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Introduction of Asphalt Mixture Pavement

Asphalt mixture is a pavement structure composed of asphalt material as binder to bind mineral material and various base and cushion.
Because asphalt pavement uses asphalt binder, it enhances the bonding force between mineral aggregates, improves the strength and stability of mixtures, and improves the durability of pavement quality. Compared with cement concrete pavement, asphalt pavement has the advantages of smooth surface, seamless, comfortable driving, low noise, good wear resistance, small vibration, short construction period, convenient maintenance and suitable for phased construction. As a result, it has been applied more and more widely.
Pavement Performance of Asphalt Mixture
(1) High temperature rutting resistance, also known as high temperature stability, is the ability to resist the deformation of asphalt mixture caused by repeated action of flow load under high temperature conditions.
(2) Low temperature crack resistance, that is, the ability to resist low temperature shrinkage cracks caused by cooling;
(3) Water stability, also known as the ability to resist water damage, is the ability to resist the erosion of asphalt mixture by water, which gradually produces asphalt membrane peeling, peeling, loosening and pitting damage.
(4) Fatigue resistance, that is, the ability to resist the damage of asphalt mixture under repeated loads;
(5) Anti-aging performance, that is, the ability to resist various good properties of asphalt mixture, such as gradually losing its toughness due to climate influence;
Classification of Asphalt Concrete Pavement
According to technical characteristics, asphalt pavement can be divided into asphalt concrete, hot mix asphalt macadam, emulsified asphalt macadam mixture, asphalt penetration type, asphalt surface treatment, asphalt horseshoe macadam macadam and open graded asphalt wear layer. Among them, asphalt concrete is commonly used.
Composition Design of Asphalt Concrete Mixture
Asphalt concrete mixtures mainly refer to asphalt concrete mixtures that have not been paved and compacted. Asphalt concrete mixture is a kind of asphalt mixture which meets the technical standards by mixing the required gradation of mineral aggregate and asphalt, which is composed of appropriate proportion of coarse aggregate, fine aggregate and filler.
Marshall stability method is used in mix design of hot mix asphalt mixture. The method is to design asphalt mixtures according to mix ratio, and then make specimens of specified size. The physical indexes of specimens (including gross volume density, void fraction, asphalt saturation and mineral void fraction) are measured after 12 hours, and then the stability and flow value are determined. When necessary, the water stability and high temperature stability are also checked. 。 Asphalt concrete mix design includes three stages: target mix design, production mix design and production mix verification. Material variety and aggregate gradation asphalt dosage of asphalt mixture are determined by mix design.
At present, modified asphalt concrete is widely used as surface layer in asphalt concrete pavement. The commonly used modified asphalt is SBS modified asphalt.  Modified asphalt has better pavement performance. It has good high and low temperature stability and fatigue resistance.
Construction Technology of Asphalt Concrete Pavement
Mixing of asphalt mixtures - transportation of mixtures - paving of mixtures - paving of asphalt pavement - compaction - joints - open traffic and others.
1. Mixing of Asphalt Mixture
Asphalt mixtures must be mechanically mixed in asphalt mixing plants (yards and stations). In order to ensure the gradation of asphalt mixtures, batch mixers are usually used for mixing. Several problems should be paid attention to in the mixing process:
(1) The mixing time and mixing time shall be determined by trial mixing according to specific conditions, and the degree of uniform coating of aggregate with asphalt shall be taken as the degree. The mixing time of SMA mixture should be prolonged appropriately.
(2) The size of the vibrating screen of the grading mixer should match the size of the ore, and the maximum sieve hole should be slightly larger than the maximum size of the mixture. Samples should be taken in time to do a good job of relevant testing.
(3) The mixing temperature, the heating temperature of asphalt and the heating temperature of mineral materials should meet the requirements of specifications.
(4) The temperature and gradation of the asphalt mixture should be measured by car when the asphalt mixture is discharged from the factory. It is found that the flowers should be handled in time, and the factory time record of the asphalt mixture should be made and the bill of lading should be issued.
2. Transportation of Asphalt Mixture
The transportation of asphalt mixture should pay attention to the following problems:
(1) Asphalt mixtures should be transported by large-tonnage trucks, which should be covered with canvas to ensure temperature, dust and pollution prevention of mixtures.
(2) The truck must be cleaned after each use, and a layer of separator or anti-sticking agent is applied on the carriage board to prevent asphalt bonding.
(3) When loading, the carriage should be loaded before and after, and the middle should be installed at last. This can reduce the segregation of the mixture.
(4) During the paving process, the truck should stop at 10-30_in front of the paver, wait in neutral, and be propelled forward by the paver and unload slowly.
3. Asphalt Mixture Paving
(1) Hot mix asphalt mixture should be paved by asphalt paver. When spraying modified asphalt mixture or SMA on pavement with sticky oil, tracked paver should be used. The receiving hopper of paver should be coated with thin layer separator or anti-binder.
(2) The paver should pre-heat the ironing plate 0.5-1 h before the start of construction and not less than 100 C. In order to improve the initial compactness of pavement, the vibration frequency and amplitude of the compacting device of compacting plate or rammer should be adjusted correctly in the course of paving.  Widening connection of ironing plate should be carefully adjusted to the paved mixture surface without obvious segregation marks.
(3) The paver must pave slowly, uniformly and continuously during the paving process, and must not change its speed or stop in the middle at will, so as to improve the smoothness and reduce the segregation of the mixture. The paving speed should be controlled in the range of 2-6 m/min for modified asphalt mixture and SMA.

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