What is ready-made concrete? How is it produced?
Concrete that is produced by mixing inert materials in an automated concrete plant or mixers and is offered to the consumer as a” concrete “ is called ”ready-mix concrete".
The qualification of the finished concrete is specified in TS EN 206. In contrast to preparing concrete manually on construction sites, ready-made concrete is produced using computer control in modern factories, concrete mixing plants.
The composition of the finished concrete consists of two components. The solution is obtained by mixing water and cement at the concrete plant or transmitere.
Aggregates and cement are mixed at a concrete plant, delivered to the construction site using a transmixer, and water and chemical additives are added on site. This method of preparing concrete is called dry. With this method, attention is paid to the ratio of water and the mixing time required for a mixture of this type of concrete. Ready-made wet concrete is obtained by mixing and preparing all its components, including water, at a concrete plant.
Ready concrete batching plant
Concrete plants are divided into" wet and dry method of preparation", depending on what kind of concrete it will be produced. The process of mixing aggregates is controlled by the operator. Facilities where concrete is produced and transmitters are filled are called "concrete plants".
A properly selected material determines the quality of the manufactured concrete. Materials such as cement, aggregates, water and additives are subject to laboratory tests before use. The materials used are checked regularly to prevent defects.
Production of ready-made concrete begins with the launch of a concrete plant by the operator. The operator enters the necessary information into the computer system, the formula of the concrete mix to be produced. After selecting the desired mix, the aggregates, cement and water located in different compartments are weighed. After the weighing process is complete, the inert aggregates are transported by a conveyor belt or skip conveyor. At the same time, cement, water and chemical additives, if present, are also mixed in the boiler.
The volume of the concrete hopper varies depending on the concrete plant, but most often it is 1-3 m3. The mixing time must correspond to the volume of the mixture and is determined by the established standards. The solution is mixed until it is unloaded into the transmixer, and the same process continues until shipment.
Classes of concrete
a) classes of compressive strength
According to compressive strength, concretes are divided into classes. Basically, the compressive strength of concrete is determined using cube samples (based on the 28-day normal compressive strength of cubes with a face length of 150 mm). When denoting the compressive strength class "C", the number before the fraction line shows the cylindrical compressive strength. Classes of compressive strength in ready-made concrete, the same cylinder strength are given in the table below.
b) Consistency classes
The difference in the use of concrete is determined by its consistency. The consistency differs depending on the layout, the DGU will use concrete (formwork geometry, iron, slope). Placement, compression, calibration and features of concrete, methods of concrete delivery (pump)- this is an aspect that should be paid attention to. In accordance with TS EN 206, the concrete consistency is determined by the settling and compression classes.
The consistency of the concrete mix is measured by the precipitation of the cone and is designated by the precipitation class from S1 to S5. The consistency of the concrete mix must be determined during the use of the concrete mix. The consistency of the concrete mix is determined by a standard cone and measured in millimeters.
The consistency of the finished concrete depends on the temperature. The transport time does not affect the consistency. But if the temperature rises and the transportion takes longer, then there is a high probability of a violation of the consistency on the way to the construction site. In some cases, water is added to restore the consistency.
When brushing or pouring concrete.
Razgruzochnyi chute is placed on a flat ground.
We will describe the concrete Bay for you using the example of the Foundation Bay. First, you need to study the geological features of the construction site. Then they make calculations and prepare a set of documentation. After that, start clearing and marking the site. Fall asleep rubble-sand pillow, spend the device drainage system. Install the formwork and install reinforcing rods. Pour concrete, level the surface and remove the formwork. Pouring concrete to form different building structures has its own specifics.
The use of a vibrator is unavoidable during the concrete pouring process. The" Ordinance on structures to be constructed in disaster zones " also prohibits the process of pouring concrete without the use of vibrators.
Possible reasons for loss of consistency when transporting concrete.
Industrial violations. Illiterate mixing of all components can have a significant impact on the quality of prepared concrete. Therefore, it is desirable to order ready-made concrete at factories where it is prepared by professionals.
Moving the finished mixture. Transporting concrete from the manufacturer to the consumer is very important. If you delay delivery, then welding of the composition is not excluded. Special attention should be paid to the delivery time at high air temperatures. The buyer must initially take care of instant transportation, as well as prepare the site or container for concrete. Sometimes concrete hardens much faster. Therefore, such a mixture should be laid in the shortest possible period, otherwise it will threaten to deteriorate the quality of concrete.
Weather conditions play a particularly important role. At high air temperature, the consistency of concrete is broken much faster and more often. To avoid this trend, the Board of Directors of the Turkish ready-mix concrete Association advises its members to keep the concrete consistency at the K4 level (subsidence >16 cm) when delivered to the construction site, while paying attention to the ratio of water and cement. Customers who are aware of the possibility of this problem, order concrete of the K4 consistency.
C) aggregate largest (maximum) grain size classes
The main features of the standardized classification of various aggregates for concrete (According to TS EN 206-1) are: origin, grain size, grain shape, density.
By origin placeholders are divided into three groups:
1) natural, including from incidentally extracted rocks and enrichment waste;
2) from industrial waste;
3) artificial (specially prepared).
Natural materials and materials from industrial waste, obtained without changing their chemical composition and phase state, are characterized respectively by the origin and petrographic name of rocks or the type of waste. For example, igneous deep (Intrusive) rocks — granite, syenite, diorite; blast furnace slag. Artificial aggregates are characterized by the type of raw material (natural, from waste or a mixture of them) and production technology (processing method). For example, those obtained from natural raw materials by firing with swelling — expanded clay; get porizatsii of molten blast-furnace slags — slag pumice.
By grain size, aggregates are divided into:
1) large-with grains (pieces) over 5 mm (crushed stone, gravel);
2) small— with grain size up to 5 mm (sand).
By the nature of the shape of the grains are distinguished:
1) aggregates having an angular (irregular) shape obtained by crushing (crushed stone, sand from crushing screenings, etc.);
2) aggregates having a rounded grain shape (gravel, natural sand, etcaggregates having a rounded grain shape (gravel, natural sand, etc