Concrete

Concrete - artificial stone material made from a mixture of binder, aggregates and water and special supplements to its formation and hardening. Curing of concrete - a complex of physical and chemical processes occurring between cementitious materials and water. Aggregates (crushed stone, gravel, sand) in these processes are not involved. Cementing materials (cement, lime, gypsum) after mixing with water form a plastic-viscous mass, which hardens in air or water, relates the grain aggregate and form an artificial stone material. To change the properties of cementitious materials in concrete mix is ??introduced additives that may be active mineral fillers, surfactants, accelerators, curing, retarder, antifreeze. Active mineral additives are divided into natural - diatomite, tripoli, flask, ash, tuff, and artificial - granulated blast slag, glinity, concrete block, agloporit etc. When mixed in finely powdered form with hydrated lime and mixing with water they form a dough that can after hardening in air to continue to gain strength and long to keep it in the water. Additives, fillers are used to reduce the consumption of cement and increasing the density of concrete. Surface-active additives change the properties of the surface on which they were adsorbed. Curing accelerators promote rapid set concrete strength: chloride and calcium nitrate, potash, sulfate and sodium nitrate, etc. Setting retarders, on the contrary, increase the duration of preservation of concrete mix plasticity: natural gypsum, sulphate, ferric iron (up to 1%) and surface-active substances (animal glue, RRT naphthenate soap) - up to 0.3% by weight of cement. Antifreeze additives reduce the temperature of freezing, which is mixed concrete or mortar, resulting in negative temperature remains unfrozen water, heating the material without gaining strength. Such additives are salt-electrolytes (potash, sodium nitrite), or mixtures of these salts. Number of additions depends on the temperature of curing concrete. Depending on the relative amount, type and properties of the constituents and conditions for preparation of concrete are very diverse. During the construction of small commercial buildings of interest are only a few of them: design - with the strength of not less than 50 kg / cm 2 for the manufacture of the foundation, structural and thermal insulation - with the strength of not less than 35 kg / cm 2 for the walls and insulation, for thermal insulation of walls and ceiling, with density of less than 500 kgs/sm3. For the preparation of meaningful concrete as a filler, you can use sand with clay content less than 3%, gravel, rubble, broken bricks, stone. For the preparation of structural and thermal insulation and thermal insulation of concrete as aggregate use powdered pumice, tuff, limestone, shell and other light rock, gravel, expanded clay, expanded perlite, expanded vermiculite, agloporit, slag pumice, ash gravel, slag and other artificial materials. Grades are determined by them, depending on bulk density and are in the range from 150 to 800 kg/m3 and above. The higher the grade, the harder material and the lower its thermal insulation properties. When construction of concrete buildings or parts of concrete products perform the following operations: manufacturing shuttering or forms, manufacturing fixtures (if the concrete is reinforced), preparation of concrete, installation of valves, laying and compaction of concrete mix and temperature-humidity treatment (or waiting uncured). Front surface of concrete products can be finished with decorative solution oblitsevat ceramic glass tiles come. To improve insulation properties during laying and forming the concrete can be laid thermal insulation materials. To obtain high-quality concrete should be used commercially pure sand, gravel or crushed stone and water in a sand and gravel should not be impurities of clay and topsoil. Of great importance is the ratio of sand and gravel in the mix. Gravel should be 1,5-2 times more than the sand. Water was added to the mixture on the basis that it should make 30-50% of cement weight. It should be noted that after the rain the sand and gravel contain up to 20% moisture. In cold weather to accelerate the curing of concrete should be used heated to 40-50 ° C water and in hot weather, on the contrary, to avoid fast-setting must be used with cold water. Preparation of concrete mix manually perform on the steel sheet or in a box with studded steel plate bottom. On the sheet or in a drawer pour measured amount of sand (by volume), add the dry cement and the mixture was stirred until uniform in color masses. Then add the necessary amount of gravel (macadam) and dry again 2-3 times the mass is stirred. The resulting mixture is poured from the garden watering can with water, metered based on the weight of cement in the mixture, and stir. In a qualitative stirring the mixture and squeezing (compaction) the strength of the resulting cast stone increased by 1,5-2 times. Packing and plugging of concrete layers are no more than 15 cm need to tamp until the concrete surface gleams from speaking laitance. Curing. To create the necessary conditions for curing the laid concrete must be supported by a certain temperature and humidity conditions. In summer conditions, especially in hot climates, curing is to protect fresh concrete from direct sunlight and wind moistened canvas, burlap or a layer of damp sawdust (sand), irrigated with water up to 5 times a day, while moisturizing the wooden formwork. Such curing should continue for 7 ... 14 days, depending on the weather and the brand of cement, concrete to reach 50 .. 70% of its design strength. Brand of hardened concrete can be determined with a hammer weighing 0,3-0,4 kg and a chisel. If the blade chisel penetrates about 5 mm, concrete has a mark of 70-100. If you are separated from the surface of thin leaves - a brand of concrete 100-200. With over 200 brand chisel leaves a shallow trail. Water. Used to make concrete and mortar water should not contain impurities that impede the normal setting and hardening binder. This requirement fulfills the usual rain or drinking water. Not recommended for use stagnant water from containers and reservoirs, and water having dissolved salts in large quantities. Use for preparing a solution of water saturated with different salts, leads to the appearance of efflorescence on the surface in the form of dirty spots, which act through the whitewash. The contents of all salts in the water should not exceed 5000 mg / l, and sulphate - not more than 2700 mg / liter. Sulfates - salts of sulfuric acid - destroy the cement, ie, cause its sulfate corrosion. Unsuitable for mixing binders, mortars and concrete wastewater containing a variety of oils, sugar, fats, and various acids. Water marshes, peatlands and other sources, overgrown plants, use is not desirable because it may contain humic acid that breaks down the cement. In summer the water with a temperature of 10-12 ° C taken from the well, the winter is heated it up to 25-30 ° C.