All of the concrete products (concrete products)

Zhukov DA, Cand. MSSU 1. From what is made of reinforced concrete products (concrete products) reinforced concrete - a material which are joined into a single unit steel reinforcement ibeton. Concrete partially protects the metal fittings from corrosion and treats in this composite, the compressive stresses, fittings - tensile forces: it is known that the metal works well in tension, and relatively fragile concrete stone - on the grip. Cement and water are the active components of concrete - the reaction between the cement stone formed, cementing grains aggregate into a single monolith. Between cement and aggregate is no chemical interaction, so fillers are often called inert materials. However, the large aggregate (crushed rock or limestone) and fine aggregate (quartz, also known as river sand) significantly affect the structure and properties of concrete. As a reinforcement in metal (steel) rods or bundles of wires. Armature is subdivided into the working and assembly. Working valves at the bottom of articles, working on a bend: slabs, beams, at the foot of foundation blocks. Mounting hardware creates a volume skeleton product captures the location of the rods of fixtures contributes to blocking and bracing inserts and mounting hinges. One variety of concrete is stressed concrete. Through the application of special techniques, during the manufacture of materials stressed concrete reinforcement in concrete zamonolichivaetsya in partially stretched form. The fact that the floor slabs and supporting beams in the construction work on a bend. First, they take the load of the floor construction (including own weight), and secondly - the load of household items placed on the floor, in the third - the load transmitted from the walls to the frame of the building. As a result, lower layers of the slab or supporting beams are in a slightly stretched form, which affects their reliability. If the lower layers of the panel or beam in the manufacturing process have been artificially compressed ("tense" reinforced concrete), then the household and structural load, they will be in a neutral state, the stresses in them will be minimal, and therefore will be minimal problems associated with the operation of construction . 2. As is made of reinforced concrete slabs product (hollow and ribbed), jumpers, elements of fences, basements and foundations, paving slabs, the details of wells and lighting columns - all items of reinforced concrete. It is obvious that each product has its characteristic system of reinforcement, concrete formulation and manufacturing technology. Slabs and bridges, working on a bend, is made of prestressed concrete. In the prepared form of special stops install reinforcing bars, pull them (mechanically, with the help of jacks, or thermomechanical by heating electric shock) and fixed in the tense situation in the bortosnastke form. Pouring the concrete mix, followed by vibration compaction can be carried out on the stands (with the introduction pustotoobrazovateley) or on the conveyor lines, including ways to hire or roller forming, after which the products in the forms are sent to a heat treatment in a special chamber. The purpose of heat treatment - acceleration of hardening concrete, and after 8 ... 12 hours steaming at an ambient temperature of 80 ... 95 ° C the product is gaining 65 ... 75% of its brand strength, equivalent to 28 days of hardening under natural conditions. Once the product is dry, intense reinforcing bars exempt from attaching to the walls of the form. Rods partially compressed length and tension of them passed the concrete in the product - in the adjacent areas of concrete reinforcement bars formed by the state of stress. Products cylindrical shape (bar, rings, etc.) are produced by centrifugation. Previously in the half-forms, placed on a stand centrifuges, stacked reinforcement bars (if necessary, pull), which circumferential metal wire - shaped frame products. With Stretcher bond concrete distributor throughout the length distributed semiform concrete mixture, cover with a half-forms on top of another and include a centrifuge. In the first stage, the concrete mixture due to centrifugal forces, is distributed at the outer envelope surface of a cylindrical shape. In the second stage, due to the changing speed centrifuges, is seal the concrete mix and molding products. Further products (half-form or raspalublennye) are sent to a heat treatment. 3. What not to do when installing reinforced concrete Any construction products, including reinforced concrete, designed for certain loads, above which is undesirable or unacceptable. For products operating on a bend, building codes and regulations established regulatory allowable load. Make a reservation straight away that the magnitude of these loads provides very, very substantial margin of safety and, if the correct installation of construction, destruction of goods is impossible. Each building design (including floor slab) are designed for specific arrangement. These schemes are known to builders, and their violation may lead to undesirable consequences for all. Often, there is a need to make a hole in the floor panels, and if it is formed will the integrity of the reinforcement cage bar or, equally important, will cut reinforcing bars to ensure the carrying capacity of this panel, the positive effect of "prestress" will be almost entirely eliminated. Such a damaged panel will not match the scale of the regulatory allowable loads. If, however, make a hole in the panel still necessary, it is necessary to provide a console consolidation of cut panels on the intermediate support (for example, on the inner walls or jumper) and use the harness of metal profiles along the perimeter of the cut plate with fixing (threaded or welded) on this profile ends of rebars. 4. About delivery and intermediate storage of concrete products have already mentioned that the factory concrete products have a high degree of reliability and only on the consumers themselves depend to decline if this reliability in the future. Products, before the fall in construction and designed them to take place, may be exposed to excessive mechanical stress or to be in high humidity conditions. In addition, concrete is subject to biological corrosion (the appearance of mold, fungus, etc.) that must be taken into account in the store. Damage to products can occur both during transportation (shipping), and at their storage (intermediate storage). Moisture usually enters the product in contact with the ground (capillary leak), or precipitation that can lead to a deterioration of the mechanical characteristics of the product, and to develop it corroding microflora. The most common type of injury - mechanical. For example, when transporting slabs (position, as it should, on wooden blocks, strips) on top of them were placed concrete blocks. As a result, the product arrived on the deformed object: the disclosure of cracks wider than 1 mm on the bottom, with spalling concrete and exposed reinforcement. If this has happened through the fault of the provider, then such products should be replaced. But suppliers generally comply with the conditions of carriage, and such situations hardly arise. But when the products arrive at the place of intermediate storage, where they have already paid for the money and goods taken by the customer, the owner should have to take care of products belonging to him. Even if the products purchased for use within weeks or months for them to provide some "comfort" conditions of storage. Platform for their storage needs to be leveled; between products and the ground should not be a contact; desirable overhang or harboring a product of the film. Slabs preferably stored horizontally (in the "position") by laying them together pieces of wood for the airing and to relieve the stresses. 5. Deficient, explicit and implicit times in the acquired party products come with obvious defects. Some of these defects is easy to handle and can not affect the quality of products, some - are inevitable and are "fatal" character. Sometimes defects are the origin of the factory, sometimes they arise in the self-delivery of products as a result of improper transportation. If the product is apparently not destroyed, and there are only small chips, they are quite easy to be eliminated by the termination of their cement-sand mortar or special repair mixes. If the defect is serious (offset reinforcing cage, bad anchoring fixtures and installation of loops, a thin protective layer of concrete), then such products should be returned to the manufacturer and subsequent replacement. But, as a rule, such defective products reveal to another stage of acceptance of technical control, and if they go beyond the factory, then as sub-standard. Some manufacturing defects (for example, the grid surface of thin cracks in the floor slab) are not "lethal" nature and do not affect the reliability and load-carrying capacity of the product. Such defects are eliminated in the process of assembling products. 6. On the properties and classes of concrete on the density of concrete is divided into very heavy, heavy (density D = 1800 ... 2500 kg / m 3), light and very easy. On aggregate size heavy concretes are divided into concrete in large aggregates and fine concrete. Slabs, paving slabs, lintels, the elements of fences, basements and foundations, details of wells and lighting columns are made on the basis of heavy concrete. Classes of concrete on the compressive strength (B), axial tension (in t), tensile bending (B tb) are characterized by the respective strength of the concrete base size in the age specified in the project (usually - 28 days). Table of indicators of heavy concrete strength from his class is listed below. Concrete grade at an average density (D) is determined by the actual rate of mass concrete in the dry state per unit volume of sample (kg / m 3). Grade of concrete on frost resistance (F) is determined by the number of alternating cycles of freezing and thawing in various media that can withstand the control samples without reducing the compressive strength of more regulated (for the Moscow region, F must be not less than 35). Mark Concrete waterproofing (W) is determined by water pressure, which is not observed it spilling over control samples. Regulated parameters of quality of concrete shall be provided with the selection of its members, the implementation of technological modes of preparation, compaction of concrete mixtures, curing of concrete products and monitored in production. Table 1: The class of heavy concrete and indicators of the strength class of concrete axial compression (prism strength), MPa axial stretching, MPa, at 15 11.00 1.15 15.00 1.40 In 20 In 25 In 1.60 18.50 30 22 , 00 1.80 25.50 1.95 In 35 In 40 In 45 29.00 2.10 32.00 2.20 36.00 2.30 V 50 V 55 39.50 2,40 60 42.00 2,50