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 bitumen or tar composition. Such processing is necessary to obtain a product with higher indicators of wear resistance and adhesion (the quality of adhesion to other building compounds).
Types and applications
According to GOST, black gravel 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 - a coarse-grained material, during the laying of which a splitting is usually performed (redistribution of stone to remove voids).
The specific gravity of black gravel is 2.9 t / m 3 , so it is transported only by heavy vehicles.
Most often this material is used when laying sidewalks, city malls and platforms. Also, asphalt concrete pavements are made from it. In the construction of houses with basement or basement, raw materials are used for waterproofing.
Sometimes this unusual material is used to decorate suburban areas.
The bulk density of black gravel is 2900 kg.
Advantages and disadvantages
Among the advantages of this material, it is worth highlighting:
- Reduced cracking. That is why standard asphalt concrete is increasingly being replaced with black gravel.
- Increased shear resistance of coatings made using this material.
- Good slip resistance.
- Long shelf life.
- Easy sealability.
- Possibility of laying material in a cold form.
Of the shortcomings of black gravel, usually distinguish:
- High water permeability of raw materials.
- Too long period of pavement formation (up to 1 month). If the material will be laid in late autumn at freezing temperatures, then the base will gain the required strength only after a year.
Also, when laying a new pavement, it will not be possible to exert strong pressure for up to 5 days.
The scope of this building material largely depends on the method of its manufacture.
Cold Production Technology
Such black crushed stone is used only for the repair of road surfaces. Cold production technology is performed in two ways: directly at the facility or in a special installation with subsequent transportation to the place of work.
Such raw materials are prepared using tar, bitumen and their emulsions at temperatures from +100 0 C to +200 0 C. The resulting material is placed in a cold form. In this case, the necessary condition is the air temperature, which should not be lower than +5 0 .
Cold crushed stone 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 +80 0 to +120 0 . Warm crushed stone is used for laying new road surfaces with reduced mechanical stress. It is necessary to use the material at temperatures from +60 0 to +100 0 .
Hot Production Technology
Hot black crushed stone is made at a temperature range from 120 0 C to 180 0 C. Tar and bitumen are also used to process the material. You can use it only when its temperature is in the range + 100-120 0 C.
It is necessary to lay warm and hot crushed stone immediately after its manufacture. That is why specialized paving equipment is always used when installing pavements.
In production conditions, expensive equipment is used to make black gravel.
It is also worth considering that raw materials made under the influence of high temperatures have a very low resistance to the formation of fungus and mold. In order to eliminate this disadvantage, boric acid, diethanolamine and fatty acid suspensions are added to the crushed stone composition.
How to cook with your own hands?
To make black crushed stone yourself, you need to mix the following components:
- Crushed stone (limestone is most suitable) of a brand not lower than M600. It is better to use a medium fraction material (20-40 mm), as it has good absorbent properties.
- Astringent component. As it is recommended to use bitumen BND 200/300. The volume of the binder should be about 4-5% of the total mass of gravel.
- An aqueous solution of NaOH (this substance will be used as a bitumen emulsion).
- Synthetic fatty acid in a volume of 3% of the total mass of bitumen.
- Electric pear-shaped concrete mixer.
- Device for extracting hot material.
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 tracks on a 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 is worth considering that in private construction you can use other materials that are much simpler and cheaper to make yourself without the use of heating elements. In addition, the laying of black gravel is very difficult to produce alone.