I have repeatedly heard from craftsmen and sellers that dry building mixtures come in different binders. That is, they can be classified according to the binders used. True, when I began to find out what binders exist in nature, I could not remember anything except cement and gypsum or anhydrite. Only these options are mentioned by craftsmen and sellers. Let's work together to figure out this issue.
In general, mineral binders are finely dispersed powders of mono- or polymineral composition, which, when mixed with water or salt solutions, are capable of forming coagulation and crystallization structures that have a certain strength and durability. Based on the ability of binders to form a structure, they are divided into three groups:
All the considered binders belong to hydration-hardening binders, i.e. to obtain a hard stone from them, it is necessary to mix the binder with water, only in the first case hardening occurs in air, in the second in water, in the third - in water at temperature and pressure.
Portland cement is often called simply cement - it is the most important mineral binder. It serves as the base material for most modified specialty cements, but at the same time it can be used without modification in a wide range of cementing conditions. Portland cement is a powdered material containing artificial minerals, most of which are not found in nature or are extremely rare. These minerals are highly chemically active and are able to interact with water.
Portland cement is a hydraulic binder obtained by finely grinding Portland cement clinker with gypsum and other special additives. Clinker is produced by firing a finely dispersed homogeneous raw material mixture consisting of limestone, clay, and silica until sintering. Gypsum is introduced for the purpose of regulation, setting speed and some other properties. Clinker powder without gypsum, when mixed with water, quickly sets and hardens into cement stone with reduced strength properties. According to GOST 1581-96, up to 15% of active mineral additives are allowed to be added to Portland cement during grinding. At the same time, the name of the cement does not change. The properties of Portland cement are determined primarily by the quality of the clinker.
Historical reference . It is believed that Portland cement was invented in England by mason Joseph Aspdin, who received a patent in 1824 for the production of a binder from a mixture of lime and clay by firing it until carbon dioxide is completely removed. He called this binder Portland cement. However, in Russia, Portland cement was obtained somewhat earlier, in 1817, by the head of the military work team E. G. Cheliev. In 1825, he published a book on the production of a binder, similar in composition to the Portland cement currently used.
How does this work in epoxy adhesives or grouts? What kind of binder is there? I mean, I know that there are two components and when mixed they harden, but what is happening there, so to speak, at the molecular level? What goes into what and who knits whom :)))))))
All my life I thought that Portland cement was named after the city of Portland :)))))) Thanks for the historical information!
According to GOST 31189, according to the binders used, dry mixtures are divided into:
We will gradually get to epoxy adhesives and grouts. So far, only the cement ones have been slightly covered.
First, you should familiarize yourself with the definitions of the following terms: gypsum , anhydrite . Depending on the method of production, gypsum binders are divided into three main groups:
Group I includes: gypsum binders, the main component of which is α- or β-calcium sulfate hemihydrate (or a mixture of them), as well as soluble anhydrite;
anhydrite binders, consisting mainly of completely dehydrated gypsum or even partially dissociated anhydrite containing a small amount of free calcium oxide. Group II includes: binders obtained from natural calcium sulfate dihydrate;
binders obtained from natural anhydrite. To activate the hardening of these binders, special additives are introduced. Group III includes binders obtained by mixing gypsum binders of groups I and II with various components (lime, Portland cement and its varieties, active mineral additives, chemical additives, etc.).
Binders of groups I and II are non-waterproof (air) gypsum binders. Group III binders refer, with some exceptions, to waterproof gypsum binders.
The main characteristics of gypsum binders are: color, density, specific surface area, fineness of grinding; water demand; dough setting time; mechanical strength, aging, etc.
The color of gypsum binders depends on the chemical purity of gypsum raw materials, the content of impurities and the production method.
White gypsum binders are obtained from pure raw materials, and gray binders are obtained from raw materials with impurities of mineral and organic origin. Density is determined according to GOST 6427. The values of the true, bulk in a compacted and bulk in a loose state density of gypsum binders are 2.6–2.75 g/cm 3 , 1200–1450 and 800–1100 kg/m 3 .
The external specific surface of gypsum binders - this is the total surface of all grains per unit volume or mass - is in the range of 0.3–0.5 m 2 /g, and for high-strength binders - 0.09–0.12 m 2 /g.
The fineness of grinding characterizes the degree of grinding of the gypsum binder and is expressed by the residue in mass percent on a standard sieve No. 02, or by the specific surface of the binder powder in m 2 /kg (cm 2 /g).
Water requirement is the most important property of gypsum binders and characterizes the minimum amount of water required to obtain a dough of a given consistency.
The ratio of the amount of water to the mass of gypsum binder is called the water-gypsum ratio (W/G). Theoretically, hydration of calcium sulfate hemihydrate requires 18.62% water by weight of the binder. In practice, to obtain a dough of normal thickness from calcium sulfate β-hemihydrate, 50–70% is required, for calcium sulfate α-hemihydrate – 30–40%, for anhydrite binders – 30–35%. Waterproof gypsum binders, depending on the composition and production technology, can have a normal density of 30 to 65%. The water remaining in the gypsum stone after hydration evaporates, forming pores and capillaries in it, which negatively affect the physical and technical properties of the binders. The mechanical strength of the hardened gypsum binder is determined by the results of tests of standard samples for bending and (or) compression after hardening. Under standard hardening conditions, the strength of dried samples becomes 2 or more times higher than the strength of samples 2 hours after molding. Thus, the strength of samples from building gypsum after 2 hours is 4–6 MPa, and dry 10–16 MPa; from molding gypsum, respectively, 6–8 and 18–20 MPa; from high-strength gypsum, 15–20 and 35–40; and supergypsum, 22 –30 and 60–70 MPa.
The raw materials for the production of puffed lime are dense limestone, shell rock, chalk, and dolomitized limestone, provided that the content of clay impurities in them does not exceed 6%. The raw materials are fired at a temperature of 1000 ... 1200°C until carbon dioxide is completely removed. After firing, lump lime or boiling lime is obtained (as it is called because of the violent chemical reaction with water). This substance has highly developed internal microporosity and a large supply of free internal energy, which manifests itself when slaking lump lime, i.e., the addition of water with the release of a large amount of heat. When fired, limestone decomposes into lime, CaO and carbon dioxide, which is completely removed. The decomposition reaction of limestone is reversible.
A sign of high quality lime is its high content of CaO + MgO. Underburning and overburning of lime in a kiln reduces its quality. Vitrified lime is especially dangerous when burned. Burnout particles slowly extinguish as they increase in volume and can cause cracks in plaster and products. The content of pure oxides CaO + MgO in the total amount of lime is called its activity. The type of lime is determined by the activity and content of unquenched grains. If lump lime is crushed, you get ground quicklime. Slaked lime is more common in construction, obtained by mixing quicklime with water. When heat is released, part of the quenching water turns into steam, under the influence of which the lump lime turns into the finest particles of hydrated lime several microns in size with a high specific surface area. Slaked lime sets and hardens slowly and has low strength, so in addition to slaked lime, quicklime is used in construction. Based on the content of magnesium oxide in lime, it is divided into calcium (MgO < 5%), magnesium (MgO = 5 ... 20%) and dolomite (MgO = 20 ... 40%); Based on slaking time, lime is distinguished between fast slaking (slaking time < 8 min), medium slaking (slaking time 8 ... 25 min) and slow slaking (slaking time at least 25 min).
Air lime is used for the preparation of masonry and finishing mortars, the production of piece concrete products, for example, lime-slag bricks, sand-lime bricks and other autoclaved lime-sand products.
The raw materials for magnesium binders are magnesite and dolomite. Magnesite is fired at a temperature of 750 ... 800°C (in rotary kilns up to 1000°C) until MgCO 3 into MgO and CO 2 with the removal of carbon dioxide. After grinding, MgO is an air binder called caustic magnesite, it has a compressive strength of 40 ... 60 MPa, sometimes reaching up to 100 MPa.
Dolomite is fired at lower temperatures in the range of 650 ... 750°C, since when the firing temperature increases, CaCO 3 with the formation of lime. A special feature of the use of magnesium binders is their mixing with aqueous solutions of magnesium salts, and the beginning of setting occurs no later than 20 minutes, and the end - no later than 6 hours. Magnesia binders have good adhesion to organic fillers and are used for the production of either with sawdust - xylolite , or with wood wool (narrow and long wood shavings) - fiberboard . Xylolite is used for the production of seamless floors and facing tiles, fibrolite - for the production of thermal insulation products and room partitions in village construction.
Polymer binders are a class of binders based on products from the processing of organic compounds (polymers and copolymers of various chemical compositions). Polymers are used natural, but more often - synthetic high-molecular substances. Among them are divinyl and divinylstyrene rubbers, polyvinyl acetate, polyvinyl chloride, polyacrylates and polymethacrylates, polystyrene, phenol-formaldehyde, urea, polyesters, organosilicon, etc., as well as combined polymers. Natural ones include natural rubber (latex), bitumen, carbohydrates (dextrin, alginic acid), protein (casein), etc. The choice of hardeners, catalysts and fillers is determined by the type and nature of the polymer used.
Since the production of polymer binders is a rather expensive process, their use in pure form is limited. They are most often used as additives to mineral binders. This creates another type of binder - composite.
Composite binders are a class of binders that are a composition selected in a certain proportion (mixed at the factory) of mineral and polymer binders. Both components usually participate in the hardening of binders with polymer additives. The degree of such participation largely depends on the properties and composition of both the mineral binder (Portland cement, aluminous cement, gypsum, magnesite, etc.) and the polymer additive. As a result, bases on such compositions acquire properties borrowed from each component of the original mixture. Thus, they can promote plasticization of mixtures with a significant reduction in the water content in them, as well as air entrainment and hydrophobization with a sharp increase in frost resistance. Polymer additives increase ultimate elongation, impact strength, tensile and bending strength, abrasion resistance, adhesion to other materials, etc.
The following are added as additives to mineral binders and concrete mixtures:
aqueous dispersions of polymers - latexes (natural and synthetic rubbers), polyvinyl acetate, polyvinyl chloride and other emulsions that, when mixed with a mineral binder, can disintegrate with the release of water, which is bound during its hydration, and polymer particles that stick together into thin elastic films on the surface of new formations from inorganic binder, strengthening their connection with each other due to gluing;
water-soluble polymers - phenolic, urea, epoxy and so on, capable of transforming into a solid insoluble state in hardening cement stone under the influence of heat or an alkaline environment that occurs during cement hydration, or specially introduced hardener additives.