Astringents: properties, classification, description, application

Knitting substances are known for their wide use in the construction industry for the preparation of concretes and mortars used in the erection of buildings, structures and other structures. There are many of their varieties, and today we will briefly touch on the main existing subgroups.

Classification of binders

By their origin, they can refer to an organic or inorganic group. To the first belong all kinds of bitumen, tar, tar and pitch. The main scope of their application is the production of roofing coatings, which can be rolled or piece type, asphalt concrete and a variety of various waterproofing materials. The main distinctive quality of these is the hydrophobicity, that is, the ability to soften and take on an operating state during heating or when interacting with some organic liquid.

The second group - inorganic binders - consists of lime, gypsum and cement. All of them are in demand in the process of preparing concrete and various mortars. Appearance of inorganic binders is a thin-milled material that has the property of turning into a liquid-plastic dough-like mass, hardening to the condition of a strong stone.

What is characteristic of them

The main properties of astringents of inorganic origin - hydrophilicity, plasticity in the interaction with water and the ability to move to a solid state of semi-liquid dough. This is what distinguishes them from the representatives of the first group.

By way of hardening, inorganic binders are considered to be air, hydraulic, acidic and autoclave hardening. This division depends on the ability to prolong the counteraction to natural climatic factors.

Air binders harden, interacting with water and, forming a strong stone, can remain in this state in the air for a long period of time. But if the products and building structures made with their use are subjected to regular moistening, then this strength will be quickly lost. Buildings and structures of this type are easily susceptible to destruction.

What is included in this group? This traditionally refers to plaster magnesian binders - clay, air lime. If we consider their chemical composition, then the entire given group, in turn, can be subdivided into four more. This means that all air binders are either lime (based on calcium oxide), or magnesia (in which caustic magnesite), or gypsum binder based on calcium sulphate, or are a liquid glass - potassium or sodium silicate, Existing in the form of an aqueous solution.

We turn to "water" materials

Now let's look at another group - hydraulic binders. They tend to harden, and also for a long time to retain the strength characteristics in an environment not only of air, but also of water. Their chemical composition is quite complex and is a combination of various oxides.

The whole of this large group, in turn, can be divided into silicate-based cements, in which about 75% of calcium silicates (mainly portland cement with its varieties, this group forms the basis of an assortment of modern building materials) and another sub-group - aluminate cements Based on calcium aluminate (the most famous representatives are all varieties of aluminous cement). The third group is considered to be romant cement and hydraulic lime.

What astringents are considered to be acid-fast? It is acid-resistant quartz cement, existing as a fine-grained mixture of quartz sand and silicon. This mixture is closed with an aqueous solution of sodium silicate or potassium.

A characteristic feature of the group of acid-resistant binders is their ability, having passed the initial stage of hardening in air, long enough to counteract the aggressive influence of various acids.

Organic in construction

Another large subgroup - organic astringents (consisting, as already mentioned, mainly from varieties of asphalt and bituminous materials) has a completely different nature. The same asphalt can be artificial or of natural origin. In its composition, bitumen is mixed with representatives of minerals in the form of limestone or sandstone.

In the construction industry asphalt is widely used in the construction of roads and the construction of airfields as a mixture of sand, gravel or rubble with bitumen. The same composition has asphalt, used in the form of waterproofing.

What is bitumen? It is an organic matter (either natural or artificial), in the composition of which - high-molecular hydrocarbons or their derivatives containing nitrogen, oxygen and sulfur. The range of bitumen application is very wide and varies from road and housing construction to the chemical industry and the paint and varnish industry.

By tar means astringent substances of organic origin, in the composition of which - aromatic high-molecular carbohydrates and their derivatives - sulfuric, acidic and nitrogenous.

Their useful qualities

The main requirements for the organic group of binders are that they possess a sufficient degree of viscosity at the time of interaction with a solid surface, which would allow the appearance of high wetting and enveloping properties to form a waterproof film. Another requirement is the ability to retain these qualities over a long period of time.

These binders have found their application when laying roads and city streets, they cover airfields and motor roads, arrange sidewalks and floors in cellars and industrial buildings.

Consider now the main types of building materials belonging to the two listed groups. Let's remind once again - the inorganic group is basically subdivided into those that harden in the air and those that are able to do it in the aquatic environment.

Binders - building materials

All well-known clay refers to the most common of astringent materials hardening in the air. It has found its application in the construction of a variety of buildings. It is clay sedimentary rock, existing as a mixture of dust particles of microscopic size with sand and fine clayey impregnations. The smallest of them were called fine particles. It is their presence that, when exposed to a moist environment, can be converted into a dough substance. Having dried up, this plastic mass easily solidifies in its prescribed form.

If such a form is burned, then the obtained artificial stone has a sufficiently high strength. Like other mineral binders, because of the different composition of the clay can be a variety of shades. From solutions on their basis put fireplaces, stoves, and also form bricks. They can be skinny, fat and medium. Clay chamotte has refractory qualities, so it is indispensable for the installation of fireplaces and stoves.

What is lime?

Another very famous and widely used cementitious material is called air building lime and can be obtained from rocks such as chalk, dolomite, limestone, shell rock. The basic oxide in it can be different, depending on which, air lime is usually divided into dolomite, magnesian, calcium. All three varieties are obtained by calcining limestone of the corresponding origin in the furnace.

There may be air lime, either quicklime, or slaked (or hydrated). The latter is formed during the quenching of one of the three above.

If you look at the existing calcareous fractions, you can refer it to lumpy or powdery. Unexpired lime is a fairly large porous lump. In the process of quenching with water, a calcareous dough is formed from it. To "get" powder from powdered lime, it is necessary to produce a process of hydration (quenching), or grind lumps. It can be applied with or without additives. Additives are slags, active minerals and sand of quartz origin.

All about plaster

The next material is alabaster, which is also a cast. It is obtained by heat treating the crushed gypsum stone. Gypsum hardens, passing three intermediate stages, consisting of its dissolution, followed by colloid and then crystallization. During the passage of the first stage, a saturated solution of two-water gypsum is formed. Hardening, it increases in volume and acquires a flat white surface.

Applying coloring pigments, it is possible to give products from gypsum any color shades. The setting process of this astringent normally starts 4 minutes after the start of the mixing. The end of freezing occurs in the interval from 6 to 30 minutes later.

During the setting process, the mixture of gypsum and water should not be mixed and tamped in order to avoid the risk of loss of binding properties. There are a lot of gypsum stamps, they are denoted by different figures characterizing the degree of compressive strength.

It is sold in bags of different sizes. Gypsum found the widest application in the design of interiors of residential buildings and public buildings. From it it has long been customary to cast a wide variety of figurative forms. Store it should be exclusively in a dry room, and the storage period is limited in connection with the possible loss of strength as the main useful quality.

And more about the cast

The building gypsum looks like a powder in color from greyish to bright white. If it is mixed with water, a characteristic reaction begins, while the mixture is heated. In gypsum it is customary to add special materials called retention additives, whose purpose is to improve the consistency and adhesion to the surface during plastering, and also slightly prolong the hardening time.

To increase the volume of the material without loss of working properties, fillers are introduced (for example, from expanded perlite or mica). Special high-strength gypsum is fired at high temperatures, in the process, the crystalline water is removed from it. The time of its hardening is increased to 20 hours, and the hardness is much greater than that of other varieties.

Stucco gypsum is impregnated and obtained marble (bright white, slowly hardening and used for plastering internal surfaces), and in the manufacture of various fillers and retaining additives are introduced into it. The main meaning of most of these additives is to serve as a retarder of grasping. For the purpose of producing internal plaster, it is prepared in plastering machines with the possible addition of certain fillers, for example sand.

Dry plaster or gypsum boards are also made from it, and gypsum is also used to fill the joints between them. There is gypsum shpatlevochny, which has similar properties.

Let's talk about cement

What other properties have hydraulic binders? The process of their hardening, which began in the air, continues in the water, and their strength remains and even grows. Characteristic and most famous representatives of the family of hydraulic binders are, of course, cements. They are marked depending on the strength, and the brand of a particular sample is determined by setting the maximum load on bending and compression. Moreover, each of the samples should be made in the accepted proportion of cement and sand and pass the test at a certain period of 28 days.

The speed of setting the cement can also be different - slow, normal or fast. Similarly, depending on the rate of hardening, any cement can be conventional, fast-hardening, or particularly quick-hardening.

As an example in this group can be called Portland cement, existing in the form of a fine gray powder with a light greenish tinge with the possible introduction of additives, which can be from granular slag (slag Portland cement).

On the rate of hardening

The quality test (as well as production) of binders is carried out in compliance with numerous standards. For each of the existing groups, limitations are established that determine the normative start and end of setting, counting from the moment of water immersion.

Another cement - alumina - refers to fast-hardening hydraulic binders. In appearance it is a fine powder of brown, gray, greenish or black color (depending on the method of treatment and the initial constituents). On the fineness of grinding, it slightly exceeds portland cement and requires a slightly larger volume of water.

Mixed types of binders are those that can harden in both air and water environments and are used in the production of only non-reinforced concrete or mortar.

Bitumen and the sphere of their application

As for the most popular organic binders, their family includes a lot of bitumen and tar, having colors from black to dark brown. The traditional sphere, in which such binders are used, are waterproofing works. This building material is waterproof, waterproof, resistant to weathering and very elastic. To soften and put into liquid state this group of binders can be heated. As the temperature is lowered, their viscosity increases and can be completely lost.

This group, first of all, consists of bitumen of natural origin, as well as obtained from oil processing. Their chemical composition is a combination of molecules of oxygen, hydrogen, sulfur and nitrogen. In the construction of demand for petroleum bitumen (liquid, solid and semi-solid).

By their designation, they can also be classified as one of three groups - roofing, construction or road. Of the roofing, an impregnating composition is prepared, a roofing material is produced, and many different mastics are produced.

Industrial bitumens of solid and elasto-solid grades are produced by a high vacuum method with additional processing steps, on which the oil boils at high temperatures. Particularly resistant to changes in heat and cold are oxidized. There are also mixtures of bitumens with polymers that affect the degree of their viscosity. A characteristic feature of all types is the ability to change the consistency as a function of temperature, and different phases can alternate repeatedly. The same is based on the adhesive properties of the family of bituminous binders.

Than they are valuable

The degree of expansion of bitumen under the influence of high temperatures in comparison with mineral materials is 20-30 times more. Their valuable qualities are water resistance, resistance to salts, alkalis, corrosive acids and effluents. An example is salt, which is sprinkled with snow in the winter on the streets for melting.

The persistence of bitumen is reduced by organic solvents, oils and fats, from light, heat and air oxygen, which oxidize their constituent parts. When heated, the soft particles evaporate, and the bitumen surface hardens.

Advantages of them are low flammability, that is, this material does not belong to flammable. Petroleum bitumens are not harmful to health substances and are not classified as such. As their other properties we can talk about thermal bonding, high thermal insulation, good wetting.

The hardness of the bitumen is determined by the depth of penetration of the needle immersed in them (measured in hundredths of a millimeter) under the normalized load for a certain time under conditions of a specific temperature. The transition between the solid and liquid state in them has a sliding character and is determined by the softening point at low temperatures. In addition, they are characterized by a so-called break point - a term for the temperature at which the bent bitumen layer is cracked or destroyed.

Other materials

What other astringent substances of organic origin can be called? Coal-tar pitch, which is a viscous or solid black substance and serves as a tar distillation product, is infiltrated only. This material is quite dangerous and if it gets on the skin it can cause a burn. Work best with it cloudy weather or in low light.

Coal tar is a substance that is released as a by-product in coke-chemical production. It has found its application in the manufacture of mastics for roofing and road construction.