Asphalt concrete is mainly made of coarse aggregate, fine aggregate, mineral powder, asphalt, etc.
Coarse aggregates are aggregates with a particle size greater than 2.36 mm. It forms a framework in the asphalt concrete to maintain stability. Therefore it should meet the requirements of mechanical properties and have good shape. Low content of elongated and flaky particles, no weathering, no impurities, rough surface and high internal friction.
Fine aggregate refers to large sand, stone chips, etc. with particle size between 0.075 and 2.36. In appearance it should be clean, no weathering, no impurities, and have proper particle composition and possible angularity to increase the embedded locking effect between particles and reduce the porosity between aggregates.
Before using asphalt, the asphalt penetration, ductility, softening temperature and other indicators should be checked to ensure that all indicators are in line with the technical requirements of the traffic petroleum asphalt. In the choice of asphalt use, it should take into account the high temperature stability and low temperature crack resistance of asphalt pavement.
Since the higher the grade of asphalt, the greater the penetration and the lower the consistency, different types of asphalt must be used according to the different layers of the pavement. The surface layer uses thinner asphalt to improve the crack resistance of the surface layer; the middle and lower layers use thicker asphalt to improve the rutting resistance.
The paraffin content should be controlled at less than 3%. Too much paraffin content has an effect on the high temperature stability and low temperature crack resistance of the pavement, and also affects the adhesion of asphalt.
The role of filler is to form asphalt mastic with asphalt to increase the bonding force of the asphalt mixture. The filler ratio is directly related to the free bitumen in asphalt mixture. If there is free bitumen, it will reduce the adhesion of asphalt mixture, and will appear the phenomenon of bleeding asphalt surface.
The filler should meet the fineness requirements and be free of impurities. On the occasion of using bagged mineral powder, there should be a storage site, which is protected from rain and moisture, and ventilated and dry to prevent the mineral powder from getting wet. The mineral powder that has been caked with moisture should not be used.
Sometimes in order to improve the adhesion of asphalt, it is necessary to add admixtures such as slaked lime. The slaked lime must be thoroughly disintegrated to meet the fineness requirements. Otherwise, it will have the opposite effect and affect the quality of the asphalt mixture.