Crack control of asphalt pavement with the hottest

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Crack control of asphalt pavement with cement stabilized macadam base

at present, China's highway traffic has two obvious characteristics, namely, the rapid increase in traffic volume and the increasing number of heavy-duty vehicles. The number of market analysts of PWC Consulting - Global polyurethane network is increasing. Therefore, the requirements for the performance of pavement structure are becoming higher and higher. Semi rigid base has become the main structural type of asphalt pavement of high-grade highway in China because of its high strength, large bearing capacity, good fatigue resistance and erosion resistance. According to the statistics of statistics, more than 90% of the asphalt pavement base and subbase of high-grade highways in China are made of semi-rigid materials. However, the disadvantages of semi-rigid base material are low deformation resistance, high brittleness, and easy to crack when the temperature or humidity changes, forming pavement reflection cracks, which has become one of the important reasons for the early damage of expressway asphalt pavement

cement stabilized graded aggregate is the most widely used semi-rigid base material at home and abroad, among which cement stabilized macadam has the best performance. However, cement stabilized macadam base does not eliminate the shortcomings of semi-rigid materials, so how to further reduce the generation of reflection cracks is still one of the keys to give full play to the overall performance of pavement structure. Considering that China is a large country of cement production, with a wide range of raw materials and low prices, cement cemented materials will still be used as the main road construction materials for a long time in the future, so it is necessary to study the cement stabilized crushed stone base, so as to provide experience for more extensive application in the future

1, crack formation mechanism

1.1 causes of cracks

the forms of cracks in semi-rigid base asphalt pavement are diverse, but the main causes of formation can be divided into two categories. These five factors play a decisive role, namely, load type structural damage cracks and non load type cracks, including reflection cracks and corresponding cracks. The load type structural failure crack is caused by the vertical or horizontal stress generated by the dynamic load of the vehicle, and the tensile stress exceeding the allowable tensile limit stress of the material in the base course; The non load crack can only work in the process of movement, but it is the result of environmental action, mainly the influence of humidity and temperature, which is caused by dry shrinkage, temperature shrinkage and fatigue. In some cases, it may also be caused by uneven settlement of subgrade. In addition, cracks caused by Subgrade Frost Heave may be found on the asphalt pavement in frozen areas

the bearing capacity of semi-rigid pavement, rigid pavement and rigid composite pavement of China's built expressways is sufficient from the design point of view. However, the investigation shows that cracks are very common on Asphalt Pavement in all regions of China, no matter in the South or in the north, there are a large number of cracks in the first year and the second year after opening to traffic at the latest. Therefore, load alone is not enough to cause surface damage, and the cracking of asphalt pavement should be the result of the joint action of many factors

there are three possible reasons for the cracks of asphalt pavement with semi-rigid base: one is the poor performance of the surface course itself, the other is the cracks reflected on the surface course due to the dry shrinkage and temperature shrinkage cracking of the base course, and the third is the interaction between the surface course and the base course. Foreign countries generally believe that the cracks of asphalt pavement with semi-rigid base are reflection cracks caused by semi-rigid base, and this kind of reflection cracks are mainly caused by the dry shrinkage cracks of semi-rigid base materials. In China, it is considered that the cracks of semi-rigid pavement include load type cracks, temperature shrinkage cracks of asphalt pavement, and reflection cracks or corresponding cracks caused by temperature shrinkage cracks or dry shrinkage cracks of semi-rigid base course

although researchers at home and abroad have done a lot of research on reflection cracks, there are still different understandings, including the generation mechanism of reflection cracks. The fundamental reason is that the pavement performance is affected by many factors, such as environmental factors, traffic factors, material composition and structure, and even economic factors, research methods, etc

China is a vast country with many mountains. Natural factors vary widely, and the economic level of various regions is uneven. Therefore, the main reasons for reflection cracks on semi-rigid pavement cannot be the same. The drying shrinkage of cement stabilized base course mainly occurs in the initial stage after completion. When the asphalt or cement concrete surface course is paved on the base course, the water content of the base course generally changes little. At this time, the shrinkage is transformed into temperature shrinkage. For temperature shrinkage, when the low temperature shrinkage is above - 1 ℃, the temperature shrinkage changes little; When it is below - 10 ℃, the temperature shrinkage coefficient increases sharply, which is several times or even dozens of times that of - 1 ℃. Therefore, temperature shrinkage cracks mostly occur in the northeast and other areas that are easy to form a negative temperature, while for most areas in southern China, the shrinkage cracks are mainly caused by dry shrinkage, and the influence of low temperature shrinkage can be ignored

1.2 crack formation process

for semi-rigid base, cracks are often not caused by traffic load. Due to the influence of water evaporation and temperature change, cement stabilized macadam base is easy to produce cracks. Before bearing the load, there are a large number of micro cracks and holes. Therefore, in fact, it bears the traffic load in the state with cracks, and the temperature shrinkage and dry shrinkage of the base are the internal causes of cracks

the formation of reflection cracks is due to the tensile stress at the bottom of the surface course exceeding the ultimate strength of asphalt concrete. After the cracking of the base course, capital participation will bring a stimulating effect to the new material industry. Because the base course loses its role of resisting tensile stress, it will transfer the stress to the surface course at the cracking position, resulting in the stress concentration of the surface course at the crack. If the principal tensile stress (or shear stress) of eccentric load is added at this time, its stress value may exceed the ultimate strength of the material, and the surface layer will crack accordingly. The main tensile stress (or shear stress) under eccentric load is the reason for the formation of reflection cracks. Therefore, the reflection crack of pavement is mainly caused by the horizontal and vertical displacement after the cracking of base course

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