Advantages and disadvantages of polyurethane concrete primer

Advantages and disadvantages

Unlike grades M200, M300 and others, concrete M500 demonstrates very high strength, durability, resistance to various environments and influences. But the cost of the material is also high, therefore, before using it in construction, it is necessary to carefully study all the properties and determine the feasibility of preparing the solution.

The main advantages of concrete M500:

• High compressive strength, different types of mechanical stress - damage to the material can only be done with a special tool with diamond coating
• A high hardening rate is not a quick-drying cement, of course, but the mixture still sets quickly, even in conditions of high humidity
• Excellent indicators of resistance to moisture - due to the fact that the composition uses fine sand, which does not give a chance for water to enter the pores of the monolith: thanks to this, the structure can be operated even under water
• The composition of M500 concrete guarantees its resistance to strong winds, ultraviolet radiation, atmospheric precipitation, etc.
• Long service life - structures and objects made of material are not subject to independent deformations at all

Of the shortcomings, it is worth noting, first of all, that the M500 is very expensive and its increased characteristics are not relevant in everyday life, since they remain unclaimed. And the preparation of the solution will require considerable costs and efforts. In Moscow and the region, other regions, you can purchase a dry mixture (there is only no crushed stone in it), but special equipment is required for kneading.

Concept and historical background

The first reinforced concrete was made by a French gardener who grows exotic plants in the greenhouse of Versailles - Joseph Monier. He was selling palm seedlings with little income. Most of the proceeds had to be given to the cooper, who prepared wooden pots for future palm trees.

A ceramic vessel became a cheap option, but it is a very fragile product, and if the gardener accidentally fell, who did not notice the bag of cement on the floor, it simply broke. But this incident led him to the idea of ​​making pots from cement and sand... And here our hero suffered a fiasco - the material was easily destroyed over time, the roots of plants with great growth force. To strengthen the structure, he sewed it into a metal frame, but the product is, lost its aesthetic appearance, so the gardener covered it with another outer layer of concrete.

As a result, these pots are practical and inexpensive. After that, Joseph Monier patented his technology and was right, because the properties of such a material have become in demand in construction. Reinforced concrete began to be used everywhere for the creation of buildings and structures that were distinguished by their strength and reliability, resistance to various environmental factors.

Calculation of the composition and mixing

When calculating the future mixture, it is necessary to adhere to the recommended values ​​and requirements, since they determine the strength and reliability of the structure. Experts offer ready-made proportions that allow you to correctly calculate the ratio of all components:

When doing kneading with your own hands, you must be guided by the following instructions:

1. We prepare a container where the mixture will be kneaded.
2. We put water in the container (in the case of other types of concrete, a filler is initially placed).
3. We add cement, sand and filler to the composition, while continuing to mix the solution.
4. Then we add additional components and plasticizers, if necessary.
5. The solution is mixed until a homogeneous consistency is obtained without lumps.

By adhering to such a guide, you can make a high-quality concrete solution that will meet all the requirements and standards.

Material features

The main difference between a reinforced concrete monolith is that it is made directly at the construction site. At the same time, prefabricated products are manufactured in the factory in special forms and delivered to the site ready-made.

Monolithic reinforced concrete is produced in this way:

The configuration of the structure being erected can be any, but it directly depends on the possibilities for the installation of the formwork and the strength of the hardened concrete. It is worth considering that the internal reinforcement of the structure is responsible for the ability to withstand loads of different types and mechanical characteristics. The frame is prepared from thick reinforcement, in several rows, right before laying the concrete.

Concrete can be prepared directly at the facility or transported from the plant (this requires the use of special equipment). In the second case, the price of the solution rises significantly, but it is possible to carry out large-scale concrete pouring continuously, which significantly improves the operational characteristics of the entire reinforced concrete monolith.

Grinding methods

The concrete floor is polished in two main ways: dry and wet. The dry method is used more often, it is faster, it does not require drying time. Dry grinding is carried out with large diamond fractions, which eliminate all errors. The only drawback of the method is a huge amount of dust, which can only be dealt with by a vacuum cleaner.

The wet method is more expensive and less frequently used. Most often, a mosaic floor with marble chips is treated in this way. Grinding is carried out with powdered solid particles of various sizes or fine-grained.

Due to the difference in particles, it is possible to achieve a perfect specular shine. Lack of the process - the surface gets wet, then requires time for complete drying.

The process of pouring concrete structures

Monolithic and precast concrete are made in strict accordance with the technology

It is imperative to pay attention to each of the stages of creating a structure in order to achieve the desired parameters and properties.

Formwork construction

The creation of a monolithic reinforced concrete structure begins with the installation of formwork, which will not allow the liquid solution to spread and will support the concrete at all stages of solidification.

What are the types of formwork:

• Collapsible panel - includes several separate blocks for rigidity, can be made independently at the facility.
• Block - used for a single fill of not one, but several walls at once without overlapping with a supporting structure.
• Pneumatic - with a durable shell, air permeable, it is made for complex cavities of small volumes.
• Volume-adjustable - for the installation of monolithic ceilings, walls in high-rise buildings, is constructed with the involvement of a crane.
• Sliding - used to create high-rise buildings, installed around the perimeter, in the process of solidification of the monolith at different levels, it gradually rises up with jacks.
• Fixed - for decorative finishing.
• Tunnel - for filling two overlapping walls with mortar.

The creation of formwork during the construction of a structure is one of the simplest stages of construction.

It is important to properly strengthen the shields, check the evenness of the building level, choose sufficiently rigid and reliable materials so that the structure does not deform under the influence of the weight of the mortar.

Preparation of the solution

After the installation of the formwork, a solution is prepared, which for pouring monolithic reinforced concrete should include the following components: a part of cement of at least M350 grade, 2 parts of sifted fine sand, 3 parts of filler (crushed stone, gravel), water in sufficient quantity to obtain a solution of the desired consistency. First, all dry substances are mixed, only after thorough mixing, water is added a little at a time.

To improve the characteristics of the solution, detergents are added to it (a teaspoon of anti-fat agent on a bucket of liquid concrete will increase strength, reduce shrinkage), PVA glue (200 milliliters per bucket to improve fluidity and increase the adhesion of materials), water glass (to increase heat resistance and accelerate setting at the initial stages of pouring).

The cement mortar can be prepared in a concrete mixer on your own, or you can order the required volume and organize its continuous supply to the object.

Reinforcement and pouring

The reinforcing frame of monolithic reinforced concrete is created from steel ribbed rods of different diameters. In the formation of large elements, rods with a cross section of 15-25 millimeters are used, for ordinary walls they are taken with a cross section of up to 10 millimeters. The frame is tied with a knitting wire, lowered into the formwork. The reinforcement should stand on special clamps at a height of at least 30-50 millimeters from the concrete surface.

After the reinforcement is completed, concrete is poured: the formwork is gradually filled in by feeding liquid concrete from the gutter. Small objects are filled in at a time, large ones are divided into captures (horizontally) and tiers (vertically). First of all, the grips of one tier are filled, then the reinforced concrete structure is sequentially poured further.

After the filling is completed, the mortar is compacted with a vibrating tool. Dry the concrete by covering it with a film so that the water does not evaporate quickly and the concrete is strong. The first days, it is advisable to periodically spray it with water to exclude cracks.

Specifications

The properties of heavy concrete directly depend on the raw materials used in the mixing process and the scope of the material.

The modern classification is based on the following characteristics:

1. By class.
2. By brands of concrete.
3. According to GOST.
4. At cost.

By class

The existing ones differ in both operational characteristics and quality. According to GOST standards, a whole line of material with different classifications is distinguished. It includes solutions such as B3.5, B5, B7.5, B10, B12.5, B25, B30, B70, B90, B100, etc. GOST standards also allow the production of intermediate classes, such as 27.5.

The listed varieties are characterized by special properties that need to be paid attention to when choosing or creating a concrete solution. The main characteristics are specified in the standard.

Concrete grades

Brand identification is determined by indicators compressive strength and axial tensile strength... Depending on these properties, such brands are distinguished as:

1. M50 and M100 are characterized by low compressive strength, which does not allow them to be used for a wide range of construction works. The main area of ​​application is landscaping.
2. М150 - the brand is in demand in the production of screeds and blind areas.
3. M200 is considered the most popular material for the restoration of foundations, landings and stairs.
4. М250 and М350 are used for the construction of monolithic buildings and other concrete structures.
5. The M350 demonstrates an increased degree of strength and is used in the manufacture of airfield slabs.
6. M400 is used to create secure bank vaults, hydraulic structures and bridges.
7. М500-М600 are used in the construction of the subway.

There are also especially strong compounds with a brand up to M800, but their use is quite rare.

GOST

Each composition of heavy concrete must meet certain requirements of GOST. Any deviation from the specified rules is unacceptable.In the production of this building material, it is necessary to take into account the GOST 26633-2012 standard, which provides for the following values:

1. Frost resistance - F500.
2. Water resistant - W6-W12.
3. Shrinkage during setting is 0.15 mm per 1 m.
4. Tensile strength - Bt10-Bt40.

Price

The cost of a solution is determined by a host of factors, including the price of all components. If water, gravel and clean sand are easy to find, then buying plasticizers and other additives will require some effort and financial investment. Another price tag depends on the brand of the mixture. The production of 1 m³ of solution under the M100 brand will be 2,400 rubles.

The use of super-heavy concrete in private construction does not justify itself, which is due to the high cost of all components. The solution provides for the presence of rare elements.

Advantages and disadvantages

Monolithic reinforced concrete has certain features, which are explained both by the properties of each of the materials separately (concrete and steel reinforcement), and by the technologies for its production. The quality of the solution (proportions of the components) and the technological process largely affect the strength and.

The main advantages of monolithic reinforced concrete:

• Reduction of time and labor costs for the construction of a structure in comparison with its construction from stone or brick.
• Reducing the thickness of the walls (respectively, increasing the internal area of ​​the room).
• The ability to implement any idea when creating a project.
• High level of durability.
• Seismic resistance at the level of 8 points without destruction.
• Absence or reduction of the number of seams in the monolith, which improves the thermal insulation characteristics.
• Resistance to various chemical attack, oxidation, corrosion.
• Long service life

Among the disadvantages of monolithic reinforced concrete, it is worth mentioning such as the need to attract lifting special equipment, additional workers due to the fact that almost all stages of production are carried out at a construction site. It is worth noting such nuances as the need to build a powerful foundation due to the large weight of the monolith, the mandatory implementation of hydro and thermal insulation, the difficulty in processing concrete.

How to do it yourself

The technology for creating artificial stone includes the use of already known components. Home craftsmen use the following proportions:

• liquid glass - 250 g;
• potassium hydroxide - 200 g;
• slag and fly ash - 750 g each;
• water - 130 g.

But what kind of sand concrete is best used for floor screed can be found here from the article.

The recipe is designed for the preparation of 1 liter of concrete mixture. After performing the calculations, you can get the consumption of components to create the required amount of environmentally friendly concrete. To date, there are no scientific publications with an exact composition. When creating a concrete mixture according to this recipe, some changes in its quantitative composition may be necessary.

The video tells how make geopolymer concrete with your own hands:

All of these components can be easily purchased from the retail network. However, it should be borne in mind that the cost of ready-mixed concrete based on polymerization technology will be higher than that of a concrete mixture from Portland cement. The mixture sets very quickly. To slow down this process, tetraborate decahydrate is introduced into the formulation. Additionally, water-based resins, latexes and PVA can be added to the composition.

Cooking technology

First you need to prepare tools and containers. You will need:

• gloves, goggles, overalls, respirator and other means of protection against aggressive substances;
• mixing container;
• a mixing tool that does not react with alkalis (wooden spatula);
• scales to control the observance of proportions;
• molds for ebb (formwork).

From the article you can find out what kind of concrete can be used for the foundation of a house.

When mixing the components of geopolymer concrete, heat is generated. This must be taken into account when choosing a mixing vessel.

If there is a need to accelerate the solidification of the mixture, electrolytes can be laid in the formwork, but this is important to take into account when calculating the proportion concrete for foundation at home

KOH is pretty aggressive. On contact with the skin, and especially the mucous membranes, it causes severe burns. You need to work with him with glasses and gloves.

It is equally necessary to work with potassium metasilicate (water glass) with equal care. It also has a crystallized structure and is very hygroscopic.

Composite concrete is one of the few existing methods of slag and ash disposal. Fly ash is a waste product from the combustion of solid fuels. This component can be up to 75% in the composition of geopolymer concrete mixture. The substance has a dubious environmental record. But its use makes concrete durable and strong.

All components are mixed in a concrete mixer in the following sequence:

• pour water;
• slag and fly ash are poured;
• the components mix well;
• add polymers;
• mix the concrete until tender.

Pour the molds in a dry place. When solidified, this type of concrete forms a film. It tends to swell on contact with water. To prevent this from happening, you need to protect the filled forms from high humidity.

But if everything is done correctly, then as a result you will get the material:

• with high compressive strength;
• with low shrinkage;
• with resistance to high temperatures and acids;
• comparable to granite in impermeability.

DIY polishing

All work on concrete polishing is carried out after the floor has completely hardened. For grinding, you may need: a milling machine with elements from hard alloys, a grinder with elements with corundum / diamond dusting, a grinder, brushes with corundum dusting, a respirator and goggles for protection.

First, the surface is cleaned of old coatings, dust and dirt, then all irregularities and defects are removed. If the damage is significant, it must be machined with deep milling. The waves will not go away (for them you will need to fill the screed), there will be grooves that are removed by grinding.

Sanding removes the hardened top layer of concrete. It is the milk that prevents the composition of the sealant from getting into the concrete structure, therefore, to expose the aggregate (crushed stone, granite chips, limestone, gravel), a small layer is removed. This should be done only after at least 2-3 weeks after pouring, when the concrete is already strong and holds the aggregate.

The type of cutting segments is chosen in accordance with the grade of concrete - for M250 and above, diamond spraying is suitable, if the grade is lower, you can take corundum. But it is desirable that the grade of concrete for the floor is at least M300, otherwise it will not be possible to guarantee positive characteristics and high-quality processing.

If there is no special equipment, polishing is carried out with suitable corundum-coated metal brushes. Surfaces with protruding reinforcement parts are cut off with a grinder.

The sequence of work is the same as for professional polishing: first, the surface is cleaned from dirt and old coatings by shot blasting or milling, then cracks / potholes are removed, all expansion and shrinkage joints. Then they roughly grind with diamond discs up to 400 grit, harden the layer with impregnation, grind again with discs with a grain of more than 400 grit and finish all with segments with a sputtering grain up to 3000 grit.

Composition

The increasing demands of the construction industry have led to concrete modification. The basis of the process is the optimization of the composition of the cement paste, which increases the strength of the material.

High-strength concrete is produced using:

1. Astringent components. It is plasticized, hydrophobic or simple Portland cement.When creating a base, the following are important: the density of the cement mass (25-26%) and activity (not less than 500-600). Highly active Portland cements accelerate hardening and reduce the need for setting agents.
2. Companion placeholders. These are coarse or fine fractions of igneous rocks and artificial impurities:
   • standardized additive - microsilica - a by-product of the production of silicon and ferrosilicon;
   • pozzolanic premixes: volcanic ash, pumice, tuff;
   • fractions of clinker, expanded clay, chamotte, slag (with a calcium oxide content of less than 40%).
3. Water component. It is permissible to use tap water and from natural reservoirs with a pH of at least 4. It is forbidden to use:
   • water with a high concentration of sodium chloride, as well as other salts of sodium, calcium and magnesium;
   • swamp, sewage, domestic and industrial waste water.

Microgranules of impurities are hundreds of times less than cement ones. They change the properties of the material, filling the space between its particles, enhance adhesion and increase. The size of the granules in the specific application must comply with GOST. An inert free-flowing aggregate makes up about 80% of the weight of concrete and 70-75% of its volume.

In addition to the main components for the creation of high-strength concretes, water impurities (plasticization), thinning additives, impurities for aeration and acceleration of hardening are used.

Composition and properties of natural concrete

Formwork scheme for geopolymer blocks.

The modern development of the composition of the geopolymer concrete mixture was carried out several decades later after the introduction of the concept of “geopolymer” by Professor Davidovich. Erez Elloch, a professor at the Louisiana Institute of Technology, together with a group of scientists, announced to the world the full composition of the concrete geopolymer. These are the following natural ingredients of natural origin:

• fly ash, it is fly ash;
• liquid glass;
• slag;
• 45% KOH (potassium hydroxide);
• water.

The slag in the composition of the polymer gives the concrete mixture high strength, but does not protect against cracking during shrinkage. Therefore, it must be mixed in half with fly ash in a 1: 1 ratio, then the composition will acquire the necessary strengthening properties. In connection with the addition of slag to the composition of polymer concrete, such a composition received the second name slag-alkaline. This is due to the polymerization process that occurs during production, in which aluminum silicates react with alkali.

The industrial method for the manufacture of natural concrete consists in mixing at a low temperature all the necessary elements of it in precise proportions. This allows the monolith to acquire such physical properties as:

The final hardening of geopolymer concrete occurs after 28 days.

• anti-corrosion resistance;
• high level fire resistance (exposure up to 1316 degrees);
• resistance to compression and tension;
• low responsiveness to various acids and other effects of aggressive media;
• small level of shrinkage;
• a small amount of greenhouse gas emissions from the surface of rocks;
• low vapor permeability;
• lightness and flexibility when applying mechanical action (even with diamond wheels).

The above properties of geopolymer concrete in the course of its research were compared with other types of standard concrete materials.

This once again can convince him to apply it in any kind of construction and industry.

Benefits of geopolymer blocks.

In the manufacture of geopolymer blocks, shredded wood is used. It is strongly soaked in water and treated with an ozonizer. The processed wood is added to the concrete mixer to the concrete solution and the ready-made geopolymer mass is poured into the formwork-electrode. In such a formwork, a current acts on it through the converter for an hour.When the block hardens, becomes a uniform color, the formwork is removed from it. After complete hardening, the finished geo-concrete does not change color.

Having learned more about the useful physical and chemical properties of geopolymer, scientists at the world level continue to improve them in order to fully use them in housing, transport and industrial construction. Moreover, this environmentally friendly material is still quite cheap and can be produced from industrial waste. Which, in turn, has a positive effect on the environmental situation.

A concrete foothold for science

For the first time the concept of "geopolymer" was introduced in 1978 by professor-chemist Joseph Davidovich. Analyzing the chemical composition of the blocks from which the ancient Egyptian pyramids were built, he hypothesized that they were made of polymer concrete.

The composition of geopolymer concrete contains only natural components: ash, water, liquid glass, slag.

Explaining the theory of Professor Davidovich, one should remember what concrete is made of. The cooking technology is not difficult even for the inhabitants of ancient civilizations. Soft rock, for example, limestone, was thoroughly dried, thus freeing it from moisture. The climate of Egypt, where rainfall can fall once every five years, made it possible to dehydrate the substance naturally. The finished dry limestone powder was then poured with water and mixed. Any small stone, for example, crushed stone, could be added to the mixture. Upon final drying, the solution hardened and turned into a concrete stone block.

In this case, the scientific theory of Joseph Davidovich could fully confirm itself, since the manufacture of concrete from natural components could be made right on the pyramid itself. That is, it was possible to manually mix the powder with water in a primitive wooden formwork, erected specifically for this on the foundation of the future structure. After the concrete hardened, the formwork was removed and moved on to the next one. So, block by block, the monolith of the entire pyramid grew.

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