Concrete is a very common material in construction. Its main components in most cases are cement and sand. A variety of structures of buildings and structures, including those responsible, are poured from a mortar of this variety. And of course, the preparation of concrete mix should be carried out with the exact observance of all the required technologies.
Requirements
Cement mortar is supposed to be prepared so that the concrete subsequently has a given strength. Quality material of this type should:
The main components of concrete
When preparing a concrete mixture, the following three types of ingredients are always used:
sand as a filler;
cement as a binder;
water as a conductor.
Also in some cases, plasticizers may be added to concrete. The cheapest and most popular of these is lime. Sometimes, more expensive polymer compositions can be used to increase the elasticity of such solutions.
When preparing the concrete mix, crushed stone is also often used. This material makes the finished structure more durable and allows you to save on cement, the cost of which on the market today, as you know, is quite high.
Varieties
There are only two main types of concrete - plastic and hard. The first type of solution fits well into the formwork and compacts under the influence of its weight. It is such concrete in construction that is most popular. Hard mixtures contain little water. At the same time, they add a lot of rubble or gravel to them. Prefabricated structures made of such concrete are more durable than plastic ones. But at the same time, solutions of this variety are not very convenient in laying. During the construction of various kinds of structures, such concrete has to be subjected to vibration, vibro-stamping, vibro-rolling. In addition, such solutions are usually quite difficult to prepare. Dosages when mixing them have to be observed as accurately as possible. Otherwise, such a mixture can dramatically change its properties for the worse.
Where can it be prepared
Most often, a mortar of this variety is kneaded at concrete plants and delivered to the construction site with special vehicles. Material prepared in this way is usually of excellent quality. In some cases, concrete can also be prepared directly at the construction site using special mobile equipment. In this way, cement mortars are made, for example, by the construction of private low-rise buildings, owners of suburban areas.
GOST
When preparing cement-based solutions, of course, first of all, the requirements of GOST must be observed. Only in this case, finished designs will be strong and durable. Regulates the production of concrete mixtures in Russia GOST 7473-2010. In this document, among other things, the acceptable parameters of the delamination of solutions, deviations of their workability indicators, etc. are indicated.
The main methods of concrete preparation
Purely technologically, the operation of mixing cement is nothing complicated. The only thing when doing this work is to follow the dosages exactly. According to the requirements of GOST 7473-2010, for example, errors in this regard should not exceed 2% for water, cement and additives and 3% for aggregates. If this rule is not observed, the construction erected from the solution is too strong and durable. And this, in turn, of course, will adversely affect the quality of the entire building or structure as a whole.
The main methods for preparing concrete mixtures, there are only two:
In this case, the first technology can be used both for mixing mortar at the plant and at the construction site. The second method is used, of course, mainly by the owners of suburban areas when erecting any structures with their own hands. No equipment is used in this case. Kneading is carried out using most often ordinary garden tools.
Mechanical technology of kneading, in turn, can be:
In the first case, all operations in the manufacture of concrete mortar are carried out using special equipment. This is exactly the kind of kneading used in factories.
Simple technology for the mechanical preparation of concrete mix involves loading the ingredients manually. In this case, the actual mixing of the components is carried out using equipment. This technique is also often used by the owners of suburban areas for self-construction of concrete structures.
Equipment
Of course, concrete mixers are used as the main equipment when mixing cement. Such machines for the preparation of concrete mixtures can have different sizes and power. On the market today there is inexpensive and not too oversized equipment of this type, designed specifically for owners of suburban areas and small developers.
Standard Manual Kneading Method
The technology for mixing mortar in concrete mixers of different capacities and dimensions is usually the same. When using this equipment, in order to obtain high-quality material, it is important first of all to observe the loading order of the ingredients.
The standard technology for the preparation of concrete mix in this case is as follows:
crushed stone and sand are loaded into the bowl of the concrete mixer;
thorough mixing of these ingredients;
cement is poured into the mixer, after which the concrete mixer is turned on for several minutes;
water is poured into the bowl.
Auto Kneading Technology
The procedure for supplying ingredients in the preparation of concrete mortars at the plants is the same as for kneading at construction sites with manual filling of components. In the first stages, in this case, sand and gravel are also laid in the bowl. After mixing, cement is added to them. Then the mixer is turned on again until a homogeneous mass of dry ingredients is obtained.
The methods of automatic and simple preparation of concrete mix differ only in the way they add water. In factories, a dry, homogeneous mixture of cement, sand and gravel is first poured into 70% of the required proportion of grout. Next, the concrete mixer is turned on for 1 min. Then the rest of the water is poured into the solution.
Is it possible to disrupt the kneading order
It is desirable to lay the ingredients in the mixer of the concrete mixer precisely in the sequence that was indicated above. Otherwise, the mixture may subsequently, for example, contain lumps. In addition, a violation of the order of actions during preparation can lead to the fact that the solution will have the wrong consistency, which is necessary.
If for some reason the concrete at the construction site was mixed up incorrectly and turned out not to be of high quality, you can, without wasting time, try to correct the situation. If there are lumps, the solution needs to be mixed once again in a mixer. If the concrete turned out to be liquid, sand and cement should be added to it. If the mixture is too thick, it must be diluted with a small amount of water. Perform all these operations as soon as possible. The cement slurry retains its performance characteristics for no more than 2-2.5 hours after preparation.
Hand kneading technology
This technique allows you to get not as high quality as when using a concrete mixer, but still quite suitable for the construction of not too heavily loaded structures, the solution. Inventory in this case is usually used as follows:
shallow trough;
chopper and shovel;
buckets;
garden car;
garden hose.
The actual method of preparing the concrete mixture in this case is as follows:
sand and gravel are poured into the trough;
thoroughly mix these dry components;
add cement to the trough and again mix everything until smooth;
pour water into a trough and again knead everything.
Cement mix is kneaded using this technique most often with a hoe. It is believed that preparing the solution with such a tool is easier than with a shovel. At the final stage, the cement is transferred to buckets and poured into the formwork.
Materials for the manufacture of concrete mix: quality requirements
The ingredients for the preparation of mortars of this type are selected depending on the specific purpose of the latter. For pouring loaded structures, usually only cement of high grades is used (for example, M400 or even M500), large river sand and high-quality crushed stone. To prepare the plaster mortar, a less expensive and high-quality binder is used. Sand at the same time use a shallow quarry.
In any case, cement for the preparation of concrete mixtures is supposed to use exclusively fresh. During storage, this material usually absorbs water and as a result loses the quality of the binder. Sand must be sieved before preparing solutions. Such material, both in the river and in the quarry, may contain dirt, garbage, organic residues.
Like sand and cement, crushed stone is usually prepared before mixing. In some cases, such material can be preliminarily distributed into fractions. It is believed that the addition of such stones of a different, but not the same size to the mixture improves its quality.
There are certain requirements for the water intended for concrete preparation. It should not contain too many minerals. And of course, the water for the solution should be used exclusively pure without organic impurities and debris.