Brick soil

Brick clay is a loose and unconsolidated soil deposit, which is composed of clay minerals with a diameter of < 0.0039 mm and a recrystallization of < 0.0 1 mm. Contains clay minerals, detritus and various associated minerals. Clay minerals generally include kaolinite, sericite and muscovite; Debris and associated minerals mainly include: timely, calcite, dolomite, siderite, pyrite, limonite, gypsum, anhydrite and organic matter in free sand.

The main chemical components of brick clay are Al2O3, SiO2, Fe2O3, CaO, MgO, K2O, Na2O, moisture and organic matter. The composition is complex, but as long as its physical and chemical properties meet the requirements, the allowable chemical composition range is very wide. Clay for brick and tile has plasticity after mixing with water, maintains its original shape after drying, has rock-like hardness after baking, and has water absorption and adsorption properties. There are many kinds of clay that can be used for firing bricks and tiles, and the variety requirements are also wide. Clay used for firing bricks and tiles can be divided into ordinary clay, sandy clay, iron clay, marl clay, loess and red clay according to the different impurities contained in clay. In addition, clay shale or coal gangue can also be used for firing bricks and tiles.

Second, the general industrial requirements

Brick and tile mud, as its name implies, is mainly used for firing bricks and tiles. It is a traditional industrial and civil building material, which consumes a lot and is widely used in the construction industry. Although new building materials are increasing day by day, they cannot replace traditional bricks and tiles, especially in vast rural areas. At present, there are no uniform quality requirements and technical standards for clay raw materials for bricks in China, but only general industrial indicators, mainly including: chemical composition, particle composition, plasticity, impurities, moisture content and color. Generally speaking, any clay that can be made into brick and tile products under the existing processing technology can be called brick and tile clay.

1. Chemical composition of brick clay

See table 3-28- 1 for the chemical composition and allowable fluctuation range of brick clay.

Table 3-28- 1 Chemical Composition of Brick Clay

2. Particle composition of brick clay

The particle composition of clay has great influence on the molding and drying of clay. The particle composition of clay in China is generally divided into three grades: clay grade, particle size < < 0.005mm；; Dust or dust level, with a particle size of 0.005-0.05mm; Silt or sandy soil, particle size > 0.05 mm. See Table 3-28-2 for the types and contents of clay with different particle sizes.

Table 3-28-2 Clay Types and Particle Size Content

Fat clay and clay with many fine particles are suitable for making ceramic tiles and thin-walled hollow products; Sandy clay and clay are suitable for making ordinary bricks. See Table 3-28-3 for the particle composition range and content of general brick clay.

Table 3-28-3 Composition and Content of General Brick Clay Particles

3. Plasticity of brick clay

Plasticity is the basic property of clay, which mainly depends on the properties of solid phase and liquid phase, such as the chemical properties, dispersibility, particle content and shape of solid phase. For the same kind of clay, plasticity still depends on the kind and quantity of mixed liquid. According to plasticity index, clay can be divided into three types: high plasticity clay with plasticity index > 15; Medium plastic clay with plasticity index of 7 ~ 15; Low plasticity clay with plasticity index < 7.

Generally, the plasticity index of clay and sandy clay for brick making should be greater than 7. Because the tile body is thinner and the shape is more complicated than that of brick, the requirement for tile mud is higher than that of brick mud, which is not only fine in particles, but also less in impurities, and the plasticity index is correspondingly higher.

4. Dry shrinkage (air shrinkage)

Dry shrinkage refers to the shrinkage of clay blank after air drying. The drying shrinkage of clay is directly proportional to the plasticity index. Generally, the length shrinkage of clay is between 1.5%- 15%, while the drying shrinkage of clay for brick and tile is between 3%- 12%.

5. Sintering shrinkage

When a completely dry clay product is baked, the glass phase material melted by the fusible substances in the clay fills the gaps between the particles, thus causing the volume shrinkage of the product, which is called firing shrinkage. The firing shrinkage of brick clay is generally 2% ~ 8%.

6. Fire resistance

Fire resistance refers to the temperature at which clay begins to soften and melt during roasting. Fusible clay with fire resistance below 1350℃ is generally used to make brick and tile products.

7. Other factors affecting product quality

Other factors affecting product quality mainly refer to the influence of common minerals or impurities in clay, which generally include the following.

(1) is loose and granular in clay, or forms interlayer and lens. The plasticity and drying shrinkage of clay can be reduced in time.

(2) Alumina often exists in the form of aluminosilicate minerals. High Al2O3 content, high clay roasting temperature and high fire resistance.

(3) The common minerals of iron oxide are limonite and hydrated hematite. Iron oxide is both a flux and a colorant in clay. When iron oxide is roasted under oxidation or reduction conditions, the products are red or grayish black to black respectively.

(4) Calcium oxide and magnesium oxide exist in clay in the form of carbonate (calcite, dolomite) minerals, ranging from powder or debris to nodules. The dispersed carbonate will reduce the fire resistance of clay, increase the firing shrinkage and weaken the coloring ability of iron. If it exists in fragments or nodules, it will produce quicklime after roasting, and it will become hydrated lime after absorbing water, which will expand the volume and crack the product.

(5) Potassium oxide and sodium oxide often exist in clay in the form of feldspar particles. Feldspar can be regarded as flux, which will reduce the fire resistance of clay.

(6) Organic matter is mainly formed by plant decay, which dyes clay and increases the porosity of fired products.

Brick clay is mostly made from local materials, and there is no requirement for mining technical conditions. General test items include the following. ① Basic chemical analysis: SiO2, Al2O3, Fe2O3；; ② Joint analysis: silica, alumina, ferric oxide, calcium oxide, magnesium oxide, loss on ignition, K2O, sodium oxide and SO3；; ; ③ Physical property test: particle size analysis, plasticity index determination, pottery making test, etc.

Three, brick clay resources and their development and utilization

China is rich in brick and clay resources, which are widely distributed all over the country. From the distribution characteristics, yellow loam is dominant in Northeast China and North China, loess is dominant in parts of Northwest China and North China, and red loam is dominant in South China. The main horizon is Quaternary loose clay layer, and its thickness varies greatly. Clay deposits in China can be divided into residual clay and sedimentary clay according to their formation conditions. Quaternary clay is mainly residual clay, called primary clay, and clay minerals are accumulated in situ, which is the main clay type for making bricks and tiles. Sedimentary clay, also known as secondary clay, contains clay minerals that are transported and redeposited, mainly referring to clay formed before Quaternary, such as clay shale and coal gangue.

Clay brick and tile products are mass-produced wall materials in China, and the demand for clay for brick and tile is huge. Based on the principle of using local materials and selling nearby, the manufacturers of ordinary bricks and tiles are all over the country, mainly mining Quaternary loose clay layers. With the development of science and the requirement of farmland protection in China, new wall materials are being popularized and will gradually replace some loose clay mining. Enterprises should make active efforts in this respect. More mature technologies include: clay shale, coal gangue, fly ash and other production wall materials. Technical indicators and industry requirements can refer to the indicators of relevant manufacturers. In addition, sand can be used to produce lime-sand bricks in mountainous areas, hills and beaches where soil is scarce and sand is abundant. The main process is to take 85% medium-fine sand, add 15% lime, add a small amount of coagulant aid, add water, stir, melt, press and shape, and then cure with high-pressure saturated steam. This kind of brick has low production cost, good quality and high strength, and can meet the requirements of 8 ~ 12-story brick-concrete wall building.

There are hundreds of millions of cubic meters of brick clay resources in Henan Province, which are mainly produced in the Middle Pleistocene and Upper Pleistocene of Quaternary. Middle Pleistocene clay is brownish red and brownish yellow, and Upper Pleistocene clay is grayish yellow and brownish yellow clay and sandy clay. There are generally no or few gravel layers and calcareous nodule interlayers in the seam. The thickness of ore body is relatively large, reaching 10 ~ 30m in plain area and 2 ~ 10~30m in hilly area. The ore body is open-pit mining without cover. The quality of clay varies greatly. According to the comprehensive data of Hebi City, the main minerals contained in clay are kaolinite, illite, montmorillonite, quartz, feldspar, calcite and iron-containing minerals. Chemical composition: SiO2 is 57.6% ~ 7 1.5%, Al2O3 is 10.76% ~ 13.98%, Fe2O3 is 4.8% ~ 5.23%, and Na2O+K2O is1.4. The liquid limit is 25.5% ~ 34.2%, the plastic limit is 16% ~ 2 1%, and the plastic index is 9.3% ~ 15%, which accords with the indexes of ordinary brick clay.

There are many manufacturers of brick and clay products in Henan province. According to the data of 1998, there are 3,233 state-owned, collective and individual brick and tile enterprises in the province, with an annual consumption of 30.85 million m3 of clay resources, production of 60 160 million bricks and 2.202 billion tiles, an annual industrial output value of 824.5 million yuan and employees of/kloc-0.65438. There are also some manufacturers who use new materials to make wall tiles. Most of them use coal gangue, fly ash and other wastes discarded by coal mines and power plants.