Cause analysis and maintenance of asphalt pavement diseases?

With the rapid development of economy, highway construction has made remarkable progress, and a large number of asphalt concrete has been used to increase the mileage of highway construction. The diseases of asphalt concrete have seriously affected the quality and service life of highways, and corresponding measures need to be taken to solve them.

2. Types of pavement diseases

Yuyuan Highway is a section of highway from Yuxi to Yuanjiang with a total length of112km, which is an important highway in Yunnan Province. The damage conditions and causes of diseases are also different.

2. 1, deformation class

A typical example of deformation class is rutting. Rutting is a longitudinal strip groove with a depth exceeding 1.5cm, which is the result of repeated action of driving load and pressure. Rutting not only affects the beauty and smoothness of the road surface, but also causes water accumulation in the frog groove when rutting reaches a certain depth, which is easy to cause traffic accidents in which cars slip under wet conditions. There are two main reasons for rutting, one is unreasonable design, and the other is serious vehicle overload. 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.

2.2, cracks

Cracks are divided into longitudinal cracks, transverse cracks and cracks according to their shapes. Cracks usually appear three to five years after the pavement is opened to traffic, and serious local cracks will lead to structural damage. Longitudinal cracks are generally caused by surface water entering the subgrade, softening the base, reducing the bearing capacity of the pavement and cracking the pavement. Due to the uneven density and texture of foundation and fill, longitudinal cracks inevitably occur on asphalt pavement under the action of water intrusion. The transverse cracks are mainly due to the following reasons: asphalt does not meet the standards suitable for local climatic conditions and use requirements when paving, and its deformation resistance will be poor at low temperature, resulting in shrinkage and cracking of asphalt surface layer at low temperature; When the thickness of asphalt pavement surface is insufficient, transverse cracks will also occur under the action of driving load pressure. Cracking refers to the tiny net cracks on the pavement due to insufficient compaction of the pavement and subsidence of the subgrade.

2.3, loose class

Loose asphalt pavement means that the pavement binder loses its cohesive force and the aggregate is loose, with an area above 0. 1m2. Loose pavement is a kind of pavement disease that directly affects driving safety. Loose pavement may appear in local areas or the whole pavement. Generally, the looseness in the wheel track area is more serious.

3. Causes of pavement diseases

Through the long-term inspection of the roads under construction and operation, we find that the main causes of asphalt pavement diseases are design, construction, maintenance and environment:

3. 1, design

First of all, there are some limitations in the current design standards. It is stipulated that the lowest index should be used in road design, and the index higher than the design speed is not limited, which leads to the inconsistency between linear design elements and actual driving speed, poor continuity of linear balance, unreasonable combination design of linear elements, and differences between design speed and actual running speed.

For example, the downhill section of expressway, all indicators meet the design and standard requirements. Although there are corresponding tips and warning signs, the driver suddenly braked after entering the steep bend section of the mountain from Shannan Expressway, and the probability of accidents greatly increased. Secondly, because the survey is not in place or the surrounding terrain is not considered. Due to the lack of more detailed survey data, the toe of slope is excavated during construction, which leads to landslides, such as Wang Jiahe section of Huang Tong first-class highway and the entrance of Haozhuangliang tunnel. The toe of ancient landslide is destroyed during construction, and the cost of landslide control is high.

Thirdly, blindly promote immature design concepts. For example, an expressway adopts AC- 16II asphalt concrete in the upper layer and AC- 16I asphalt concrete in the middle layer, aiming at improving the anti-skid performance of the pavement, becoming the first expressway with a speed limit of 120km/h in this province. Unfortunately, one month after opening to traffic, early water damage appeared on the pavement. In addition, it is not uncommon that other functions of the highway are not considered too much, which leads to continuous problems after opening to traffic.

3.2. Architecture

(1) raw materials

Selection of raw materials: In order to obtain qualified projects, qualified raw materials must be selected. For asphalt, pay attention to viscosity, ductility, temperature sensitivity, wax content, aging degree and other indicators; Pay attention to polymerization for polymerization.

Strength, angle and other indicators.

(2) Construction technology

The quality control of highway engineering is that the structures and structures that make up the highway have expected response (function) under the influence of traffic load and abnormal environmental factors; The key links of quality control are raw material quality, standard test (mix design) and construction technology. Advanced and reasonable construction technology is the key factor that directly affects the quality and progress of the project, and reasonable and reliable construction technology also directly affects the safety of the project construction.

First of all, it is necessary to comprehensively and correctly analyze the engineering characteristics, technical keys and environmental conditions, and make clear the key points and difficulties of quality objectives, acceptance standards and control. Secondly, it is necessary to formulate a reasonable and effective targeted construction technical scheme and organization scheme. The former includes construction technology and methods, while the latter includes construction section division, construction direction and labor organization. Secondly, it is necessary to reasonably select construction machinery and equipment and temporary facilities, and reasonably arrange the general construction plan and construction plans at various stages. Finally, the special technical scheme and quality management scheme of new materials, new technologies and new processes used in the project are compiled. Any link goes wrong, which will lead to hidden dangers of engineering quality, and then various diseases will gradually appear. For example, aggregate segregation and temperature segregation in asphalt mixture transportation lead to uneven pavement compaction, and early water damage is easy to occur at the segregation place.

3.3, later maintenance

Highway maintenance, one is to prevent diseases of roads and facilities along them, and the other is to repair diseases and damaged facilities in time. Namely active maintenance and passive maintenance. At present, the widely used preventive maintenance technologies include micro-surfacing and ultra-thin wear layer. For roads with good bearing capacity that have been used for a certain period of time, the service life of the road can be effectively extended by paving after the treatment of point diseases. Of course, we also have precedents of losses caused by untimely maintenance: in a mountainous area, the drainage ditch under the bridge overflowed, which affected the access path of local villagers. When the villagers shoveled soil, they changed the direction of water flow, soaked the abutment for a long time, and cracks appeared on the bridge deck. When the maintenance personnel found it, it had caused a lot of economic losses.

3.4. Environmental aspects

The road is in the natural environment where the vehicle runs safely, and the ambient temperature also has a direct impact on the road performance, such as the highest temperature, the lowest temperature, the cooling rate, the duration of low temperature, the number of cycles and other factors will cause pavement diseases. In addition, the influence of traffic load also has a direct impact on road performance, such as large traffic volume, fast braking of vehicles and heavy vehicles. There are also some unexpected events that we don't want to encounter, which also have a direct impact on road performance, such as geological disasters, extreme weather, sudden traffic accidents and so on.

3.5 Water damage

The so-called water damage is the phenomenon that surface water or groundwater penetrates into the pavement structure layer, which leads to the early damage of the pavement. It is the most common and destructive disease in the early stage of asphalt pavement in Pu 'er general section. The most intuitive and common is that the repair rate of asphalt pavement is obviously higher than that of uphill lane due to the influence of brake water. The main forms of water damage are: net crack, pit groove, pumping slurry, frog groove and so on. The mixture ratio of asphalt concrete is not strictly controlled, the asphalt mixture is not evenly mixed and the rolling effect is not good, which often causes water damage. At the longitudinal slope of the mountain crossing line, in order to obtain greater pavement smoothness, the water damage is particularly serious when the semi-open asphalt pavement surface is used.

Because water permeates the surface layer and stays at the interface between the lower part of the surface layer, under the long-term traffic load, the asphalt film begins to peel off from the bottom of the surface layer and gradually expands upward. With asphalt peeling off from a large number of gravel below, asphalt concrete loses its strength, resulting in network cracking and deformation.

When water permeates the asphalt pavement and stays on the top surface of semi-rigid base, under the load of a large number of high-speed vehicles, free water generates great pressure, which washes away the fine materials on the surface of the base mixture to form mortar, which is pumped by vehicles and forms pumped slurry on the pavement through various cracks (longitudinal, transverse, oblique and reticular cracks). In the case of a large amount of mortar, more serious cracks may soon form, and in the case of a small amount of mortar, the pavement may crack or deform. Once the mortar is pumped out of a certain place, it will soon produce cracks and deformation, and the subsequent precipitation will be easier to penetrate, forming a vicious circle, which will eventually lead to serious damage to the pavement.

4, asphalt concrete pavement disease treatment

4. 1 Synchronous macadam seal coat

4. 1. 1 Overview

Synchronous macadam seal coat is to spread macadam and binder (hot asphalt, modified asphalt and emulsified asphalt) synchronously on the road surface with synchronous macadam seal coat truck, and form asphalt macadam wear layer by rolling (rubber tire roller and smooth wheel roller). This technology is mainly used as the surface layer of asphalt pavement, which can prolong the service life of asphalt pavement. Because the synchronous macadam sealing layer completes the paving of macadam and asphalt at the same time, the asphalt is evenly wrapped by macadam particles and paved evenly, so that macadam and asphalt form a better bond. Therefore, the synchronous seal coat of asphalt macadam has the following characteristics: it can increase the crack resistance of pavement, solidify the turtle net crack of pavement, reduce the reflection crack of pavement, improve the waterproof performance of pavement, and has high wear resistance and skid resistance. Moreover, the synchronous sealing construction technology of asphalt macadam is simple, the construction progress is fast, the traffic can be opened in time and quickly, the energy consumption is low, the cost is saved, and it has a good application prospect.

4. 1.2 construction preparation

(1) original pavement repair treatment

Because the gravel synchronous sealing truck spreads gravel and asphalt synchronously, it does not have the function of leveling the plain pavement, and the thickness of the double-layer surface is only 1.6 ~ 2.0 ㎝, so the gravel synchronous sealing can only deal with the early damage of asphalt pavement. Before construction, the original pavement should be carefully treated, and the rutted, potholes, flatness, transverse slope and ultra-high uncomfortable sections should be adjusted by layered paving method. For soft foundation sections, hand-thrown stones or cement stabilized macadam should be used for base treatment, and then layered paving method should be used for repairing and flattening. Wider cracks should be filled first, and then filled with hot asphalt, which will lay a good foundation for the implementation of synchronous macadam sealing.

(2) Determination of construction elements and preparation of construction materials, machinery and equipment

In order to ensure the construction quality and effect of synchronous macadam seal coat, 90 # asphalt is selected, and the ex-factory temperature of asphalt is controlled at 160 ~ 180℃, and the spraying temperature of hot asphalt is controlled at 160 ~ 170℃ when paving on the construction site. Crushed limestone is selected as the gravel, and the particle size of the first layer of gravel is 1 ~ 20mm, and that of the second layer is 5 ~10mm; In order to better cooperate with the construction of synchronous gravel sealer, a 50 loader, a 10T smooth roller, a 20T rubber roller and two blowers are selected as auxiliary construction machinery.

4. 1.3 construction technology

(1) Carry out the construction of the test section first, adjust various operation parameters according to the test results, and finally determine the data before the construction operation.

(2) Construction technology of the first floor: After the synchronous gravel truck travels to the construction starting point, the feeder, 10T smooth roller and 20T tire roller will follow closely, with manual cooperation. Start the synchronous macadam sealer and spray hot asphalt and 10 ~ 14 ㎜ stone synchronously. When paving, technicians will follow closely, feedback the paving effect to the operator with walkie-talkie, control the speed of the vehicle, and cover the uneven and missing parts manually immediately. Immediately after completion, use 10T smooth roller to roll it twice, and then use 20T rubber roller to roll it for 4-6 times. After molding, the flow can be opened. After release, the vehicle speed should be controlled below 40㎞/h, and the driver should turn off the brakes and spray water.

(3) Two-layer construction technology: spray hot asphalt and 2-4 ㎜ stones on the first layer of paving and compaction. When rolling, it should be noted that it should be rolled for 4-6 times with a 20T rubber-tyred roller, then rolled for 2 times with a 10T smooth roller, and then the traffic is opened after rolling.

4.2 Disease control

4.2. 1, crack treatment

In view of the fact that cracks are common diseases of pavement, more attention should be paid to their maintenance. For small cracks (2 ~ 5 mm), emulsified asphalt or new grouting material (sealant) can be used for joint filling; For coarse cracks larger than 5mm, modified asphalt (such as SBS modified asphalt) can be used for joint filling treatment; Before caulking, it is necessary to remove the broken materials and garbage in the seam and the seam edge, and ensure that the seam is dry. After caulking, the surface should be sprinkled with coarse sand or (3 ~ 5) mm stone chips; If there is a section with a large area of rough cracks, the plan of milling and resurfacing can be adopted until there are no cracks. If there are cracks at the grass-roots level, the cracks at the grass-roots level should be treated. For cracks caused by insufficient strength of the base and foundation settlement, the base must be completely replaced and filled, and then the road surface layer is paved.

4.2.2, flooding treatment

For floods, treatment and maintenance are relatively simple. For example, there is no need for special treatment for road sections where road signs are flooded and stones are still exposed. For those sections with more accumulated water, which affect the driving safety to a certain extent, it is necessary to mill and resurface the pavement. For pavement flooding caused by construction quality, effective methods should be taken to deal with it. In addition, in the mix design stage, the best asphalt-aggregate ratio should be selected in strict accordance with the test procedure. In the process of construction, the construction shall be carried out in strict accordance with the production mix approved by the engineer.

4.2.3 Maintenance of ruts and passages

Rutting and traffic have great influence on the safe driving of road traffic. In the process of maintenance, we need to pay special attention to the following points: if the rut and passage are less than 30m, there will be a small swing when driving, which can be solved by baking the pavement, adding new materials, compacting, etc. If the length is more than 30m, there will be obvious swing when driving, and the method of planing the middle and upper layers of the pavement and then resurfacing the pavement can be adopted. In addition, for the rutting and displacement caused by the quality of base construction, the weak base should be dealt with before re-paving.

4.2.4, pits, pumping mud, loose disease treatment.

For continuous pits, boiling, loosening and other diseases, milling and resurfacing are adopted. After all the upper, middle and lower layers are milled flat, the base layer should be treated locally to remove the loose parts, dust and sundries at the bottom and wall of the tank, and the adhesive layer oil should be painted. After milling and planing, use the mixture of the original pavement design to fill and compact layer by layer, and pay attention to the oil sticking between layers when filling. For a small number of local diseases, it can be standardized through daily maintenance and minor repairs.

Through the analysis of the causes of asphalt pavement diseases, effective measures can be taken to control and treat them. In the process of construction, quality control should be strengthened from the aspects of design and construction to ensure the quality of asphalt pavement and provide a solid guarantee for driving safety.

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