Fine concrete. features of the preparation of the solution.

Often from builders can hear such a term as "fine-grained concrete." But what is this material, and how does it differ from ordinary concrete solutions? The difference lies in the fact that fine-grained concrete according to GOST 27006-86 does not contain a large aggregate, the diameter of which exceeds 5 mm.

Next, we take a closer look at what constitutes this concrete, its areas of application and preparation features.

Features of granular concrete

So, fine-grained or sandy concrete, as they are also called, are a mixture of water, cement and sand, which are taken in a certain ratio. The characteristics and properties of the material depend on its structure, which, in turn, forms the structure of the cement stone. When cement is combined with sand, glue is formed, which is able to hold sand grains together in a strong and dense monolith.

It must be said that as a result of the absence of coarse aggregate, the price of fine concrete is higher than the cost of a conventional composition. This is due to the high consumption of cement.

Recall that cement stone acquires certain properties as a result of chemical reactions that occur as a result of mixing cement with water. Its duration is quite significant and requires a certain humidity and temperature. However, it is possible to influence the reaction with the help of various technological processes.

Sandy concrete is used in the construction of cement-reinforced structures. The material, as a rule, is reinforced with woven steel grids of wire of small diameter (up to 2 mm).

In addition, this concrete is used for pouring thickly reinforced structures. Also, the use of fine-grained concrete is advisable in those situations where there are no rock deposits, gravel-sand mixtures or crushed stone production in the construction area.

GOST 26633 91 for heavy and fine-grained concretes allows their manufacture of different strength and water resistance classes. Accordingly, the material can be used in various areas of construction.

Its characteristic features include the following properties:

• Good bending strength;
• Water resistant;
• Frost resistance.

Thanks to them, the material used for the installation of pavements in areas where there is a shortage of quality gravel. In addition, it is actively used in the construction of hydraulic structures and concrete pipes.

The properties of fine concrete are characterized by the same parameters as the properties of ordinary concrete. However, it has some features that are associated with its structure.

In particular, it is peculiar to him:

• Increased content of cement stone;
• Fine grain and great uniformity;
• Increased porosity, etc.

Tip! Reinforced sand concrete is very difficult to process. Therefore, to perform various mechanical operations using a diamond tool, for example, it is not uncommon to cut reinforced concrete with diamond circles or diamond drilling holes in concrete.

Preparation of fine concrete

Composition

Due to the fact that the composition of fine-grained concrete does not contain coarse aggregate, an important point of its manufacture is the optimization of the particle-size composition of small aggregates of various fractions. In addition, it is necessary to pay attention to the quality of the aggregate, on which the final quality of the composition depends.

The GOST for heavy and fine-grained concretes allows the use of homogeneous pure sand as a filler with a fineness modulus of no more than 2.5, together with fine crushed stone of fractions - 2.5-5.0 mm. Significantly improve the quality of the material by adding plasticizers. This allows to reduce the water requirement of the solution, reduced W / C, etc.

As for the binder, the concrete is heavy and fine-grained according to GOST 26633-91 performed on the basis of:

• Portland cementов;
• Slag portland cement;
• Sulfate-resistant and pozzolanic cements, as well as other types of cements, depending on the application and types of structures being built.

Features of the preparation of the mixture

With values ​​of В / Ц equal to 0.4 or more, the best material strength is achieved with a certain ratio of sand and cement. With an increase in the cement content, the amount of water in the mixture increases, which leads to a decrease in strength and an increase in porosity.

If the content of cement in the solution is below the optimum rate, then the material life becomes difficult, which also leads to a decrease in density and its strength. Therefore, in the manufacture of mortar is extremely important to observe the proportions that regulates GOST for heavy and fine-grained concrete.

Note! In some cases, during the preparation of the cement-sand mixture and the use of vibro-installations for compacting the composition, the mixture draws air in as a result of which the mass is filled with small bubbles. This phenomenon reduces the strength of the material, as it increases its porosity. Especially the tendency to air intake appears when the stiffness of the solution increases.

When dosing the ingredients, it should be borne in mind that when the content of cement in the solution is more than 1: 3, there may not be enough cement paste to envelop the sand grains and fill all the voids formed. As a result, the porosity of the mass increases, which significantly reduces the strength of the material.

As a result of this circumstance, it is quite difficult to get durable sand concrete with low cement consumption (within 200-300 kilograms per cubic meter). This situation can be somewhat remedied by applying large clean sands or enriching fine sand with fine gravel or large bran from crushing rocks.

It should also be said that due to the increased need for water, for the preparation of mixtures similar in mobility and strength to ordinary concrete, the consumption of cement increases by 20–30 percent.

To improve the quality of the cement-sand mixture, as a rule, it is compacted in the following ways:

• Pressing;
• Roller seal;
• Vibropressovaniem;
• Tramping.

Tip! Material testing should be carried out on samples of small sizes. To assess the strength, you can use halves of beams of 4x4x16 cm. The mobility of the solution is checked by pouring on the table.

Concrete Preparation Procedure

Instructions for the preparation of fine-grained concrete is as follows:

1. The first step is to prepare fractional sand..

To do this, pre-scatter quartz or other sand into three fractions:

• 5-1.25 mm;
• 1,25-0,315;
• 0.315-0.14 mm.

1. Then the fractional sand is mixed in the following ratio:

• 5-1.25 mm - 57-63%;
• 1.25-0.315 mm - 17-23%;
• 0.315-0.14 mm - 17-23%.

1. Next, it is necessary to dose portland cement, fractional sand and silica-containing component, which is ground quartz sand with a specific surface equal to 120-170 m2 / kg.
2. After that the water dosage is performed..

1. The next step is the dosage of plasticizer.. For example, you can use Melflux 2651 F. Means must be added to the prepared water.
2. Further, all of the above components need to be added to the concrete mixer, where they are mixed before preparing the concrete mix.. At the same time can use vibration installations for tamping composition.

Tip! Certain studies of fine-grained concrete have shown that it is useful to add sodium nitrite in an amount of two percent by weight of cement. Such an additive will prevent corrosion of the thin reinforcing mesh.

At the same time, the preparation of concrete with your own hands is complete.

Pneumonia

As a result of the above features of fine-grained concretes, when used, some specific styling methods are used. In particular, their properties are improved by pneumonic spraying.

The principle of this technology is that the solution is prepared in a conventional mixer, after which it is injected with a mortar pump into the working pipeline. After leaving the mortar pump, the mixture enters the mixing chamber of the system, where a special hose also supplies compressed air from the compressor at a pressure of about 7 atm.

As a result, transportation of the solution and application to the surface is performed under the influence of compressed air. Moreover, in the process of transportation, the mixture in the pipeline is suspended.

According to research institutes, this technology allows to improve the properties of the transported cement-sand mortar, removing from it a significant part of the water, due to the aerodynamic effects on the mixture. As a result, the applied material differs significantly in physical and mechanical properties from the original cement-sand mortar.

Conclusion

В итоге можно сказать, что мелкозернистый бетон – это материал, который обладает рядом особенностей и своими свойствами существенно отличается от стандартного бетона, выполненного с применением крупного наполнителя. Благодаря этому, в некоторых случаях его применение более целесообразно (см.также статью «Мелкозернистый асфальтобетон: свойства и область применения»).

However, it should be borne in mind that the solution is very demanding on the quality of components and respect for proportions. From the video in this article, you can get more information on this topic.