Comments:
Lightweight concrete is characterized by fairly high porosity (about 35-40%), average density (from 150 to 1800 kg/m³), low cost and ease of manufacture. He received widespread, is used in the construction of monolithic and prefabricated, enclosing and load-bearing structures, as well as thermal insulation. This material has a relatively light weight and good heat-shielding properties, although it is inferior in strength to brick and heavy concrete. When using it, you can significantly reduce the thickness and weight of the walls being constructed. As a result, construction costs will be significantly reduced.
Lightweight concrete is a concrete mixture of cement, water, sand and large porous aggregates.
Main Features
Such concretes are usually made by mixing various binders, light porous materials and water in certain proportions, sometimes with the addition of sand, foam and gas formers, water repellents, plasticizers, antiseptics, etc.
Typically used as a binder different types cement (magnesium cement, Portland cement), gypsum, lime, cement-lime mixtures.
The following can be used as fillers:
- Lungs natural materials from rocks porous structure(dolomite or limestone of volcanic origin, pumice, shell rock, opoka, etc.), obtained by crushing and fractionating.
- Artificial materials obtained from waste from metallurgical, coke-chemical, and oil refining production, when processing waste in city household landfills. Fuel, metallurgical and chemical slags are used without any preliminary processing. Expanded expanded clay, vermiculite, and perlite are obtained by special firing of clay raw materials. At high temperature and rapid heating, products expand 17-40 times.
- Organic materials such as softwood sawdust, flax or hemp brome, etc.
To improve the strength characteristics of lightweight concrete, sand can be added to the mixture.
Return to contents
Basic properties of porous lightweight concrete
The following can be distinguished:
- The density of the material, which depends mainly on the dry bulk density and the fraction of the aggregate used. A coarse aggregate is considered to be from 5 to 40 mm in size, and a small aggregate is from 0.2 to 5 mm. The ratio of coarse to fine aggregate should be 6:4. On average, the ratio of the bulk density of coarse dry aggregate to the density of the concrete produced from it is approximately 1:2. The following grades of lightweight concrete are available depending on the volumetric mass: D200, D300, D400..D2000 (with an interval of 100 kg/m³). Density decreases with porosity cement stone.
- Strength directly depends on the amount and brand of cement used in the mixture, as well as on the quality of porous aggregates. If the strength of the aggregate used is low, then it may well start with it, regardless of the characteristics of the cement stone. Concrete compressive strength classes have been established from B0.35 to B40, depending on their purpose.
- Thermal conductivity can vary within a fairly wide range from 0.055 to 0.75 W/(mx°C). This value is significantly influenced by both the density of the concrete itself and the nature of the porosity structure and moisture content of the material. If volumetric humidity increases by 1%, then thermal conductivity increases by 0.01. 0.03 W/(mx°C). Excellent thermal insulation properties are obtained by using lightweight expanded polystyrene fillers (coefficient from 0.055 to 0.145 W/(mx°C)) and expanded perlite with a coefficient of 0.15 W/(mx°C) at a density of D600.
- The frost resistance of the material directly depends on the quality characteristics of the aggregates and the binder; the structure of the concrete also plays a huge role. Frost resistance varies from F15 to F200. You can get values up to F300 and even F400. Typically, such concretes are used for external structures;
- Water resistance depends on the type of binder, the ratio of it to water in concrete, the content of various chemical and finely ground additives, the conditions under which hardening occurred, and the age of the concrete itself.
It is quite high, and as the material ages it increases more and more. Depending on water resistance, the following grades of lightweight concrete are distinguished: W2, W4, W20 (numbers indicate pressure in kgf/cm²).
Return to contents
Difference in structural features
The following types of lightweight concrete are distinguished:
- Ordinary ones, which are usually made from fine or coarse aggregate, water and a binder, and the solution almost completely fills the various voids between large particles. The air involved in such a mixture should not exceed 6% of the total volume.
- Sandless, large-porous: in such concrete, between the particles there are voids free from mortar. The structure contains more than 25% of pores filled with air.
- Porous or usually made on a binder base and special pore-forming additives. In their structure, so-called closed cells appear, filled with gas or air (up to 85% of the volume). Such materials may lack sand and coarse aggregates.
Return to contents
Division by purpose
Lightweight concrete with porous aggregates can be divided into the following types:
- Thermal insulation with thermal conductivity up to 0.2 W/(mx°C) and volumetric mass from 150 to 500 kg/m³, which are used for the production of special thermal insulation structures and as slabs for insulation.
- Structural and thermal insulation, the volumetric mass of which is from 500 to 1400 kg/m³, their compressive strength should be M35 and higher, and thermal conductivity - 0.6 W/(mx°C), no more. They are usually used for the construction of enclosing and some load-bearing structures (various floors, walls and partitions).
- Structural ones have the highest volumetric mass for lightweight concrete (from 1400 to 1800 kg/m³), have a strength of more than M50 and frost resistance of at least F15. These are usually used for load-bearing external structures.
Quite durable and relatively lightweight material You can make concrete with your own hands using metallurgical or fuel slag. It is used for monolithic construction; small blocks can be made from it. And then use them to build walls using cement mortar.
Such blocks are usually produced in a factory, but they can also be produced directly at construction site, preparing formwork forms and pouring concrete made with your own hands from slag into them. When casting blocks yourself, in order to reduce thermal conductivity and save cement, you can even use paper sleeves (old newspapers) filled with sand, as well as special inserts made of lighter sawdust or polystyrene concrete, as void formers. Lightweight concrete grade M10 can be used for such thermal inserts.
To obtain blocks, you can make concrete with your own hands, using sawdust as a filler. The construction of walls from such material significantly reduces the cost of the entire construction. If such walls are well protected from weathering, they will last more than 50 years.
There are several types of concrete mortar, which differ both in quality and proportional composition. The use of one or another solution option is determined individually, depending on the location of concreting. We will learn further about how to make concrete with your own hands.
How to make concrete with your own hands, proportions and technology
The most important component of concrete mortar is cement. Its function is to connect the other components with each other. Portland cement is an ideal option for making concrete. This is explained by the fact that it contains a large amount of calcium silicates. Thus, it is possible to achieve high adhesion between all components.
The type of cement used in the process of making concrete mortar is determined by the individual indicators of the scope of its application. Most often, grade 500 cement is used. Lower quality grades are used to prepare concrete for surfaces that are not subject to high loads.
Portland cement is used to improve adhesion between all components at both high and low temperatures. However, minimum temperature the use of concrete mortar is fifteen degrees. If concrete is still used at low temperatures, then its composition must contain special substances in the form of additives and plasticizers. The substance in the form of Portland slag cement is used if work is carried out at temperatures above 25 degrees Celsius.
The amount of impurities in the cement substance should not exceed twenty percent. This is indicated in the marking with the letter D. When choosing cement for the mortar, pay attention to its external indicators. It should be free-flowing and should not contain additional moisture. Material that has lumps and is damp appearance, buying is not recommended.
Critical elements are built from concrete, which will quickly collapse due to poor quality cement. The material should also be stored in specially designated conditions, at a temperature of 10 degrees Celsius and a humidity not exceeding 60%. Cement easily absorbs from external environment moisture, odors and quickly loses its positive characteristics. We recommend purchasing fresh cement that will be used within one or two weeks.
The second component of concrete mortar is sand. There are varieties concrete solutions in which you can do without sand. This is only possible if the filler composition has no gaps or they are minimal.
The optimal sand fraction is from one to five millimeters. When choosing sand, give preference to materials that have sand grains of equal size. Sand should not contain clay or other impurities. The presence of remains of vegetation, stones, construction waste- negatively affects the quality of the resulting concrete solution.
If you have sand that is not very clean, we recommend sifting it several times before use. The best option- use of river sand, the cost of which is slightly higher than regular sand. However, such material does not have clay or foreign inclusions and has good performance characteristics.
The presence of clay in concrete is unacceptable; it negatively affects its strength and service life. The next point is to ensure maximum adhesion of concrete and coarse aggregate. These factors are the main ones in determining the overall strength of a concrete solution. In order to prepare the sand for work, we recommend washing it and leaving it to settle.
If it was not possible to purchase high-quality sand, then the option of using artificial sand is possible. To make it, rocks are finely crushed. This sand has greater density and weight. Please note that a concrete solution made from such sand will be heavy.
To increase the strength of the concrete solution, crushed stone or gravel is added to it. They act as a filler for concrete mortar. It is not recommended to use pebbles for these purposes, as their surface is smooth.
When choosing a filler, ask what type of litter it is made of. The expanded clay material is lightweight, but at the same time connects all the components well. The filler size ranges from 0.8 to 4 cm. It is recommended to choose medium-sized substances. It is recommended to choose a substance that does not contain dust and clay inclusions. The reliability of adhesion is determined by the roughness of the material.
Add a filler to the concrete solution that contains both large and medium particles. In this way, it is possible to achieve a tighter fit of the filler to the surface. Sand and filler should be located near the work site. In order to prevent contamination of sand or filler, we recommend pouring them onto a base previously covered with film.
The last of the main components of concrete mortar is water. It should not contain alkaline or acidic inclusions.
Substances in the form of:
1. Lime.
Using this material, the convenience of laying concrete mortar is increased. Thus, it is possible to improve the process of leveling the concrete solution. Lime reduces the strength of the mortar because the bond between cement and aggregates is reduced. Please note that lime must be slaked.
2. Plasticizers.
In order to make decorative concrete by hand, it is recommended to use substances in the form of plasticizers. With their help, it is possible to change the quality characteristics of the solution.
3. Additional components.
With the help of certain components, the concrete solution becomes more progressive. In addition, by using additives it is possible to improve the setting of concrete mortar. Before using additives, study their characteristics and instructions for use. If the work of pouring concrete is carried out at low temperatures, then additives cannot be avoided.
4. Reinforcing components.
With the help of special additives it is possible to perform additional reinforcement of the concrete solution. For example, it is recommended to add fibers based on polypropylene or polyvinyl chloride to the concrete solution used to screed. These components are soft and especially durable. In this way, it is possible to achieve ideal smoothness of the concrete and prevent its cracking.
How to make foundation concrete by hand - composition proportions
The composition of concrete and the amount of connection of its components is determined by the purpose of using the concrete solution. For example, in order to build a foundation, you need strong concrete, which contains large crushed stone and a mortar that secures it securely.
At the same time, it is important to achieve fluidity of the solution, since it should not contain air bubbles or foreign inclusions. Before you start pouring the solution, it is recommended to make a substrate. To do this, it is enough to use a solution that is less durable in composition and contains inclusions of fine sand. At the same time, the consistency of the solution resembles wet soil.
The foundation mortar can be made using concrete by hand. At the same time, the filler should be medium in fractional size, and the consistency should be fluid. In this way, it is possible to distribute the solution on the surface. In addition, fine or medium fraction filler is used for the manufacture of flowerpots, garden elements, and concrete balusters.
The composition and quantity of components that the concrete solution contains are determined by SNiP. In this case, the density of each ingredient should be taken into account. We recommend using a medium-density concrete solution. After completing the calculations, proceed to connecting the components together.
The most popular component ratio involves using one part cement to three parts sand and six parts filler, with the amount of water varying from 0.4 to 1. Water makes the solution more or less fluid.
After determining the optimal consistency of the solution, you should measure the components. Please note that it is not recommended to use wet sand for work; it is recommended to dry it before adding it to the solution.
Before you make concrete steps with your own hands, you need to prepare a concrete solution. Most often, a concrete mixer is used for this. This device allows you to mix all ingredients evenly and quickly. The manual method of preparing concrete mortar is relevant only if the amount of work is small. At the same time, there is no possibility of controlling the recipe in this case.
There are two ways in which you can build a concrete solution yourself:
1. First, the dry ingredients are mixed together, and then water is added.
2. Sand, aggregate and cement are added to the water.
The first option is also called dry, in which all components are uniformly mixed together. In this case, water is added last. Sometimes, this composition contains dry lumps that reduce the strength of the solution. In order to avoid their appearance, we recommend using the second method of mixing the solution. It is suitable for mixing concrete in small quantities.
In any case, we still recommend using a concrete mixer to mix the solution. If you do not have this device, then rent it. The concrete mixer must be located near the work site. Thus, it is possible to avoid delamination of concrete during transportation.
A standard concrete mixer contains about two hundred liters of solution. This amount should be used as a guide when calculating the amount of ingredients. The process of preparing a solution in a concrete mixer is as follows:
1. Measure out the required amount of water and pour it into the concrete mixer. Do not fill in all the water, leave about 10% for later to bring the solution to the desired consistency.
2. Put cement in the required quantity, also leave some cement.
4. After preparing the cement mortar, add substances to it in the form of additives and plasticizers, if necessary.
5. At the final stage, filler is added. If the solution needs to add water, then it is mixed with cement, the resulting mixture is added to the concrete mixer at this stage.
All work is completed within 10-15 minutes. If it was not possible to extract the entire solution at one time, then it is constantly stirred until complete extraction.
How to make colored concrete with your own hands
Before making a concrete flowerpot with your own hands, we recommend painting the solution with color pigments. Modern technologies make it possible to make various concrete surfaces colorful and bright.
Pigments are added either at the stage of preparing the solution or after the composition has hardened. There are two options for color pigments:
- natural;
- synthetic.
The color palette and saturation are determined by the chemical components of the pigment. It is recommended to add pigment to the composition at the mixing stage. In this case, it is possible to achieve uniform and beautiful color. In order to maximize the color effect on the surface, we recommend using sand and white cement when preparing the solution.
Before adding pigment, it is diluted with water. The quality of mixing affects the homogeneity of the solution. Moreover, such a composition is prepared exclusively in a concrete mixer. Prepare concrete solution manual method impossible.
Before making a concrete path with your own hands, it is also recommended to prepare a solution in a concrete mixer. This device not only saves time, but also significantly improves the quality of the finished solution.
When pouring concrete mortar, it is recommended to use a concrete vibrator. With its help, it is possible to remove air bubbles and improve the quality of the finished coating. Additional reinforcement is provided by steel reinforcement bars. The optimal setting time for the solution is about two days. Complete drying of the solution takes about two weeks or more.
Make concrete with your own hands video:
How to make strong concrete (concrete mortar) with your own hands.
Mortars and concretes are stone materials artificial origin, which are obtained by mixing a binder (usually lime and Portland cement) and certain aggregates. Binder when mixed with water, it forms a stone-like body, which is explained by the processes of setting and rapid hardening. The strength of the stone-like body is ensured by the filler (gravel, crushed stone, sand). Next, I will tell you about all the stages of the question of how to make concrete with your own hands.
Components for making the solution
1. Filler
For mortar, most often, fine sand or other fine aggregate is taken. For concrete mortar, you can take not only fine sand, but also coarse gravel or crushed stone. To make construction plaster or masonry mortar, it is best to use fine sand, the grains of which do not exceed 2 millimeters in diameter. If the plaster has a special texture, it is possible to add sand with a grain size of up to 4 millimeters. In our market, customers are offered two types of sand: river and ravine. River sand is considered medium-grained, it is quite expensive, but its purity facilitates its use as a component for concrete mixture. Gully sand can be fine-grained (from 0.5 to 1.5 millimeters), with a large number of clay particles and other impurities. It is not suitable for good and strong concrete, but for mortars it can be used without fear.
For lean (light) cement concrete with strength class B7.5, only sand can be used as a filler. In concrete of greater strength, in addition to sand, you can also use crushed stone or gravel with a diameter of up to 31.5 millimeters. It is considered correct to use a crushed stone mixture of different fractions so that the finished concrete contains a minimum amount of voids between the stones.
Attention! The aggregate of concrete and mortars should not contain pollutants such as soil, glass, pieces of wood, peat, plants, dusty or silty soil. If contaminants are present, they should be removed by sifting gravel or sand through a sieve.
2. Cement
Cement is a general name for binding powdery substances based on marly, calcareous and clayey rocks and various additives. The most commonly used type of cement is Portland cement, which takes its name from the British peninsula of Portland. This cement contains a large amount of calcium silicates. Under construction country house Two types of Portland cement can be used.
Type I – does not contain additives, or their content does not exceed 5 percent. The European classification for such cement indicates the name CEM I.
In Russian practice, the presence of cement additives is indicated by the letter D and a number in the marking code, which follows the brand. For example, if you see the marking PC 500-D20, then it means the presence of 20 percent of additives in grade 500 Portland cement. As we have already found out, this characterizes type II cement. As for the DO designation, it characterizes type I cement, that is, a material without additives.
To prepare plaster and masonry mortar, you need to take cement of classes M400 (32.5) and M500 (42.5). Portland cement is ideal for preparing concrete mixtures that will be used in low temperatures(daily average below 10 degrees Celsius). If the temperature is high, for example, in the heat, then it is better to use Portland slag cement or type III cement (the European classification indicates the name CEM III). It is well suited for the manufacture of masonry and plaster mortars used for fencing and flooring.
Attention! Cement can only be purchased in bags with appropriate markings. Immediately before purchasing, you need to check whether the cement is damp or caked. If all the signs are present, it is recommended to refuse the purchase. Only a trusted, reputable manufacturer who has been selling the solution for several years can guarantee compliance with the brand of cement stated on the packaging or bag. By the way, the main difference good manufacturer What makes it underground is not the cost of ready-mixed concrete, but the availability of a high-quality delivery service.
3. Lime
Lime is required for the production of cement-lime mortars. In addition, it is used to increase the workability of the solution. Today, to prepare solutions, it is no longer necessary to slak lime. Instead, you can buy low price slaked (hydrated) fluffed lime, which is sold packaged in bags in ready-made form. Alternatively, instead of a dry mixture, lime can be sold in buckets in the form of lime paste. It is added to cement-lime plaster and masonry mortars to increase their workability.
Attention! If you decide to use lime as part of the question of how to make concrete at home, be extremely careful, since lime has strong corrosive properties. It is recommended to carry out work wearing protective gloves, remembering to ensure that the material does not get into your eyes or skin. The same applies to the use of dyes, as well as subsequent work on grinding and polishing the product.
4. Additives
The composition of a concrete mixture or mortar may contain certain additives that can either improve or simply change their certain properties.
Plasticizers or plasticizing additives can increase the fluidity of the mixture, as a result of which builders receive a solution with a more liquid consistency. This solution is much easier to apply.
Thinning additives or superplasticizers can reduce the amount of water poured for mixing.
In addition, their use makes it possible to improve the workability of the mixture, increase the strength, frost resistance and water resistance of the mortar or concrete.
Certain additives allow you to accelerate the hardening of a concrete mixture or solution.
Also, there are additives with which it becomes possible to carry out work in the temperature range from 10 degrees below zero to 35 degrees hot.
There are special additives on the market that slow down the hardening of the concrete mixture, which is useful when concreting in hot conditions.
Air-entraining or aerating additives increase frost resistance and reduce the moisture capacity of the solution in the hardened state.
Typically, supplements are sold in plastic containers in liquid form. The packaging must contain information about dosage, quantity and basic properties. Additives in mass ratio should not exceed 2 percent of the total mass of cement.
5. Water
The quality of water used for mortars and concretes is regulated by GOST standards. In particular, water must meet drinking standards and must not contain foreign impurities, including sugar, oil, alkalis and acids. It is prohibited to use poorly cleaned swamp and waste water. It is better to be guided by the principle that you can use any drinkable water to stir the solution. If you prepare a concrete solution using water from a lake or river, you will have to check the suitability of such water in a special construction laboratory.
Composition and proportions
Before you begin to consider the question of how to prepare concrete or reinforced concrete, I would like to draw your attention to the fact that the composition and proportions will directly depend on its main purpose. That is, for the foundation it is correct to use strong, high-density concrete, while for pouring the fence you can choose lighter grades. Once you have decided on the ingredients, choose the right brand. In most cases, for imported concrete and do-it-yourself mortars, it is better to choose grades M300 or M400. As for proportions, the components “cement/sand/crushed stone” should be used in proportions of 1/3/5. This means that per cube of concrete, one part of cement requires the addition of three parts of sand and five parts of crushed stone or gravel. If we talk about water, then its amount should be half the weight of other fillers. For example, if you have 100 kilograms of dry mixture, then you need to take 50 liters of water.
If you get too thick (dense) mixture, you can add a little more water. The consistency should be such that you do not need to exert much effort to stir the solution with a shovel. For wet sand there should be less water. If work is carried out in the cold, the water and concrete must be heated, which will protect the composition from premature setting and loss of strength. For work, it is better to use a purchased concrete mixer or devices/mixers and containers made by yourself. You can read what material and what components they consist of (pumps, molds, vibrating screeds, etc.) in another article.
-
Aerated concrete blocks for the house and its foundation, types and production.
-
Modern technology concrete production using equipment, what is it like?
-
How to properly insulate plastic windows yourself?
After reading this article, you will learn about how to make good concrete with your own hands, what characteristics good concrete should have, what is included in the composition and in what proportion, the advantages of manual and mechanical technology for mixing concrete and pouring it.
Concrete is often called the main building material. Foundation, walls, roofs, screeds, cladding, paving slabs, balusters, vases - unlike granite or marble, concrete is easy to make yourself and in the right quantity. Depending on the scope of application, good concrete can be heavy or light, durable or frost-resistant, set quickly or for a long time, and be more or less mobile.
Typically, concrete is a mixture of cement, water and sand. To increase the strength of concrete, large aggregates in the form of crushed stone and gravel are used, and to give additional properties and ease of production and pouring, various reinforcing substances and plasticizers are added. The heaviest concrete is used in underground bunkers as a reliable radioactive barrier.
To obtain good concrete, you must carefully select all components.
Cement
The main link in concrete, a single bundle of all components and the most expensive element. For good durable concrete you will need Portland cement grade M500, and if the concrete is prepared at temperatures above 30 degrees, then slag cement is needed. If we are talking about paving bright garden path— it’s better to take white cement; gray Portland cement will drown out any pigment paint. Lime cement has a low setting speed and is optimal for creating small decorative elements.
The cement should be dry and crumbly, without lumps or moisture. If the packaging is torn or the cement was stored outside, definitely pass by. The first cement in importance is the last one in terms of timing; it is better to buy it no earlier than a few days before the start of concrete production.
Sand
The main characteristic is the absence of foreign impurities, which negatively affects the strength of concrete and its durability. By type, sand is usually divided into river sand, gully sand and artificial sand obtained by processing rocks. Gully sand is cheaper than river sand, but it contains much more silt and clay, and stone sand adds additional weight to the concrete composition in interfloor screeds.
You can buy ready-made washed sand or drive to the nearest quarry, and then use a sieve to obtain a homogeneous product at home.
To understand how clean the sand is, you need to pour it into a bottle with hot water, mix and let stand for several hours. If the water becomes cloudy, this indicates a high clay content. Concrete made from such sand will become loose and crumble.
Aggregate
To obtain durable concrete, you cannot do without coarse aggregate. For high-strength concrete, crushed stone is preferable, and for medium-strength concrete, much cheaper gravel is also suitable. The cost of the material is influenced by the type of crushing - crushed stone is obtained mechanically, differs in roughness and the presence sharp corners. Naturally, gravel has a more rounded shape. You cannot use river or sea gravel polished by the current; it will not provide the necessary adhesion to the solution. It is better to take gravel for the foundation different sizes- medium to large (with elements from 10 to 35 mm), this will give the particles the opportunity to create a more uniform base. For stairs and decorative elements you will need fine gravel with a diameter of no more than 7 mm.
Expert tip: Store crushed stone and gravel on a tarp to prevent natural contamination and moisture from the soil.
Water
The main rule: use drinking water. You can safely take water from a sewer or tap, but from a well or river it is not recommended; its composition can bring many unpleasant surprises.
Expert advice: to increase the elasticity of the solution, add liquid soap to the water.
Supplements
To make it easier to lay concrete, lime is usually added. It is sold already slaked in bags or in buckets in the form of lime paste. Sometimes it comes across under the name “fluff”. When working with lime, it is better to wear not only gloves, but also a mask, as it has strong corrosive properties.
If the foundation or concrete product has a complex shape, then plasticizers will need to be added to the solution, affecting viscosity and fluidity. They will help you quickly fill out the most hard to reach places and will significantly speed up the process.
When forming a thin screed or unstable soil, special reinforcing substances will be needed. Such substances prevent the formation of shrinkage microcracks and increase the impact strength of concrete several times.
Expert advice: additives should not exceed 2 percent of the cement mass fraction in the solution. P At sub-zero temperatures, potash is added during mixing.
Types of concrete
To form the main part of the foundation for the house, you will need strong concrete with the inclusion of coarse crushed stone and high fluidity for compaction. To equip the base for the foundation, lighter concrete made of sand and cement is used. To achieve optimal ratio price and quality, it is necessary to understand for what purpose concrete is made. Depending on the composition and grade, concrete is divided into three groups:
- Lightweight concrete (M100 and M150) - wooden house, garage, curbs, screeds, stairs. The main advantage is that crushed stone can be replaced with gravel, especially if you have a farm and have a stone crushing machine.
- Medium concrete (M200, M250, M300) - reinforced concrete products, piles, good durable houses of 2-3 floors. This concrete can be used to build walls and pour monolithic foundations.
- Heavy concrete (M400, M500 and above) - can withstand 5 or more floors. Used in the construction of swimming pools, water parks and bank vaults, it sets quickly and is expensive.
Percentage composition
The most common ratio used when pouring a foundation is one part water and one part cement, three parts sand and six parts aggregate. For an accurate calculation, it is better to use a table based on M500 cement, sand and aggregate:
| Type of concrete | Composition C-P-W, % |
| 100 | 6-36-52 |
| 150 | 8-34-50 |
| 200 | 9-32-50 |
| 250 | 11-28,5-49,5 |
| 300 | 11,5-27,5-49,5 |
| 400 | 15-23-47 |
| 450 | 16-22-46 |
Mixing concrete
If you need to make a foundation for a house of about 100 square meters, then you can’t do without a concrete mixer. The cost of purchasing it (10,000-20,000 rubles) will be justified by the ease of kneading. Mix all ingredients by hand without adding large quantity water will not be easy, which, in turn, will affect the consumption of expensive cement. On the market today you can also buy mechanical concrete mixers so as not to be tied to the power grid. If we are talking about paving a path or making concrete stairs, then improvised means are quite suitable.
To prepare the mixture manually we will need:
- Container for mixing - pallets or an old bathtub.
- The weight measure is a metal bucket.
- A pair of shovels for mixing.
Add the ingredients one by one, stirring constantly:
- Water.
- Cement.
- Sand.
- Supplements
- Aggregate.
Expert advice: we do not use all the water at once, but divide it into 2 parts. 80% - first, the rest - after adding all the ingredients.
The mixing time should take no more than half an hour, otherwise the cement will begin to set. It is better to prepare concrete in small portions for transportation by wheelbarrow to the place of installation.
Pouring concrete
The main danger when pouring concrete is uneven distribution over the surface and the formation of air voids. For this purpose, you can make a homemade vibrator from a hammer drill or drill. Depending on the thickness of the concrete coating, you will need a reinforcing rod of various lengths and a rubber hose that will prevent the solution from getting on the rod. Filling should be done gradually, in layers of no more than 10 cm. If the filler is well compacted, then cement laitance should appear on the surface.
Expert advice: the drill should be designed for long-term use; it is better to take a device with a power of 650 W or more.
To protect it from the external environment and ensure uniform drying, the concrete is covered with a film. Approximate drying time is 36 hours to 2 weeks, and the strength of the concrete will increase over time and reach its maximum after a year.
Sometimes in construction it is necessary to reduce the load on supporting structures. For example, a plank subfloor that needs to be leveled with concrete mortar for cladding ceramic tiles. It is clear that the concrete layer has a fairly large weight, which wooden structure may not stand it. In this case, experts recommend using lightweight concrete.
What is it?
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 weight 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 (and, accordingly, by mass). The density of lightweight concrete with porous aggregates is determined by the range from 500 to 1800 kg/m³ compared to conventional ones, the values of 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;
- getting more economical option by reducing the percentage of cement;
- high strength of the material.
Subtleties of manufacturing
The most difficult thing in preparing lightweight concrete with porous aggregates is to correctly and accurately select the recipe for the raw mixture, especially the water-cement balance. It is this that influences the strength of the material and its convenient use.
The thing is that porous fillers quickly absorb water, leaving practically no water for the cement to set. Therefore, experts recommend selecting the recipe during the production 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.
Example of recipe selection
There are several options for selecting the density of lightweight concrete. One of them is the preparation of experimental mixtures.
Cement and fillers
To do this, take the standard recipe used for ordinary concrete. 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 coarse 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 quantity to the purpose of the concrete mixture. If the solution will be used for screeding, it is better to make it liquid.
Checking workpieces
Then lightweight concrete is poured into a container, usually a cube. After drying, the workpiece is tested for strength. The same preparations 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 volume of cement added. In this case, you will have to increase the volume of water.
The strengths of all workpieces are compared with each other. The indicator that meets the requirements of the structure being poured is determined. But the economic component must be taken into account. For example, of two suitable formulations, it is better to choose the cheapest composition.
Classification of mixtures
The classification of lightweight concrete mortars is based on the use of various fillers in the composition and the scope of application.
Simple composition
Ordinary lightweight concrete is made according to the recipe described above. That is, it contains both large and small fillers. In this case, the volume of air between all materials should not exceed 6%.
Porosity
The composition may differ in the nature of porosity:
- Sandless (large-porous) – complete absence fine filler. Air volume 25%.
- Porous - obtained when added to cement mortar materials that form pores.
Purpose
There is another type 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 thermal insulation (density up to 1400 kg/m³, strength not less than M35, thermal conductivity - no more than 0.6).
The first group is used for pouring screeds and making heat-insulating boards. 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, its porosity and quantity. But there is an average value - this is 200 kg per cubic meter. In this case, cement consumption varies from 70 to 150 kg per cubic meter of concrete solution.
Manufacturing methods
Lightweight concrete with porous aggregates is prepared according to different technologies, which depends on the type of additive.
Mixture based on expanded perlite
Making 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 placed in a concrete mixer. And this solution is thoroughly mixed.
Gradually, water is poured into it, to which plasticizers and modifiers have been added in advance. Thorough stirring should cause the mixture to rise. This is a signal that you can start adding the remaining perlite to it. It is better to do this in small portions.
If you make the solution yourself without using a concrete mixer, then it is better to do it in a clean bucket using a mixer or drill. You can also use a shovel, but the uniformity of the components in the mixture may be low.
Fiber fibers are often added to a mixture of concrete and perlite as a reinforcing composition. They must be added to the concrete when the bulk of the filler is poured.
Composition with expanded clay
First, cement and water are thoroughly mixed 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 this, expanded clay is added in portions. Here it is important, as in the first case, to achieve a uniform distribution of the solution components throughout the entire volume.
Foam concrete
Making foam concrete with your own hands is not easy. For this you need a foaming agent and a foam generator ( special equipment, which prepares the foam). Let's just designate the production technology.
A solution of sand and cement is prepared in a concrete mixer, into which a certain amount of water is poured.
While the mixture is being prepared, a foaming agent is added to the generator, which turns into foam inside the container. Using sediment, it is added to the semi-finished solution, where pores form. The foam is supplied using a pump.