Asphalt pavement is various types of pavement formed by paving and rolling asphalt concrete. Asphalt concrete is a mixture formed by fully mixing asphalt materials with a certain viscosity and appropriate dosage and mineral aggregates of a certain grade. Asphalt concrete, as an asphalt pavement material, has to bear the repeated action of running vehicle loads and the long-term impact of environmental factors during its use.
Therefore, while asphalt concrete has a certain bearing capacity, it must also have good durability against natural factors. That is to say, it should be able to show sufficient stability in high temperature environments, crack resistance in low-temperature condition, good water stability, long-lasting anti-aging and good anti-skid property to ensure asphalt pavement and good service function.
Asphalt concrete The asphalt materials suitable for road construction are mainly petroleum asphalt and coal asphalt, in addition, there is also natural asphalt. In some countries or regions, natural asphalt is also used or blended. According to the different types of aggregates used, it can be divided into crushed stone, gravel, sandy, and slag, and crushed stone is the most commonly used. The properties and labeling requirements of asphalt vary with the type of asphalt pavement, the climate of the region and the traffic conditions of the road section; thicker asphalt should be selected for hot mixing or hot spraying and on hot areas and heavy traffic roads; cold mixing or Thinner asphalt should be used for cold sprinkling and on cold areas and light traffic roads. According to the maximum particle size of the mixture, it can be divided into coarse grain (below 35-40 mm), medium grain (below 20-25 mm), fine grain (below 10-15 mm), sand grain (below 5-7 mm), etc. number category. According to the degree of density of the mixture, it can be divided into dense gradation, semi-open gradation and open gradation. The open gradation mixture is also called asphalt macadam.
1. Asphalt binder
Asphalt binder is a general term for asphalt materials (including added external admixtures, modifiers, etc.) that play a cementing role in asphalt mixtures. It binds the mineral aggregates into a whole, increases the strength and enhances the road surface’s ability to resist driving damage, and makes the road surface water-resistant.
Aggregate is a general term for mineral aggregates in asphalt pavement materials, which play a role of skeleton and filling in pavement materials. Sometimes it is necessary to mix several kinds of coarse and fine aggregates to form the required particle size distribution. In the aggregate, those with a particle size above 5 mm are called coarse aggregates, and those with a particle size of 5 mm or less are called fine aggregates. According to different sources, aggregates can be divided into two categories: natural aggregates and artificial aggregates.
Natural aggregates include gravel, gravel, sand, stone chips, etc.; artificial aggregates include burnt bauxite, stable solid metallurgical slag, etc. The aggregate used for asphalt pavement should be clean and free of mud. The particles of coarse aggregate should be close to cubes, with many edges and corners, and less flat pieces and long strips. Pa, but also wear-resistant.
Aggregate and asphalt materials should have good adhesion, not easy to be peeled off by water erosion. If the adhesion of aggregate and asphalt is poor, it should be improved by adding an effective anti-stripping agent. When selecting aggregates, aggregates of the same particle size with similar particle sizes should be used for layered pouring; graded aggregates with particle sizes matched according to specifications are often required for mixing mixtures. The aggregates can also be blended in different proportions with aggregates of the same particle size.
Mineral aggregates with a particle size of mineral powder less than 0.074 mm. It is mostly used on asphalt concrete and asphalt macadam pavement. Its function is to fill the gap, prevent hot asphalt from flowing, and enhance the cohesive force and thermal stability of asphalt materials. Mineral powder should also have good affinity (that is, adhesion) with asphalt and be able to resist water erosion. The most commonly used mineral powder is limestone powder.
Asphalt pavement roads can be divided into two types: gravel asphalt concrete surface course (SAC) and asphalt mastic macadam mixture surface course (SMA) according to the mixing ratio of aggregate and mineral powder.
1. Multi-gravel asphalt mixture
More coarse gravel is used to form the skeleton, and asphalt mastic fills the pores in the skeleton and glues the skeleton together to form an asphalt mixture. The specific composition is: the content of coarse aggregate is 69%-78%, the mineral powder is 6%-10%, and the oil-stone ratio is about 5%. The practice of several high-level highways has proved that the multi-gravel asphalt concrete surface can not only provide a deeper surface structure, but also have smaller voids and less water permeability like traditional Type I asphalt concrete, and at the same time have better anti-corrosion properties. Deformability (higher dynamic stability).
2. Asphalt mastic macadam mixture (SMA)
A kind of asphalt mastic binder composed of asphalt, mineral powder and fiber stabilizer, which is filled in the skeleton of discontinuously graded mineral aggregates to form a dense mixture of skeletons. SMA is a discontinuously graded asphalt mixture, the proportion of coarse aggregate over 5mm is as high as 70% to 80%, and the amount of mineral powder is 7% to 13%. The resulting intermittent gradation rarely uses fine aggregates; in order to add more asphalt, the amount of mineral powder is increased on the one hand, and fiber is used as a stabilizer at the same time; the amount of asphalt is as high as 6.5% to 7%. High-performance requirements, and hope to choose asphalt with small penetration, high softening point and good temperature stability.