At a construction site of any level, from a skyscraper to a country house, one cannot do without concrete. This material is used for pouring foundations, erecting walls in monolithic construction, laying ceilings and screeds, laying bricks and other artificial stone. Preparing concrete in the right proportion not only ensures the durability and strength of structures, but also avoids unnecessary material costs.
Concrete composition
In the simplest case, concrete consists of three components:
- Astringent.
- Filler.
- Water.
Consumption of materials per 1 m3 of concrete is determined by the properties of these materials. As a binder in the production of the mixture, cement grades M100-M600 are used for strength. When mixed with water, a viscous mass is formed, upon solidification of whichfake diamond. As a filler, sand or various types of crushed stone are used. This increases the strength of the hardened mortar, since the strength of crushed stone is higher than the strength of cement. In addition, the use of aggregate reduces the shrinkage of the cement mix.
In addition to the main components, the composition of concrete includes various additives that give the mortar additional properties: frost resistance, water resistance, color, etc.
The required consumption of materials per 1m3 of concrete - crushed stone, cement, sand - is determined based on the requirements for the characteristics of the mixture.
Main characteristics of concrete
The most important characteristic of concrete is its compressive strength. Depending on it, a strength class is set. It is denoted by the English letter "B" and numbers corresponding to the strength of the sample in MPa. Concretes of classes from B3, 5 to B80 are produced, in civil engineering solutions B15 - B30 are most applicable. In addition to classes, a brand can be used to indicate strength. It is designated by the Latin letter "M" and a number corresponding to the strength in kg / cm2. Classes and brands correlate quite accurately with each other, for example, M200 solution corresponds to class B15, and M300 to class B22, 5.
Consumption of materials per 1 m3 of concrete can vary significantly depending on the required class or brand of mortar.
It should be noted that the actual class of concrete is determined only in laboratory conditions on day 28. Therefore, if it is necessary to know exactly the brand of the mixture, then at the stage of its preparation, several samples should be cast -cubes or cylinders 100 mm high. It is also possible to determine the strength of concrete using the instrumental method or the Kashkarov hammer, but these methods are less accurate.
Selecting the required concrete class
The required grade of concrete must be specified in the design documentation for the construction site. If the construction is carried out independently, you should decide on the brand of the mixture, as this will decisively affect the strength and cost of the building or structure being built.
The purpose of concrete of the most common grades is given below.
- M100 - used for footing, installation of parebriki, small architectural forms;
- M150 - used when arranging paths, sealing fence supports;
- M200 - for building walls, porches;
- M250 - production of monolithic foundations, grillages, foundation slabs, lightly loaded floor slabs, stairs, retaining walls;
- M300 - for any loaded structures: walls, ceilings, foundations;
- M350 - load-bearing walls, columns, ceilings, beams, monolithic foundations.
Sand parameters
For the preparation of the solution, sand of various origins is used: quarry or river. The second is more preferable, as it has a larger granule size and does not contain impurities. Quarry sand can vary in its granulometric composition. It is preferable to use sand with mediumand large granules. Since quarry sand may contain clay or other impurities, it is recommended to sift it.
It is extremely important to pay attention to the moisture content of the sand. Depending on this, the amount of water added to the mixture should be adjusted. Taking into account the humidity and granulometric composition, the density of bulk sand can vary from 1.3 to 1.9 t / m3, this must be taken into account when calculating the consumption of materials per 1 m3 of concrete.
Selection of gravel
Crushed stone in the composition of the concrete mix increases the strength of concrete and reduces its shrinkage during curing. When choosing crushed stone, its fraction and origin are of the greatest importance.
Crushed stone fractions are used in construction:
- 5 to 20mm;
- 20 to 40mm;
- 40 to 70 mm.
Depending on the raw material, crushed stone is classified into:
- Limestone, based on sedimentary rocks.
- Gravel from rounded rock fragments.
- Granite, obtained by crushing granite and granite-gneiss rocks.
Granite crushed stone has the best strength parameters, so if concrete is prepared for critical structures - foundations, columns, ceilings, then it is better to use it. We must not forget that the crushed stone used should not contain impurities, especially clay.
Water-cement ratio
In the production of concrete, the ratio of cement is of paramount importanceand water. Water is necessary for the chemical reaction of cement hydration, leading to the formation of cement stone. This ratio decisively determines the class of the concrete mixture. It is important to take into account the brand of cement. The lower the water-cement ratio, the stronger the concrete. The minimum ratio required for cement hydration is 0.2. In practice, concretes with a water-to-cement ratio of 0.3-0.5 are used. Mixtures with a large water-cement ratio are practically not used.
Determining the proportions of concrete mix
As a rule, cements of the M400 and M500 grades are used for the preparation of concrete. In practice, the following table is used to determine the consumption of cement per 1m3 of concrete.
| Concrete grade | Consumption of M500 cement, kg/m3 |
| M100 | 180 |
| M150 | 210 |
| M200 | 250 |
| M250 | 310 |
| M300 | 360 |
| M400 | 410 |
| M500 | 455 |
These data are given for conditions with normal temperature and humidity, as well as for cement, the parameters of which correspond to those indicated on the package. In real life, an excess of cement of 10-15% should be provided.
Further, according to the known amount of cement, the consumption of materials per 1m3 of concrete is calculated, the optimal proportion of cement to sand and gravel is given in the table.
| Concrete | proportion of shares of cement, sand and crushed stone | |
| mark M400 | mark M500 | |
| M100 | W1: W3.9: W5, 9 | W1: W5, 1: W6, 9 |
| M150 | W1: W3.0: W4, 9 | C1: W4, 0: W5, 7 |
| M200 | W1: W2.3: W4, 0 | W1: W3, 0: W4, 7 |
| M250 | W1: W1.7: W3, 2 | W1: W2, 3: W3, 8 |
| M300 | W1: R1.5: W3, 1 | Ц1: П2, 0: Ш3, 5 |
| M400 | W1: W1.1: W2, 4 | C1: P1, 3: S2, 6 |
| M450 | C1:P 1.0: S2, 0 | C1: P1, 2: S2, 3 |
For example, the consumption of materials per 1 m3 of concrete M200 will be: cement grade M500 - 240 kg, sand - 576 kg, crushed stone - 984 kg, water - 120 l.
Concrete making
With large volumes of concrete work, it is advisable to buy ready-made concrete at the nearest plant with delivery by mixer. In the conditions of industrial production, the consumption rates of materials per 1 m3 of concrete are maintained quite strictly. If this is not possible, you can prepare the required amount of the mixture at home. It is important to correctly assess your capabilities - the concreting of a separate structure must be carried out in one go.
Before mixing the mixture, the consumption of materials per 1m3 of concrete is determined. It is not necessary to calculate the consumption rate of the components, just use the table below.
| Brand of produced solution | Mixture composition, kg | |||
| M400 cement | Crushed stone | Sand | Water, l | |
| M75 | 173 | 1085 | 946 | 210 |
| M100 | 212 | 1082 | 871 | 213 |
| M150 | 237 | 1075 | 856 | 215 |
| M200 | 290 | 1069 | 794 | 215 |
| M250 | 336 | 1061 | 751 | 220 |
| M300 | 385 | 1050 | 706 | 225 |
The mixture is prepared in a concrete mixer of the appropriate volume, laying in it measured portions of dry cement, sifted sand and gravel. It is recommended to add water in portions last.
Supplements
In addition to the main components, additives for various purposes are added to the concrete composition:
- Modifiers. Designed to increase the strength and increase the frost resistance of concrete.
- Plasticizers. Increases the mobility and water resistance of the mixture.
- Mobility regulators. Allow to extend the setting time, maintain mobility during transportation.
- Anti-frost additives. Provide normal setting of the solution at low temperatures, up to minus 20 degrees.
- Set accelerators. Increase the setting speed providing the fastest set of strength in the first day.
When using additives, the consumption of materials per 1 m3 of concrete should be determined taking into account the manufacturer's recommendations. Violation of the instructions for use can have exactly the opposite effect.
