Classification and characteristics of clay

Clay is a material that can be used for a variety of purposes in construction and other fields. Selecting the appropriate clay for your purposes can be made easier by being aware of its various types and characteristics. Clay is created when rocks weather and comes in different forms, each with its own special qualities.

Clay is frequently categorized in construction based on its grain size and plasticity. The three most popular varieties, kaolinite, illite, and smectite, each have unique advantages and disadvantages. For example, kaolinite is well-known for its use in bricks and pottery, while smectite is useful in some building applications due to its exceptional water retention qualities.

Additionally, the rates at which different clays shrink and expand can have an impact on the stability and toughness of building materials. Having a better understanding of these qualities will help you choose how best to use clay in your projects.

Type Characteristics
Kaolin White, fine, and smooth; used in ceramics and porcelain.
Ball Clay Plastic and smooth; often used in pottery and tiles.
Fire Clay Resistant to high temperatures; used in making firebricks and kiln linings.
Stoneware Clay Durable and coarse; commonly used for making stoneware dishes and pipes.
Earthenware Clay Red or brown; porous and less durable; used in making flower pots and some ceramics.

By what features is clay classified

Every clay is separated into:

  • refractory (stone-like);
  • shale (which does not soak well in water);
  • kaolin.

Afterward, they are split up into three groups:

  • by degree of plasticity: fatty, medium-fat and lean;
  • by the amount of aluminum oxide content in the calcined state: acidic (less than 15%), semi-acidic (ranging from 15% to 30%), basic (up to 40%) and highly basic (more than 40%);
  • by fire resistance class: fireproof (melt at a temperature of 1580° C), refractory (melting point 1350÷1580° C) and low-melting (melt at a temperature below 1350° C).

The color of kaolinite, the appearance it takes on after firing, the length of time it takes for it to sinter and melt, and its resistance to abrupt temperature changes all influence how far it can be used in industry. According to the information above, plastic material is separated into categories such as those used in the manufacture of pipes, bricks, tiles, earthenware, and other products.

The material comes in a variety of colors, including white, black, dark brown, green, blue, yellow, and red. Everything is dependent upon the material that forms the rocks and their geological source.

Depending on where the material is extracted, one rock is used alone, while another is sifted and combined with unique additives to create raw materials for a variety of products.

Application area

Clay is commonly used to make cement, which is made up of crushed limestone (75 percent of the total volume) combined with clay. Clinker is the end product of firing this mixture in a special oven at a temperature of roughly 1450 °C. After that, the clinker materials are rapidly cooled to 130 °C, crushed, combined with gypsum, and dried to create cement.

Buildings made of adobe are occasionally constructed using plastic materials. By pressing, the material’s particles are firmly joined to one another. Clay is occasionally combined with earth or straw.

These kinds of structures have several drawbacks:

  • they are not fireproof (in case of fire, such a wall begins to crack intensively and instantly collapse);
  • the mixed straw rots (due to the slow drying of the building material), as a result of which voids are formed in the wall, which lead to uneven settlement of the building;
  • straw is an excellent bait for rodents.

The production of pottery and bricks also requires the use of clay. It produces a thick, elastic mass when combined with water, which is used to make bricks and earthenware.

Clay is used in cosmetology (as the primary ingredient in cosmetic masks and ointments), medicine (as part of many medicinal compositions and products; used in the treatment of various diseases; taken as a sorbent), the food industry (to color dishes), and agriculture (as feed additives for livestock).

Clay is a multipurpose material that can be used for construction as well as pottery. Particle size determines its classification, and the three primary types are kaolinite, illite, and smectite. Every variety possesses distinct qualities that influence its attributes and applications. Knowing these distinctions makes it easier to choose the best clay for a given project, guaranteeing both functionality and high-quality results.

The main properties of clay

Among them are the following:

  • When clay with water is combined, the material soaks and forms a plastic mass, which in raw form can be given any shape;
  • Clay products after hardening do not change their shape (but are slightly reduced in volume), and after firing they become much harder (in their strength characteristics are not inferior to the stone);
  • It has good adhesion;
  • differs in water resistance;
  • It has a hollow capacity of high quality: therefore, it is often used in the decoration of stoves and walls of structures.

Specifications

Since these indicators directly depend on the size of the material as well as its chemical and mineral composition, each subgroup of clay is identified by its values for porosity, mineralization of pore water, the exchange complex tank, volumetric and specific gravity, thermal conductivity, and so forth. The following table lists the precise weight indicators for each type of clay:

The thermal conductivity of dry raw materials is 0.1 ÷ 0.3 W/(m K), while that of wet raw materials ranges from 0.4 to 3.0 W/(m K).

Clay density

For clay, actual bulk density—which is measured in a laboratory—as well as conventional bulk density are generally indicated. Furthermore, the real always falls short of the conventional by a large margin. The body’s mass is divided by the volume it occupies to determine its density. Density is expressed in g/cm³ in the CGS system and kg/m² in the SI system. Wet clay’s density varies from 1600 to 1820 kg/m², while dry clay’s density can reach up to 1000 kg/m³.

The sealing coefficient, which measures the ratio of the actual volumetric density to the volume of normally compacted material at a specific depth (experimentally proven the dependence of clay density on the depth of its survival), is one of the technical indicators of the plastic material (as well as other bulk substances). If this ratio equals one, the density is deemed normal; if it is less than one, the rock has not been sufficiently compacted.

Selecting the appropriate material for building and remodeling projects is facilitated by knowledge of the various types of clay and their properties. Different types of clay have different characteristics, like shrinkage and plasticity, which affect how the clay acts in concrete and other applications.

You can more accurately predict how clay will behave under different circumstances and interact with other materials if you are aware of these features. To ensure that your projects have the appropriate strength and durability, you must possess this knowledge.

The correct kind of clay can be added to your mixture to improve its quality and guarantee that it will fulfill the demands of your construction projects. Like with any material, better results and more successful outcomes come from careful selection and an understanding of its properties.

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Andrey Ivanov

Experienced civil engineer with more than 20 years of experience. Specializing in the construction of industrial and civil facilities. Author of many publications in professional journals.

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