to be poured in wet weather or wet aggregate needs to be mixed with asphalt. Some anti-stripping agents are also cationic emulsifiers, such as quaternary ammonium salts such as cetyltrimethyl ammonium bromide, so cationic asphalt emulsion often has good adhesion to the surface of aggregate. ② Polymer elastomer materials are mostly natural rubber, partially synthetic rubber and plastic which can swell in petroleum asphalt or coal asphalt. They can increase the flexibility and temperature stability of asphalt. Elastomer materials that have been tried include natural rubber (including latex), waste rubber powder (including desulfurization and non-desulfurization), styrene-butadiene rubber, chloroprene rubber, polyvinyl chloride, polyethylene, polyurethane, epoxy resin, random polypropylene and so on. Some of them can swell in petroleum asphalt (such as styrene-butadiene rubber) and some can swell in coal asphalt (such as chloroprene rubber). ③ Inorganic additives, sulfur and asbestos powder. Melting sulfur in asphalt can increase the strength of asphalt mixture. Areas with a lot of sulfur by-products have been used to pave roads, but sulfur is easy to sublimate, so the processing equipment must be sealed and the operators should protect it, which is not suitable for pavement surface. Asbestos powder can improve the thermal stability of asphalt and make the mixture contain more asphalt, thus improving the crack resistance and service life. When in use, the equipment should be sealed to protect the safety of personnel so as to avoid pneumoconiosis.
(2) design.
Carefully design and do a good job in geological survey of complex terrain. Special attention should be paid to strengthening the foundation to prevent uneven settlement caused by weak foundation. Qualified fillers should be used to fill the subgrade, or after the fillers are treated, the subgrade should be filled to ensure sufficient strength and stability, so as to ensure a stable foundation for the pavement. Semi-rigid materials with good scour resistance, small dry shrinkage coefficient and temperature shrinkage coefficient and high tensile strength should be selected as the base. High-quality asphalt is selected as the asphalt surface layer; On the premise that the stability meets the requirements, the asphalt surface layer should be made of asphalt with high penetration.
(3) architecture.
Carefully construct, select advanced construction technology and mechanical equipment, formulate a perfect construction scheme, ensure the compactness meets the specification requirements, carry out soft foundation treatment in strict accordance with the design requirements, improve the construction quality of soft foundation treatment, and strictly control the water content of semi-rigid base construction during rolling. The water content of the mixture should not exceed the optimum water content required for compaction, or be controlled within the scope allowed by the construction specification; After semi-rigid base is rolled. Keep in good health in time, prevent cracks from reflecting to the surface, and protect the water content of the mixture from losing; Priming oil shall be sprayed immediately after curing, and asphalt surface layer shall be paved as soon as possible. The regeneration technology of asphalt pavement mainly includes: ① spraying softener on the aged asphalt pavement to re-soften the aged and brittle asphalt, which is mostly used for the regeneration of permeable and surface-treated pavement; (2) Digging out the aged old asphalt layer, re-rolling, adding "regenerant" to improve the quality of asphalt when necessary, and adding some new aggregates and asphalt for reprocessing; This method can be pulverized and mixed in situ or concentrated in the factory, and the quality of the factory mixed heating method is better. The recycling of old asphalt pavement materials can save asphalt, aggregate and energy consumption and reduce environmental pollution. In recent years, it has attracted the attention and promotion of highway construction departments in various countries.
(4) Maintenance
Strict maintenance management, strengthen road cleaning, and ensure good drainage performance. Scientific treatment of cracks in time to avoid further expansion of the disease.
(5) Strengthen traffic management.
Strengthen traffic management and restrict the passage of large overloaded vehicles; During the continuous high temperature in summer, the operation management unit can arrange heavy vehicles to pass at night and early morning when the road temperature is low: excessive wear of nail tires on the road surface is prohibited or the use is strictly restricted.
The detailed information of "Common Diseases of Asphalt Pavement and Preventive Measures" can be found in Zhong Da Consulting & Construction Link, and all the relevant construction information you want is available.
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