Use of quartz sand and quartz gravel
Quartz sands and quartz gravel differ from other sands and gravels mainly in their high SiO 2 content ( silicon dioxide , the mineral quartz ). There are different definitions of when one speaks of quartz sand or quartz gravel. A SiO 2 content of 96% is often regarded as the limit. This value is also stored in the trend-setting DIN and EN standards for the treatment of drinking water. A distinction is made between sand and gravel according to the grain size . Here, too, there are various delimitations, whereby gravel is often used from 2 mm grain diameter.
Properties of quartz sands and quartz gravel and their importance for their application
Quartz grains are very hard due to the high proportion of SiO 2 , but also brittle for the same reason. When handling quartz grains, care should be taken to ensure that as little abrasion or shattering occurs as possible. Ultra-fine quartz particles as alveoli common particulate matter can cause severe diseases. If quartz gravel is conveyed pneumatically , this should be done with minimum conveying pressure. Wherever possible, it should be installed in closed systems or - as in the drinking water area - by flooding.
The hardness against abrasion allows the producers of quartz gravel and quartz sands to produce very narrow and precise grain bands without the grains mutually destroying one another. A normal sand for the production of ready-mixed concrete has z. B. the grain 0/2. This means that according to the relevant standards, the smallest grain sizes start at a size of 0.063 mm and the coarsest components are 2 mm. Typical quartz grains are e.g. B. at 0.1-0.4 mm; 0.4 - 0.8 mm or 0.71 - 1.25 mm. The larger of the mentioned sieves is referred to as the upper nominal grain , the smaller one as the lower nominal grain . The distribution between these sieve sizes (or above and below) is called the sieve curve . The individual grain bands required by the manufacturing industry depend on the application.
There are basically two different fields of application for quartz gravel and sands
- Applications such as glass or ceramics manufacture, the production of silicon or chemical conversion, e.g. B. to water glass . In this group of applications, the chemical composition and purity play a major role. A large proportion of iron oxide in the raw material means that clear glass cannot be made from this sand. In all applications of this group, the original quartz grain is chemically converted and is then in a completely different form and usually also in a chemical compound.
- Applications in the drinking water industry, dry mortar or construction chemistry use the mechanical properties of quartz products. The chemical composition plays a subordinate role here. It often depends on the grain size, shape or properties. In the case of structural structures, for example, a particularly close packing of the spheres is required. The Fuller curve plays a decisive role here. Completely different requirements are made of a filter gravel z. B. is installed in a well structure. A porosity in connection with the absence of undersize is required here.
Dry mortar, dry concrete, grouting mortar and other special mortars
If you think about the uses of sand and gravel, the construction industry is one of the first areas that comes to mind. Is z. B. If a house is built, the foundation, basement or false ceilings are usually made of concrete . This is delivered by the well-known concrete mixers , which in turn are filled with ready-mixed concrete in the nearest ready-mixed concrete plant.
The production of dry mortar (and if it contains larger gravel: dry concrete), adhesives (e.g. tile adhesive ) and special mortars (e.g. grouting mortar ) is different. The principle is that the products are mixed together in a production plant and then mixed with water for the various applications. The possibilities are diverse and are used in a wide variety of construction, industrial and infrastructure areas. The unit costs of the various producers are considerably higher than those of a simple ready-mixed concrete plant. In this way, higher-quality to high-quality products are produced that can have a variety of properties and applications that go beyond normal concrete.
The special properties are achieved through the interaction of the additives and aggregates used. Because quartz sand and gravel can be precisely classified as mentioned above, the structure of the grading curve with these raw materials is the first choice here. Due to the exact matching of the grain sizes, expensive additives and surcharges can often be saved.
Water treatment
The use of filter gravel and filter sand is essential for the treatment of water. Due to the exact classification and hardness, quartz gravel is always used. In our modern society we mainly need water as drinking water . The preparation of drinking water varies greatly depending on the country. In Germany, a large part of the raw water supply is ensured from wells, while in other EU countries z. B. Dams play a much bigger role.
In addition to drinking water, the use of water as industrial water or as swimming and bathing pool water is a widespread application.
The treatment of water is inconceivable on an industrial scale without the use of filter gravel and filter sand. There are a wide variety of methods for treating drinking water or swimming and bathing pool water. The presence of suitable filter gravel is often the world is not given. The desert regions in particular have sands that are unsuitable for treating water (low SiO 2 content = too soft, rounded = hardly any filtering effect). For this reason, large quantities of quartz gravel are supplied to desert regions in this industry. (Selling “Sand in the Sahara”).
Clean and germ-free drinking water is one of the most important foundations of our modern society and, unfortunately, is by no means available to everyone on earth. From this point of view, cleanly classified filter gravel (quartz gravel) is one of the most important bases for supplying mankind.
Fillers
The fine quartz sand or the quartz powder made from it by grinding with flint stone or aluminum oxide balls are used as fillers in various industries . Fillers are insoluble additives which, when added to the base material (the matrix) in a high content, u. a. change the mechanical, electrical or processing properties of materials significantly, and at the same time significantly reduce the proportion of the typically more expensive matrix in the finished product. Large buyers of these fine materials are paint and varnish manufacturers and the plastics industry.
Leisure sands
In the leisure sector, quartz sands and quartz gravel are mainly used in the following areas:
- Riding arenas When building a riding arena, there are different requirements for the subsurface. For example, a riding arena for western riding has to be set up completely differently than a place on which dressage is to be ridden due to the constant horizontal and vertical forces involved in this sport. Yet other requirements are placed on the surface for show jumping riders or on an "all-round" course that should have a little bit of everything. Often other substances such as wood shavings or tissue particles are added to the sands in order to achieve the desired effects. Outdoor spaces must be built in such a way that rainwater can drain off easily. Regardless of the orientation of the site, the surface must be drainable. The substructure plays just as important a role as the quality of the sand.
- Golf courses There are different uses for quartz sand and quartz gravel on golf courses . In addition to the use in the "bunker", two very important technical applications are also familiar. With top dressing in the “green” area, the ground under the blades of grass is “smoothed” by sprinkling fine quartz sand in such a way that the balls are not distracted by unevenness. If this quartz sand is contaminated even slightly with coarse components, the mower blades will be damaged, which would lead to delays and high costs. During aeration , the resulting holes are filled with well-trickling quartz sand. Due to the long-term permeability of the quartz bed, nutrients can be brought to the roots sustainably.
- Artificial turf pitches Artificial turf pitches are being built more and more frequently in our society and are getting more and more acceptance also in the professional sector. The structure of an artificial turf pitch can be imagined as a carpet under which a rubber mat lies, which cushions the athletes' steps. The artificial turf (carpet) is then placed on this mat and weighted down with quartz sand so that it does not slip (technically speaking, it is laid floating). On modern artificial turf pitches, rubber granulate is placed on top, which reduces the risk of injury from falls (abrasions). The technical details are regulated in DIN 18035-7.
- Beach sand With this application, the fine quartz sands are poured into halls or outside in order to carry out a wide variety of events. Beach volleyball or beach soccer events are often used as crowd pullers. But every type of beach party is also very popular.
Refractory applications
Applications in the refractory industry are based on the high heat resistance of the quartz products. At higher temperatures, these melt later than most metals. The most common applications are moldings for the foundry industry, feeders and sliding sands.
- Moldings for the foundry industry Negative molds are made from the quartz sands in combination with special binders, which are then later filled with liquid metal. In the case of hollow bodies to be cast, the molded bodies are constructed in such a way that, after the metal has cooled (and solidified), for. B. break apart by vibrations (shaking) and then trickle out of the hollow bodies.
- Feeders Feeders are special molded bodies that are inserted at strategic points when casting larger metal objects. The feeders ensure that gaps ( cavities ) that would arise from the cooling-related shrinkage of the metal are filled.
- Sliding sands These special sands are used in the production of metals - e.g. B. Stainless steels - used. The liquid metals or metal mixtures are in refractory lined vessels. In the lower area of the apparatus there is a slide that is opened after the manufacturing process has been completed in order to drain the liquid product. To prevent the slide from being damaged by the mass or temperature of the molten metal, it is covered with the sand. The slider sands sinter and protect the slider. However, the sands may only become so stable that the sand layer "breaks" after the slide is opened and the liquid metal can run out.
Glass / ceramic / enamel
Quartz sand is the most important raw material for the manufacture of glass and also forms the basis of the product in the manufacture of ceramic products ( tiles , toilets, sinks). As a rule, quartz flour is used to produce enamel . From a technical point of view, it is the SiO 2 contained in the quartz sand that is required for this application. A high degree of purity is particularly important, as the presence of certain metals or their oxides means that the glass or enamel is not entirely clear. The metals iron (as Fe 2 O 3 ) or manganese (MnO) in particular color the melts. In contrast to most other applications, the structure of the grading curves does not matter here.
Raw material for the chemical industry
As with the use for the production of glass, mainly the pure quartz sands from tertiary deposits are used as a raw material supplier for SiO 2 . Large-scale application is z. B. the production of water glass .
Grit
When used as a grit, the high angularity of the coarser quartz sand or finer quartz gravel is used to improve adhesion. For ecological reasons, the use of the quartz as winter litter to scatter ice surfaces against the risk of slipping is a better solution than the use of salts.
Quartz sand is used as locomotive sand on many railroad vehicles. If necessary, sand is scattered in front of the drive wheels via sanding nozzles in order to improve the adhesion between rail and wheel. This is also the reason why you can find sand on the rails of trams or underground trains in cities, especially in the autumn and winter months.
Various uses
Tank filling
When backfilling old underground tanks, quartz gravel in the range of 2 - 8 mm is usually blown into the tank. Filling the tanks with inert quartz gravel prevents them from being compressed over time and, in the worst case, from collapsing on the surface.
Fall protection sand
Fall protection sand is a term from the field of play equipment construction. A thick layer of quartz gravel (e.g. 4 - 8 mm or 8 - 12 mm) is often poured under climbing equipment. Due to the good classification and the absence of supporting grains, the layer cannot compact even after a long period of time. The gravel roll to the side with every step and, like on the beach, you sink in deeply. Through this effect, falls of children from the play equipment are effectively cushioned.
Abrasives
Fine quartz sand or quartz powder ground from it is used as an abrasive in various pastes. The use in this area is limited, since considerably harder and finer ground raw materials such as corundum or aluminum oxide are available. If quartz sand or quartz flour is used here, it often has to do with the relatively low price.
Poultry grit
Since birds have no teeth, they have to break down (grind) your hard food differently. For this purpose, birds have two independent stomachs (the gizzard / gizzard and the normal stomach). All birds have the instinct to pick up small stones, which then serve as a grinding aid in the gizzard. In factory farming z. For example, chicken feeds are used that do not require digestion in the gizzard, but the animals still want to pick pebbles. The quartz gravel is fed as an alternative and taken in by the animals.
Gardening and landscaping
Quartz sands and quartz gravel are used in many different ways in landscaping, although the look is usually the only thing that matters.
Aquarium gravel
Quartz sands and quartz gravel are often used in the aquarium due to their light color. The individual particles have rounded edges and do not injure the fish. In addition, the washed gravel does not compact, so that the roots of the aquatic plants have enough hold, but still get all the nutrients from the water.
Swimming and fish ponds
When used in swimming ponds or fish ponds, as with landscaped gardens, the focus is on the visual effect. As in the aquarium, the lack of compaction of the soil also plays a role for many aquatic plants.
Individual evidence
- ↑ Winfried Koensler: Sand and gravel - mineralogy, occurrence, properties, possible uses . Ferdinand Enke, Stuttgart 1989, ISBN 3-432-97551-1 .
- ↑ German Institute for Standardization (DIN): DIN EN 12904 - Products for the treatment of water for human consumption - quartz sand and quartz gravel . Beuth Verlag GmbH, 2005.
- ↑ Fuller, WB; SE, Thompson: The laws of proportioning concrete. In: Transactions of the American Society of Civil Engineers . tape 33 , 1907, pp. 222-298 .
- ↑ DIN: Sands and gravel for well construction - requirements and test methods . Ed .: DIN. Beuth Verlag GmbH, Berlin July 2014.
- ↑ DIN 19606: Fixed bed filter for water treatment . Ed .: DIN. Beuth Verlag GmbH, Berlin 2016.
- ↑ DIN: DIN 19643 Treatment of swimming and bathing pool water . Ed .: DIN. Beuth Verlag Berlin, 2012.
- ^ Forschungsgesellschaft Landschaftsentwicklung Landschaftsbau eV: Recommendations for planning, construction and maintenance of outdoor riding arenas . 2007.
- ↑ DIN: DIN 18035-7 Sports fields - synthetic turf surfaces . Beuth Verlag, Berlin 2011.