1 Introduction
With the continuous progress of economy, people's living standards have also improved accordingly. At this time, people's modes of transportation have become more and more, so the municipal road engineering has also taken a big step forward. But because it is a municipal project, there are often many reasons, such as catching up with the construction period, overloading, serious overloading and so on. Through field investigation and statistics, there are mainly horizontal cracks, vertical cracks, mesh cracks and subsidence at the intersection of horizontal and vertical cracks. However, asphalt pavement has the advantages of smooth and solid surface, seamless, comfortable driving, wear resistance, low noise, short construction period, simple maintenance and suitable for phased construction, so it has been widely used. The pavement performance of asphalt pavement requires that the pavement has certain strength, stiffness, smoothness and sufficient bearing capacity, and at the same time, it should meet the stability requirements under different temperature conditions such as no rutting at high temperature, no cracking at low temperature and few diseases at room temperature. In addition, the asphalt pavement surface should have durability, good anti-sliding performance and wear resistance. According to the characteristics and causes of typical first-class diseases of asphalt pavement (1 ~ 3 years' service), this paper puts forward the main countermeasures in pavement design and construction.
2 municipal road asphalt pavement early damage prevention measures
2. 1 design
2. 1. 1 semi-rigid pavement design
When designing semi-rigid pavement, the mechanism of temperature cracks spreading downward from the surface should be considered first. The asphalt surface layer should be made of high-quality asphalt with good relaxation performance (modified asphalt if necessary), and asphalt with high penetration should be selected on the premise that the stability meets the requirements. Secondly, semi-rigid materials with good erosion resistance, small dry shrinkage coefficient and temperature shrinkage coefficient and high tensile strength should be selected for the base. Appropriate thickness of asphalt surface course is adopted to save asphalt, reduce investment, and prevent cracking semi-rigid base from generating dry shrinkage cracks and temperature shrinkage cracks during use.
2. 1.2 design principle of reasonable gradation
The mineral aggregate gradation design of dense graded asphalt concrete for municipal road asphalt pavement should follow the following principles:
1) Only the mixture gradation has the best use quality under the condition of maximum density, so the mineral aggregate gradation design of AC structure should be based on the design principle of pursuing maximum density, and the asphalt mixture that violates this principle will not get the proper use effect of AC structure. 2) 2) The gradation design of mixture with AC structure should be based on the maximum density line, and set a smaller target and the allowable range of gradation of production mixture ratio. Too wide classification range will confuse AC structure with ATP and AM structure, which will make the design and construction at a loss, make the project quality out of control, and may not guarantee the working characteristics of AC structure. 3) When the mineral aggregate gradation deviates from the maximum density line, the AC structure should design the possible influence of mineral aggregate gradation on the mixture and pavement performance according to the figure 1 prediction. 4) Durability, exudation, stability and proper skid resistance are the technical requirements that AC structure should have at the same time, and we can't pursue one and ignore the others. 5) In order to improve the thermal stability of AC structure, asphalt modification technical measures should be taken in sections with large traffic volume, large longitudinal slope of the route, roads before and after grade crossing and toll stations, and the adjustment of mineral aggregate gradation has little effect. Choosing a larger nominal particle size is not conducive to reducing the thermal stability of AC mineral aggregate mixture, so it is not desirable. 6) In hot mix asphalt mixture, different mixtures have different functions and use conditions. Only by fully mastering the engineering characteristics of these mixtures can we correctly choose the mixture type and then carry out reasonable gradation design.
2.2 Construction aspect
2.2. 1 materials should be excellent.
1) asphalt. According to the special requirements of asphalt concrete performance, heavy traffic asphalt or modified high quality asphalt should be selected.
2) Coarse aggregate. Coarse aggregate should be hard, clean, undifferentiated and free of impurities, and have sufficient strength and wear resistance, and its adhesion to asphalt should not be lower than Grade IV. If it does not meet the requirements, anti-stripping measures should be taken before use, and the maximum particle size should not be greater than 1/3 of the layer thickness.
3) Fine aggregate. The fine aggregate shall be made of hard, clean and weathering-free stone chips and natural sand, with hardness not greater than 12, sand equivalent not less than 60 and proper gradation.
4) Mineral powder. Mineral powder should be ground with clean limestone crushed stones of more than 5mm, and it is forbidden to use a blender to recover dust. The water content is not more than 1%, the particle size less than 0.075mm is 75% ~ 100%, there is no agglomeration, the hydrophilic coefficient is less than 1%, and the plasticity index is less than 4%.
2.2.2 Mix proportion should be accurate.
1) The target mixture ratio is used to determine the feeding ratio and feeding speed of each cold bin of the mixing equipment, and it is used as the basis for material preparation and trial mixing.
2) Sampling and screening the production mix ratio from the hot bins of the mixing building, determining the material mix ratio in each hot bin, and repeatedly adjusting the mix ratio of the cold bin to achieve the feeding balance. Marshall test and rutting test were carried out according to the optimum asphalt content of the target mixture ratio of 0.2%, and the materials, mineral powder ratio and optimum asphalt content of each hot bin were determined, and trial mixing and trial paving were carried out.
3) The standard mixture ratio is the mixture ratio finally determined through trial mixing and trial paving, which serves as the basis for production control and quality inspection.
4) If the material changes in production or the detected material gradation and Marshall technical indicators do not meet the requirements, the reasons should be analyzed and the mixture ratio should be adjusted in time.
2.2.3 Mixing should be uniform.
1) Designate a person to be responsible for testing the ex-factory temperature of the mixture and make records. 2) When the adhesion between asphalt and aggregate does not meet the requirements, hydrated lime or quicklime powder should be added and mixed evenly in proportion when producing mineral powder; Effective anti-stripping agent can also be added, and the anti-stripping agent should be added to the hot asphalt above 140℃ according to the dosage, and make it evenly dispersed. 3) Measuring equipment and temperature testing system must be calibrated and debugged, and checked regularly. Before starting, it is necessary to comprehensively check whether all parts of the mixing building are operating normally, and eliminate problems in time when found. 4) Observe and check the uniformity of the mixture. If abnormal phenomena such as ash and caking are found, measures should be taken to extend the mixing time and increase the mixing temperature. 5) Print asphalt, hot bunker materials, mineral powder consumption and mixing temperature one by one. After the daily mixing is completed, the mixer will check the total amount of asphalt, coarse aggregate, fine aggregate and mineral powder, and calculate the average asphalt-aggregate ratio, average gradation and average thickness.
Mixture transportation
Thermal insulation of asphalt mixture is an important technical measure to ensure the engineering quality, and the transportation time should be shortened as much as possible, and the material transportation vehicles should be covered with tarpaulins; When receiving materials, the truck should move the materials three times before, during and after to avoid reducing segregation. The number of trucks should meet the needs of continuous paving of pavers, and the start-stop times of pavers should be reduced as much as possible.
2.2.5 mixture paving and rolling
1) Check the lower bearing layer. Before laying the lower layer, the kerb and kerb construction should be completed first, and the oil in the prime coat should be supplemented.
2) Equipped with sufficient construction machinery and accessories, and matched with the mixing, transportation, paving and rolling capacity. Do a good job of maintenance, debugging and trial operation before construction to ensure that there are no faults that affect the construction quality and progress during construction.
3) The paver shall start operation after the screed is fully preheated, and shall travel evenly, and ensure the balance between paving speed and feeding speed; The rotating speed of the paver screw conveyor should be uniform, so that the material level of the mixture is constant and higher than 2/3 of the height of the screw conveyor.
4) Reasonable control of paving width. For the mixture with medium and coarse particle size, segregation is inevitable when the paving width is more than 7m.
5) Scientifically arrange the roller, and follow the paver evenly to roll it in time. When rolling, the principle of "high frequency and low amplitude" should be followed, and it should be carried out from two sides to the middle, so as to ensure that the mixture at the lap joint of two pavers is dense. When turning back, the vibration should be turned off to avoid squeezing and pushing the asphalt surface.
6) High-temperature follow-up rolling is an important means to improve the rolling effect, so as to ensure that the initial pressure temperature and the final pressure completion temperature meet the requirements, and ensure the compactness and porosity meet the requirements.
3 Conclusion
To sum up, the early damage of municipal road asphalt pavement is not only closely related to the formation of pavement such as design and construction, but also closely related to road maintenance. In order to eliminate the early damage of asphalt pavement, prolong the service life of asphalt pavement and improve the investment benefit, it is particularly important to take responsibility from the aspects of design, construction and management, formulate corresponding work plans and priorities respectively, and organize and construct carefully.
The detailed information of "asphalt pavement disease prevention and control" can be found in Zhong Da Consulting & Construction Link, and all the relevant building construction information you want is available.
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