Sand-gravel concrete (SGMC)

Laying concrete mixture
Concrete

(from the French béton) is an artificial stone building material obtained as a result of molding and hardening of a rationally selected and compacted mixture consisting of a binder (for example, cement), large and small aggregates, and water. In some cases, it may contain special additives and also not contain water (for example, asphalt concrete).

Content

• 1. History
• 2 Manufacturing
• 3 Types of concrete
• 4 Selection of concrete composition
• 5 Laying, compacting, hardening
• 6 Performance properties 6.1 Compressive strength
• 6.2 Workability
• 6.3 Other important indicators

basic information

Ordinary concrete contains cement as the main binder . Another component without which it is impossible to make a concrete mixture is plain water. To influence the consistency and other properties, other concrete admixtures are added to the mixture. Complete drying of the material can only occur after hardening.

General classification

Types of concrete and their properties will vary depending on the composition, consistency and freshness of the mixture.

A mixture in which there is no cement paste yet is called fresh. When this ingredient is added, the building material is called young or green. Once the cement paste is finally added, the resulting mixture is called hardened concrete mix.

The composition of the mixture is determined by many parameters. The main ones are strength class and environmental conditions. In a regular concrete mixture of strength class C25/30, one cubic meter contains:

• 285 kg of cement;
• 200 l of water;
• 1900 kg of aggregate.

This corresponds to a mixing ratio of 1:0.6:7.

Consistency and strength

The consistency of the fresh concrete mixture should be chosen in such a way that it can be easily transported and laid without resorting to segregation. The main property of this building material is manufacturability. The fresh consistency must be determined before construction begins and maintained throughout the entire work process. As the fluidity of the concrete mixture increases, it becomes more expensive. When pumping out the concrete mixture, its consistency should be similar to liquid plastic.

Compressive strength is one of the most important properties. DIN 1045−1: 2001−07 for the reinforcement of reinforced concrete structures requires evaluation by testing after 28 days on 15 cm long cubes (test cubes) or 30 cm long cylinders with a 15 cm diameter.

Based on a certain compressive strength, a concrete mixture can be classified into certain strength classes. C12/15 has a characteristic cylinder compressive strength of 12 N/mm² and a characteristic cube compressive strength of 15 N/mm² . As part of the harmonization of European standards, these specific strength classes are now being standardized throughout Europe.

Story

Concrete has been known for over 4000 years (Ancient Mesopotamia) [ source not specified 527 days

], was especially widely used in Ancient Rome[1][approx. 1]. Italy is a volcanic country where components from which concrete can be made are readily available, including pozzolans and crushed lava stones. The Romans used concrete in the massive construction of public buildings and structures, including the Pantheon, whose dome is still the largest in the world made of unreinforced concrete. At the same time, this technology was not widespread in the eastern part of the state, where stone was traditionally used in construction, and then cheap plinth - a type of brick.

Due to the decline of the Western Roman Empire, large-scale construction of monumental buildings and structures came to naught, which made the use of concrete impractical and, combined with the general degradation of crafts and science, led to the loss of the technology for its production. During the early Middle Ages, the only major architectural objects were cathedrals, which were built from natural stone.

Modern concrete based on a cement binder has been known since 1844 (I. Johnson). Joseph Aspdin received a patent for Portland cement in 1824; James Parker received a patent for “Roman cement” in 1796.

The world leaders in concrete production are China (430 million m³ in 2006)[2] and the USA (345 million m³ in 2005[3] and 270 million m³ in 2008)[2] In Russia in 2008 52 million m³ were produced.

Manufacturing

Cement concrete is produced by mixing cement, sand, crushed stone and water (their ratio depends on the brand of cement, fraction and moisture content of sand and crushed stone), as well as small quantities of additives (plasticizers, water repellents, etc.). Cement and water are the main binding components in the production of concrete. For example, when using 400 grade cement to produce 200 grade concrete, the ratio is 1:3:5:0.5. If grade 500 cement is used, then this conventional ratio produces concrete grade 350. The ratio of water and cement (“water-cement ratio”, “water-cement module”; denoted “W/C”) is an important characteristic of concrete. The strength of concrete directly depends on this ratio: the lower the W/C, the stronger the concrete. Theoretically, W/C = 0.2 is sufficient for cement hydration, but such concrete has too low plasticity, so in practice W/C = 0.3–0.5 and higher are used.

A common mistake in the artisanal production of concrete is the excessive addition of water, which increases the mobility of concrete, but reduces its strength several times, therefore it is very important to accurately observe the water-cement ratio, which is calculated from tables depending on the brand of cement used[4].

Proportions of ASG and cement for concrete

The quality of the cement-sand mixture with crushed stone directly depends on the components. At the same time, their ratio, as well as quality, is important. There are construction formulas that are accepted as axioms. They have been developed experimentally and have proven their effectiveness in practice.

This universal formula gives the following proportions:

• cement – ​​4 hours;
• OPGS – 1 hour;
• sealer – 0.4 tsp.

A binder is a construction term that refers to a liquid used to dilute dry ingredients to give them elasticity. More often, water is used as a sealer.

To measure ingredients correctly, we recommend that you choose the same unit of measurement. For example, count everything in kilograms or liters.

For ease of calculations, the builders compiled the indicators into a table. In it we can see the consumption of cement, cement or crushed stone to obtain a solution of a certain brand.

For example, let's see what we need to mix the M400 brand solution:

1. Select the intersection of the corresponding row with the columns. We find that per kilogram of Portland cement M400 you need to take 3.9 kg of ASG.
2. The next column shows the consumption of sand and gravel mixture per 10 liters of Portland cement.
3. Next we see that from 10 liters of cement powder and the required amount of ASG, 31 liters of concrete will be obtained.

For the purposes of “home” preparation of building mixtures, the universal unit of measure is a bucket. Anything will do: plastic, metal, enameled, colored. The main thing is that it is 10 liters.

Let's learn how to calculate in buckets. At the same time, we will find out how many components are required to mix 1 cube of concrete.

The equation for calculating the amount of cement looks like this: 1000 * 10:31 = 323 liters or 32.2 buckets. And we calculate the ASG using the following formula: 1000 * 35:31 = 1129 liters or 112.9 buckets.

We take all the numbers from the line which brand we want to prepare. In the example, we calculated the dry ingredients for the M400 brand.

If you find it difficult to navigate the tabular figures, you can use an online construction calculator to calculate the amount of materials needed.

Water is calculated individually in each situation. The sand in the mixture can be dry or wet, and the stones can have different porosities. Together, these characteristics affect the final grout consumption.

What is the best thing to do so as not to make a mistake with the volume of water? Just don't add all the liquid at once when mixing. First, it is better to pour 2/3 of the expected volume, and then pour it in parts until the desired consistency of the solution is achieved. So, experimentally, you will determine the optimal consumption of the sealer.

The table we reviewed contains the volumes of starting materials for different grades of concrete. To determine which brand is best, look at where other types are used:

• M150 - for the blind area of ​​small buildings, one-story houses.
• M200 - when pouring bases in the form of strips or slabs.
• M250 – for dense monolithic slabs.
• M300 – for the construction of a monolithic foundation.
• M400 – in the production of ultra-strong concrete structures.

Grinding concrete with a grinder

As you can see, it is not at all necessary to prepare a super-strong composition if you need to build a country house or fill a platform for a car.

Types of concrete

According to GOST 25192-2012[5], GOST 7473-2010 (formerly 7473-94), concrete is classified according to its main purpose, type of binder, type of aggregates, structure and hardening conditions:

• Conventional concrete is classified according to purpose (for industrial and civil buildings)
• special - hydraulic, road, heat-insulating, decorative, as well as special-purpose concrete (chemically resistant, heat-resistant, sound-absorbing, for protection against nuclear radiation, etc.).

• Based on the type of binder, cement, silicate, gypsum, slag-alkaline, asphalt concrete, plastic concrete (polymer concrete), etc. are distinguished.
• Based on the type of aggregates, concretes based on dense, porous or special aggregates are distinguished.
• Based on their structure, concrete is classified into dense, porous, cellular or large-porous structure.
• According to the hardening conditions, concrete is divided into those that harden under natural conditions, under conditions of heat and humidity treatment at atmospheric pressure, or under conditions of heat and humidity treatment at pressure above atmospheric pressure (autoclave hardening).

In addition to the GOST 25192-2012 classification, the following classification is used.

• Based on average density, concretes are divided into:

• especially heavy (density over 2500 kg/m³) - barite, magnetite, limonite;
• heavy (density 2200-2500 kg/m³);
• lightweight (density 1800-2200 kg/m³);
• light (density 500-1800 kg/m³) - expanded clay concrete, foam concrete, aerated concrete, pumice concrete, wood concrete, vermiculite, perlite;
• especially light (density less than 500 kg/m³).

• Based on the content of binder and fillers, concrete is divided into:

• lean (with a reduced content of binder and a high content of coarse aggregate);
• fatty (with a high content of binder and a reduced content of coarse aggregate);
• commercial (with the ratio of fillers and binders according to the standard recipe).

Selection of concrete composition

Standard area for sifting sand to select the composition of concrete
One of the most important components of a concrete mixture is sand. To prepare concrete, it is better to use medium to coarse natural sand. The size of the sand and its ratio with coarse aggregate (crushed stone or gravel in heavy concrete, expanded clay in light concrete) in the concrete mixture affects the mobility and amount of cement. The finer the sand, the more mineral filler and water required. The most important limitation when using natural sand is the limitation on the presence of clay or clay particles in the sand composition. Fine (clay) particles greatly influence the strength of concrete. Even a small amount of them leads to a significant decrease in the strength of concrete. Therefore, in the absence of natural sand without clay particles, the available sand is improved (enriched) using the following procedures: sand washing; separation of sand into fractions in a water stream; separation of the required fraction from sand; mixing sand available in the work area with imported high-quality sand.

After beneficiation and preparation, the sand must satisfy the conditions defined by the so-called standard screening area. The grain composition, determined by sifting sand through sieves with different holes, should fit into the area shown in the figure with dashes. You can use sand with particle sizes taking into account the unshaded area, but only for concrete grade 150 and below [6].

Instead of sand, production waste from metallurgical, energy, mining, chemical and other industries can be successfully used[7].

How to mix concrete

Let's take a break from theory and move on to practice. There are 2 ways of mixing the solution: mechanical and manual. When using the manual method of diluting PGS with cement, containers and shovels are used. For the mechanical method you will need the same thing, plus a concrete mixer.

In one approach in a concrete mixer, you can prepare an amount of mixture equal to 2/3 of the volume of the container. If the drum has a volume of 160 liters, then about 120 liters of concrete can be made from gravel mass at a time. About 3 m3 of composition can be produced per work shift.

Let's start kneading using a mechanized method:

1. First, turn on the centrifuge without filling.
2. Turn the drum up to position 1 and add water (5 liters or half a bucket).
3. We lay enriched ASG (6 buckets).
4. Turn the mixer to position 2 and add cement (1 bucket).
5. You need to stir for no more than 10 minutes, otherwise the cement will begin to set. The resulting mixture should be uniform in color and consistency. Lumps are not allowed.

Always prepare the concrete solution immediately before pouring it. The entire amount must be consumed within 2 hours after preparation.

For the production of small volumes, you can do it manually. See how the sequence of adding ingredients changes:

1. First, pour dry substances (sand, gravel, cement) into the construction bath. Mix them until smooth so that you don’t see unmixed lumps.
2. We begin to pour water in portions. Do not forget that you need to constantly mix the components.

When mixing dry ingredients, you do not need to dilute them with water. When the liquid solution dries, it will shrink and the surface of the foundation may crack.

Laying, compacting, hardening

Laying and compacting concrete.
After preparation and placement, the concrete mixture should be compacted as quickly as possible. During the compaction process, they get rid of air in air pockets, and also redistribute the laitance for closer contact with the solid fractions of concrete. This leads to increased strength of the finished concrete. Vibration is used for compaction. For vibration compaction in monolithic construction, hand-held vibrators are used, and in block construction, vibration presses are used. Curing temperature - from +5 °C to +30 °C.

Types of sand and gravel mixture

Today, concrete is so popular for construction that a separate article can be devoted to it. The basis for the strength of the building composition is a sand-gravel mixture (SGM). As the name suggests, the main components are gravel and sand.

Everyone knows what PGS looks like. Mountains of a mixture of sand particles and stones of different sizes can be seen along the roads when they are dumped. But let's take a look at GOST and find a description of the terms that will help us define exactly what sand is and what gravel is:

Helpful information:

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• Sand refers to particles that range in size from 0.05 to 5 mm. These rock fragments may have rounded or sharp edges.
• Gravel includes larger mineral fragments. Their size can be from 5 to 70 mm. The surface of the stones is rounded to varying degrees.

The gravel mixture is formed naturally in nature. It is even classified as a non-metallic mineral. Perhaps someone has seen how ASG is mined in rivers and quarries. It is believed that the highest quality material is washed from the bottom of the seas.

I want to see everything!

I want to see everything!

According to the place of origin of sand and gravel mixtures, they are given appropriate names. Let's look at the characteristics of the main types:

If you look at the natural mixture of sand and pebbles from the beach, you will see that most of it is sand (about 80%), as well as stones of different sizes (up to 20% of the total). The diameters of the pebbles can have a difference of 300 mm, which is unacceptable for many construction works.

In order for the concrete to be of high quality, the amount of solid elements in the sand must be 65-75%. This is the most optimal ratio. This mixture is called enriched (abbreviated as OPGS). In artificially created PGS, the granules have a small range in diameter. For example, you can prepare compositions with gravel sizes from 5 to 25 mm or from 10 to 50 mm.

To make ASG grains of the same size, special crushing plants are used. And sorting machines separate gravel by size. The resulting gravel is then mixed with sand.

Looking at the following photo, you can appreciate the differences between natural material and rocky material that has undergone enrichment.

In practice, a mixture of sand and crushed stone is divided into 5 groups. As the serial number increases, the percentage of gravel content increases. This figure can be 15, 25, 35, 50, 65 and 75%. The higher the indicator, the better the quality of the OPGS. The most durable concretes M200 and M150, which comply with GOST, are prepared from enriched mixture No. 5.

For information: the standards of the document GOST 23735–2014 “Sand-gravel mixtures for construction work” determine the composition of building materials. GOST contains a section describing the permissible particle size. Here are their characteristics:

Cement brand M500: how to choose and characteristics

There are also a number of standards that industrial companies use to produce concrete. They determine the requirements for levels of strength, frost resistance, and the amount of permissible impurities in concrete solutions.

Performance properties

Compressive strength

The main indicator that characterizes concrete is compressive strength. The class of concrete is determined according to it.

Concrete class B

is the cubic strength in MPa, taken with a guaranteed probability (confidence probability) of 0.95. This means that the property set by the class is satisfied in at least 95 cases out of 100, and only in five cases can it be expected to fail.

According to SNiP 2.03.01-84 “Concrete and reinforced concrete structures”, the class is designated by the Latin letter “B” and numbers indicating the withstand pressure in megapascals (MPa). For example, the designation B25 means that standard cubes (150×150×150 mm) made from concrete of this class can withstand a pressure of 25 MPa in 95% of cases. To calculate the strength indicator, it is also necessary to take into account coefficients, for example, for concrete of class B25 in terms of compressive strength, the standard resistance Rbn used in the calculations is 18.5 MPa, and the design resistance Rb is 14.5 MPa.

The age of concrete, corresponding to its class in terms of compressive and axial tensile strength, is assigned during design, based on the possible actual timing of loading the structure with design loads, the method of construction, and the conditions of concrete hardening. In the absence of this data, the concrete class is established at the age of 28 days.

Along with classes, the strength of concrete is also specified by grades, designated by the Latin letter “M” and numbers from 50 to 1000, indicating the compressive strength in kgf/cm². GOST 26633-91 “Heavy and fine-grained concrete. Technical Specifications" establishes the following correspondence between grades and classes with a coefficient of variation in concrete strength of 13.5%:

This table has been removed from the current version of GOST 26633-2015 because it is misleading.

Until testing, concrete samples must be stored in normal hardening chambers; the strength of the finished structure can be checked by non-destructive testing methods using Kashkarov, Fizdel or Schmidt hammers, sclerometers of various designs, ultrasonic devices and others.

Workability

According to GOST 7473-2010 “Concrete mixtures. Technical conditions", according to workability (indicated by the letter "P"), concrete is distinguished:

• super-hard (hardness more than 50 seconds);
• hard (hardness from 5 to 50 seconds);
• movable (hardness less than 4 seconds, divided by cone draft).

GOST establishes the following designations for concrete mixtures for workability:

The workability index is critical when concreting with a concrete pump. For pumping, use mixtures with a workability index of at least P2.

Other important indicators

• Flexural strength.
• Frost resistance - indicated by the Latin letter “F” and the numbers 50-1000, indicating the number of freezing-thawing cycles that concrete can withstand.
• Water resistance - indicated by the Latin letter “W” and numbers from 2 to 20, indicating the water pressure that the sample cylinder of this brand must withstand.

Climatic test chambers are used to test concrete for frost resistance and water resistance.

How to prepare concrete correctly

So, you are building a monolithic house or repairing a reinforced concrete foundation. Or you are simply going to build a blind area or concrete the paths. The main thing is that you already know that you will make the concrete mixture yourself or carefully control the process. We'll tell you how to calculate the proportions of the mixture in order to obtain concrete with the desired parameters, why it is important to carefully select the components for the composition, and what to pay attention to when you start mixing the solution and pouring it into the formwork.

Concrete is a building material that hardens after being poured into a mold. Concrete is produced from a mixture of binder, aggregate, sand, water and special additives. Requirements for concrete, its properties and components, technologies for working with it are strictly regulated by Construction Norms and Rules (SNiP and SP) and State Standards (GOST).

Key documents: GOST 25192-12 “Concrete. Classification and general technical requirements", GOST 7473-10 "Concrete mixtures. Technical conditions", GOST 26633-12 "Heavy and fine-grained concrete", SNiP 82-02-95 on cement consumption standards for concrete and reinforced concrete structures, SP 63.13330.2012 on concrete and reinforced concrete structures. There are hundreds of documents that in one way or another relate to concrete and working with it.

Concrete is divided into types according to various criteria: depending on the filler, light, heavy and especially heavy concrete are distinguished. For private construction, heavy mixtures are used. They are obtained when crushed stone or granite chips are used as a filler. With their help, ready-made reinforced concrete products are produced, monolithic foundations and floors are erected. Concrete is classified according to its composition, and there are many types of concrete depending on the aggregate or binder. In private construction, cement-based concrete is used.

Concrete is also classified according to strength, frost resistance, water resistance and mobility. Manufacturers reflect these properties in the labeling system.

The strength of concrete is indicated by its brand and class - they are the same thing, but in different units of measurement. The grade is designated by the letter M and has a value range from 15 to 800. The class is marked by the letter B, followed by a number ranging from 1 to 60.

Table 1. Correspondence of grades and classes of concrete.

If you are placing a concrete pad under a slab or foundation strip, or you are constructing curbs, take M100 concrete. If you want to build the foundation of a small building - a bathhouse or an outbuilding, or pour a screed on the floor, just take M150 grade concrete. To build paths or a blind area - a strip of waterproof material around the house, M200 concrete is suitable. The same brand is worth taking if you are building a concrete staircase or landing.

To build floors between the floors of a cottage, a foundation strip for a fence or garage, retaining walls, the best option is M250 concrete.

To build a foundation on stable soil that does not swell in winter from frost, concrete grades M200-M350 are suitable. If you are building on heaving soil, your choice is limited to the M250-M400 brands. The heavier the material of the foundation and walls and the more floors in the building, the higher the grade of concrete you should choose. For example, to base a one-story frame-panel house on stable soil, it is enough to take M200 grade concrete. For a three-story brick cottage on heaving soil, it is better to choose M350-M400 concrete.

• The frost resistance of concrete is indicated by the letter A followed by a number from 50 to 500. The number is the number of thawing and freezing cycles that concrete can withstand.
• The water resistance of concrete is marked with the letter W and a number from 2 to 12. The higher the number, the better the concrete copes with moisture pressure.
• Workability of concrete is the ability of concrete to fill the form into which it is poured. It is indicated by the letter P and a number in the range from 1 to 5. The higher the indicator, the more mobile the mixture. This property depends on the amount of water. Although it is easier to fill the form with a flowable mixture, it is important to remember that excess water reduces the strength of concrete: it will begin to delaminate and collapse.

The properties of concrete depend on the parameters of the components, mixture proportions and the mixing and pouring process.

The components of cement concrete are cement, sand, aggregate and water.

Cement is a binding material in powder form. It is made from a mixture of limestone, clay and gypsum.

Cement in Russia is produced according to the new GOST (state standard) 31108-2003. The key parameter of cement is strength. In the marking according to the old version of the standard, this indicator is indicated by a number, for example, M400. The number 400 means that the hardened cement can withstand a load of 400 kg per cm2. The marking according to the current GOST indicates the strength class. This is a figure equal to the pressure in MPa that the cement can withstand.

Table 2. Correspondence of classes and grades of cement.

The packaging also indicates additives that improve the basic qualities of cement - frost resistance, water resistance, strength, and resistance to chemical influences. If there are no additives in the cement, the marking contains the Roman numeral I, if there is - II. The letters indicate additives: P - pozzolan - an active mineral additive that gives cement resistance to corrosion, I - granulated slag, which improves strength, MK - microsilica - prevents concrete from delaminating and enhances strength, frost resistance, prevents corrosion, Z - fly ash strengthens concrete.

In private construction, cement grades M400 and M500 are used. M400 is suitable for slabs, stairs, paths, borders, finishing work. M500 is worth choosing if you are building a foundation, monolithic floors and load-bearing walls.

Sand for concrete work must be free of impurities. Particle size – 2.0-3.5 mm.

The filler can be expanded clay, gravel, crushed stone, slag, and even wood materials. For load-bearing structures, the best option would be granite crushed stone - its uneven edges adhere better to the mortar, making the concrete stronger. In addition, among all types of aggregates, granite crushed stone has the best compressive strength and the highest density. The optimal particle size for small concrete structures is 5-20 mm, for large-scale ones – 20-40 mm. It must be remembered that the particle size, or fraction, cannot be more than 0.7 of the minimum distance between the reinforcing elements.

• Disturb proportions . If you determined the proportions yourself, or the project specifies specific values ​​for each component, adhere to the specified parameters. When too much cement is put into concrete, it dries out and shrinks too much, eventually cracking and losing strength. When there is too little cement, the aggregate particles do not stick together tightly. Such concrete will crumble and deform under load.
• Use expired cement . If cement is stored beyond its expiration date, even in sealed packaging, it absorbs water from the air. The cement particles stick together, and part of the mass in the bag is no longer suitable for the concrete mixture. More of this cement will be required to achieve the required concrete strength. During three months of storage after the expiration date, the strength of cement will decrease by 20%. Over the year - by 40%. The higher the grade of cement, the faster it loses its beneficial properties.
• Mix cement with dirty water . Dirty water in this case is water that contains impurities, clay, and plant remains. Mineralized or stagnant water from the nearest body of water is also not suitable. Some chemical compounds, such as sulfates, cause corrosion of concrete. Foreign components will not allow the cement to firmly adhere to the aggregate and sand; as a result, the concrete will lose strength and subsequently begin to flake and crumble. Use clean tap water.
• Use sand or crushed stone with impurities . The reason is still the same - you will not get a homogeneous concrete mass, the concrete will turn out to be fragile.
• Use excessively wet bulk materials . The amount of water that needs to be added to the solution depends on the humidity of the sand. If you do not take into account the actual moisture content of the sand, there may be more water in the solution than necessary. Wet aggregate can be a ticking time bomb: if the water contained in the pores begins to freeze and expand in winter, the concrete will crack from the inside. This means it will begin to lose strength and collapse.

• Pour concrete of heterogeneous consistency . The mass should be completely homogeneous by the time you start pouring it. Otherwise, you will not get reliable adhesion to the reinforcement frame. Air bubbles form inside the mixture. Concrete loses strength. It is worth using small concrete mixers or mixers.

• Do not compact the concrete mixture in the formwork after pouring . In this case, the concrete may not fill the form completely and voids will remain inside it - a structure made from such a material will not be strong. To compact concrete, it is better to use construction vibrators.

For any concrete structure, the proportions of the mixture are determined individually. To approximately calculate the costs of the material, we suggest using Table 2, in which we have collected the calculation results based on the desired grade of concrete.

Table 3. Concrete mix proportions.

You can mix the components manually - in a trough with a shovel, but it is worth remembering: a homogeneous mass is much easier and more reliable in a concrete mixer.

Install it as close to the pouring site as possible: if the solution shakes in a wheelbarrow on its way to the formwork, the concrete may delaminate.

If you are building a structure in winter, mix heated water with the aggregate first. The cement goes into the mixing container last, otherwise it will set sooner.

Important: the time it takes for the cement to set after it has been mixed with water is 1-2 hours. During this time, you need to have time to place it in the mold.

Pour in layers - this makes it easier to compact the concrete into the form and lay it evenly.

Take care to keep the concrete moist after you pour it. It is better to cover the concrete with polyethylene and regularly moisten the surface with a small amount of water. This will reduce the likelihood of cracks forming in the concrete.

Plan to carry out all concrete work in the warm season, in dry weather: you will get fewer risks and surprises.

In conclusion, let us recall that even the most basic concrete structure requires design and individual calculation of the mixture. Concrete proportions are calculated values. What we recommend does not replace a full-fledged architectural and construction plan.

It is quite possible to reduce design costs to a comfortable level. Order projects in parts, or buy ready-made standard documents that were made taking into account the parameters of your area. If you try to save on this, you will have to overpay immeasurably more for excessive consumption of materials - for a grade of cement higher than necessary, for reinforcement with a safety margin. In addition, designers bear criminal liability for the quality of engineering documentation. Therefore, in the house that you build according to the project, you will sleep peacefully.

Additives for concrete

The use of additives allows you to significantly influence mixtures, concretes and mortars, giving them specific properties. GOST 24211-2008[8] offers the following classification of additives:

1. Additives that regulate the properties of concrete and mortar mixtures:
   plasticizing additives
   increase the mobility of the concrete mixture, thereby making it possible to obtain the desired consistency with less water consumption;
2. water-reducing additives
   make it possible to obtain highly mobile mixtures with low water content, therefore, with a relatively small volume of cement stone;
3. stabilizing additives
   ensure the preservation of consistency, thereby preventing the mixture from separating during laying and compaction;
4. additives that regulate the stability of
   the mixture’s mobility are in demand during the hot season, when long-term transportation of the mixture is necessary;
5. additives that increase the air (gas) content of the mixture
   or air-entraining additives increase frost resistance, water resistance and corrosion resistance, but somewhat reduce the strength of the future structure;
6. Additives that regulate the properties of concrete and mortars:
   regulating the kinetics of concrete hardening: retarders
   are used when there is a need to increase the time before the concrete mixture begins to set in case of long-term transportation;
7. accelerators
   reduce concrete hardening time;
8. increasing the strength of concrete -
   additives of this type increase the resistance of concrete to abrasion, impact and splitting;
9. reducing permeability
   - substances that increase the density of the concrete structure;
10. additives that increase the protective properties in relation to steel reinforcement
    are used to prevent corrosion during direct contact of concrete with reinforcement in reinforced concrete structures;
11. Additives that increase frost resistance
    increase the number of cycles of alternate freezing and thawing of concrete without loss of strength properties;
12. additives that increase the corrosion resistance
    of concrete in environmental conditions that cause deterioration of the properties of the material;
13. expansion
    additives are used to compensate for the shrinkage of concrete during the operation of the structure;
14. Additives that give concrete and mortars special properties:
    antifreeze
    additives, when dissolved in water, greatly lower the freezing point of the mixture, preventing it from freezing during transportation, and also prevent freezing of freshly laid concrete in the cold season;
15. water-repellent
    additives impart water-repellent properties to the pore walls of concrete, increasing the water resistance of concrete, and also prevent the occurrence of capillary effect;
16. Photocatalytic
    additives give concrete self-cleaning properties; as a result of this reaction, almost any contaminant found on the walls of any structure decomposes - dust, mold, bacteria, exhaust gas particles, etc.
17. Mineral additives for concrete:
    type I - active mineral: having astringent properties;
18. having pozzolanic activity;
19. possessing both astringent properties and pozzolanic activity.
20. type II - inert mineral.

How much ASG is needed for 1 cubic meter of concrete?

Let's continue the calculations. From the ratio of the amount of ingredients in the “buckets”, we derive the ASG values ​​in liters and kilograms. This will allow us to find out how much OPGS is needed per 1 cubic meter of concrete.

1. Let's calculate how many liters 1 serving takes in total. Let's convert the previously obtained values ​​of the mixture components into liters, and then add them up. 10 (cement) + 63 (gravel) + 5 (grout) = 78 l.
2. Let's find out how many servings fit in a cubic meter: 1000 m3:78 l = 12.82.
3. Let's calculate the volume of sand and gravel mixture in liters per 1 cubic meter: 63*12.82=807.66.
4. Let's convert liters to kg. To do this, multiply the specific density by the volume. 1650*0.80766 = 1332.63 kg.

How to properly mix the solution in a concrete mixer

As a result of calculations, we found out that the consumption of PGS per 1 m3 of concrete will be 807.66 liters (1332.63 kg).

Designation of concrete mixture

According to GOST 7473-2010[9] “Concrete mixtures. Technical conditions", the designation of the concrete mixture should consist of:

• type of concrete mixture (abbreviated designation);
• strength class;
• grades for workability,
• if necessary, frost resistance grades, water resistance grades, medium density (for lightweight concrete);
• designation of the standard.

For example, a ready-to-use concrete mixture of heavy concrete with compressive strength class B25, workability grade P3, frost resistance F200 and water resistance W6 should be designated as BST B25 P3 F200 W6 GOST 7473-2010

. In commercial practice, it is also customary to classify high-strength special concrete VS and concrete using crushed stone of fine fraction SM (the so-called “seed”) into a separate category.

Concrete protection

Waterproofing protection of concrete is divided into primary and secondary. Primary measures include measures that ensure the impermeability of the structural material of the structure. Secondary - additional coating of structural surfaces with waterproofing materials (membranes) from the side of direct exposure to an aggressive environment [10].

Primary protection measures involve the use of materials that have increased corrosion resistance in an aggressive environment, and also ensure low permeability of concrete. Primary protection measures also include issues of choosing rational geometric shapes and shapes of structures, assigning categories of crack resistance and maximum permissible crack opening width, considering the combination of loads and determining short-term crack opening, assigning the thickness of the protective layer of concrete taking into account its impermeability. Primary protection also includes the use of integral capillary materials - waterproofing with penetrating building mixtures. At the same time, the concrete structure is compacted and water resistance, frost resistance, compressive strength and corrosion resistance increase for the entire service life.

The task of secondary protection is to prevent or limit the possibility of contact between an aggressive environment and concrete. As secondary protection, dust-removing impregnations, thin-layer coatings, self-leveling floors and highly filled coatings are used. Most often, epoxy, polyurethane and polyester components are used as binders in the production of polymer compositions. The protection mechanism of a concrete base is to compact the surface layer and insulate the surface.

The problem of protecting concrete from chemical and electrical corrosion is especially acute for railway transport facilities, where stray leakage currents are combined with aggressive chemical exposure.

Warming up concrete in winter

A significant disadvantage of concrete is revealed during construction in winter, when due to low temperatures the strength of the concrete structures being erected is at risk. For this reason, there is a need for forced heating of concrete.

Basic and additional methods of heating concrete

[eleven]. Among them are:

• Warming up with wire. An affordable method that provides excellent room heating.
• Warming up with electrodes. Provides rapid heating due to the spread of the electrode network.

• plate electrodes. They are connected to the concrete mortar from the inside - they are attached to the formwork. Transfer heat directly to concrete.
• strip electrodes. Attached on both sides.
• string electrodes. Most often used in columns and attached to the central part.
• rod electrodes. They are used where it is impossible to use other electrodes.

• Concrete heating station. It is used in cases where the concrete is planned to be heated with wire. The power of the station directly affects the level of concrete heating. Controlled manually or automatically.
• Heating formwork. It is considered a more profitable and long-term solution for heating concrete than heating with wires.
• Induction method. With this choice, it is important to strictly calculate the number of turns and correlate them with the volume of metal in the structure.
• Infrared method. An effective and simple way to warm up, but quite expensive.
• Concreting in greenhouses and thermomats. A labor-intensive and expensive method that is not suitable for large rooms with columns. In such cases, it is better to protect monolithic columns or walls with canopies, stretch them over scaffolding, and install forced-type thermal generators.
• The increase in temperature affects the strength gain and timing of formwork removal; for this, in winter, it is also necessary to monitor the temperature of the concrete on the surface and inside the core. Therefore, thermal wells are made in the structure or thermocouples are installed. When dismantling the formwork, the temperature difference between the environment and the core of the concrete structure should not exceed 15 degrees.

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Concrete is an indispensable component for construction and renovation. It is obtained by mixing certain components. After hardening, the homogeneous mass is a strong monolith called “artificial stone”. It is impossible to erect a building without concrete. For this reason, certain requirements are put forward to the quality of the material. Concrete must be strong, resistant to mechanical and weather influences, and capable of maintaining its quality for a long period of time.

Table of contents:

1. What are the basic requirements for concrete quality?
2. Main components for making concrete
3. Special additives in the production of concrete
4. Types of concrete solutions
5. Tips for making your own concrete
6. Methods for mixing concrete: manual mixing and mixing with a concrete mixer
7. Proportions and composition of concrete for the foundation
8. How to make colored concrete with your own hands

What are the basic requirements for concrete quality?

In order for the concrete solution to be obtained with high technical characteristics, it is necessary to carry out the correct mixing. A high-quality solution must meet certain characteristics:

• have strength;
• be plastic;
• frost resistance;
• waterproof.

By mixing the main ingredients of cement, sand, additives and water in certain proportions, a concrete solution is obtained. Depending on the brand of cement and the purpose of the solution, concrete with different characteristics is obtained. When adding a plasticizer, the solution becomes softer. The main requirement for concrete is compressive strength. This parameter is measured in megapascals. Based on this parameter, concrete is divided into classes.

Each of the options is used for certain types of work: the higher the brand, the more professional the solution is to use.

Plasticity is a very important indicator of a solution; the higher the plasticity indicator, the more completely the structure is filled. If the plasticity of the solution is low, voids are formed in the screed or foundation - unfilled areas, which cause poor quality of the finished product. The indicator is indicated by the letter P; for complex structures and structures with a high level of use, it is recommended to use a solution with the maximum degree of plasticity.

Water resistance is directly dependent on the brand, that is, the amount of cement in the concrete solution. Frost resistance increases when plasticizers are added to the mixture. But if the quantity is calculated incorrectly, the solution will become unsuitable for work, as it will turn into a monolith even before finishing work with it.

Main components for making concrete

To prepare high-quality concrete, it is recommended to follow the recommendations of specialists.

For concrete mortar you will need: sand, cement, aggregates, various additives.

Not only the binding function, but also the strength of the concrete solution depends on the quality of cement. Cement is a special material that loses its properties if storage rules are violated. You cannot buy cement in advance - as it is stored for a long time, it loses its properties. The binding ability of the component is partially lost after just a month, and after a year the cement cannot be used. Fresh cement will also become unusable if kept damp; the product has a very high water absorption capacity.

Sand is an equally important component for making a high-quality solution. It is practically not replaced with another component. Very rarely granotsev is used instead of a stove. Before mixing, it is recommended to sift the sand to remove foreign objects. To ensure high quality concrete, it is recommended to use coarse sand without impurities. Coarse-grained material is more valuable than fine sand. It is necessary to ensure that there are no additional unnecessary impurities in it: earth, silt or clay.

The filler for concrete is most often crushed stone. The recommended material size is from five to thirty-five millimeters. Expanded clay and gravel are often used along with crushed stone. The main requirement for the filler is the roughness of the edges. It is also recommended that the aggregate be of different fractions. If necessary, foreign objects and especially large fragments should be removed.

As for additives, these can be plasticizers, construction fiber, steel fiber. These elements give the concrete solution frost resistance and water resistance. With the help of such ingredients, high solution adhesion, viscosity or plasticity is achieved. Supplements should be used only as needed and only in recommended proportions. The reinforcing component must be added only in individual cases as necessary.

Special additives in the production of concrete

To improve the quality of the concrete solution and increase its properties, additives are added. This is a common fact in modern construction. When making concrete yourself, you can use the components as needed:

• plasticizers increase the frost resistance of the material and make it more plastic, which increases the comfort of the laying;
• hydraulic seals - protect the concrete solution from the penetration of excess moisture;
• dust removers - prevent abrasion of the material and make the solution stronger;
• stimulants or hardening retarders - used to adjust the setting time of the solution;
• anti-frost additives - make it possible to carry out masonry at temperatures below zero.

You should not get carried away with additives, as in some cases there is a complex effect on concrete and is not always required. It is necessary to carefully read the instructions for supplements, as some components may conflict with each other.

Types of concrete solutions

To make the foundation, you can use not only concrete mixtures, but also types of mortar. Additives make it possible to make a home warmer, with higher energy-saving capabilities.

• Reinforced concrete is the most durable material, allowing the construction of structures of any height, but due to the reinforcement located inside, the cold passes through, a building made of reinforced concrete needs additional insulation from the outside.
• Expanded clay concrete is concrete with the addition of expanded clay. The higher the porosity of the material, the warmer the home will be, but expanded clay concrete makes the wall of the building less durable and unable to withstand high loads.
• Slag concrete - slag is used, the building is warm and vapor-permeable, but has the same disadvantages as expanded clay concrete: it is not able to withstand very heavy loads.
• Sawdust concrete - pine sawdust is added to the solution. The housing turns out to be environmentally friendly, warm, but not durable enough. Such a structure requires the installation of external waterproofing.
• Wood concrete - when wood chips are added to concrete. The walls are stronger than when adding sawdust, the home is warm, environmentally friendly and fireproof.
• Foam concrete is obtained when concrete is foamed due to chemical reactions. The building turns out to be very warm, with good characteristics.

Tips for making your own concrete

It is possible to make concrete on your own, but you must follow the advice and recommendations of experts:

• if the concrete was poured incorrectly, a void may form inside, this will negatively affect the quality of the product, so in this case it is recommended to use a vibrator;
• when building a strip foundation, it is necessary to select a grade of concrete from M 200 and higher;
• It is not recommended to work with concrete at low temperatures; water inside the solution can damage the structure and quality of the structure;
• When pouring a foundation at high air temperatures, it is necessary to moisten it for several days to prevent the material from cracking.

Methods for mixing concrete: manual mixing and mixing with a concrete mixer

Concrete can be mixed manually or using a special machine - a concrete mixer. Manual mixing is a complex and time-consuming process, so it is not suitable for preparing large quantities of concrete.

For manual kneading, you need to prepare tools and equipment. You will need a mixing container, preferably with low edges, a bucket, a shovel and a hoe.

Sand, crushed stone and cement are placed in the container. Dry ingredients are mixed thoroughly. The amount of ingredients depends on the brand of cement. After the dry solution is mixed, you need to add water. The liquid is added in small portions and during this, mixed with a hoe until a homogeneous consistency is obtained.

The method is quite exhausting, so it is optimal only for small doses of concrete.

Mixing with a concrete mixer is a simple and quick option for preparing concrete mortar. It is advisable to install the equipment close to the construction site, since the solution is very heavy and delivering it to its destination is not easy.

Mixing with a concrete mixer is done as follows:

• a third of the normal amount of water is poured into the kneading device;
• pour cement;
• sand is poured;
• if necessary, add plasticizers and additives;
• crushed stone is poured.

Each stage is accompanied by stirring for several minutes. In total, mixing should not take more than seven minutes, otherwise the solution will begin to set. If it is not possible to use the entire solution at once, it should be mixed with water.

The disadvantages of manual kneading are that it is a time-consuming and labor-intensive process. In addition, a hand-made solution should be used almost instantly, as processes will begin that reduce the quality of concrete. When making concrete in a concrete mixer, the solution is ready for use within forty minutes.

Proportions and composition of concrete for the foundation

Before starting work on pouring the foundation, a logical question arises: how to make the concrete consumption optimal, the material durable and of high quality. Even for the foundation, the proportions of the mixture may differ.

Any foundation mortar will contain cement, sand, gravel and water. Depending on the requirements for the foundation, the proportions for the solution look like cement, sand and gravel - 1 to 3 to 5 or 1 to 2 to 4.

The strength of the mortar depends on the brand of cement. There are such brands: M 100, M 150, M 200, M 250, M 300, M 400, M 450.

Grade 100 cement is practically not used for building foundations, only as a means for preparatory work. For single-story buildings, M 200 is used; multi-story buildings require the use of grades 300 and 350.

You can mix it in a large iron trough, on a sheet of iron with edges, or in a concrete mixer. First of all, mix the dry compounds and only then add water. The resulting homogeneous thick mixture (similar in consistency to thick sour cream) is poured into pre-prepared molds and formwork. For large volumes of work, the formwork is poured over several days, but the best option is to make the foundation in one go. In this case, the design will be of higher quality.

Most often, a strip foundation is built, so the amount of mortar is calculated as follows. Having calculated the perimeter, you need to multiply the numbers by the width and height of the formwork that will be poured.

How to make colored concrete with your own hands

Modern technologies make it possible to make concrete bright; to do this, you need to add pigments to the solution or to the still dry mixture. Color additives come in two varieties:

• natural;
• artificial.

Color and saturation depend on the chemical composition of the material. To make the color uniform and attractive, it is best to add it to a dry mixture of sand and cement. The quality of mixing directly affects color uniformity. It is worth noting that the production of colored concrete is only possible when mixed using a concrete mixer.

Every owner has to prepare a concrete solution with his own hands at least once in his life. This is not difficult to do, especially if you follow all the recommendations. If you have any questions about how to make concrete with your own hands, watch the video, which will answer the most frequently asked questions.

see also

• Cellular concrete
• Lightweight concrete
• Concrete with organic aggregates
• Gas-slag concrete
• Hydraulic concrete
• Reinforced concrete
• Fiber concrete
• Foam concrete
• Architectural concrete
• Microsilica
• Durability of concrete
• Climate chamber
• Concrete pump
• concrete mixer truck
• Self-loading concrete mixer truck
• Concrete mixing plant
• Composite reinforcement
• Concrete bridges
• Photocatalytic concrete
• Abrams cone
• Mineral additives for cements

Links

1. Kochetov V. A. Roman concrete. - M.: Stroyizdat, 1991.
2. ↑ 12
   Concrete statistics: comparison of countries in Europe, Russia and the USA
3. European Ready Mixed Concrete Industry Statistics based on the Y2007 production data Archived March 26, 2012.
4. Making concrete with your own hands, water-cement ratio, proportions
5. GOST 25192-2012 Concrete. Classification and general technical requirements, GOST dated December 27, 2012 No. 25192-2012. docs.cntd.ru. Retrieved July 5, 2020.
6. P. P. Borodavkin Grain composition of sand for preparing concrete mixture (inaccessible link)
7. Turkina I.A.
   Concrete from industrial waste // Concrete Technologies. - 2013. - No. 8 (85). — P. 42-44.
8. GOST 24211-2008 Additives for concrete and mortars. General technical conditions (with Amendment No. 1) (with Amendment), GOST dated April 29, 2010 No. 24211-2008. docs.cntd.ru. Retrieved March 8, 2018.
9. GOST 7473-2010 Concrete mixtures. Technical specifications, GOST dated May 13, 2011 No. 7473-2010. docs.cntd.ru. Retrieved July 5, 2020.
10. A. N. Klyuev, V. B. Semenov. Cement-free concrete based on alkali-containing waste from the petrochemical industry Archived on April 3, 2008.
11. Warming up concrete in winter: basic methods Archived September 3, 2014.