With the large number of highway construction. Semi-rigid material with its excellent engineering class performance and significant economic benefits have been widely used in the construction of highway and road construction increasingly occupies a special importance. However, the disadvantage is that the semi-rigid material of low resistance to deformation when the temperature and humidity changes is easy to crack, when the asphalt surface layer is thin and easy to form a reflective cracking, asphalt pavement itself is easy to produce low-temperature cracks, asphalt pavement cracks once, may lead to structural damage pavement, pavement affect functionality. 

1, in the form of asphalt pavement crack formation and damage 

Asphalt pavement cracking is one of the major diseases of asphalt pavement in the world will encounter, whether it is frozen regions, or non-frozen regions, but the severity of their different crack it. Causes and forms of cracking asphalt pavement cracks are varied, but in terms of the main asphalt pavement cracking, cracks can be divided into two categories, namely, non-load-type cracks and load-type cracks. 

Load-type cracks, that was mainly due to lower traffic loads generated by fatigue cracks. In the semi-rigid asphalt pavement design reasonable, good construction quality condition, caused by a simple loading surface cracking possibility is unlikely. Non-load-type cracks, mainly temperature type cracks. Asphalt Pavement including low temperature shrinkage cracking and shrinkage cracking temperature fatigue cracking, are reflected in the way of cracking open type. For asphalt pavement cracks grassroots situation, according to the asphalt surface cracks cracking site, can be divided into the corresponding reflective crack crack. 

Due to ambient temperature, traffic load and other factors, the initial generation of asphalt pavement cracks on asphalt pavement performance often had no effect, but because of their semi-rigid base Shrinkage and Temperature Shrinkage strain tensile stress generated by expansion and contraction of more than semi-rigid base itself The ultimate tensile strength to produce a break from the intensity of weakness, with the pavement prolongation. Existing cracks gradually extended up to the road surface, increasing transverse cracks. Aperture is increasing, transverse cracks and then continue epiphytic longitudinal cracks, eventually forming a separate plate sizes, the role of the surface of the water, causing cracks in the vicinity of the water content of the grass-roots increase, even saturation. As a result, the road surface strength decreases. Under heavy traffic load repeated action, resulting in erosion, jack pulp and subsidence phenomenon. Poly eventually cause structural damage to the road soon have to make gradual loss of carrying capacity of the road structure. How to understand the mechanism of the asphalt pavement cracking, prevent or delay the development of cracks, prolong the service life of asphalt pavement, the project is on the problem. 

2, commonly used in asphalt pavement crack prevention and treatment measures 

Delay and reduce the load Cracks semi-rigid base asphalt concrete surface layer and the non-load-type cracks, can be two types of methods: First, during the construction of the cracks on the use of appropriate preventive or treatment measures, the second is the appropriate choice at the time of repair and maintenance The overlay system. Usually. When the conditions, in order to obtain the best results can be integrated use of these two methods. In this paper, only the prevention or treatment of semi-rigid asphalt pavement crack every aspect elaborate. 

2.1 to improve the strength and stability of the roadbed workspace 

Roadbed is the foundation of the road, roadbed subgrade work area is subjected to traffic loads greater impact on the depth of the area, the depth of the region as a whole has sufficient strength and stability to ensure the strength and stability of the pavement structure is very important, otherwise it will produce uneven settlement so that the road cracking. 

Therefore, we must take effective measures to deal with the impact the stability and strength of the roadbed of the key work areas, to minimize the settlement after the completion of the roadbed. 

(1) the strength of subgrade work area is mainly formed in the filling process. Must strictly control embankment filling process to ensure that the strength of the roadbed. Filling material of choice for stone, gravel, sandy soil, followed by selection of gravel, sand low liquid limit clay, again choose low liquid limit clay. Silty soil and organic soil can not be used for filling roadbed. 

As can be seen from the above equation, the heavier vehicle loads P, depth z roadbed workspace is bigger. In the subgrade and pavement design, vehicle load rating is based on the standard axis (BZZ a 100) to consider, when the road was built, the depth of subgrade work area is already shaping up fixed. After the road delivery, when overloaded vehicles on the road running. Za roadbed depth workspace will certainly become larger. Due to overloading sake. The actual depth of the roadbed work area beyond the preset depth, subgrade strength such excess untreated, stability, stiffness is obviously insufficient, in actual use, road embankment will be cracks, subsidence, rutting, deformation is too large, etc. diseases. So, faced with the current widespread highway overload situation, I recommend when to control the depth of roadbed subgrade construction work area preferably greater than the depth of the roadbed design workspace, as a preventive measure. 

(2) is an important indicator of the degree of compaction of subgrade strength, but also enhance the economic strength and stability of the embankment, the most effective technical measures to control the construction must be rigorous testing. It reaches a predetermined value. Fill soil thickness direct impact on the degree of compaction, construction should plunger thread, the thickness of each layer of loose laying should not exceed 30cm. Detecting the degree of compaction test pit to hit the top surface of the next layer, all the test results to be less than the required value of the pressure-treated, or push except refill. 

(3) lower the water table is an important measure to improve the subgrade strength. 80cm road pavement below the bottom bed is a key part of the roadbed, which directly withstand and absorb stress diffusion road, to have sufficient strength and stability. When the excavation was found under water seepage, regardless of size needs to handle the traffic. Fill the lot to be used better materials filling, poor soil, fill the lot to be changing treatment to ensure its strength and stability. 

2.2 grassroots should have a reasonable thickness 

When increasing the thickness of the grass-roots, its carrying capacity is also increasing rapidly, the test proved, semi-rigid base thickness from 10cm to 25cm, its carrying capacity increased to 3 times the original. 

2.3 crack pavement construction 

Studies have shown that the surface layer of reflective cracking significantly affected by the thickness of the asphalt surface, the thickness of the surface layer than 15.0cm can effectively prevent cracks under tensile fatigue generated, but also can reduce the shear stress caused by vehicle load. Foreign materials. When paving asphalt surface 10.0cm on lean concrete, before the formation of reflective cracks can be accumulated through a standard axle load 10 × 10 times. If the asphalt surface layer thickened to 15.0cm, can by 20 × 10 times. Such as asphalt surface layer thickened to 17.5cm can be assured. 

2.4 Select cracking good performance materials 

(1) The selection of anti-erosion ability, drying shrinkage, temperature shrinkage coefficient, high tensile strength of semi-rigid material for the grass-roots level, it is best to use a low coefficient of thermal expansion of aggregate. 

(2) selection of the relaxation properties of a good quality asphalt surface layer to do to ensure the penetration bitumen, ductility and other indicators; in the absence of high-quality asphalt situation. Certain additives or polymer should be used. To improve the asphalt cracking resistance and high temperature stability. 

(3) the stability of the meet