Black crushed stone is not always a natural raw material extracted from rocks of the corresponding color by crushing and subsequent processing. Sometimes it is a bulk material that is coated with a special bituminous or tar composition. Such processing is necessary to obtain a product with higher wear resistance and adhesion (adhesion quality with other building compounds).
Types and applications
According to GOST, black crushed stone is classified by fraction size:
- From 5 to 20 mm - gravel screening (crumb), which is the most fine-grained composition.
- From 20 to 40 mm - medium-grained crushed stone. Most often used in construction.
- From 40 to 70 mm - coarse-grained material, when laying which is usually carried out gusseting (redistribution of stone to remove voids).
The specific gravity of black crushed stone is 2.9 t/m3, so it is transported only by heavy vehicles.
Most often this material is used when laying sidewalks, city alleys and playgrounds. It is also used to make road asph alt concrete pavements. When building houses with basements orbasements, raw materials are used for waterproofing.
Sometimes this unusual material is used for decorative decoration of suburban areas.
The bulk density of black crushed stone is 2900 kg.
Advantages and disadvantages
Among the advantages of this material it is worth highlighting:
- Reduced cracking. That is why standard asph alt concrete is increasingly being replaced with black gravel.
- Improved shear resistance of coatings made using this material.
- Good slip resistance.
- Long shelf life.
- Easy sealing.
- Cold stackable.
From the shortcomings of black gravel, they usually distinguish:
- High water permeability of raw materials.
- Too long time for the formation of the pavement (up to 1 month). If the material is laid in late autumn at negative temperatures, then the foundation will gain the required strength only after a year.
Also, when laying a new pavement, it will not be possible to exert strong pressure on it for up to 5 days.
The scope of this building material largely depends on the method of its manufacture.
Cold production technology
This black crushed stone is used only for the repair of road surfaces. The technology of production by the cold method is carried out in two ways: directly at the facility or in a specialinstallation with subsequent transportation to the place of work.
Preparing such raw materials using tar, bitumen and their emulsions at temperatures from +1000С to +2000С. The resulting material is laid cold. In this case, a necessary condition is the air temperature, which should not be lower than +50С.
Cold gravel has a low viscosity, so it can be stored in cold rooms for a long time.
Warm production technology
In this case, the material is subjected to heat treatment from +800С to +1200С. Warm crushed stone is used for laying new road surfaces with reduced mechanical stress. It is necessary to use the material at a temperature from +600С to +1000С.
Hot production technology
Hot black crushed stone is produced at temperatures from 1200С to 1800С. Tar and bitumen are also used to process the material. It can only be used when its temperature is within +100-1200C.
Laying warm and hot crushed stone is necessary immediately after its manufacture. That is why when installing road surfaces, specialized asph alt paving equipment is always used.
In production conditions, expensive equipment is used to produce black crushed stone.
It is also worth considering that raw materials,manufactured under the influence of high temperatures, has a very low resistance to the formation of fungus and mold. In order to eliminate this drawback, boric acid, diethanolamine and suspensions of fatty acids are added to the crushed stone.
How to make your own hands?
To make black gravel yourself, you need to mix the following ingredients:
- Crushed stone (limestone is most suitable) grade not lower than M600. It is better to use a material of medium fraction (20-40 mm), as it has good absorbent properties.
- Astringent component. As it is recommended to use BND 200/300 bitumen. The volume of the binder should be about 4-5% of the total mass of gravel.
- Aqueous solution of NaOH (this substance will be used as a bituminous emulsion).
- Synthetic fatty acid in the amount of 3% of the total mass of bitumen.
- Electric pear-shaped concrete mixer.
- Hot material extractor.
The mixer must be equipped with a heating element, which will allow you to get the temperature necessary for processing crushed stone.
The mixing time of all components in a concrete mixer directly depends on the volume of raw materials and the size of the mixer.
With the help of black gravel, you can pave all the paths in the suburban area, make the top layer of the blind area around the house or organize a reliable and durable parking space for your car. Nevertheless, it should be borne in mind that other materials can be used in private construction,which are much easier and cheaper to make with your own hands without the use of heating elements. In addition, laying black gravel is very difficult to do alone.
