Non-metallic bulk materials are the main components in the construction industry. Sand and gravel are used in the production of concrete and reinforced concrete structures, building mixtures. These materials are used for ground preparation, planning, landscaping. In road construction, crushed stone is used as the underlying layer of the roadway. Some types of crushed stone are used to improve the local area.
Types of rubble and sand
All bulk building materials are classified according to several main criteria:
- origin
- physical and mechanical properties (density, strength, frost resistance, moisture absorption);
- the shape and size of grains;
- the level of radioactivity, the presence of organic and inorganic impurities.
The nature of the origin of crushed stone and sand depends on the source material. There are crushed stone from rocks, ore crushed stone, which is made from metallurgical recyclables and secondary, obtained by crushing building waste (concrete, brick). Physico-mechanical properties of crushed stone directly depend on the material of its origin. The most demanded materials, the basis of which are rocks of high strength - resistant to deformation and fracture under mechanical stress. By grain size, crushed stone is divided into several types: screening (up to 5 mm), medium (5-25 mm), large (25-40 mm).
Sand by origin is divided into natural and artificial. Natural bulk material is obtained in the development of sand or sand and gravel deposits. Depending on the occurrence, there are sea, river or mountain sand. The first two species are distinguished by more rounded grains and a lower content of impurities, compared with materials mined in quarries. The size of the granules of sand is divided into large, medium and fine.
Natural sand production
The production of natural non-metallic bulk materials includes several stages:
- production;
- processing and enrichment (if required);
- storage.
Almost all types of bulk materials are mined open-pit. Quarry sand is mined by excavators or bulldozers. In the production of mountain sand, due to the presence of a large number of impurities and different sizes of granules, additional processing and enrichment of raw materials is required. This process involves flushing and sorting the material. For the production of the smallest fraction used in the production of cement-based building mixtures, additional grinding of sand with roller crushers is possible. Natural sand refers to materials prone to caking, therefore, in its production, a bunker for bulk materials is often used - a device in the form of an inverted truncated pyramid for storage and supply of bulk raw materials.
River sand is extracted hydromechanically in ponds. Barges with hydraulic pumps pump raw materials from the bottom of the river to a shore dump. Water flows back into the river, and sand remains in the dump. If the bottom surface is too dense, an bucket elevator is additionally used.
Artificial Sand Production
The geographical location of natural sand deposits is uneven, which may lead to a shortage of this material in some regions. The production of artificial sand allows us to solve this problem in many ways, providing the necessary needs. Artificial bulk material is obtained by crushing hard rocks and raw materials of other sources. Depending on the material of origin, the following types of artificial sand are distinguished:
- Crushed . Used in acidic and decorative compositions. It is produced by crushing marble, diabase, basalt or dense metallurgical slag.
- Light sands, organic and inorganic. Bulk material obtained from pumice, volcanic slag, tuff, agricultural and wood waste.
- Sedimentary sands are the result of grinding shell rock.
- Expanded clay sand obtained by crushing expanded clay rocks is a heat-insulating material, aggregate for light concrete and mortar.
- Porous sands from slag.
Crushed stone production
Raw materials for the production of crushed stone are mined open-pit in quarries of various rocks. Depending on the characteristics of the field and the produced rock, a method of developing deposits is selected. For particularly hard rocks, preliminary blasting is carried out. A charge is laid in pre-drilled wells. Explosion rock splits into pieces, which are received for further processing.
The extracted raw materials go to crushing, which is carried out by crushers of various types (roll, jaw, shock, cone). The choice of equipment is made depending on the type of final product. After crushing, the finished crushed stone goes to sort. By screening, the material is divided into fractions according to grain size. The installation consists of several large sieves with holes of different diameters. The smallest fraction passes all levels of sieves, settling in the pan. In the process of sorting into fractions, crushed stone can be washed to remove clay impurities.
The main types of crushed rock
There is a fairly large group of these materials, but among them the following types are most in demand:
- Granite - the most durable crushed stone of magmatic origin. Its basis is made up of quartz, mica and spar. The most common shades are red, pink, gray. Due to its origin, special attention should be paid to the certificates of radioactivity when choosing this material. Due to the physical and mechanical properties, the most popular type of crushed stone.
- Gravel . The basis of this material is rocky rocks. This type of crushed stone is produced in two ways - crushing rocks (crushed gravel) and sifting of river or sea soil (rounded gravel). It is significantly inferior in strength to granite, but cheaper with a low radiation background.
- Quartzite . Bulk material from quartz rock. Its strength is not inferior to granite, but at the same time it has a slight radiation background. Due to the original structure and attractive colors, it is very popular in decoration.
- Limestone . It is produced by crushing sedimentary rocks. It is inferior in strength to all other types of crushed stone. The basis is dolomite and lime. Favorable difference - low price.
Areas of application for bulk materials
The range of application of non-metallic bulk materials is extremely large, covers almost all stages of construction and is quite in demand in other types of work:
- Preparation of concrete of various grades.
- Production of concrete products.
- Road construction.
- The device of railways, runways.
- Landscaping.
- Livestock.
- The device of the protective layer on the road surface with ice.
Bulk material transportation
Bulk materials are transported by rail (over long distances), by road and by river. Gondola cars, open platforms, dumpcars — special gondola cars with the possibility of automated unloading by tipping, are most suitable for rail transportation. Dump trucks are the most suitable for transporting sand and gravel by road. Delivery of bulk materials by river barges is the cheapest transportation option, but only relevant if the waterways are close. When transporting, it is not recommended to transfer these materials to another transport on the way to the delivery place in order to avoid losses.
Storage and sale
After mining and, if necessary, enriching the sand, crushed stone in the form that the consumer sees it is sent to the warehouse. Each type and fractional composition of bulk material is stored separately. Storage areas should be flat, rainwater should not collect in them. If necessary, additional protection against groundwater is done. In winter, materials are cleared of snow and ice.
The supply of non-metallic materials from the place of storage is most often carried out by road. Exceptions are large enterprises with separate railway lines. For safe and convenient shipment of materials to the final consumer, the storage area is equipped with convenient access roads. Usually organized one-way ring traffic. For the convenience of loading and preventing caking, a bunker for bulk materials is used. For night work, artificial lighting is provided.