Do-it-yourself concrete how to correctly calculate the proportions for its manufacture. Modern lightweight concrete Making lightweight concrete with your own hands

Sometimes in construction it is required to reduce the load on the supporting structures. For example, a plank subfloor that needs to be leveled with concrete mortar for ceramic tiling. It is clear that the concrete layer has a sufficiently large weight, which the wooden structure may not withstand. In this case, experts recommend using lightweight concrete.

What it is?

This is a special type of concrete mixtures, in which porous materials are used as fillers: expanded clay, expanded perlite, foam balls and waste from various industries. It is these fillers that reduce the mass of the concrete itself, hence the name "light".

There is a certain classification of concrete solutions, one of the categories of which divides them by density (respectively, by mass). The density of lightweight concretes on porous aggregates is determined in the range from 500 to 1800 kg/m³ compared to conventional ones, which range from 2000 to 2500 kg/m³.

Properties of lightweight concrete

The main characteristics of the solution are as follows:

• reduced density (mass);
• convenience of construction work;
• obtaining a more economical option by reducing the percentage of cement;
• high strength material.

The subtleties of manufacturing

The most difficult thing in the preparation of lightweight concrete on porous aggregates is to correctly and accurately select the raw mix formulation, especially the water-cement balance. It is he who affects the strength of the material, its convenient use.

The thing is that porous fillers quickly absorb water into themselves, leaving practically no water for cement to set. Therefore, experts recommend that the selection of the recipe be carried out during the manufacture of the concrete solution itself.

Particular attention must be paid to the cement-water ratio, but the porosity of the filler will also have to be taken into account.

Recipe selection example

There are several options for selecting the density of lightweight concrete. One of them is the preparation of experimental closures.

Cement and fillers

For this, the standard recipe used for conventional concretes is taken. This is one volume of cement and six volumes of aggregate. If a combination of two or three types is used as fillers, for example, expanded clay and expanded perlite, then 4 parts are added to the large fraction (expanded clay), and 2 parts to the fine fraction (perlite).

Water

It is more difficult with water, here you will have to adjust its amount to the purpose of the concrete mixture. If the solution will be used for screeding, then it is better to make it liquid.

Checking blanks

Then, lightweight concrete is poured into a container, usually a cube. After drying, the workpiece is tested for strength. The same blanks will have to be made from solutions prepared according to other recipes. For example, you can increase the amount of expanded clay or, conversely, perlite, reducing the amount of cement introduced. In this case, you will have to increase the volume of water.

The strengths of all blanks are compared with each other. The indicator that fits the requirements of the structure to be poured is determined. But at the same time, the economic component must be taken into account. For example, from two suitable recipes, it is better to choose the cheapest composition.

Classification of mixtures

The classification of lightweight concrete mortars is based on the use in the composition of various fillers and the scope.

Simple Composition

Ordinary lightweight concrete is made according to the recipe described above. That is, it includes both large fillers and small ones. In this case, the volume of air between all materials should not exceed 6%.

Porosity

The composition may differ in the nature of porosity:

1. Sandless (large-pored) - the complete absence of fine filler. Air volume 25%.
2. Porous - obtained by adding materials that form pores to the cement mortar.

purpose

There is another kind of classification based on the purpose of lightweight concrete:

• thermal insulation properties (density 500 kg / m³, thermal conductivity 0.25 W / m * K);
• structural properties (density 1400-1800 kg / m³, strength M15, frost resistance not lower than F15);
• structural and heat-insulating (density up to 1400 kg / m³, strength not less than M35, thermal conductivity - not more than 0.6).

The first group is used for pouring screeds, making heat-insulating plates. The second is used in load-bearing structures. The third is in self-supporting enclosing structures or in load-bearing ones.

Material consumption

As for the consumption of concrete mass, everything will depend on the type of filler used, on its porosity and quantity. But there is an average value - it is 200 kg per cubic meter. At the same time, the consumption of cement varies from 70 to 150 kg per cubic meter of concrete solution.

Manufacturing methods

Lightweight concretes on porous aggregates are prepared using different technologies, which depend on the type of additive.

Expanded Perlite Mix

Preparing lightweight concrete with your own hands is quite simple. First of all, perlite is wetted with water. It is a hygroscopic material, so it quickly absorbs it. Then 30% of the filler and the entire volume of cement are put into the concrete mixer. And this solution is thoroughly mixed.

Gradually, water is poured into it, into which plasticizers and modifiers were added in advance. Thorough mixing should cause the mixture to rise. This is a signal that you can start adding perlite residues to it. It is better to do this in small portions.

If the mortar is made by hand without using a concrete mixer, then it is better to do it in a clean bucket using a mixer or drill. It is possible with a shovel, but the uniformity of the components in the mixture may be low.

Often, fiber fibers are added to the mixture of concrete with perlite as a reinforcing composition. They must be introduced into the concrete when the main part of the filler is poured.

Composition with expanded clay

First, cement is thoroughly mixed with water until cement laitance forms on the surface. Please note that first, water is poured into the container (concrete mixer drum), then cement is poured in portions.

After that, expanded clay is introduced in portions. Here it is important, as in the first case, to achieve a uniform distribution of the components of the solution throughout the volume.

foam concrete

Making foam concrete with your own hands is not easy. This requires a foaming agent and a foam generator (special equipment that prepares foam). Let's just denote the production technology.
In a concrete mixer, a solution is prepared from sand and cement, where water is poured in a certain amount.

While the mixture is being prepared, a foaming agent is placed in the generator, which turns into foam inside the tank. With the help of a deposit, it is added to a semi-finished solution, where pore formation occurs. The foam is supplied by a pump.

According to GOST 25192-82, concrete is called light if its density does not exceed 1800 kg/m3. This is a popular building material that reduces the total cost of mixing the mortar by up to 20%, and the labor intensity - by up to 50. Its thermal insulation, quality and structural parameters are very high, the bonus of application is the ability to process and cut after reaching strength. Lightweight concrete is divided depending on the components, structure and subgroups, united exclusively by reduced density. Some types are easier to buy than to cook yourself, others are quite suitable for do-it-yourself kneading.

The group includes mixtures based on porous fillers, weight reduction occurs due to a decrease in the proportion of cement and hard rock components. The size of large fractions is limited to 20 mm, in rare cases gravel is added no more than 40. As a result, the material is 1.5 times lighter than gypsum mortars, and 2.5 times lighter than cement mortars. The effect is achieved not only by changing the filler, but also by the porous binder, the cellularity of lightweight concrete reaches 40%. As a result, it is characterized by a decrease in strength and minimal thermal conductivity.

Composition, performance characteristics

The structure and volume of the gas or air involved in concrete differ for different types, they are divided into: dense, porous and coarse-meshed. In addition to cement, gypsum, lime, slag, polymers, kiln clays, and industrial waste are added as a binder. Depending on the filler, there are mixtures based on expanded clay, perlite, agloporite, crushed stone from porous rocks, vermiculite, slag, ash gravel. As a fine-grained filler, in addition to sand, marble chips, pumice, volcanic puff and limestone are introduced into the compositions. An important role is played by the ratio of water, light materials on aggregates that give porosity are less sensitive to its excess, but when a certain proportion is exceeded, they sharply lose strength. Modifiers and foaming ingredients regulate the amount of air involved, frost resistance and protection of cells from moisture.

The introduction of porous aggregates into the composition leads to a decrease in the cost of concrete. When choosing a particular brand, they are guided by such properties and features as:

1. Average density, kg/m3.

2. Strength (depends primarily on the type of aggregate, and not on the brand of cement). The main indicator is the class: from B2 to B40. For high-strength grades, the compressive strength reaches 70 MPa, for ordinary grades it varies between 2–20.

3. Thermal conductivity: 0.07 to 0.7 W/(m∙C). Depends on porosity, density, maximum thermal insulation is observed in concrete with the lightest aggregates (expanded perlite).

4. Frost resistance: on average from F25 to F100. This characteristic depends on the type of binder (high-grade Portland cement withstands low temperatures best) and the base used. Maximum frost resistance is observed in concretes with the addition of pumice, expanded clay and agloporite.

5. Dry density or porosity is an important characteristic, ranging from D200 to D2000.

6. Water resistance: grades from W0.2 to W1.2.

Useful properties include fire resistance, lightness, plasticity, almost all grades are suitable for reinforcement (to increase the withstand loads).

Scope of application

It is suitable both for the production of finished products: building blocks, slabs for screeds and ceilings, wall panels, and for monolithic pouring. It is convenient to fill voids in structures and dips in the ground with light concrete mortars. For private purposes, they are used for thermal insulation of buildings, external and internal fire protection, construction of partitions and load-bearing walls (subject to proper reinforcement). In industrial - for the repair of tunnels, the construction of supports, columns, small bridges, large-block apartment buildings. Separate mention is stifled by the use of specialized grades: high-strength ones are relevant for construction work in seismically hazardous areas, light heat-resistant ones - for laying and lining furnaces.

The material has a minimal load on the foundation and, as a result, is recommended for restoration work, the creation of decorative and small architectural forms. For the same reason and because of its good thermal insulation properties, it is optimal for horizontal floors. With rare exceptions, lightweight concrete on porous aggregates is not used for pouring or laying foundations, this is due not to a concession in strength to heavy grades, but to the risk of groundwater getting inside the cells and freezing.

External blocks of large-pore concrete need to be plastered to enhance the thermal insulation properties. But the material itself does not apply to water-absorbing, when used in rooms with high humidity (baths, pools, showers), problems do not arise. In general, lightweight concrete is a full-fledged replacement for bricks and conventional cement mortars in the construction of walls, a bonus is the reduction in weight and thickness of structures.

Production technology

The process largely depends on the structure and composition of the material. The most difficult thing is to prepare foam and aerated concrete: special equipment is used: foam concrete mixers, autoclaves, steaming chambers and complex chemicals. Coarse fractional filler is not introduced into lightweight cellular concrete; some grades are completely sand-free.

The main condition of the technology is the distribution of the binder with maximum uniformity, this is largely due to a decrease in the proportion of heavy cement in the total mass. For this reason, these solutions are mixed longer, more intensively and more thoroughly. Another requirement is the vibration of cast structures: light, unlike heavy concrete, does not delaminate into heavy crushed stone and water, but with weak compaction of the layers, its quality decreases.

How to do it yourself?

The process depends on the type of solution: it is almost impossible to prepare foam concrete at home, but mixtures with expanded clay or light porous additives are completely. The main problem concerns the choice of W/C ratio, most aggregates are rough and absorbent. Therefore, the proportions are selected empirically, a small portion is kneaded, a test sample is poured and aged. The easiest way is to prepare lightweight concrete with your own hands based on expanded clay: water is poured into the concrete mixer, cement is added in portions (until milk condition) and only then - aggregate, all components are mixed until homogeneous.

When kneading at home, there is a constant risk of uneven distribution of the binder. For this reason, any modifiers are simply added to the water at the beginning of the batch (and not at the end, as with heavy concretes). The exception is fiberglass, it is introduced into the composition last. Porous heat-insulating aggregates need pre-wetting (such as perlite or vermiculite).

Manual mixing is not recommended; in the absence of a concrete mixer, you should use a drill or a construction mixer. Lightweight porous concretes retain their structure well and are optimal for the use of slipform technology, the final strength development depends on the composition.

The cost of ready-made solutions

Modern technologies have greatly simplified the life of builders. For example, lightweight concrete has replaced the traditional one. Lightweight "bricks", popular expanded clay concrete blocks, porous materials are rapidly gaining popularity. Let's talk about what their advantage is, what are the disadvantages, is it possible to make such products with your own hands.

Main advantages

Those species are called, the average density of which in dry form fits into the range from two hundred to two thousand kg / m3 (for comparison, for the traditional one this figure is 2400-2500 kg / m3). There are many advantages to lightweight concrete. One of the main ones, as the name of the material implies, is light weight. Thanks to this, the construction of buildings is faster, it costs less due to savings on the delivery of building materials directly at work. And there is no need to strengthen the foundation of the building.

As for engineering and operational qualities, lightweight concrete is a plus:

• the possibility of high-altitude work without the use of special lifting mechanisms;
• universal use (walls, partitions, ceilings, etc. are built from "weightless" blocks);
• low thermal conductivity;
• resistance to sub-zero temperatures (products using high-quality Portland cement have the best characteristics in this regard);
• excellent sound insulation performance.

disadvantages

Specially created pores are considered to be the trump card of lightweight concretes, which give them the above positive properties. However, they also cause the disadvantages of the blocks:

• less strength compared to traditional, heavy materials;
• higher level of moisture absorption. It penetrates precisely through artificially created voids. Therefore, plastering of external, internal surfaces is strongly recommended.

Material types

Lightweight concrete is:

• Cellular (gas-, foam concrete). In the first, bubbles are obtained due to the reaction of lime and aluminum powder included in the mixture. In the second, pores are made by combining cement mortar with foam, which is prepared separately.
• Porous. These include products with the use of porous aggregates. In particular, these are popular expanded clay concrete blocks, which, along with cement, water, sand, include expanded clay gravel (granules are obtained by firing clay or shale in special furnaces). This group also includes polystyrene concrete - a mixture of Portland cement, water, expanded polystyrene granules, as well as wood saponified resin (air-entraining additive).
• On organic aggregates (aggregates) - fiber, shavings, sawdust. Examples of such products are fibrolite, heraclitus.

In addition, classification by purpose is applied. According to it, lightweight concrete is classified as either structural or heat-insulating materials. There is a division and depending on the binder component (cement, lime, gypsum, mixed type).

Application for facades

Lightweight concrete is readily used in the reconstruction of facades. For these purposes, both cellular materials and expanded clay concrete blocks are used (mainly on the socles of buildings that are most vulnerable to external influences).

A prerequisite is the subsequent plastering of wall blocks.

The only way to lighten the weight of a concrete material is to use various methods to enrich it with air. Achieve goals like this:

• Replacing traditional fillers with lightweight ones. These include pumice, slag (metallurgical granular, expanded perlite and vermiculite), sawdust, rice husks and others. These aggregates are fire-resistant, thanks to the cellular structure they improve the self-setting of the mortar.
• By introducing gases or air bubbles when mixing. Thanks to special additives-reagents, hydrogen or oxygen is released into the mixture. For foam concrete use (synthetic, protein). It can be made with your own hands, for which they practice the use of pine rosin, carpentry bone glue, caustic soda.

A mortar of concrete is a mixture of various components (sand, crushed stone, water and cement), as a result of mixing and subsequent solidification of which, a solid, incredibly durable building material is obtained, which is sometimes called "artificial stone". For obvious reasons, no building can do without concrete. It is the main component in the construction of foundations, walls, floor slabs, floor screeds, curb and paving slabs and much more. Therefore, it is very important that the concrete solution be of high quality, which means that the concrete production technology must be strictly observed.

Do-it-yourself concrete - the main components

For one reason or another, it is sometimes impossible to order ready-made concrete in production. Either the manufacturer set the price too high and it is much more profitable for you to make it yourself, or you need very little of it, so there is no need to bring concrete with a mixer.

Before starting work, it is important to remember the following - the proportions of the added components, depending on the brand of concrete, may differ. For example, to get concrete M200- the ratio of the proportion of cement (M400), sand and crushed stone is 1: 2.8: 4.8 (respectively). If you need concrete grade M300- in the presence of the same components, the proportion will look like this 1: 1.9: 3.7 (respectively). Further below in the table you can get acquainted in detail with the exact ratio of components.

Cement

This is exactly the connecting element without which, regardless of the brand of concrete, it is impossible to make a solution. The strength and speed of its solidification will directly depend on its quality.

Necessary marking of cement, for obtaining concrete of various grades, under natural hardening conditions

Now in the construction markets you can find various types of cements that have different indicators in compressive strength. All of them are divided into groups, which determines their ultimate load in the frozen state.

The percentage of additives and impurities is indicated by the letter "D". For example, cement M400-D20 it means content in it 20% additives. It is impossible not to take into account this indicator, the plasticity and strength of the material directly depend on it.

From the products presented on the markets, it is possible to single out the well-proven Portland cement. Among its main advantages are:

• Sufficiently long service life;
• It has excellent strength indicators;
• Resistant to sudden changes in air temperature;
• Not afraid of moisture.

Important! Whatever the brand of cement, it should be crumbly, without the presence of lumps in it and not expired.

Sand

For the preparation of concrete mortar according to GOST 8736-93 it is possible to use sand of various fractions of granules ( see fig. one). The final characteristics of concrete will directly depend on its quality.

rice. 1 The size of the fractions of sand used for the preparation of concrete

Regardless of the type of sand, the absence of clay in its composition is a prerequisite, its presence will significantly reduce the strength of concrete. Usually, quarry sand is used to prepare the mixture, in which there are often many foreign particles (dirt, debris, bark and tree roots.).

Such sand must be washed and sifted through a sieve before adding. If this is not done, voids may form in the hardened concrete, which over time will lead to the formation of cracks in it.

It is also important to pay attention to the moisture content of the sand, which is present in a small amount even in a dry product. In wet sand, the percentage of moisture can reach 12% from its total weight. This point will need to be taken into account when drawing up the correct proportions of the necessary components, in particular water.

Without a special device, you can measure the exact amount of moisture in the sand in the following way:

1. Prepare a small metal container, an old unnecessary pan will do. Weigh her net weight and record;
2. Next, pour into it, pre-weighed and prepared 1 kg. sand and place the container on 10-15 min. on a hot stove, while constantly stirring the contents;
3. Without letting the sand cool down, re-weigh the container along with the hot sand. From the result obtained, we subtract the weight of the container (pot) known to us and multiply it by the number 100 ;
4. The resulting product will be the percentage value of the moisture content of the sand.

When dry, the sand should have a crumbly consistency.

rubble

Another important component of the concrete solution is crushed stone. This material is made by crushing rocks (limestone, granite, stone) into smaller ones, resulting in crushed stone having various fractions. Their size determines the original product into the following types:

• The smallest gravel - the size of the fractions is less than 5 mm. It is applied at internal and external finishing works;
• Fine crushed stone - the size of fractions is 5-20 mm. The most commonly used size when pouring foundations and screeds;
• Medium crushed stone - the size of fractions is 20-40 mm. It is impossible to do without it in the construction of railways and roads, as well as in the construction of a foundation for large industrial buildings that create increased loads;
• Large crushed stone - the size of fractions is 40-70 mm. It is necessary for the construction of large-scale structures that require a huge amount of mortar;

When calculating the preparation of a concrete mixture, it is necessary to take into account another important indicator, such as the void space of the material (VPM). Calculating it is quite simple. To do this, pour crushed stone to the very top in a bucket of 10 liters. After that, with measuring utensils, slowly begin to pour water into it until it appears on the surface. The number of liters of water you fill in is an indicator of void space. For example, if in a bucket of rubble fit 3 liters of water, then the PPM indicator will be 30% .

Required amount of water

How to make a quality mixture? The answer is simple, for its preparation it is necessary to use only clean water. It should not contain impurities of oils, chemical and petroleum products, as well as various household waste. All these substances can significantly reduce the strength characteristics of the finished product.

The plasticity of concrete is also an equally important indicator, which directly depends on the quantitative content of water in it in proportion to crushed stone and gravel. You can get acquainted with the optimal ratio of water to filler in the table below. №1 .

Table No. 1 - the required amount of water (l / m³) depending on the filler

It is important to adhere to this table, since the lack of moisture in concrete, just like its excess, will negatively affect its quality.

Calculation of the composition of concrete

• Required brand of concrete;
• Required level of solution plasticity;
• Marking of the cement used;
• The size of the fractions of sand and gravel.

As an example, we will calculate a solution of maximum plasticity, the strength of which corresponds to the marking M 300.

Calculation of concrete by weight - from the first we take the recommended brand of cement M400 with crushed stone filler with medium-sized granules. Using the table №2 we determine the necessary proportions of the mass of water and cement (W / C - water-cement ratio).

Table. No. 2 - W / C indicator used for different markings of concrete

Knowing all the data (concrete - M300, cement - M400, filler - crushed stone), according to table No. 2, we easily find the water-cement ratio, which is equal to - 0.56 .

It remains to find the required volume of water in order to obtain the finished product of maximum plasticity, taking into account the use of crushed stone fractions 20 mm. To do this, we return to where we see that the result obtained is equal to 210 l/m³.

After all the basic data became known to us, we calculate the required amount of cement for the preparation 1m³ concrete mix. Divide 210 l/m³ on the 0.56 , we get 375 kg. cement. Using the table №3 we derive the final proportions of all the necessary components.

Table number 3. Proportions of the ratio of components (cement, sand, crushed stone)

So, if for the preparation of 1 m³ of concrete (M300) we need 375 kg. cement (M400), then, following the calculated indicator of table No. 3, we get sand - 375 × 1.9 = 713 kg., crushed stone - 375 × 3.7 = 1,388 kg.

Methods for mixing concrete

There are two ways to prepare building concrete with your own hands:

1. Mix the solution manually;
2. Use a concrete mixer to mix.

Manual mixing of concrete

• First, pour the required amount of sand into a clean container;
• Strictly observing the proportions, pour cement on top. Mix both fillers well until their color is uniform;
• Measure the required amount of water, and add it in small portions to the container with sand and cement, while distributing and mixing the mixture over the entire area. The result should be a gray mass without lumps and visible residues of sand and cement;
• The final step is to add crushed stone to the resulting solution. Mixing should take place until each pebble is covered with a solution. To give the concrete the necessary plasticity, add water if necessary.

Among the disadvantages of the manual method, the following can be distinguished:

• Quite a laborious and lengthy process;
• Immediate use of the solution after kneading. Otherwise, the solution may begin to delaminate, which will lead to a deterioration in its quality.

Mixing with a concrete mixer

• Pour a small amount of water into the drum of the concrete mixer, then add cement there and mix well until a gray milk is obtained. From now on, the drum should rotate continuously;
• Further, according to the calculation of proportions, proceed to backfilling of fillers (sand and gravel). Stir for another 2-3 minutes;
• Add a couple more liters of water to the resulting mixture until a homogeneous consistency is obtained.

The main advantage of this method of mixing is the possibility of using concrete for another hour after mixing the solution.

Everything is already created by nature. We can only use her tips in the development of high-tech materials. The developers of permeable concrete, which imitates natural soil, went this way.

Everything is already created by nature. We can only use her tips in the development of high-tech materials.

The developers of permeable concrete, which imitates natural soil, went this way. Permeable concrete is a highly porous material made of concrete particles glued together. The pore space occupies 15-25% of the total volume of the material. It turns out such a cheese with a lot of holes. High porosity provides filtration of large volumes of water - up to 200 liters per minute per 1 m2 of coating. What are the advantages of this technology?

There is a natural water cycle in nature. Rain water reaches the surface, is absorbed by the roots of plants, and the excess flows into the groundwater. Further, water evaporates through the leaves of plants and from the surface of reservoirs that are fed from groundwater. In cities where asphalt has literally "gobbled up" the entire surface, rainwater is discharged through drainage systems outside the city. As a result, the natural cycle is broken. Plants suffer from a lack of water, and groundwater does not receive the necessary nutrition. Permeable concrete, unlike asphalt, allows rainwater to pass through, which ensures its free access to the soil. At the same time, the load on the city's drainage systems during rainy seasons is reduced.

The cost of such a coating is much lower than asphalt. Do not forget that a quarter of the "miracle concrete" is air. On the other hand, asphalt is a petroleum product. In addition to the unstable cost of its production, asphalt contains a large amount of toxic substances that pollute the environment.

Eco-friendly concrete is ideal for harsh environments. Due to its porosity, unlike asphalt, it is resistant to temperature extremes. This eliminates the need for frequent road repairs, and in our reality, the annual re-laying of the asphalt pavement. Manufacturers of "miracle concrete" guarantee 15 years of operation in such conditions!

Aerated concrete is used in the US and Europe to build sidewalks, parking lots, highways, recreation area pavements, retaining walls, and slope reinforcement. Manufacturers are confident that over time, its scope will expand.

The developers of the Portuguese studio e-studio went even further. They "revived" the concrete by adding lawn grass seeds to it. Organic concrete is a unique material that, thanks to its porous structure, allows seeds to germinate directly from this substrate. Even during dry periods, plants will not lack water, safely stored in its pores.

Organic concrete opens up new possibilities for architects and landscape designers. In fact, the originality of "green structures" and living forms is limited solely by their imagination.