What is asphalt made of?
What is Asphalt Made Of? Asphalt concrete is an artificial non-fired building material made from a mixture of bitumen, large and small aggregates (gravel, crushed stone, sand), mineral powder, and other components. In everyday life, asphalt concrete mixtures are not quite correctly called asphalt because it is the Greek name for the black rock tar (bitumen) that forms in coal rocks. There are several types of artificial asphalt, differing in composition and manufacturing technology. Each variety has an individual set of performance properties and is designed for specific areas of application.
What components are asphalt made of?
The main components of asphalt concrete:
Large aggregates – crushed stone and gravel. They must adhere firmly to the binder. This requirement is met by cuboid grains of crushed stone from dense rock and metamorphic carbonate rocks. In the production of asphalt concrete mixtures, an aggregate with a grain size of 10-40 mm is used.
The fine aggregate is sand. For this purpose, natural quarry sand (river sand is not suitable) or screening of crushed stone is used. In the raw asphalt concrete mixture, the sand of different grades is used, which allows reducing the porosity of the layer. Fine aggregate increases the density of asphalt concrete, improves resistance to high temperatures, and improves the strength of the road surface.
Mineral powder. Its quantity and quality significantly affect the properties of the binder. Too much mineral powder reduces the strength of the road surface, especially in winter conditions.
Astringent. Its functions are most often performed by bitumen, which can be liquid or viscous. The required viscosity coefficient of bitumen is indicated in the technical documentation; it depends on the composition of the raw mixture and the temperature of asphalt laying. When carrying out road works in winter conditions, liquid bitumen with additives and thinners is usually used.
Types of asphalt concrete mixtures by the composition
By the size of the aggregate grains, there are three types of asphalt concrete, each of which has a specific area of application:
- Coarse-grained. This material is in demand for the lower layers of the road cake. For its manufacture, crushed stone of large (20-40 mm) and small fractions (5-15 mm) is used.
- Fine-grained. The aggregate of such asphalt concrete is fine-grained crushed stone 5-15 mm. In two-layer road surfaces, fine-grained material is used for the construction of the top layer of the road.
- Sandy. This artificial asphalt is suitable for pavement applications. The main filler in it is sand. Also, in the composition, there are fine crushed stone and a little mineral powder.
According to the composition, the following types of asphalt concrete are also divided:
- Classic. Designed for the construction of urban and village roads, sidewalks.
- Crushed stone-mastic. They contain stabilizing additives of the fibrous type. They are used to create high-strength road surfaces of highways with high traffic intensity.
- Polymer asphalt concrete. They contain copolymers and plasticizers that increase the strength and maintenance-free period of road surfaces. Polymer asphalt concretes are effective for paving bridges, airfields, passages along which heavy equipment moves.