Concrete partially protects the metal from corrosion of reinforcement and perceives this composite compressive stresses and fittings - tensile force: it is known that the metal works well in tension, and relatively fragileConcrete stone - compression.
Cement and water are the active ingredients of the concrete - the reaction between the cement stone produced, bonding grain aggregate in a single monolith.Between the cement and the aggregate is no chemical interaction, therefore often called inert filler materials.However, the coarse aggregate (gravel or limestone rocks) and fine aggregate (quartz, it is river sand) greatly affect the structure and properties of concrete.
as reinforcement in metal (steel) bars or bundles of wires.Reinforcement is divided into working and assembly.Working valves located in the bottom of the product, working on bending slabs, beams, in the soles of the foundation blocks.Mounting fittings creates a surround skeleton p
One variety is intense reinforced concrete.Due to the use of special procedures in the manufacturing process materials of stressed concrete reinforcement in concrete zamonolichivaetsya partially stretched form.
The fact that slabs and the girders in the construction work in bending.First, they take the load floor structure (including the own weight);secondly - the load of everyday items placed on the floor;in the third - the load is transmitted from the walls to the frame of the building.As a result, the lower layers of the floor slab or support beams are in a slightly stretched, which negatively affects their reliability.
If the lower layers of the panel or beam during fabrication were artificially compressed ("busy" concrete), then the consumer and structural load they will be in a neutral state in which the voltage will be low, and thus will get problems withExploitation of construction.
how to make concrete products
Plates of overlap (hollow and ribbed), bridges, fencing elements, basements and foundations, paving slabs, parts of wells and lighting poles - all products of reinforced concrete.It is clear that each product has the characteristic of a system of reinforcement, concrete recipe and manufacturing technology.
slabs and lintels, running on a bend, made of prestressed concrete.In the prepared form for special stops installed reinforcing bars, pull them (mechanically with a jack, or thermomechanically by heating electric shock) and secured under tension to form board equipment.
pouring concrete mixture, followed by vibration compaction may be performed on the stands (introduction blockouts) or conveyor lines, including rolling means or roller molding, after which the product in the form is submitted to thermal treatment in special chambers.The purpose of heat treatment - the acceleration of concrete hardening and through steaming 8..12 hours at ambient temperature 80..95 ° C the product is gaining 65..75% of its branded strength equivalent to 28 days of hardening under natural conditions.After the product has solidified, tense reinforcing rods free from attachment to the walls of the mold.The rods are partially compressed in length and tension of them transferred to the concrete in the product - in the surrounding areas of concrete reinforcing bars formed the stress state.
products of cylindrical shape (racks, rings, etc.) is made by centrifugation.Previously in the half shell, placed on the bench centrifuges, stacked reinforcing rods (if necessary, pull them), which wound metal wire - shaped frame of the product.With the stretcher betonorazdatchika mold halves over the entire length distributed concrete mixture, one on top of another mold half and covered with the centrifuge.In the first phase, the concrete mix, due to the centrifugal force is distributed on the outer surface of the cylindrical shape of the partition.In the second stage, due to the changing speed of the centrifuge, is compacted concrete mix and molding products.The following products (in the mold halves or raspalublennye) is sent to a heat treatment.
What not to do when installing reinforced concrete
Any construction product, including reinforced concrete, designed for a specific load, the excess of which is undesirable or unacceptable.For devices running on a bend, building codes established regulatory allowable load.Say at once that the magnitude of these loads provides a very, very significant safety margin and with the correct mounting structure, the destruction of the product is practically excluded.
Each building structure (including slabs) are designed for specific installation schemes.These schemes are known builders, and breaking them may lead to undesirable consequences for all.It is often necessary to make a hole in the slab, and if it is formed will be broken integrity of the reinforcement cage or panel, but not least, will be cut rebars, providing load-bearing capacity of the panel, the positive effect of "preload" will be almost completely eliminated.Such damaged panels will not match the scale of legal and permissible loads.
If you make a hole in the panel is still necessary, it is necessary to provide cantilevered panels cut by the intermediate support (for example, the inner bearing wall or bridge) and run piping from the metal profile cut along the perimeter of the plate with fixing (threaded orby welding) to the ends of this profile rebars.
shipping and intermediate storage of concrete products
have already mentioned that the factory concrete products have a high degree of reliability, and only by the consumers themselves depends on whether this decrease reliability in the future.Products before they reach the design and intended take their place, they may be exposed to excessive mechanical stress or be in a humid environment.Furthermore, concrete is exposed biological corrosion (occurrence of mold, mildew, etc.)., Which should be considered during storage.
product damage can occur both during transport (shipping), and in their storage (intermediate storage).Moisture is usually enters the product in contact with the ground (capillary leak) or precipitation, which can lead to deterioration of the mechanical characteristics of the product, and the development of microflora on it corroding.
most common type of injury - mechanical.For example, when transporting slabs (position, as it should be, on wooden sticks, pads) were placed on top of concrete blocks.As a result, the product arrived at the object deformed: a crack-opening width of more than 1 mm in the lower part, with a chip and bare concrete reinforcement.If this was the fault of the supplier, then these products should be replaced.But vendors usually comply with such transport conditions and situations hardly occur.
But when products arrive at the place of intermediate storage when they already paid for the money and the product accepted by the customer, the owner must take care of the very product of its own.Even if the product purchased for use within weeks or months, they need to ensure a certain "comfortable" conditions of storage.Area of storage should be lined;between the products and should not be ground contacting;desirable canopy or harboring the product film.Plates of overlap should preferably be stored horizontally (in the "operating position"), laying them together wooden bars for ventilation and to relieve the stresses.
Defects, explicit and implicit
Sometimes acquired party products fall with apparent defects.Some of these defects are easy to handle and can not affect the quality of products, some - are inevitable and are "lethal" nature.Sometimes defects are factory origin, sometimes they occur when Pickup products as a result of improper transport.
If the product is apparently not destroyed, and there are only small chips, they are quite easy to be avoided by sealing their cement-sand mortar or special repair mortar.If the defect is serious (the displacement of the reinforcing cage, incorrect anchoring fixings and assembly loops, a thin protective layer of concrete), then such products shall be returned to the manufacturer and subsequent replacement.But, as a rule, such defective products to identify more technical control of the stage of acceptance and if they go beyond the plant, how sub-standard.
Some factory defects (eg, thin mesh surface cracks on the slab) are not "fatal" character and do not affect the reliability and load-bearing capacity of the product.Such defects are eliminated in the process of installation products.
On the properties and classes of concrete
According density concrete is divided into very heavy, heavy (density D = 1800..2500 kg / m?), Light and very light.The size of the heavy concrete aggregate is divided into concrete on major aggregates and the fine-grained concrete.Overlap plates, pavements, bridges, fencing elements, basements and foundations, parts of wells and lighting poles are made on the basis of heavy concrete.
Classes concrete compressive strength (B) axial tension (Bt), tensile bending (Btb) are characterized by the respective strength of the concrete base size in the established project age (usually - 28 days).Table depending of the strength of its heavy concrete class is listed below.
Mark concrete at the average density (D) is determined by the actual weight of the concrete measure of the dry sample per unit volume (kg / m?).
Mark concrete frost resistance (F) is determined by the number of alternate freezing and thawing cycles in different environments that sustain control samples without compromising the compressive strength of a regulated (for Moscow region F should be at least 35).
Mark concrete waterproofing (W) is determined by the pressure of the water in which it is observed through leakage control samples.
Regulated quality concrete should be provided with the selection of its members, the implementation of technological modes of preparation, compaction of concrete mixtures, curing of concrete products and controlled in the workplace.