Fillers for concrete

Aggregates for concrete are divided into natural, artificial and aggregates from the waste industry. Natural aggregates are produced by mechanical processing of rocks. Artificial fillers serve especially of prepared materials, which is produced from natural raw materials and industrial waste by thermal or other processing (concrete block, Termoli, slag pumice, etc.). Fillers from the waste industry - slag, ash, slag mixture. The most important indicators of quality aggregates are density, grain and mineral composition, shape and surface texture of the grains. Depending on the density of aggregates are distinguished dense - more than 2000 kg/m3 and porous - less than 2000 kg/m3. Durability: fillers directly affects the strength of concrete. Requirements set by the strength in the main only for large aggregates, since it is usually used as, filler sand is obviously higher strength concrete strength (tensile strength of quartz sands above 1000 MPa). Strength is characterized by gravel mark corresponding to the ultimate strength of the source rock in the water-saturated condition (20-140 MPa). To obtain the heavy concrete using aggregates from rock density 1800-2800 kg/m3. Fillers having a density less than 1800 kg/m3, characterized by high porosity and are used for the manufacture of lightweight concrete. For fine aggregate include natural and artificial sand. Natural sands are distinguished by its mineral composition - quartz sand, feldspar, carbonate, etc. In terms of education distinguish sea, river and ravine sands. Grains of sea and river sand are rounded shape and smooth surface. In ravine of sand grains mostly awkward. The sand contains particles ranging in size from 0.14 to 5 mm (particles less than 0.14 mm are clay and dust-like impurities). Grain of Sand is the best, if the sand contains grains of different sizes, and small grains are located in the voids to be filled with cement dough in the manufacture of dense concrete. Emptiness of the sand can vary within wide limits - from 30 to 45%. Artificial sand produced by crushing rock or food industry, such as metallurgical slag. Depending on the grain composition distinguish the sand by size: increased size, large, medium, fine and very fine. Clayey and silty impurities in the sand envelop the grains and prevent the coupling of the cement. Thin flour particles have large specific surface, and therefore require more cement paste for coating of the concrete. Therefore, the content of such particles may be, depending on the purpose of the concrete, up to 2-5%. Apply artificial sand as fine aggregate in almost all types and grades of concrete. Fine sand used for the manufacture of concrete only when appropriate mechanization and economic rationale. In this case it is obligatory introduction to the concrete plasticizers. As the major aggregates for concrete use gravel or crushed stone. Grain composition of coarse aggregate is selected because of its largest and smallest particle size, sifting through a standard set of sieves. Crushed stone is better than gravel, adhesion to the cement stone and provides a more durable concrete, but concrete mix at the rubble with all things being equal has less mobility than on gravel. For concrete grades 400 and above apply only to rubble. Gravel is a grain size of 5-70 mm, with rounded, rounded, smooth surface, usually in the gravel contains a certain amount of sand. When the content of sand, 25-40% of the material referred to as sand-gravel mixture. Apply gravel depending on the amount of impurities for the preparation of various types of concrete up to M400. Crushed get rock crushing in pieces the size of 5-70 mm. Grains are angular rubble form and a rough surface than gravel. With this grip with the cement stone with rubble above. Crushed stone, gravel, and as is usually used fractionated, which divides it into factions. The strength of large aggregates normalized taking into account the strength of concrete. Thus, the strength of the rubble of natural stone should be above the concrete strength by 1,5-2 times. Apply gravel is preferred for manufacturing high-strength concrete. In order to aggregate distributed uniformly throughout the volume of construction, it is the largest particle size should be used with light density of reinforcement and dimensions of the construction. To increase mobility to concrete add various plasticizing additives. To slow the process of setting concrete - retarder gypsum, ferrous sulfate, etc.) to accelerate the setting time of concrete - accelerator, antifreeze additives (sodium chloride, calcium chloride, etc.).