Without this material, it is impossible to imagine a modern construction site. For more than a hundred years, cement has been able to build the strongest structures, it is used for repair work, it is used for interior decoration, but few people think about what cement is made of.
So what is cement? This material is a powder based on inorganic compounds. Interacting with water, this powder begins to harden and acquire the strength of a monolithic, strong material, filling in a pre-prepared form.
The reaction occurs while ensuring sufficient humidity. After curing, cement structures can serve for a long time without changing the basic properties. Factories engaged in the production of this material are trying to locate in close proximity to the source of extraction of raw materials, since the volumes of processing and transportation of materials for the manufacture of cement are quite high.
To understand what cement consists of, it is enough to show the chemical composition of the cement itself used in construction - Portland cement. It is made using the following proportions:
- calcium oxide - not less than 60%;
- silicon dioxide - not less than 20%;
- alumina - not less than 4%;
- iron oxide - not less than 2%;
- magnesium oxide - not less than 1%.
The formulas of other types of cement are similar, only the amount of each ingredient is adjusted.
The main characteristics of cement
Building materials, including cement, are most often checked for compliance with the following characteristics:
- Strength. To verify this characteristic, it will be necessary to manufacture a concrete cylinder, which is subsequently subjected to compression tests. Sample exposure time & mdsah; not less than 28 days. It is this period that is required for a full set of strength for the material. After checking and comparing the indicators in MPa, you can set the brand of this cement, which are indicated: M200, M300, M400, M500, M600;
- Resistance to corrosion. When in a humid environment, concrete structures that are not treated with special formulations undergo corrosion. To eliminate this process, it is recommended to use special additives when forming a concrete mortar. The same applies to protection against exposure to active substances and various household chemicals. To work in aggressive environments and at high humidity, a special brand has been developed - pozzolanic cement;
- Frost resistance. This characteristic is determined in the cycles of freezing and thawing of the material, in which it is able to maintain its original properties. When moisture freezes in the pores and microcracks of the concrete base, expansion occurs, which affects the quality of the concrete and leads to its destruction. To strengthen the structure of concrete, it is necessary to use special additives that allow concrete to withstand sudden temperature changes. Additives are also used to organize work in the winter;
- Water demand. It is expressed as a percentage in relation to the total volume of the solution of the required plasticity. The maximum value of water demand in Portland cement is 28%. It should be understood that a mixture that requires a minimum amount of water gives more durable and reliable concrete, and a solution saturated with water gives a porous structure of concrete, which is characterized by lower strength;
- Setting time. This indicator is important for the organization of work. It should not be too long or short so as not to disrupt the process of filling the base or masonry. This characteristic is governed by the amount of gypsum in the dry mix. If the volume of gypsum is higher, setting takes place faster, if lower, it is slower. Optimally, the process of cement rising occurs within 10 hours, and the beginning of setting is within 40-50 minutes.
Product Types by Use
For carrying out various types of work, certain qualities of the solution are required. Portland cement, which can be used for most types of work, has gained widespread use. But for special conditions, other brands are required:
- White Portland cement. This material is distinguished by finer grinding and increased gypsum content. It is used for equipment of bulk floors, as white cement allows to achieve high quality of the base and attractive appearance. If necessary, various pigments can be added to the cement composition, which allows to obtain a colored solution.
- Sulfate-resistant Portland cement. Designed for the construction of structures exposed to repeated exposure to aggressive and humid environments. This material is used in the manufacture of piles and bulls for bridges.
- Slag cement. It is used for casting structures and elements intended for work under water or in the ground.
- Pozzolanic cement. It is characterized by excellent resistance to fresh water and is used for the installation of hydraulic structures.
- Alumina cement. This material is used for the construction of structures operating in sea water, as well as for the repair work at low temperatures.
Starting materials for cooking
Try to plan the placement of cement production next to the main reserves of raw materials. Raw materials are natural rocks mined by open pit mining. So, what cement is made of:
- Carbonate rocks. These include: chalk; shell rock and other limestones; dolomite; marl. In industrial production, limestone rocks are mainly used. This material allows you to increase the efficiency of interaction in the firing process.
- Clay rocks. These include: clay; clay shales; loam; loess. This material is necessary for gaining the plasticity of the mixture and is mainly used in the manufacture of cement by the dry method.
- Additives. To obtain certain qualities of the cement mortar, it is necessary to add substances to the basic composition that are able to adjust the properties of the material. Additives include: alumina; silica; fluorspar; apatity.
How to prepare cement in production
The main substances from which cement is made are limestone and clay. Clinker is specially prepared from these two components, which is subsequently mixed with other additives that determine the quality, brand and properties of the solution. Among the required additives are: gypsum, dolomite, cementite.
In nature, there is clinker in its pure form - marl, but because of the small reserves of this mineral, it cannot be used on an industrial scale, therefore, domestic and foreign manufacturers prepare clinker from traditional materials.
Cement production is divided into the following stages:
- To prepare the clinker, it is necessary to thoroughly mix the ingredients in special high-capacity drums.
- At the next stage, the prepared mass enters the furnace, where it is fired for 3-4 hours at a temperature close to one and a half thousand degrees. As a result, clinker is formed in the form of small fractions (up to 5 cm in diameter).
- Next, the obtained clinker grains are crushed in drums using ball screens. In the process of processing the material, it is necessary to achieve a powdery state of the mixture.
- At the final stage, the necessary additives are added to the finished cement and sent for packaging in bags or hoprams.
There are three ways to make cement. They differ in clinker processing techniques.
- Wet way. Clinker is produced using water, chalk and clay. As a result of mixing substances in the drum, a wet mass is formed - the mixture. It is sent for roasting, after which the obtained granules are crushed and mixed with the necessary additives. This method is considered quite expensive, therefore, other methods are currently used more often.
- Dry way. It allows you to reduce the stage of mixing the finished mixture with additives, since the whole process is reduced to the preparation, crushing and mixing of ready-made ingredients. This technology is becoming increasingly popular, as it allows to significantly reduce production costs and the final price of the product.
- The combined method. This technology uses various forms of clinker production, combining the stages of production used in dry and wet processes.
How to make cement at home
First of all, you should immediately understand that a high-quality product in home or garage conditions cannot be obtained. It’s not enough to know how to make cement yourself, because besides this, you will need to purchase special equipment, or make maximum muscular efforts, which ultimately turns out to be quite costly and tedious. It is much easier to purchase the finished product in the store.
The easiest way to obtain a mortar suitable for cementing small cracks at home is to prepare a mixture based on the following ingredients: water, aqueous lime and stone ash. These substances are mixed until a homogeneous, viscous mass is obtained, which must be used immediately, since the shelf life of this solution is no more than two hours.
Other options for self-production of cement include a furnace for burning material and a mill for grinding clinker into powder.
How to make a cement mortar
To prepare the cement mortar, you will need cement itself, water and aggregate (for plaster and masonry mortars, river or quarry sand is used).
The ratio of ingredients in the solution depends on the application of this material, but in most cases it is recommended to use the formula: 3 parts of sand per 1 part of cement. Water is added based on the need for a more plastic or viscous solution.
If you want to get a design with higher strength characteristics, increase the proportion of cement. It is right to start the preparation of the solution by mixing the dry fractions, and only after obtaining a homogeneous mass begin to fill the water in small portions, gradually achieving the required consistency.