What is ceramsite made of?

Ceramsite, as its name implies, is a kind of ceramic particles. The appearance characteristics of ceramsite are mostly round or oval spheres, but some broken-like ceramsite are irregular broken stones instead of round or oval spheres. The shape of ceramsite varies with different processes. Its surface is hard shell, ceramic or enamel, which has the function of isolating water and gas and giving ceramsite high strength. The particle size of ceramsite is generally 5 ~ 20 ㎜, and the maximum particle size is 25㎜. Ceramsite is generally used to replace gravel and pebbles in concrete. The appearance color of ceramsite varies with different raw materials and processes. Most of the fired ceramsite colors are dark red and ochre, and some special varieties are grayish yellow, grayish black, grayish white and cyan gray. Because there are many raw materials for producing ceramsite, there are many varieties of ceramsite, so there are many colors. Non-burning ceramsite has different colors because of the different solid wastes used, which are generally gray-black and have no luster on the surface, which is not as smooth as the fired ceramsite. Lightweight is the most important of many excellent properties of ceramsite, which is also the main reason why it can replace heavy sandstone. The internal structure of ceramsite is characterized by fine honeycomb micropores. These micropores are all closed, not connected. It is formed because the gas is wrapped in the shell, which is the main reason for the light weight of ceramsite. The fine particles of ceramsite are called pottery sand. There are many fine particles smaller than 5㎜ in ceramsite. In production, this part of fine particles is screened out by a screening machine, which is customarily called pottery sand. Ceramic sand has slightly higher density and good chemical and thermal stability. Ceramic sand is mainly used to prepare lightweight aggregate concrete and lightweight mortar instead of natural river sand or mountain sand, and can also be used as acid-resistant and heat-resistant concrete fine aggregate. The main varieties are clay pottery sand, shale pottery sand and fly ash pottery sand. The purpose of using pottery sand is also to reduce the weight of buildings. Pottery sand can also be used for soilless culture and industrial filtration. Type of ceramsite 1, according to the raw material of ceramsite (1), fly ash ceramsite takes solid waste as the main raw material, adds a certain amount of cementing material and water, and after pelletizing, sintering, expansion or natural curing, the light and coarse aggregate with particle size greater than 5㎜ is referred to as fly ash ceramsite for short. (2) Clay ceramsite is a kind of light and coarse aggregate with a particle size greater than 5㎜, which is made of clay and loam. It is the main raw material, processed, granulated and fired. (3) Shale ceramsite is also called expanded shale. Clay shale, slate, etc. After crushing, sieving or grinding into balls, the light and coarse aggregate with particle size greater than 5㎜ is shale ceramsite. According to the process method, shale ceramsite is divided into: ordinary shale ceramsite, which is made by crushing, screening and expanding; Spherical shale ceramsite made by grinding, granulating and firing. Clay ceramsite, fly ash ceramsite and shale ceramsite are suitable for lightweight aggregate concrete for thermal insulation and structural insulation, and can also be used for structural lightweight aggregate concrete. At present, the main use of shale ceramsite is to produce lightweight aggregate concrete small hollow blocks and lightweight partition boards. (4) Garbage ceramsite With the continuous development of the city, there are more and more garbage in the city, and the treatment of urban garbage has become an increasingly prominent problem. Garbage ceramsite is a kind of sintered ceramsite made by processing, granulating and roasting municipal solid waste. Or adding garbage cinder into cement for granulation, and naturally curing to prepare unburned garbage ceramsite. Garbage ceramsite has the characteristics of sufficient raw materials, low cost, low energy consumption, light weight and high strength. Garbage ceramsite can be made into new wall materials such as wallboard, block and brick, and can also be used for heat preservation, floor slab, lightweight concrete, water treatment and purification, with a broad market. (5) Coal gangue ceramsite coal gangue is a black waste rock with less carbon content discharged during coal mining, and it is the largest solid waste in China. Its emission and accumulation not only occupy a lot of cultivated land, but also cause great pollution to the surface and atmosphere. The chemical composition of coal gangue is similar to clay. Coal gangue contains high carbon and sulfur, and has a large loss on ignition. Only in a certain temperature range can a sufficient amount of molten substances with suitable viscosity be produced, which is expandable. According to its characteristics, China has developed coal gangue ceramsite. Coal gangue ceramsite is made by crushing, preheating, expanding, cooling, grading and packaging coal gangue that meets the expansion requirements. The quality of the obtained ceramsite products completely meets the national standards, and some technical indexes exceed the national standards, reaching the quality of similar products abroad. Product innovation, development and environmental protection. (6) The sewage produced by the biological sludge ceramsite sewage treatment plant contains a lot of biological sludge, some of which are made into agricultural fertilizers, some are directly used for greening, and some are discharged into the sea or burned, which will cause secondary ecological environmental pollution. At present, the ceramsite made from biological sludge through drying, grinding, granulating and sintering is called sewage treatment biological sludge ceramsite. Using biological sludge to replace part of clay to burn ceramsite not only saves clay, but also protects cultivated land, which plays a certain role in environmental protection. (7) A large number of rivers and lakes have formed a large amount of sediment after years of deposition. The ceramsite made by dredging, natural drying, raw material granulation, preheating, roasting and cooling with river mud instead of clay is called river mud ceramsite. Using river mud to make ceramsite not only reduces the competition between building materials manufacturing industry and agricultural land, but also finds a reasonable way out for river mud, solves the problem of secondary pollution of river mud and achieves the purpose of waste reuse. 2. According to the strength of ceramsite, ceramsite can be divided into high strength ceramsite and common ceramsite. (1) High-strength ceramsite According to the new standard GB/T17431.1-1998, high-strength ceramsite refers to light and coarse aggregate with strength label not less than 25MPa. Its technical requirements are the same as those of ultra-light and ordinary ceramsite except density grade, cylinder compressive strength, strength label and water absorption. When producing high-strength ceramsite, the output is low, the energy consumption is high, the added value is high, and the sales price is about 50% higher than that of ultra-light ceramsite and ordinary ceramsite. The preparation of high-grade and prestressed lightweight aggregate concrete with high-strength ceramsite must be uniform. (2) Ordinary ceramsite According to the new standard GB/T17431.1-1998, ordinary ceramsite refers to light and coarse aggregate with strength grade less than 25MPa. Ordinary ceramsite has a wide range of uses and huge market potential. 3. According to the density of ceramsite, ceramsite can be divided into general density ceramsite, ultra-light density ceramsite and ultra-light density ceramsite. (1) General density ceramsite General density ceramsite refers to ceramsite with a density greater than 500kg/m3. Its strength is generally high, and it is mostly used for structural thermal insulation concrete or high-strength concrete. (2) Ultra-light density ceramsite Ultra-light density ceramsite generally refers to 300 ~ 500 kg/m3 ceramsite. This kind of ceramsite is generally used for thermal insulation concrete and its products. (3) Ultra-light density ceramsite Ultra-light density ceramsite refers to ceramsite below 300kg/m3. Its thermal insulation performance is excellent, but its strength is poor. It is generally used to produce ultra-light thermal insulation concrete and its products. 4. According to the shape of ceramsite, ceramsite can be divided into crushed stone ceramsite, spherical ceramsite and cylindrical ceramsite. (1) Gravel ceramsite Gravel ceramsite is generally made of natural ore. Stone is first crushed and baked, and then sieved. It can also be obtained by directly crushing and sieving natural and artificial light raw materials such as pumice, volcanic slag, coal cinder, natural or calcined coal gangue. (2) Spherical ceramsite Spherical ceramsite is produced by disc granulator. Firstly, the raw materials are ground into powder, then granulated with water, made into balls, and then baked or aged. At present, most ceramsite in China is of this variety. (3) Cylindrical ceramsite Cylindrical ceramsite is generally formed by plastic extrusion. Make mud strips first, and then cut them into cylinders. This kind of ceramsite is suitable for clay raw materials with high plasticity, and its output is relatively low. If the cylindrical blank is fired in a brick kiln, the cylinder will roll into an ellipse in the kiln. 5. According to the performance of ceramsite (1), high-performance ceramsite refers to ceramsite with high strength, low water absorption and low density after firing or not. Lightweight aggregate is rich in resources and has a wide variety. It can be divided into natural lightweight aggregate, solid waste lightweight aggregate and artificial lightweight aggregate. According to its forming conditions and properties, only specially treated high-performance ceramsite can be used to prepare high-performance concrete. It is generally called high-performance lightweight aggregate abroad, and it can also be called high-strength ceramsite at home. High-performance ceramsite is an artificial lightweight aggregate with different density grades, high strength, low porosity and low water absorption, which is made of suitable raw materials and special processing technology. Some properties of this lightweight aggregate are similar to those of ordinary dense aggregate, and its performance is better than that of ordinary lightweight aggregate. (2) Ordinary performance ceramsite Ordinary performance ceramsite is relative to high performance ceramsite. That is, its strength is slightly lower than that of high-performance ceramsite. The porosity is slightly higher and the water absorption is also higher. But its comprehensive performance is still better than ordinary aggregate. The reason why the performance particles of ceramsite have developed rapidly in the world is that it has many excellent properties that other materials do not have. This excellent performance makes it play an irreplaceable role. These excellent properties have the following aspects. 1, low density and light weight. The bulk density of ceramsite itself is less than 1 100kg/m3, generally 300 ~ 900 kg/m3. The density of concrete made of ceramsite is1100 ~1800 kg/m3, and the corresponding compressive strength of concrete is 30.5 ~ 40.0 MPa. The biggest feature of ceramsite is its hard appearance, but there are many micropores inside. These micropores give ceramsite light weight. The density of No.200 fly ash ceramsite concrete is about 1600kg/m3, while the density of ordinary concrete with the same grade is as high as 2600kg/m3, with a difference of 1000kg/m3. 2, heat preservation, heat insulation. Ceramsite has good thermal insulation performance because of its porous interior, and the thermal conductivity of concrete prepared with it is generally 0.3 ~ 0.8 w/(m? 6? 1k), which is 1 ~ 2 times lower than ordinary concrete. Therefore, ceramsite building has a good thermal environment. 3, the fire resistance is good, and the ceramsite has excellent fire resistance. Ordinary fly ash ceramsite concrete or fly ash ceramsite block integrates heat preservation, earthquake resistance, frost resistance and fire resistance, especially the fire resistance is more than 4 times that of ordinary concrete. In the same refractory period, the thickness of ceramsite concrete is 20% thinner than that of ordinary concrete. In addition, fly ash ceramsite can also be used to prepare refractory concrete with fire resistance below 1200℃. At the high temperature of 650℃, the strength of ceramsite concrete can maintain 85% at room temperature. Ordinary concrete can only maintain 35% ~ 75% strength at room temperature. 4. Good seismic performance Ceramsite concrete has good seismic performance because of its light weight, low elastic modulus and good deformation resistance. 1976 during the Tangshan earthquake, four ceramsite concrete slab buildings built in Tianjin were basically intact and can be used as usual. However, a considerable number of brick-concrete buildings around were damaged to varying degrees in the earthquake. Although this is related to the building structure system, the excellent seismic performance of ceramsite concrete is also an important reason. From 65438 to 0976, a strong earthquake of magnitude 9 occurred in Ferruri, Italy. Statistics show that the damage rate of brick-concrete buildings is 40% ~ 60%, that of clay hollow brick buildings with frame structure is 33%, and that of ceramsite concrete buildings is only 5%. This shows the seismic performance of ceramsite. 5, low water absorption, good frost resistance and durability. The acid resistance, alkali resistance and frost resistance of ceramsite concrete are better than ordinary concrete. After 15 freeze-thaw cycles, the strength loss of 250 # fly ash ceramsite concrete is less than 2%. 1976, the relevant departments have calculated the ceramsite concrete projects built in China since 1985. The results show that no matter whether it is prefabricated or cast-in-place, the steel bars are not corroded indoors and outdoors, and the measured carbonation depth is generally less than 30㎜, and the strength can continue to improve in the later stage. It can be seen that ceramsite concrete is an excellent building material and should be widely used. 6. Excellent impermeability According to many tests, the impermeability of ceramsite concrete is better than that of ordinary concrete. Taking 20MPa ceramsite concrete and ordinary concrete as examples, the impermeability index of ordinary concrete is B6, while ceramsite concrete can reach B 18 to B25. 1970 Tianjin built a civil air defense passage with 20MPa ceramsite concrete (3m deep and 0.9 m underground water level). 1980 found no leakage. Two 20MPa ceramsite concrete oil storage tankers (with a load of 80t) built in Ningbo have been working on water for 13 years, and no leakage has ever occurred. Therefore, ceramsite concrete is one of the excellent building materials for dams and underground engineering. 7. Excellent alkali-resistant aggregate reaction performance. Ceramsite concrete not only has better corrosion resistance (acid and alkali resistance) than ordinary concrete. But also has excellent alkali-aggregate reaction resistance. The main components of concrete are cement and aggregate. Aggregates include gravel and sand. If these aggregates are dolomite, limestone or other rocks containing SiO2 _ 2, such as opal and volcanic rocks, the alkali in cement will react with these aggregates, causing the disintegration or expansion of rock minerals, cracking and collapse of concrete and damage to buildings. This is the alkali-aggregate reaction. A large number of buildings are damaged by alkali-aggregate reaction of concrete every year at home and abroad. In 1980s, there were 500,000 highway bridges in the United States, of which 200,000 were damaged to varying degrees due to alkali-aggregate reaction. The losses caused by alkali-aggregate reaction in the world can reach hundreds of billions of dollars every year. Because ceramsite does not contain these flint components, the alkali content is very low, and it will not react with cement during use. So far, there is no case of alkali-aggregate reaction in ceramsite concrete buildings at home and abroad. Facts have proved that ceramsite has excellent anti-alkali aggregate reaction ability, which can increase safety and prolong the service life of buildings to a certain extent. 8. Strong adaptability. Decades of production practice at home and abroad have proved that ceramsite can be produced from clay, shale, fly ash or other solid wastes according to different resource conditions in different places. According to different uses and market demand, we can produce ceramsite products with different packing densities and particle sizes (ultra-light ceramsite, structural thermal insulation ceramsite, structural ceramsite), as well as special-purpose ceramsite, such as high-temperature resistant ceramsite, acid-resistant ceramsite, flower ceramsite and so on. When using ceramsite, different types of ceramsite can be used to prepare sand-free macroporous, all-light and ultra-light steel bars or prestressed concrete with different densities and strength grades according to actual needs; It can be prefabricated into various types of wall products and building components, and can also be used for filling, cast-in-place, slip-form and other construction operations. It can be applied to various building systems, such as frame-filled or self-supporting block building, one-mold-three-board, fully assembled large board, internal pouring and external hanging, whole-line pouring slip-form building and so on. In any building, ceramsite concrete can be used for walls (blocks, external wall panels, internal partition panels), floors, roof panels, beams and columns and some foundations, which is incomparable to any other new wall. The application of ceramsite ceramsite has excellent properties such as low density, high cylinder pressure, high porosity, high softening coefficient, good frost resistance and excellent alkali aggregate reactivity. In particular, ceramsite has the characteristics of light weight, corrosion resistance, frost resistance, earthquake resistance and good isolation because of its low density, porous interior, uniform shape and composition, and certain strength and firmness. Using these excellent properties, ceramsite can be widely used in building materials, horticulture, food and beverage, fire-resistant insulation materials, chemical industry, petroleum and other departments, and its application fields are getting wider and wider, and it is still expanding. At the beginning of the invention and production of ceramsite, it was mainly used in the field of building materials. Due to the continuous development of technology and people's understanding of the properties of ceramsite, the application of ceramsite has already exceeded the scope of traditional building materials, expanding its new application fields. At present, the application of ceramsite in building materials has dropped from 100% to 80%, and its application in other fields has accounted for 20%. With the continuous development of new uses of ceramic particles, its proportion in other aspects will gradually increase. The main equipment for ceramsite production mainly includes: raw material storage bin, dust settling chamber, induced draft fan, main kiln body, coal injection system, control cabinet, etc. Among them, the feeder at the lower part of the raw material bin, the rotating speed of kiln body and the amount of arch coal are all stepless speed regulation, so as to adjust their process parameters and obtain the maximum output on the premise of ensuring the product quality. Auxiliary equipment for producing shale ceramsite includes: crusher, screening machine, belt conveyor, feeder, unloader, etc. Auxiliary equipment for producing fly ash and clay ceramsite includes: wheel mill, double-shaft mixer, granulator, screening machine, feeding belt conveyor, etc. Production technology of shale ceramsite: mining-primary crushing-secondary crushing-screening-temporary storage-feeding-sintering-grading and screening of finished products-stacking-transportation (bagging). During the operation, we should pay attention to the matching relationship among coal feed, coal feed, kiln speed and air intake, so as to adjust it to the best process state. Using industrial waste residue such as fly ash to produce ceramsite is a subject developed by many related people for many years. Nowadays, high-strength lightweight fly ash ceramsite has been successfully produced, and its performance index is better than shale and clay ceramsite. In addition to mastering the process requirements, additives are also the main reasons that affect its properties. Admixtures mainly include adhesives, expansive agents and mineralizers. The admixture composition of fly ash with different components is also different Production technology of fly ash: raw materials (fly ash+quantitative additives) are mixed, ground, granulated, burnt, stacked and transported (bagged) to produce fly ash ceramsite, that is, the rotating speed of preheating section and drying section of kiln body can be controlled independently, so that the preheating time can be controlled according to the state of raw materials. In recent years, due to the limitation of land resources, the production and use of clay ceramsite have been banned in some areas. However, in some areas, river silt and abandoned mountain soil can be used for production. The technological process is as follows: raw materials are stirred, granulated, screened, sintered, stacked and transported (bagged). Attention should be paid to prevent the materials from caking in the kiln and affecting the quality. At present, China's ceramsite production equipment adopts industrial rotary kiln. The cylindrical main kiln body is placed on the supporting wheels at an inclination angle of about 3 with the horizontal plane. The material enters the kiln from the high end, and under the action of the rotary motion of the kiln body, the material rolls down from the high end (kiln end) to the low end (kiln head). At the same time, at the kiln head, the high-pressure fan injects pulverized coal (or other fuels such as natural gas) into the kiln to make it burn fully. The generated heat makes the material undergo physical and chemical changes and expand, and after cooling, it is ceramsite.