Production of reinforced concrete and reinforced concrete products

Reinforced concrete is a material obtained by pouring liquid concrete into a reinforced structure. Reinforced concrete concrete works in compression, and metal works in tension. The active components of concrete are cement and water; the solution may also contain fillers. The reinforcement is a frame made of welded or interconnected steel rods. Reinforced concrete is used in the production of a wide variety of structures - beams, trusses, piles, voids, pillars, etc. Moreover, each structure has its own reinforcement system, concrete formulation and manufacturing technology.

Concrete production

Properly prepared concrete is necessary for any construction work - laying a foundation, pouring a floor, installing partitions, etc.
The work is one of the most labor-intensive, and the durability and reliability of the entire structure depends on its quality. There are several ways to prepare concrete mixtures, and each specific composition is used for specific construction conditions. Concrete is divided according to: density, type of binder, purpose. Concrete is the most important material in construction, which is why it is very important that it is manufactured correctly.

Traditionally, concrete is prepared from the following components: cement, water, gravel or crushed stone, construction sand. Tools you will need: buckets, shovels, a concrete mixer, a mesh for sifting sand, a mug or watering can for water. To prepare one cubic meter of concrete you need: 200 liters of water, about 350 kg of cement, 0.6 m3 of crushed stone and 0.6 m3 of sand. If you need to prepare 100 liters, the number of components will be as follows: cement - 3 buckets (30 kg), crushed stone - 8 buckets (100 kg), sand - 5 buckets (70 kg). When preparing, 400 grade cement is most often used as a binder. When using a lower grade of cement, its quantity increases. For example, when using grade M300, the amount of cement must be increased by 30%.

To prepare concrete mortar, the water must be very clean.

To properly produce a concrete mixture, the water must be as clean as possible, without oil, impurities or other foreign elements. When making in hot weather, cold water can be used to prevent setting prematurely.

It is difficult to determine the required amount of water in advance, since the moisture content of crushed stone and sand, as well as the moisture requirement of cement, matters here. The required volume of water is determined during the mixing process itself. It is better to use coarse, clean sand for concrete mixtures, without additional inclusions of silt, clay, or organic particles. To eliminate foreign particles, it is advisable to sift the sand in advance. The strength of the sand will depend on how clean the sand is. The ingress of dirty sand leads to an increase in cement consumption (approximately 10-20% of the standard norm). It is advisable to use fine aggregate (crushed stone) (fraction 5-20 mm). Good results are obtained by using crushed or small river gravel and crushed stone from natural rocks. You can use artificial crushed stone, slag, broken brick or limestone, expanded clay, but a concrete structure using such aggregates will be less durable, the frost resistance of the concrete mixture is reduced, which is undesirable for materials located at low temperatures or in moist soil.

Modern technologies for mixing concrete

To prepare mixtures of high rigidity, concrete plants use vibrating mixers, which combine the functions of mixing and vibration. Under a certain vibration mode, the adhesion and friction forces between the particles of the solution are disrupted, and the force of gravity begins to be counteracted by the excitation pressure of the concrete mixture. It becomes suspended, its mobility increases, which promotes intense mixing.

A jet technology for mixing concrete mixture has been developed. The bottom line is that the constituent components are exposed to turbulent flows of compressed air or superheated steam, which are fed into a specially designed jet mixer.

Modern concrete plants introduce into production the technology of producing concrete mortar by mixing with simultaneous heating to 60″C. To do this, a stream of hot steam is supplied to the concrete mixer, which provides faster and more efficient mixing than when using electric heating or preheated water.

See also: Winter concreting

Mixing methods

First you need to decide on the required volumes. Concrete is prepared in several ways. If a large volume of concrete mixture is required, you need to use a concrete mixer, but medium and small volumes can be mixed by hand.

The technology for preparing concrete is as follows: first, mix the dry ingredients: cement, crushed stone, sand, mix thoroughly until a homogeneous consistency is obtained, then water is added in small portions.

If you need a lot of mortar for work, then you can use a stationary concrete mixer to make it.

The mass of concrete mortar should be similar to thick sour cream and should not be too fluid. It must be kneaded at a positive temperature. The readiness and correctness of concrete preparation can be checked as follows: squeeze a little concrete in the palm of your hand, and it should take some shape with the release of a small amount of liquid. During the concrete hardening period, which takes about 10 days, it is important to prevent the concrete from freezing, since the appearance of ice can cause its fragile structure to collapse. Excess cement can cause concrete to crack during shrinkage. It is advisable to use the prepared concrete mixture within several hours after mixing. Manual method of preparing concrete. Take two buckets: one for cement (it must be clean and dry), the other for sand and aggregate (crushed stone). It is recommended to work with two shovels. The components must be measured as accurately as possible, leveling them along the edge of the bucket. When filling containers with cement or sand, compact the loose materials by tapping the side of the bucket with a shovel.

Making concrete requires a lot of effort as the ingredients of the concrete mixture need to be mixed very thoroughly.

Crushed stone and sand are mixed on a flat and hard surface, then a depression is made in the resulting mound, cement is added to it and the mixture is mixed until a uniform color is obtained. Next, make a hole in the pile of dry materials again and add water from a watering can or mug into it. The mixture is poured into the well with water from the edges until it is absorbed, then the components are mixed with chopping movements of a shovel. Then water is added and the concrete is raised again from the bottom of the pile until a homogeneous mass is formed. You can check the readiness of the concrete: use the back of the shovel to make a row of ribs, moving the tool in your direction.

The concrete should have a flat and smooth surface, and its ridges should not fall off and remain the same shape.

Machine cooking method

This method uses a concrete mixer, which is installed on a flat surface. Before turning on, you need to make sure that the drum is in a vertical position. Using a bucket, half the crushed stone is loaded into the drum and water is poured. Cement, sand and coarse aggregate are added in small parts in turn. The mixture must be stirred for several minutes. Next, to check readiness, tilt the drum and pour a small amount of concrete mixture into a wheelbarrow. If the mixture is not yet ready, it is loaded back into the drum and mixing continues.

Concrete and reinforced concrete in industry: status and development paths

In the Soviet Union in the sixties of the 20th century, a program of mass housing construction was launched and successfully completed. To implement it, a gigantic building materials industry was created; almost the majority of reinforced concrete and DSK factories were built in those years. More than 50 years have passed since the program was implemented. However, the industry for the production of concrete and reinforced concrete - the basis of the construction industry, which has no incentive to improve, has changed little over the years - basically the same flow-aggregate technology, mobile mixtures, aggregates “from the street”, reinforcement no higher than class IV, insufficient use of chemical additives, unreasonably high energy consumption, etc.

It is no less difficult with personnel. Employees of enterprises, who were brought up on fifty-year-old technologies and practically did not improve their skills (in the Soviet Union there was no mandatory system of retraining and certification of personnel), not only cannot cope with new technologies, but, as a rule, hinder their implementation in every possible way.

Essentially, it is necessary to reinvent the concrete and reinforced concrete industry. And you should start with aggregates and cement. What needs to be done to bring concrete production to the level of the world's leading manufacturers.

In the same sixties, despite declarations about the need to reduce construction costs and strict regulation of cement consumption, the issue of preparing aggregates for concrete was not even raised at the state level, which slowed down the development of the country's construction industry for many years. While the global building materials industry worked on washed, dry, fractionated aggregates, the domestic industry used unprepared, contaminated aggregates and cements with unstable characteristics. Thus, one of the primary tasks facing the Russian construction industry is to obtain high-quality aggregates and cement, which will reduce the cost of building structures by 10-15%.

Let's specify the problem.

Crushed stone.

To a certain extent, the preparation of crushed stone is ensured by the technology of its production by crushing, sieving, re-crushing, etc.

The main tasks in the technology of production and use of crushed stone:

• organize separate storage of different fractions;
• prevent clogging of crushed stone with foreign impurities during transportation and storage
• remove dust fractions during crushed stone production by washing or air classification;
• make maximum use of such a valuable product as crushing waste, which is currently actually waste disposed of in landfills;
• increase the yield of cube-shaped crushed stone after crushing;
• ensure the production of 50-8 mm fractions for use in prefabricated and monolithic foundations and lightly reinforced structures.

Let us note that the problems listed are not a matter of significant investment in the industry, but rather the organization of its work.

Sand

Preparing sand for concrete requires more effort and investment than preparing crushed stone, primarily due to the degree of neglect of the problem.

During the Soviet Union, despite numerous speeches by scientists and practitioners about the need to prepare sand for concrete and constant calls for saving cement, practically no measures were taken to prepare sand.

Departmental policies (the Ministry of River Fleet was mainly responsible for the extraction and supply of sand) and costly economics led to the collapse of the industry.

National standards practically did not prohibit the use of low-quality sands in concrete, which not only increased the cost of construction, but also reduced the durability of buildings and structures.

Research by domestic and foreign scientists has shown that the consumption of cement in concrete mainly depends on sand as the main surface carrier, the granulometry of which determines the voidness of the filler. And therefore, it is natural sand that must first be processed. The use of washed fractionated sand allows savings of 15-20% in cement consumption.

You have to pay twice: for random granulometry, contaminants and for the instability of the technological process caused by differences in grain composition and moisture content in neighboring batches.

Understanding the significance of the problem, outstanding domestic scientists dealt with it: B. G. Skramtaev, A. E. Sheikin, Yu.M. Bazhenov, I.M. Frenkel, S.M. Itskovich. However, even approaches to solving the problem have not been formulated. And only with the advent of the method of planning a multifactorial experiment and a computer, its solution became possible.

The author has developed a calculation apparatus (formulas, nomograms, simplex diagrams) that allows one to determine the optimal granulometric composition of sand for a particular enterprise. The calculation apparatus establishes the dependence of cement consumption on the sand granulometry, and the final result depends on the brand (class) of concrete and the hardness and mobility of the concrete mixture.

Figure 1 shows a scheme for the preparation of washed fractionated sand, which provides for the simultaneous waste-free production of three types of sand: for heavy and sandy concrete, for mortars and finishing materials, for foamed aerated concrete.

Figure 1. Scheme for preparing sand for concrete

Cement.

The situation with the production and quality of cement should also be considered unsatisfactory:

— By the amount of cement produced. A number of cement factories remained on the territory of the CIS country; at the remaining ones, the long-term lack of capital investments in the industry has led to the fact that their equipment is extremely worn out. The author’s expert assessment of the degree of wear and tear of the final equipment is 60-70%.

The annual volume of cement production in Russia is about 50 million tons, which only satisfies 60% of construction needs. To achieve the average European level of housing construction of 1 m 2 / year per person, the volume of cement production must be increased three times. It is impossible to do without the construction of new and reconstruction of existing factories.

- According to the quality of cement. Fewer and fewer pure clinker cements with guaranteed characteristics are produced and more and more cements with additives are produced, and the type of additive is not even reflected in the cement passport. The shortage of cement and the lack of reliable express methods for determining its activity leads to the fact that users are forced to “take what they give” and, under the current situation, cannot even make a complaint to the manufacturing plant. Since the additives themselves and their grinding are much cheaper than clinker and clinker grinding, cement is saturated with additives, and in most cases its activity according to the passport does not correspond to reality. The question of supplying factories producing concrete and reinforced concrete with cement clinker is so unprofitable for cement producers that it is not even raised, although this event would allow large concrete producers to grind cement at the enterprise and obtain freshly ground cement, the activity of which would correspond to the range of products produced, and also produce mass grade concrete using low activity cements.

— At the cost of cement. The monopolization of the industry and the growing shortage of cement led to a constant increase in its cost, which in market conditions cannot be restrained by administrative measures. Thus, since 2001, cement prices have increased more than fourfold.

There are also objective factors for the increase in the cost of cement, which in Russia at the vast majority of enterprises is produced using the outdated “wet” method, which requires significant energy consumption. An increase in energy costs automatically leads to an increase in the cost of cement.

It is obvious that the cement production industry needs, on the one hand, reconstruction, and on the other, the construction of new cement plants. The funds required for the construction of a cement plant with a capacity of 1 million tons per year are about 100 million dollars. The payback period is 7-8 years. This is quite serious money for a domestic investor, despite the fact that banks are reluctant to lend to such projects. Loans for construction, food industry, and retail trade are much more effective due to quick payback.

Preparation of concrete mixture

Concrete is a conglomerate material, the homogeneity of which, first of all, depends on the quality of mixing of the ingredients included in the mixture. The quality of mixing depends on the type of mixer, mixing time, type and quantity of mixed materials, the order of their introduction into the mixer, etc.

The influence of each of these factors has been quite well studied, but is completely ignored by practitioners.

Until now, the use of forced mixing concrete mixers (vertical shaft - horizontal blades) is considered a guarantee of high-quality mixing of any concrete mixtures. However, if such mixers, with the correct order of introducing ingredients into the concrete mixer, give satisfactory results for mixtures, the workability of which is assessed by a cone draft of more than 5 cm, then with an increase in the rigidity and “fine-grainedness” of the mixtures, the homogeneity of mixing decreases.

Assessing the quality of mixing is complicated by the method recommended by the standard, which evaluates not the “quality” of mixing, but its “uniformity,” for example, a concrete mixture that is equally bad, but uniformly mixed throughout the entire volume, satisfies the requirements of the standard.

The massive transition of the building materials industry to the production of products from fine-grained concrete and the use of hard and especially hard mixtures in new, including imported technologies, has shown the insufficient efficiency of existing concrete mixing equipment.

It has been established that in rigid mixtures, and especially in fine-grained rigid mixtures, mixing occurs in macrovolumes, while mixing within microvolumes is insufficient.

In foreign practice in the production of equipment for the preparation of such concrete, mixers are equipped with activators that additionally mix the mixture in microvolumes. High-speed mixer-activators are placed in such a way that the entire volume of the batch is sequentially exposed to their action. Increasing the homogeneity of mixtures significantly (up to 7%) increases the strength of concrete.

The lack of serial production of such units in domestic practice makes it advisable to implement a different mixing scheme, much simpler to implement and almost as effective.

We are talking about mixers that perform mixing in counter flows.

The domestic industry produces a twin-shaft concrete mixer SB-163 (1500/1000), in which the quality of mixing is close to the quality of mixing in mixers with activators (Figure 2).

Fig 2. Diagram of operation of a twin-shaft mixer

Thus, the implementation of a set of measures, including the preparation of aggregates, the supply of high-quality cement and chemical additives, the use of the best examples of domestic mixing and dosing equipment, automation of the technological process, including adjustment of the batch according to water consumption with feedback algorithms, the use of optimal schemes for managing materials in

mixer - all this allows you to achieve the quality of concrete mixtures close to the best

samples obtained in foreign practice.

Here is a list of the main tasks that should be solved to bring the concrete industry into line with its condition abroad.

Technologies and equipment for the production of building materials

The main technology of the sixties was (and remains to this day) flow-aggregate, where at each of the technological stages operations are carried out with molds and

using crane operations. The absence of molds significantly simplifies, reduces the cost and speeds up the technological process, so modern technologies are, first of all, formless molding technologies: vibration pressing for the production of small-piece, mainly unreinforced products and continuous molding of molded products on long stands.

Both of these technologies are widely covered in the technical literature, and their assessments are practically established. Consumers have decided on the most promising equipment options, in particular, for use in Russian conditions.

Essentially, the main direction of development of these technologies is their modernization in relation to expanding the range of manufactured structures.

In the future, these technologies may make it possible to produce the entire range of products for housing and road construction (for low-rise construction this has already been done by the author), but the movement must be mutual: not only change the technological process in relation to the structural form of the products, but also design the structure in relation to the capabilities of the technology. Promising for production are small-piece products made by vibrocompression: thermoblock - load-bearing and heat-insulating wall stone, the cheapest wall material in Russia; tray cement-sand tiles are a very promising roofing material (Figure 3); side stone with material consumption reduced by 35%; slabs for covering tram tracks - one standard size without reinforcement and hinges in the inter-rail space, between tracks and on the side of the road. A square meter of coating made from these slabs is 40% cheaper than standard ones.

Reinforced concrete structures that are promising for production

on continuous molding lines: floor slabs, beams, crossbars, piles (Fig. 4.) - all this is already produced, as well as road slabs, power line supports, wall panels, sheet piling.

Fig. 3. Vibropress VCh-2 for the production of tray tiles

Figure 4. Continuous molding line for sand concrete piles

Design of concrete compositions

This is one of the most difficult and important tasks in the development of a technological process. What is the asking price? What is the excess consumption of cement compared to the optimal composition by 20 kg/m 3? A vat concrete mixer, mixing concrete with OK = 5-6 cm, has an average daily cycle of 3 minutes, or 300 batches during 2-shift work, or 6 tons of cement costing 30 thousand rubles. per day or 7.5 million rubles. in year. Very serious money. And if there are two concrete mixers, as is usually the case in factories, the savings are 40 kg/m 3 (which is quite realistic). All this means that this stage of work must be carried out very carefully.

In prefabricated reinforced concrete factories, the design of compositions is usually carried out by employees of the factory laboratory interested in designing concrete compositions that are guaranteed to provide the required characteristics regardless of the type of cement, aggregates, etc., that is, uneconomical. In Soviet times, an obstacle to this path was the requirements of the norms on the maximum possible consumption of cement, and the norms were quite strict and controlled by supervisory authorities. Now the system is collapsed, there is no control, and in conditions of private property there should not be any. But there is also no market that should stimulate a reduction in the cost of concrete.

There are objective reasons for using suboptimal formulations. One of them, the personnel problem, has already been mentioned above. The second is more complex and is determined by the composition design methodology.

This issue was dealt with by outstanding scientists in Russia - Skramtaev, Soroker, Kayser, Sizov, Bazhenov. However, it is very difficult to use the composition design methods they proposed. The methods contain a large number of empirical formulas and graphs that depend on poorly defined characteristics. Thus, the coefficient of expansion of coarse aggregate grains is set depending on the workability of the concrete mixture (with different graphs for flexible and rigid mixtures), the amount and normal density of cement paste, and sand coarseness, that is, with a very high uncertainty.

Yes, it cannot be any other way: with four unknowns - the consumption of cement, crushed stone, sand, water - there are two and a half dependencies: the equation of absolute volumes, the Bolomey equation or the law of the W/C ratio, and the dependence of “constancy of water content” proposed by MacMillan, operating within a limited range of cement consumption.

Moreover, it is impossible to determine whether the result obtained as a result of composition design is optimal, or whether an even better one can be obtained.

Essentially, the proposed methods are of little use to plant personnel.

In our opinion, the way composition is designed must be fundamentally changed. Indeed, the design of the composition in all the methods offered here and abroad begins with the fact that we, as if for the first time, select the composition. In reality, thousands and thousands of compositions have been selected, and many of these selections have been published. Among these many, you can find the one that is as close as possible to the given one, that is, it was selected to produce concrete of the same grade, with the same workability, on the same cements, etc. The point is to enable the performer, based on the processing data of already carried out selections, to establish a composition that is as close as possible to the specified one.

To process data on published compositions, we can use a tool that neither Skramtaev nor Sizov had - a computer and the method of planning a multifactorial experiment. And this work was carried out by the author for sand concrete.

Now, using the obtained formulas and graphs, the preliminary composition of concrete can be established within 10 minutes. After this, using the proposed method, test batches are made to clarify the workability of the mixture and samples are made to obtain the K=G(C/W) relationship. This dependence is used to determine the composition that is as close as possible to the optimal one. All other data, depending on the properties of aggregates, cement, etc., are automatically taken into account by the proposed (patented) method, where samples are manufactured from specified materials and in accordance with the requirements of the manufacturing technology of the structure for which the composition is selected.

Heat and humidity treatment

In vibratory pressing technology, 20 concrete wall stones are produced in 20 seconds or less. Thus, the manufacturing time of the product is one second. After immediate stripping, the stones are sent to the TVO chamber, where they undergo heat treatment for 12-14 hours. An obvious anachronism.

These HPT modes and 70% tempering strength are a legacy of flow-aggregate technology and the use of concrete mixtures with high mobility. Where did this 70% come from? It was assumed that immediately after production the product should be sent to the construction site and installed in operation. And why? Why not remove the wall stone from the molding pallet at 20% strength (this is enough for transport operations and packaging), reload it onto a transport pallet and send it to ripen in the finished product warehouse? This is a matter of organizing the technological process. Twenty percent strength when working with “hot” aggregates and heated water is achieved in the workshop after 2-3 hours at room temperature - this is the period of structure formation of the rigid concrete mixture - a period of intensive strength gain during the initial period of hardening.

Thus, after 2-3 hours you can release the molding tray and return it to the molding station.

Similar proposals can be made for other formless molding technologies.

Summing up the disappointing results of assessing the state of the concrete and reinforced concrete industry, it is necessary to answer a much more important question: will the reorganization of the industry allow us to solve the main task set for it: to organize mass housing construction under the program “Affordable and comfortable housing for Russian citizens.”

Let's compare the needs of the population with the real possibilities of the construction industry. Today, about 40 million square meters of housing are built in Russia annually, and if construction continues at this rate, it will take more than 100 years to complete the program—for several generations of Russians, owning their own housing will remain a pipe dream.

And no matter what you do with mortgages and no matter how you increase the income of the population (another pipe dream), in Russia there is no construction industry capable of solving this problem. It must be created anew, and it must be a different industry, mainly low-rise housing construction, as is done all over the world.

How to create it, given the obvious reluctance of the state to change anything in the existing construction practice? And in general, can anything be done to build affordable and high-quality housing? Without a doubt!

We draw conclusions from a similar situation: at the beginning of the 2000s, in the production of cement, primarily due to a shortage of capacity, prices for it increased sixfold. And then at the state level it was decided to reduce duties when construction companies purchase cement from Turkey. As a result, prices for domestic producers fell significantly. Why not do the same with housing construction at the first stage? Persuasion, appeals, prohibitions are useless - the market can only be influenced by market methods. If you don’t want to build it yourself (the author proposed the “Thermoblock” construction system [1,3], where the construction cost (sale price) is 13 thousand rubles/m2), there are offers from Chinese companies: turnkey low-rise housing at a price 300 $/m2 (in both cases without land and connection to networks).

Land is a national treasure and belongs to Russian citizens by birthright. Infrastructure and networks around the world are the responsibility of the welfare state.

By the way, about prices. Russia ranks 123rd among 127 countries surveyed by England in terms of the ratio of average annual income of citizens to the cost of m2 of economy class housing. The average Russian needs to save for housing for 26.1 years. Behind us is only Belarus 28.1; Montenegro 30.2; Pakistan 40.6; Kingdom of Morocco 67.5 years.

The experience of solving the housing problem in a number of countries - America (the famous Levittowns), pre-war Germany, China - has shown the possibility of implementing a program for the construction of affordable housing, including for low-income segments of the population.

Author: K.I. Lvovich, Doctor of Technical Sciences, Professor:

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Bibliography

1. K. I. Lvovich. Thermoblock. System for the construction of affordable housing // Concrete goods and structures, No. 1, 2017.
2. K. I. Lvovich. Preparation of sand for concrete // Concrete products and structures, No. 2, 2022.
3. K. I. Lvovich. Sand concrete is a building material in Russia // Concrete products and structures, No. 3, 2022.

Seal

Compaction of the concrete mixture is usually carried out using vibration.

Proper concrete technology implies a compaction process. A sign of good concrete is a dense structure. Without compaction, concrete cannot achieve the properties of rigid concrete. To obtain high-quality concrete, it is important to choose a compaction method. The effective and most popular method of compacting monolithic concrete is vibration. It reduces the adhesion between the grains of the concrete mixture, and it acquires the properties of a viscous heavy liquid. At the end of the vibration, the strength of the structure is restored.

Under the influence of vibration, the concrete mixture liquefies, acquiring increased fluidity and mobility. In this form, it better fills the formwork and is distributed in it, including the space between the reinforcing bars. When vibration is used, stronger working seams and better concrete surfaces are obtained, good adhesion of the new layer of concrete to the previously laid reinforcement. Vibrators should not be used to move concrete mixture over long distances in the horizontal direction. It is necessary to unload the concrete mixture as close as possible to the place where it is laid, level it in layers and then vibrate. To ensure a smooth surface and reduce the formation of pores on surfaces adjacent to the formwork, the concrete mixture is bayoneted or compacted before vibrating.

Technology for the production of concrete mixtures

The modern version of the technology for using cement-based building mixtures dates back to 1824, when the British builder D. Aspdin took the first patent for the production of Portland cement. The name of the material includes the town of Portland, which is distinguished by its picturesque terrain and gray rocky mountains, so similar in color to the new building material. Since that time, cement began to spread widely throughout Europe and the world, constantly gaining popularity and conquering markets.

Domestic concrete mixtures were produced in accordance with GOST 25192. The regulatory document lists various classes, chemical and physical parameters, and grades.

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Types of vibrators

Vibrators for compacting concrete mixture: a – vibrator with a flexible shaft; b – vibrating mace; c – packet vibrator; g – surface vibrator; d – vibrator rearrangement diagram.

There are 3 types of vibrators used in construction: external, surface and internal (deep). Immersed in the concrete mixture, the working part of the internal vibrators transmits vibrations to it through the body. Surface vibrators transmit vibrations through the work platform and are installed on the concrete mixture to be compacted. External vibrators transmit vibrations through the working platform; they are fixed to the formwork with a vice or other devices. The use of one or another type of vibrator depends on the shape and size of the structure being concreted, its reinforcement and the required intensity of concreting. Internal vibrators with a flexible shaft are used in densely reinforced structures.

Internal mace-type vibrators are used for compaction intended for massive structures. Surface vibrators are used when concreting floors and thin slabs; they compact only the top layers of concrete. External vibrators are used to compact concrete mixtures in densely reinforced thin-walled structures: beams, columns.

Diagram of a deep vibrator with a flexible shaft: 1 - platform; 2 – electric motor; 3 — cam clutch; 4 - flexible shaft; 5 — vibrating tip; 6 — body; 7 - track; 8 — slider; 9 – coupling; 10 – spindle.

The vibration method can be used effectively for moderately plastic concrete mixtures (mobility 6-8 cm). If mixtures are more fluid, separation occurs during vibration. When using surface vibrators, compaction is carried out within 20-60 s, deep - 20-40 s, external - 50-90 s. The vibration time of rigid concrete mixtures must be no less than the stiffness index of the mixture. Visually, the duration of vibration can be determined by the following signs: the acquisition of a homogeneous appearance of the concrete mixture, the cessation of its settling, the horizontality of the surface, the appearance of laitance on the surface of the mixture.

Conveyor lines

Conveyor production is an improved type of flow-aggregate production. With it, forms are moved from one post to another by special vehicles in a forced rhythm. The process of manufacturing a reinforced concrete product is divided into a number of technological operations, one or more of which are performed at a specific point. This determines the same or multiple distances between posts and the same sizes of units.

Conveyor lines are divided:

1. by the nature of the work - on a line of periodic and continuous action;
2. according to the method of transportation - with forms moving on rails or rollers; with forms formed by a continuous steel strip or composed of a number of elements and side equipment;
3. according to the location of the thermal units - parallel to the conveyor in a vertical or horizontal plane; in the alignment of the molding part of the conveyor.

The number of posts on conveyor lines is 6...15; work rhythm 8…30 min; conveyor speed ranges from 10 to 60 m/h.

table 2

Duration of the rhythm of conveyor and flow-aggregate technological lines

Note. The numerator contains the cycle duration values ​​for the production line, the denominator - for conveyor lines

The conveyor line for the production of external wall panels is shown in Fig. 3.

Depending on the layout and composition, the equipment complex can be located in construction spans 18 or 24 m wide. Technological stations for preparing molds, molding and finishing products are located on the floor of the workshop. The heat treatment chambers are underground, tunnel type, single-tier. Two chambers with a capacity of ten molds are intended for heating and isothermal holding of products during heat treatment, and the third (with a capacity of five molds) is for cooling.

The following equipment is installed on the first branch of the conveyor: lift SMZh-789-01; device for opening and closing sides SMZH-793; jib crane SMZH-23B; tilter SMZH-493A; transfer device 2784/124; concrete paver SMZh-787; vibration platform SMZh-773; lifting rails SMZh-806 for lowering the mold onto the vibrating platform; conveyor drive SMZh-790; transfer trolley SMZh-444-02.

The following equipment is installed on the second branch of the conveyor: concrete paver SMZh-787; lifting rails SMZh-806; vibrating platform SMZH773 for compacting the solution layer; drive SMZh-790; finishing machine SMZh-461; lift SMZh-789.

Rice. 3. Equipment complex 7981/1 of the conveyor line for the production of external wall panels : 1 - transfer cart SMZh-444-02; 2 — lifting rails SMZh-806; 3, 19 — vibrating platforms SMZh-773; 4 — concrete paver SMZh-787; 5 — pallet SMZh-805; 6, 18 — pumping unit SMZh-3003V; 7 — finishing machine SMZh-461; 8 — lift SMZh-789; 9 — shutter SMZh-791; 10 — lift SMZh-789-01; 11, 15 — device for opening and closing the sides SMZH-793; 12 — tilter SMZh-439A; 13 — console crane; 14 — transfer device 2784/124; 16 — clamps SMZh-788; 17 - reserve space for the finishing and packaging line

The following types of surface finishing of products are produced on the molding line: colored concrete in three colors; relief (using matrices); ceramic or glass tiles; exposing the decorative filler. On the finishing line, painting with water-based paints and finishing with decorative chips are carried out.

A description of technological operations at the posts is given in Table. 3.

Table 3

Description of technological operations at posts

Vibration technology

Deep vibrators should be located at a distance of 50 cm from each other.

The most effective are internal vibrators. They vibrate concrete intended for beams, foundations, walls, columns. When laying a new layer, the vibrator is moved from one position to another. When working with internal vibrators, the maximum thickness of the compacted layer is taken to be no more than 1.25 times their length. It is necessary that the vibrator goes 5-10 cm deeper into the previously laid layer to work out the joint between the layers and for better connection of the layers. The vibrator must be immersed below the front surface of the newly laid concrete. Internal vibrators are equipped with vibrating elements immersed in the concrete mixture. They must be immersed in a vertical position at a distance of 50 cm from one another.

You should not use the vibrator in one place for too long.

The vibration zones from each dive should overlap each other slightly. You cannot vibrate at one point for too long, as this can lead to separation of the concrete mixture. If a concrete mixture that is too plastic is used, prolonged vibration should be avoided. But it is necessary to strive to ensure that there are no unvibrated areas left. The immersion of coarse aggregate particles into the solution and the release of the solution along the formwork indicates the possible end of vibration. Delaying the start of vibration is safe until the mixture can liquefy during vibration and the vibrator does not leave depressions in it. If the reinforcement is rigidly fixed and cannot move, the vibrator should not touch it.

The deep vibrator must not come into contact with the formwork, otherwise it will damage it.

Internal vibrators should not come into contact with the formwork, as they will damage its surface, which will affect the quality of the concrete surface. Using internal vibrators, monolithic concrete is compacted. When laying concrete, each layer is compacted by vibration. During this process, the working tip of a switched-on hand-held vibrator is placed into the concrete mixture at an angle of 30-35° so that the end of its working part passes through the interface between the old and new layers of concrete by 5-10 cm. Vibration causes compaction of the concrete mixture, displacement of air and sedimentation of grains seal. Due to this, the interface between the layers disappears in the concrete mixture. During the compaction process, the working tip of the vibrator is quickly placed to the required depth and carefully removed. During this, the surface of the concrete should be closed. The vibrator impact zones must overlap by at least 10 cm.

Equipment for concrete production in small businesses Mobile and stationary mini-plants

The production of building concrete in mobile mini-plants is equipped with automatic equipment, which allows the production of a finished product of impeccable quality. A stationary small plant for the production of concrete mixtures can produce up to 60 m³ per hour.

To purchase equipment for concrete production, a small enterprise will have to count on an amount exceeding 430,000 rubles. To purchase an automated production line, you need to count on a capital of 1.6 million rubles. Mobile lines (local) can be moved from one construction site to another, which is quite convenient for some developers. To successfully create your own small production, you need to choose how much productivity is needed.

Mobile mini concrete production plants are cheaper and suitable for small businesses

Investing in automated equipment for the production of concrete from cement can bring in about 1 million rubles monthly in the future. The advantages of such a business idea include the need to use minimal units of labor. To ensure full service of the ready-mixed concrete production process, it is enough to hire three specialists. Concrete production, manufacturing technology, methods and recipes for preparing cement mortars do not require special scientific knowledge and special skills, so the cost of working staff can be significantly reduced. These calculations apply to stationary and mobile concrete mini-plants.

To transport the mixture, you will need to purchase a concrete mixer truck. The cost of this equipment, for example, based on a KAMAZ truck, varies starting from 2.8 million rubles. This will also allow equipment to be transported using a trailer body.

Vibrating in other ways

External vibrators are used for concreting densely reinforced walls up to 30 cm thick and columns with sides up to 60 cm. External vibrators are mounted on the outside of the formwork, and vibrations of the concrete mixture are transmitted through it. When concreting flat structures - floors, floor slabs, roads, etc., surface vibrators are used. It is necessary to vibrate these devices correctly. They are installed on the surface to be compacted and transmit vibrations through the working platform. The surface vibrator can be attached to the formwork or moved across the surface of the concrete mixture.

Using surface vibrators, the mixture is compacted in continuous strips, each subsequent one must overlap the previous one by 10-20 cm. With single reinforcement, the thickness of the compacted layer is taken to be up to 250 mm, with double reinforcement – ​​no more than 120 mm. The layer thickness in unreinforced structures can be no more than 40 cm. If the concrete mixture is sufficiently compacted by vibration, then:

• air bubbles disappear on the surface and cement laitance with fine-grained sand appears;
• the concrete surface closes quickly after removing the vibrator;
• the concrete mixture stops settling.

If, after removing the tip of the vibrator, the hole is not filled with concrete mixture, this means that the duration of vibration was not sufficient, the consistency of the concrete was too thick, or the concrete had begun to set. Under no circumstances should you distribute the mixture in the formwork using the vibrator tip, or rest the tip on the reinforcement and formwork fastening elements. If deformation or displacement of the formwork is detected, concreting must be stopped and the formwork must be corrected before the concrete begins to set.

Prompt delivery of concrete is a guarantee of its high quality

To maintain the mobility and uniform consistency of the concrete solution in order to prevent a decrease in its quality, it is necessary to ensure its prompt delivery to consumers. During long-term transportation, cement hydration occurs. Some of the water evaporates, some is absorbed by the aggregates, as a result of which the concrete solution thickens and its mobility decreases.

In factory conditions, belt conveyors, self-propelled carts, electric vehicles or concrete distributors are used to transport concrete mixtures. Concrete solutions of high mobility are transported through pipelines, the operation of which is ensured by powerful pneumatic installations.

For construction sites where concreting is being carried out, concrete delivery is the optimal solution. The composition is delivered by truck concrete mixers, where it is directly mixed for a certain time before arrival. Factory-made concrete solutions are characterized by high technical and economic indicators; they are produced on mechanized or automated lines, which ensure high quality and low cost of the finished composition. Each batch of concrete mixture is supplied with a quality certificate and a passport, which indicates the class and composition of the concrete.