Analyze the causes and prevention measures of asphalt concrete pavement diseases

Abstract: This paper analyzes the causes of early diseases in asphalt pavement. Based on my years of working experience and in response to the causes, some preventive measures are proposed for the reference of engineering and technical personnel.

Key words: Asphalt pavement Engineering diseases; Prevention and control

I. Preface

At present, with the increasing traffic volume on roads, the road surface is facing severe tests. Many asphalt pavements have shown certain early damage. The most common disease phenomena of asphalt concrete pavement include: cracks, water damage, loosening, oil seepage, and pushing, etc. These diseases are common problems in road engineering quality and seriously affect the normal use of roads. This article analyzes the causes of the above-mentioned several common diseases, and in light of the generation mechanisms of several common diseases of highway asphalt pavement, puts forward suggestions for preventing and controlling the occurrence of diseases, and provides their treatment methods.

Ii. Analysis of the Causes of the Disease

The influence of raw materials

(1) Mineral materials: The well-designed asphalt mixture should first carefully select mineral raw materials and strictly control the quality of mineral raw material preparation. At present, the aggregates supplied in the market are mostly produced by traditional small jaw crushers. The processed crushed stones have a large content of needle and flake particles, and the gradation and material uniformity are poor. It is difficult to produce asphalt mixtures with stable quality using such mineral materials.

(2) Asphalt: Each region selects the type and grade of asphalt that are suitable for its local climate and traffic conditions based on the climate zone, and uses high-quality asphalt. This is of great significance for preventing rutting on asphalt pavement at an early stage, effectively preventing pavement cracking, and ensuring that the pavement has good fatigue resistance.

2. The impact of vehicle overloading

With the rapid development of China's economy, some departments, only considering their own interests, have caused serious overloading of vehicles, even reaching an unimaginable extent. Severe overloading is one of the main causes of early damage.

3. The impact of defects in subgrade construction

Some early road damage is related to the quality of subgrade construction, especially in soft soil areas. Unstable soft soil foundation of the roadbed, incomplete replacement or siltation treatment of the foundation, insufficient density of roadbed filling, high liquid limit of roadbed fill material, and uneven settlement of the embankment can all lead to the early damage of the pavement.

4. The influence of construction factors

Problems existing in the mix proportion design of asphalt concrete

The proportion of asphalt mixture is unreasonable. For instance, if the oilstone is relatively large, the already paved road surface will develop bulges and oil seepage. The oilstones are relatively small, and the road surface will become loose. Poor quality of mineral materials, too low crushing value of aggregates and compressive strength of stones, as well as excessive content of fine and flat particles, reduce the stability of pavement mixtures and make it prone to various pavement diseases.

(2) Control of asphalt concrete mixing

Unexpected situations occur in the mixing equipment: When the furnace is just started, if the material temperature is low and the moisture content is high, uneven material temperature will occur. When problems occur in the screening system, it causes significant changes in the aggregate gradation. Sometimes, white and mottled materials may also occur, making it difficult for the road surface to be paved and formed. Excessively high temperatures cause asphalt to age, which cannot guarantee the quality of asphalt concrete paving. The mixing capacity is too small, resulting in a shutdown and lack of materials, which causes the temperature at the joint to drop, creating a temperature difference and forming a series of obstacles. When the transportation equipment is not well-matched or the driver's skills are poor, it will hit the paver, causing the machine body to move backward and form steps.

(3) Paving and compaction of asphalt concrete

The paver is the main machinery and equipment for the surface layer construction of asphalt pavement. Its own performance and operation have a significant impact on the smoothness of the paving. At present, there are quite a few problems in China. Some transportation departments have outdated paving equipment, the paving surface is too narrow, and there is no automatic leveling system. Construction is carried out completely based on experience and the feeling of the operators. Even some expressways require full-section paving, only considering that the cross slope is easy to control and the longitudinal joints are eliminated. Due to the wide paving section, the asphalt mixture is conveyed from the middle to both sides through the hinge wheel. Due to the large distance, segregation is bound to occur.

The compaction after the asphalt surface layer is laid has a significant impact on the smoothness. The selection of compaction equipment, compaction temperature, speed, route, and sequence are all related to the smoothness of the pavement surface layer.

5. Maintenance and Management

Untimely and incomplete early maintenance measures for the pavement are also reasons for the early damage of asphalt pavement on trunk highways. Allowing overloaded vehicles to enter trunk roads or not strictly controlling overloaded vehicles are even more direct causes of early damage.

Iii. Prevention and Control Measures for Road Surface Diseases

1. Raw material quality control

(1) Asphalt should be high-quality domestic or imported asphalt with excellent high and low temperature performance, anti-aging performance, low wax content and high viscosity. When conditions permit, various types of modifiers can be added to asphalt to improve the base performance indicators.

(2) The aggregates selected for collection should be those with rough surfaces, hard stone texture, strong wear resistance, good interlocking effect and good adhesion to asphalt.

(3) The gradation of the mixture determines the high-temperature stability and fatigue performance of the asphalt mixture, as well as its low-temperature crack resistance. The surface characteristics and durability of the pavement are two pairs of contradictions that restrict each other. Neglecting one aspect of performance may reduce the performance of the other.

(4) The design of the mix proportion of the mixture is actually about balancing or optimizing various road performance aspects. It involves conducting specific analyses based on local climatic conditions and traffic situations, and striving to take both into account as much as possible. Of course, to enhance the performance of asphalt pavement, the following two approaches can also be considered: The first is to improve the gradation of mineral materials by using asphalt mastic crushed stone mixture (SMA); the second is to improve the asphalt binder by using modified asphalt.

2. Optimize design

The key to improving long-term performance should lie in optimizing the structural combination design. The surface layer of the road should be designed based on the data obtained from the actual conditions of each road. Only in this way can the data be more reasonable and suitable. Optimize the design of asphalt mixtures for each oil surface layer. When designing mineral mixtures, a dense skeleton structure should be adopted. The optimal amount of asphalt should be carefully selected based on the required functions of different oil surface layers. To enhance the high-temperature stability of asphalt pavement, the amount of asphalt used in the construction of the Heilonggang Basin should be selected at ± 0.3% of the optimal amount of asphalt (OAC), and the lower limit is recommended for the middle and lower oil surface layers. It is recommended to use asphalt for SBS modification on the middle and upper layers of heavy-load roads or expressways.

3. The strength of the roadbed

Firstly, compaction degree is an important indicator reflecting the strength of the roadbed and also the most economical and effective technical measure to enhance the strength and stability of the roadbed. During construction, strict detection and control must be carried out to ensure it meets the specified values. The thickness of the fill layer has a direct impact on the degree of compaction. The loose-laid thickness of each layer should not exceed 30cm. The filling process of the roadbed must be strictly controlled to ensure its strength.

4. Quality control during the construction process

The selection of asphalt is extremely crucial. It is necessary to choose asphalt that meets all the requirements of the specifications, especially the penetration, softening point and ductility indicators of asphalt must be strictly controlled. Due to the warmer climate in recent years, it is advisable to choose low-grade asphalt within the specified range for the asphalt grade. In addition, the asphalt for the prime coat and tack coat should be of the same type as that used in asphalt concrete. Especially, the selection of the oil-to-stone ratio should take into account the impact of the return oil of the tack coat and prime coat.

(2) Special attention should be paid to the design of asphalt mixture mix proportions.

(3) The temperature control of asphalt mixture mixing time, factory temperature, paving temperature, and compaction molding must be strictly carried out in accordance with the requirements of the specifications. The construction period should be reasonably arranged to avoid construction under adverse weather conditions.

(4) Skilled pavers should be selected, and two pavers should be used alternately in front and back for simultaneous construction. Umbrella section pavers should be used sparingly. During the paving process, machine stops should be avoided as much as possible, and attention should be paid to the forming and compaction process of the longitudinal joints of the road surface.

Iv. Conclusion

Early damage to the pavement has become one of the main hazards of asphalt pavement. All levels of traffic management departments should pay sufficient attention and take a series of targeted preventive and improvement measures from pavement design, raw material entry to specific construction based on its causes. At the same time, it is necessary to establish and improve the quality assurance system, with emphasis, control and implementation at all levels from the management department, design department to construction department. Only in this way can the occurrence of early damage to asphalt pavement be fundamentally reduced, and the quality of highway construction be comprehensively improved to a new level.

References

[1] China Highway (October 2006), ISSN1006-3897.

[2] Road and Bridge Maintenance Manual (October 2005), authored by Li Shihua, published by China Architecture & Building Press.

[3] Asphalt Pavement Engineering Manual (March 2003), authored by Zhang Dengliang, published by People's Communications Press.

[4] Road Performance of Asphalt and Asphalt Mixture (August 2008), by Shen Jin 'an, published by People's Communications Press.