What is concrete?
Cement, or concrete mortar, is a hydraulic binder mortar. It is a finely divided inorganic material (powder) that when mixed with water forms a paste which coagulates and hardens through reactions and hydration processes and after hardening regains strength and stability even in water.

The term cement or cement paste refers to the binder powder, usually before mixing with water, without other inert additives such as sand and gravel.
What is concrete (beton)?
Concrete(beton) is a mixture of cement and gravel with water and possibly some chemical additives in appropriate proportions. It is used for the construction of building frames.
What kind of concrete (beton) should I use for the construction of my house?
The engineer-designer writes the concrete specifications on the drawings. Concrete according to the Concrete Technology Regulation (KTS) is characterized by the strength class (C16/20, C20/25 etc.) and the workability class (S1, S2 etc., for example. how soft it is before it sets).
What does concrete strength class C20/25 mean?
It means that we can reasonably safely assume that it will be able to withstand pressures of 20 Mpa (megapascals) without being damaged, 28 days after concreting. In order to certify its actual strength, special specimens are taken during each concreting operation, which are kept in a place with suitable conditions and broken with a special press 28 days after concreting. The strength of the cubic specimens (with a 15 cm edge) should be in the range of 25 MPa. The whole procedure is described in detail in the Concrete Technology Regulation. According to the law, taking the specimens is one of the obligations of the owner.
What needs to be taken care of for the correct composition of the concrete?
a)To observe the minimum required quantity of cement per cubic e.g. 270 kg. Cement, on the one hand, has the role of the glue of the concrete, on the other hand, it prevents the oxidation of the reinforcement (steel).

b) Do not add more water than is required. The composition of the concrete should ensure workability without the need to add too much water. Adding water to the barrel may possibly make the workability of the concrete easier but reduces the strength of the concrete.
What does settling in concrete mean?
There is a scale (S1 to S5) which measures how "soft" the concrete is during concreting or how easy it is to work with (concrete workability). On this scale S1 is very tight concrete while S5 is very soft. Without the addition of special fluidizers, workability is very dependent on the water dosage, so since too much water reduces strengths, S2 or S3 grades are usually specified. Under no circumstances should additional water be added. If there is a need for higher workability, this should be done exclusively by using special chemical additives (fluidisers)
What is an essay and how much should we take in concreting?
Tests are samples of the concrete used in the construction. Usually 6 or more specimens are taken in each concreting operation. They are taken on site. Special iron molds (dies) are used which are filled with the concrete used. These are sent to special laboratories where they are preserved for 28 days and then tested for strength. The procedure is described in detail in the Concrete Technology Regulation. It is the owner's responsibility to take the tests.
Why do we need to wet the slab after the end of concreting?
In order for concrete to "cure" properly, it must be in a moist environment. The slab must be wet for at least the first 7 days after concreting. So it is either covered with wet cloths or watered down frequently. Concrete that is properly preserved throughout the curing phase is much more durable than one that is preserved one day.
When and how to order.
The order must be submitted to the supplier in time, for example. at least three days before the desired day of receipt. This facilitates proper planning and processing on the part of the producer of ready-mixed concrete.

The order should specify the exact details, such as:

1. The desired date of concreting

2. The date of the desired date of placing the concrete

3. The desired (premeasured) quantity

4. The requirement for the so-called "workability" of the concrete (slump class)

5. If an additional superplasticizer or other additive is required

6. The minimum cement content

7. The maximum water/cement ratio

8. The form specified in the factory (12.2.KTS)

9. The maximum aggregate grain

10. Concrete coated or uncoated

11. Paving quantity less than 20 m3 (application of "criterion E")

12. The use of a pump (height, type or specific characteristics)

13. Any special requirements for the product e.g. concrete resistant to surface deterioration or chemical attack or exposed to air saturated with sea salts (coastal environment), etc.

14. Element to be concreted (foundations, columns, walls, slabs, etc.)

15. Required rate of concrete supply to the project (barrels/hour)

In the construction of projects located up to one kilometre from the sea (coastal environment), the use of concrete with a minimum cement content of 330 kg/m3 and a water/cement ratio not exceeding 0,60 is required.
Receipt of concrete from the client (company or individual) to the project
Particular attention should be paid by the client to the following actions during the receipt of the concrete: the client should designate a specific person to receive and inspect the concrete:

Α. If the shipment comes sealed directly from the production plant and if it has a lead seal on the barrel lever.

Β. All shipping manifests, prior to receipt of the product, to agree with its order as to the following items:

If the Shipping Note is accompanied by an Analytical Record Sheet.

The seating category (S2, S3, etc.)

The time of loading of the concrete at the production plant

The time of arrival of the concrete at the project

The quantity check (sealed barrel, weighing, weighing on a bridge scale))

The temperature of the concrete

The quantity of cement

The water/cement ratio

The maximum aggregate grain

Check the cleanliness of the pump's "well" before it is used.

If a change in workability is required, this should only be achieved by adding superplasticizer, in the appropriate dosage, after ensuring remixing in the transport car, for a minimum time of 1 minute/m3 of concrete, e.g. 9 cubic metres 9 minutes, 5 cubic metres 5 minutes, at the maximum number of revolutions (10-14 revolutions per minute).

The addition of any material (and water) is expressly prohibited
Any improvers/additives used must be approved, in terms of type and quantity, by the production plant. In any other case, the customer is solely responsible for the quality of these and any effects they may have on the strength, the setting - hardening process of the concrete, as well as the percentage of air content in the concrete.
The time of arrival of the barrel and the start and completion times for unloading the concrete (from the barrel) must be recorded on the delivery note.

It is reminded that, according to the Concrete Technology Regulation (C.T.S. '97), the maximum time allowed to elapse between the production of concrete in the plant and its unloading-use should not exceed one hour and fifty minutes in case a retarder has been used in the production plant or one hour and thirty minutes without a retarder. In no case shall concrete pours that have exceeded the above time be accepted.
What is the weight of 1 m3 of concrete?
The apparent weight of fresh concrete usually ranges from 2,350 to 2,400 kg in m3. In areas with riverine (natural) aggregates it can be as high as 2,320 kg and/or 2,300 kg. This means that a 10 m3 barrel has a net unweight of 23.5 - 24 t, and this is found by weighing the barrel loaded and after unloading the concrete, without pouring the barrel rinse water out, before weighing.
How much concrete do I need?
To calculate the amount of concrete we need, we need to do a simple mathematical operation. We multiply the length by the width by the height of the area we want to cover with concrete. E.g. we have a yard 5 meters long, 6 meters wide and we want the height of the concrete to be 10 cm. 5X6X0,1=3 cubic meters (m/3).


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