Concrete mixtures - plastic and hardening compositions over time, consisting of a binder material, fillers, plasticizers, special additives and water. As a binder, for the preparation of concrete, cement of various compositions and grades is used. Fillers for the classic composition are sand and gravel. Special types of concrete can be filled with expanded clay, crushed slag, wood waste and other materials that change the technical characteristics of the material.
The addition of plasticizers facilitates the concrete laying process and contributes to a better compaction of the mixture. Special additives allow working with the material at low temperatures, foaming the mixture, increasing strength and resistance to moisture, or achieving other special properties.
Component Requirements
The quality of concrete, its technical and operational characteristics depend on the ratio of components. In addition, we should not forget about the economic component, which is determined, first of all, by the amount of cement consumed.
Therefore, the correctly selected composition of the concrete mix and the determination of how much cement is needed per 1 cubic meter of concrete not only ensures the quality of construction, but also makes the cost of its production economically justified.
Cement
Modern industry produces several different types of cement, manufactured using various technologies. For concrete, in most cases, Portland cement of four grades is used, from M300 to M600. Cement grade means the amount of load that a prototype is able to withstand.
In private construction, the most common is Portland cement grade M400.
Industrial construction of buildings and structures, as well as the work of factories of reinforced concrete products based on the use of cement M500. The lowest grade is used for the preparation of concrete structures. not subject to stress. For example, for wall partitions and hollow fillings.
Sand
For the preparation of concrete, sea, river or washed sieved sand is used. Such a filler does not contain dust, debris, clay particles and other additives that may impair the quality of the final material.
The size of the constituent particles of sand is divided into:
- thin less than 1.2 mm;
- very shallow 1.2-1.6 mm;
- small 1.6-2.0 mm;
- average 2.0-2.5 mm;
- large 2.5-3.0 mm.
All types of fractions can be used for concrete, but the best particle size would be a range of 1.2-2.5 mm. During the preparation of the concrete mixture, it is necessary to take into account the moisture content of the sand, which can reach 10% of the volume and introduce amendments when adding water to the mixture.
Crushed stone and gravel
Used as a second filler, crushed rocks also have a gradation in size and are divided into:
- very small 3-10 mm;
- small 10-20 mm;
- medium 20-40 mm;
- large 40-70 mm.
The first two fractions are called gravel, and the larger stone is called crushed stone. Sea or river pebbles having a smooth surface cannot replace artificially ground particles, as they will not ensure proper adhesion of the components.
When choosing a large aggregate, it must be taken into account that the size of the largest particles should not exceed 1/3 of the future concrete layer.
An important technical characteristic of crushed stone and gravel is their voidness, which determines the amount of free space between individual particles.
The higher the void rate, the more cement and sand will be required to prepare a high-quality concrete mix. Depending on this, stone fillers are divided into porous up to 2000 kg / m3 and dense more than 2000 kg / m3.
Calculation of the consumption of components for the preparation of concrete
For the correct determination of the ratio of the components of the concrete mixture and cement consumption per 1 cube of concrete, the following initial data are required:
- necessary concrete grade;
- fraction size of purchased sand and gravel;
- brand of cement that is available;
- desired plasticity of the prepared mixture.
The calculation is made by determining the weight of each component. However, under the conditions of a construction site, weighing the amount of materials is very difficult and therefore the calculation is carried out on the ratio of volume parts. It is assumed that in a 10 liter bucket, depending on the degree of compaction, 13-15 kg of cement, 14-17 kg of sand and 15-17 kg of crushed stone are placed.
The reference literature provides ready-made data on the proportions of concrete in parts, depending on the brand of cementitious material. So, for concrete of various grades using Portland cement M400, the ratio of sand to gravel per unit of cement will be:
M100 | M200 | M300 | M400 | M500 | M600 | |
Cement kg | 183 | 263 | 338 | 444 | 500 | 533 |
Sand kg | 842 | 738 | 642 | 533 | 500 | 480 |
Crushed stone, kg | 1282 | 1265 | 1250 | 1200 | 1150 | 1120 |
Water, l | 92 | 131 | 170 | 222 | 250 | 266 |
Proportions of Ts: P: Sh: V | 1:4,5: 7:0,5 | 1:2,8: 4,8:0,5 | 1:1,9: 3,7:0,5 | 1:1,2: 2,7:05 | 1:1: 2,3:0,5 | 1:0,9: 2,1:0,5 |
When using cement M500, the ratios will be as follows:
M100 | M200 | M300 | M400 | M500 | M600 | |
Cement kg | 155 | 226 | 292 | 380 | 452 | 533 |
Sand kg | 903 | 792 | 702 | 609 | 543 | 533 |
Crushed stone, kg | 1262 | 1267 | 1258 | 1219 | 1177 | 1226 |
Water, l | 78 | 113 | 146 | 190 | 226 | 266 |
Proportions of Ts: P: Sh: V | 1:5,8: 8,1:0,5 | 1:3,5: 5,6:0,5 | 1:2,4: 4,3:0,5 | 1:1,6: 3,2:0,5 | 1:1,2: 2,6:0,5 | 1:1: 2,3:0,5 |
These ratios show that for low grades of concrete it is more profitable to use Portland cement M400, and to obtain a more durable material M500.
To simplify the preparation process, you can count how many bags of cement per 1 cubic meter of concrete, and determine the final proportions of concrete in buckets for other materials. Such a recipe may be more convenient to use.
This table is compiled for a 20 mm gravel fraction. For other sizes of stone, cement consumption per 1 cubic meter of mortar may vary depending on the void rate.
To determine it yourself, collect a 10 liter bucket of filler, take a measuring container and pour water into the bucket. If 3 liters of liquid enter, then the voidness is 30%, and if 4 liters, then 40%. To fill the excess voids between the stones, an additional amount of sand and cement will be required, which will increase the final cost of the concrete mixture.
Water for the preparation of concrete should be clean, without impurities. Its amount depends on the moisture content of the sand and the required level of ductility of the material.
The less moisture in the composition of concrete, the more difficult it is to lay and to seal properly. But so the monolithic design is more durable. A large amount of water makes the composition plastic and easy to fill, but the strength of concrete will be somewhat reduced.
10 | 20 | 40 | 80 | 10 | 20 | 40 | 80 | |
Plastic | 220 | 205 | 190 | 175 | 235 | 220 | 205 | 190 |
Medium ductility | 210 | 195 | 180 | 165 | 225 | 210 | 195 | 180 |
Low ductility | 200 | 185 | 170 | 155 | 215 | 200 | 185 | 170 |
Unplastic | 190 | 175 | 160 | 145 | 205 | 190 | 175 | 160 |
Applicable concrete mixing methods
In private construction, a manual or mechanized method of mixing concrete is used. Manual cooking makes sense for small amounts of work, but if you need to cook more than 5 m3, it is better to rent, or even buy, a mechanical concrete mixer with electric drive. If concrete needs more than 50 m3 You can recommend buying ready-made pre-cast concrete supplied in car mixers.
Manual batch
For manual kneading, a bucket or trough with a low side is required. Initially, sand and cement are poured into this container and mixed until a homogeneous gray mass is obtained. After this, water is added and an ordinary cement-sand mortar is made. Then they begin to gradually add crushed stone and, if necessary, water until a mixture ready for laying is obtained.
Use of a concrete mixer
With mechanical kneading, about half of the required water is poured into a working mixer and half of the rubble is poured. This allows you to bring down the remains of cement mortar remaining from the previous batch from the walls. After that, fill all the necessary cement, mix for 2-3 minutes and add sand. Pour the rest of crushed stone and add water to obtain the necessary consistency of the composition.
Unloading of the finished concrete must be carried out completely in a pallet placed under the concrete mixer. It is not permissible to collect the mixture with a shovel from the mixer.