Sand is the main component of modern construction concrete. According to the source, construction sand can be divided into artificial sand and natural sand.
Artificial sand is a general term for manufactured sand and mixed sand that have been treated with soil removal. Among them, manufactured sand is rock particles obtained by mechanical crushing and screening (excluding soft rock and weathered rock), while mixed sand is a mixture of manufactured sand and natural sand.
Natural sand is a particle smaller than 4.75 mm in diameter formed by natural rock through natural weathering, transportation and accumulation. From its source, it can be divided into mountain sand, river sand (including lake sand), desert sand and sea sand. We will analyze the differences between different sands from the following aspects.
Different distribution areas
The manufactured sand is mainly manufactured mountain sand, and non-metallic mine rocks in various places can be used as manufactured sand raw materials.
River sand mainly comes from rivers and lakes, and they are distributed in inland and coastal areas.
The sand that originated in the desert is called desert sand.
Natural mountain sand is mostly produced at the foot of mountains, while river sand is mainly derived from rivers and lakes, and they are distributed in inland and coastal areas. Among them, the mountain sand stock is small, and the river sand is widely distributed and the stock is large.
Sea sand is sand that has been soaked in seawater, mainly distributed in coastal areas, usually located at the confluence of seawater and rivers and shallow sea areas.
Different mineral and chemical composition
The parent rock (production raw material) of manufactured sand is mainly soft and hard rocks such as granite, basalt, limestone, and the main mineral composition and chemical composition are consistent with the parent rock. For example, the main minerals of granite manufactured sand are quartz and feldspar, and the chemical composition is mainly silica and aluminosilicate. The main mineral composition of limestone manufactured sand is mainly calcite, and the main chemical composition is calcium carbonate. The manufactured sand has stable mineral and chemical composition, and basically does not contain organic matter.
In contrast, natural mountain sand has a complex composition, more organic impurities and a large amount of mud.
The main mineral component of river sand is quartz, which contains minerals such as mica and contains many impurities.
The main component of desert sand is quartz, with a small amount of feldspar and muscovite. Its source is mainly the residual minerals from the weathering of sandstone and granite. The sand in the desert is weathered and accumulated, and the harmful substances cannot be removed, resulting in a high content of harmful substances in the sand, fine and scattered, which does not meet the standards of construction sand. In addition, the sand in the desert has a very high alkali content. The salt and alkali components in the sand are corrosive to the steel bars in the building. The sand with a high alkali content will chemically react with cement and water, which can reduce concrete strength.
The main mineral component of sea sand is also quartz, and contains shells and cuttings. It has a higher mud content, more impurities, and a higher content of organic matter and a certain content of sulfates and sulfides. The Ministry of Housing and Urban-Rural Development stipulates that sea sand used for reinforced concrete fine aggregate must be desalinated so that its chloride ion content is less than 0.06%. If unqualified sea sand is used directly, the high content of chloride ions will corrode the steel bars, resulting in damage to the building structure and greatly reducing the strength, hardness and bearing capacity of the building.
Different appearance and physical characteristics
Manufactured sand is a sand-gravel material obtained after being crushed and screened by professional sand-making equipment. Compared with natural river sand, it has the characteristics of sharp edges and sharp edges and many needles and flakes. River sand is dug directly from the river channel, so it will be mixed with small pebbles and fine sand. These small pebbles are washed by the river for a long time, and the edges and corners are relatively round. The river sand is generally bright yellow.
Desert sand is mainly weathered from rocks, and is generally golden yellow, but because the rocks contain various minerals of various colors, the deserts have various colors.
Sea sand is the sand produced in the ocean (including beach sand and seabed sand) and near the mouth of the sea. The sea sand is affected by the seawater. The sea sand that has not been desalinated has high salt content and has a sticky feel when grasped by hand. From the color point of view, the color of sea sand is relatively dull and dark brown. From the perspective of particle fragments, sea sand generally contains fragments such as shells.
The physical characteristics of sand mainly include fineness modulus, hardness and roundness. The fineness modulus is an index used to measure the degree of sand thickness. According to the fineness modulus, it can be divided into three categories: coarse sand (3.7～3.1), medium sand (3.0～2.3) and fine sand (2.2～1.6) .
The manufactured sand is basically medium-coarse sand with a fineness modulus between 2.6 and 3.6. Its particle type and gradation (that is, the ratio of large and small particles) can be adjusted according to the use and needs, and its hardness is determined by the raw material. Hardness is determined. The roundness of manufactured sand particles is very poor, mostly with edges and corners, and the surface is rough, which makes manufactured sand concrete high in strength.
Mountain sand has sharp edges and corners and rough surface.
River sand has larger fineness modulus and hardness, better roundness, and smoother surface.
The fineness modulus of sea sand is relatively small, but the hardness is greater, the roundness is better, and the surface is smoother.
The diameter of the sand in the desert is generally below 0.25 mm. The fineness of the desert sand is too fine and oily and smooth, and it is not used in construction.
Both artificial sand and natural sand can be used as construction sand. In addition, river sand and sea sand can also be used in industrial fields such as casting, grinding, and rust removal.
River sand is cement standard sand, which is mostly used in construction, concrete, cementitious materials, road construction materials, artificial marble, cement physical properties inspection materials, etc.
Manufactured sand is an aggregate prepared through centralized crushing equipment. For example, through the joint operation of jaw crusher, cone crusher, and impact sand making machine, manufactured sand below 3 mm can be produced. The raw materials can come from river pebbles, mountain rocks, quartz, granite, basalt, etc. At present, it is widely used in the sand and gravel aggregate market, effectively replacing river sand as the main source of sand and gravel. At present, the projects with large demand for sand and gravel include subway project construction, infrastructure construction such as libraries, parks, viaducts, squares, stadiums, reinforced concrete high-rise buildings, highways, railways, bridges, etc., where sand and gravel aggregates and natural materials are needed. In the industries involved in sand, manufactured sand can be used in these places.
Desert sand is mainly formed by long-term weathering of some conglomerate and quartz. Desert sand is very fine and dusty, and cannot be used as construction sand.
Sea sand is the main raw material for machinery and foundry sand, abrasive materials (sandblasting, hard abrasive paper, sandpaper, emery cloth, etc.), sand cleaning, rust removal, descaling treatment ceramics and refractory porcelain blanks and glazes, kilns Furnace high-silicon bricks, ordinary silicon bricks, silicon carbide and other raw materials, metallurgical silicon metal, ferrosilicon alloy and silicon aluminum alloy and other raw materials or additives, flux. When sea sand is used for concrete fine aggregate containing steel bars, it must undergo strict purification treatment. Many places have prohibited the illegal use of sea sand in construction. At present, the main purpose of sea sand is as a filling material for sea reclamation and road construction.