Binders are known for their widespread use in the construction industry for the preparation of concrete and mortars used in the construction of buildings, structures and other structures. There are many varieties of them, and today we will briefly touch on the main existing subgroups.
Classification of binders
By their origin, they can belong 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 manufacture of roofing coatings, which can be roll or piece type, asphalt concrete and a wide variety of waterproofing materials. Their main distinguishing quality is hydrophobicity, that is, the ability to soften and assume a working state during heating or when interacting with any 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 a wide variety of mortars. The appearance of inorganic binders is represented by a finely ground material, which, in the process of mixing with water, turns into a liquid-plastic doughy mass hardening to the state of a solid stone.
What is characteristic of them
The main properties of binders of inorganic origin are hydrophilicity, plasticity when interacting with water and the ability to transfer to a solid state from a semi-liquid pasty. That is what they differ from representatives of the first group.
According to the method of hardening, inorganic binders are considered air, hydraulic, acid and autoclave hardening. This division depends on the ability to long-term counteract natural climatic factors.
Aerial binders harden by interacting with water and, having formed a durable 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 wetting, then this strength will be quickly lost. Buildings and structures of this type are easily susceptible to destruction.
What is included in this group? These traditionally include gypsum magnesia binders - clay, air lime. If we consider their chemical composition, then this entire group, in turn, can be divided into four more. This means that all airborne binders are either calcareous (based on calcium oxide), magnesian (including caustic magnesite), gypsum binders based on calcium sulfate, or are liquid glass - potassium or sodium silicate, existing in the form of an aqueous solution.
We pass to "water" materials
Now let's look at another group - hydraulic binders. They tend to harden, as well as to maintain strength characteristics for a long time in the environment not only air but also water. Their chemical composition is quite complicated and is a combination of various oxides.
This entire large group, in turn, can be divided into cements of silicate origin, which include about 75% of calcium silicates (mainly Portland cement with its varieties, this group forms the basis of the range of modern building materials) and another subgroup - aluminate cements based on calcium aluminate (the most famous representatives are all varieties of alumina cement). The third group includes romance cement and hydraulic lime.
What binders are acid resistant? This is acid-resistant quartz cement, existing in the form of a finely ground mixture of quartz sand with silicon. Such a mixture is shut 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, for a long time to counteract the aggressive influence of various acids.
Organics in construction
Another large subgroup - organic binders (consisting, as already mentioned, mainly of varieties of asphalt and bitumen materials) has a completely different nature. The same asphalt can be artificial or of natural origin. As part of it, 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 gravel with bitumen. Asphalt has the same composition, used as a waterproofing.
What is bitumen? This is an organic substance (either natural or artificial), in the composition of which - high molecular weight hydrocarbons or their derivatives containing nitrogen, oxygen and sulfur. The scope of bitumen is very wide and varies from road and housing to chemical and paint industries.
Tar refers to binders of organic origin, which include aromatic high molecular weight carbohydrates and their derivatives - sulfuric, acidic and nitrogenous.
Their beneficial qualities
The main requirements that exist for the organic group of binders are to have a sufficient degree of viscosity at the moment of interaction with a solid surface, which would allow for high wetting and enveloping properties to form a waterproof film. Another requirement is the ability to maintain quality data over a long period of time.
These binders found their application in the laying of roads and city streets, they cover airfields and highways, arrange sidewalks and floors in basements and industrial buildings.
Consider now the main types of building materials that belong to the two listed groups. Recall again - the inorganic group is mainly divided into those that harden in the air and those that are able to do this in the aquatic environment.
Cementing materials - building materials
Well-known clay belongs to the most common of the cementitious materials hardening in the air. It found its application in the construction of a variety of buildings. Clay is a sedimentary rock that exists as a mixture of microscopic-sized pulverulent particles with sand and small clay inclusions. The smallest of them are called finely divided. It is their presence that, when released into a humid environment, can be converted into a doughy substance. Having dried, this plastic mass easily hardens in the form given to it.
If you burn this form, then the resulting stone of artificial origin has a sufficiently high strength. Like other mineral binders, due to the different composition of clay, there can be a variety of shades. From solutions based on them, fireplaces, stoves are laid, and bricks are also formed. They can be skinny, fat and medium. Clay chamotte has refractory qualities, therefore it is indispensable for the installation of fireplaces and stoves.
What is lime
Another very well-known and widely used cementitious material is called airborne lime and is obtained from rocks, namely chalk, dolomites, limestones, and limestone. The main oxide in it may be different, depending on this, it is customary to divide air lime into dolomite, magnesia, calcium. All three varieties are obtained by calcining limestones of the corresponding origin in the kiln.
It can be either quicklime or slaked lime (or hydrated). The latter is formed in the process of extinguishing one of the three of the above.
If you look at the existing calcareous fractions, you can attribute it to lumpy or powdery. Quicklime is a fairly large porous lumps. In the process of quenching with water, a lime dough is formed from it . In order to “extract” powdered lime from lumpy lime, a hydration (slaking) process should be carried out, or lumps should be ground. It can be used with or without additives. Additives are slags, active minerals and sand of quartz origin.
All About Plaster
The next material is alabaster, aka gypsum. It is obtained by heat treatment of crushed gypsum stone. Gypsum hardens, passing through three intermediate stages, consisting of its dissolution followed by colloidation and then crystallization. When passing the first stage, a saturated solution of two-water gypsum is formed. Hardening, it increases in volume and acquires a smooth white surface.
Using coloring pigments, it is possible to give plaster products any color shades. The setting process of this binder normally starts after 4 minutes from the moment of mixing. The end of solidification 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 to avoid the risk of loss of binding properties. There are a lot of brands of gypsum; they are indicated by various numbers characterizing the degree of compressive strength.
It is sold packaged in bags of various sizes. Gypsum has found the widest application in the design of interiors of residential buildings and public buildings. It has long been customary to cast from it a wide variety of curly shapes. It should be stored exclusively in a dry room, and the shelf life is limited due to the possible loss of strength as the main useful quality.
And more about plaster
Building gypsum looks like a powder in color from grayish to bright white. If you mix it with water, a characteristic reaction begins, and the mixture is heated. It is customary to add special materials to gypsum called retention aids, the purpose of which is to improve the consistency and adhesion to the surface during plastering, as well as slightly extend the hardening period.
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, crystalline water is removed from it. The hardening period is increased to 20 hours, and the hardness is much greater than that of other varieties.
Plaster gypsum is impregnated and marbled (bright white, slowly hardening and used for plastering internal surfaces), and various fillers and retention additives are introduced into it. The main point of most of these additives is to serve as a retarder. In order to produce internal plaster, it is prepared in plastering machines with the possible addition of certain fillers, for example, sand.
Dry plaster or plasterboard building boards are obtained from it, gypsum is also used when filling the joints between them. There is putty gypsum with similar properties.
Let's talk about cements
What other properties do hydraulic binders have? The process of hardening, which began in the air, continues in water, and their strength is maintained and even grows. The 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 specific sample is determined by setting the ultimate 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 for a certain period of 28 days.
The setting rate of cement can also be different - slow, normal or fast. In the same way, depending on the speed of hardening, any cement can be ordinary, quick-hardening, or especially quick-hardening.
As an example, in this group we can name Portland cement, which exists in the form of a fine gray powder with a light greenish tint with the possible introduction of additives, which can be from granulated slag (slag Portland cement).
About hardening speed
The quality test (as well as production) of binders is conducted in compliance with numerous standards. For each of the existing groups, restrictions have been developed that determine the standard time for the start and end of setting, starting from the moment of water mixing.
Another cement - alumina - refers to quick-setting hydraulic binders. It looks like a fine powder of brown, gray, greenish or black color (depending on the processing method and initial components). In terms of fineness, it slightly exceeds Portland cement and requires a slightly larger volume of water.
Mixed types of binders - those that can harden in air and water, and are used in the production of only unreinforced concrete or mortar.
Bitumens and their scope
As for the most popular organic binders, their family includes many bitumen and tar, ranging in color from black to dark brown. The traditional field in which such binders are used is waterproofing. This building material is water resistant, waterproof, weatherproof and highly flexible. This group of binders can be softened and transferred to a liquid state by heating. As the temperature decreases, their viscosity increases and can be completely lost.
This group primarily consists of bitumen of natural origin, as well as those obtained during oil refining. Their chemical composition is a combination of oxygen, hydrogen, sulfur and nitrogen molecules. In construction, oil bitumen (liquid, solid and semi-solid) is in demand.
By their purpose, they can also be assigned to one of three groups - roofing, building or road. An impregnating compound is prepared from roofing, roofing material and many different mastics are produced.
Hard and elastic-hard varieties of industrial bitumen are produced by the high-vacuum method with additional processing steps, at which the oil boils at high temperatures. Oxidized are considered especially resistant to heat and cold. There are also mixtures of bitumen with polymers that affect their viscosity. A characteristic feature of all types is the ability to change the consistency depending on the temperature, and different phases can alternate repeatedly. The adhesive properties of the family of bitumen binders are based on it.
Why are they valuable?
The degree of expansion of bitumen under the influence of high temperatures in comparison with mineral materials is more than 20-30 times. Their valuable qualities are water resistance, resistance to salts, alkalis, aggressive acids and effluents. An example is salt, which is sprinkled with snow in the winter on the streets to melt.
The resistance of bitumen to organic solvents, oils and fats is reduced, from light, heat and air oxygen, which oxidize their constituent parts. When heated, soft particles evaporate and the surface of the bitumen hardens.
Their advantages are low flammability, that is, this material is not flammable. Oil bitumen is not harmful to health and is not classified as such. As their other properties we can talk about thermal viscosity, high thermal insulation, good wetting.
The bitumen hardness is set by the penetration depth of the needle immersed in them (it is measured in hundredths of a millimeter) at a normalized load for a certain time at a specific temperature. The transition between the solid and liquid states is sliding in nature and is determined by the softening point at low temperatures. In addition, they are characterized by the so-called fracture point - this is a term denoting the temperature at which the bendable layer of bitumen cracks or breaks.
Other materials
What other binders of organic origin can be called? Coal tar pitch, representing a viscous or solid black substance and serving as a product of tar distillation, is impregnated with roofing oil. This material is quite dangerous and can cause burns if it comes into contact with the skin. It is best to work with it in cloudy weather or in low light.
Coal tar is a substance that is released as a by-product in coke production. He found his application in the manufacture of mastic for roofing and road construction.