Electric heating of concrete in winter: SNIP heating

Concrete is a very popular building material today, for the production of which components such as cement, water, aggregate and water are used. But it’s one thing when you pour concrete in the summer, because the warm season has a beneficial effect on the process of gaining strength. What happens in winter? In severe frosts, the development of strength characteristics stops, and this is extremely undesirable. In this case, it is necessary to apply a number of measures that will allow the concrete to warm up. To do this, you need to know all the features of the technological map of concrete for the winter period and the current methods of heating.

Caring for concrete according to current codes of practice

Curing and maintenance of concrete must be carried out in strict accordance with clauses 5.4.1 - clause 5.4.3 of the current SP 70.13330.2012 Load-bearing and enclosing structures.
Updated edition of SNiP 3.03.01-87 5.4.1 Open surfaces of freshly laid concrete immediately after finishing concreting (including during breaks in laying) should be reliably protected from water evaporation. Freshly laid concrete must also be protected from precipitation. Protection of exposed concrete surfaces must be ensured for a period that ensures that concrete acquires a strength of at least 70%, and then the temperature and humidity conditions must be maintained to create conditions that ensure an increase in its strength.

5.4.2 In concrete during the hardening process, the design temperature and humidity conditions should be maintained. If necessary, to create conditions that ensure an increase in concrete strength and a reduction in shrinkage deformations, special protective measures should be used.

Measures for the care of concrete (procedure, timing and control), the procedure and timing for stripping structures should be established in the technological regulations and PPR developed for a specific building and structure.

In the technological process of heating concrete in monolithic structures, measures must be taken to reduce temperature differences and mutual movements between the formwork form and concrete.

In massive monolithic structures, measures should be taken to reduce the influence of temperature and humidity stress fields associated with exotherm during concrete hardening on the operation of structures.

5.4.3 The movement of people along concreted structures and the installation of formwork on overlying structures is allowed after the concrete reaches a strength of at least 2.5 MPa.

Source

Technological map and methods of heating concrete

Warm up with a welding machine

This heating method involves the use of the following materials:

• pieces of reinforcement;
• incandescent lamps and a thermometer for measuring temperature.

The process of installing pieces of reinforcement is carried out parallel to the circuit, with adjacent and straight wires, between which the pouring lamp is mounted. It is thanks to it that it will be possible to measure voltage.

To measure temperatures, you should use a thermometer. This process takes a long time, approximately 2 months. At the same time, during the entire heating process it is necessary to protect the structure from the influence of cold and water. It is advisable to use heating with a welding machine when there is a small volume of concrete and excellent weather conditions.

Infrared method

The meaning of this method is that equipment is being installed that operates in the infrared range. As a result, it is possible to convert radiation into heat. It is thermal energy that is introduced into the material.

Infrared heating of concrete mixture represents electromagnetic vibrations, the wave propagation speed of which will be 2.98 * 108 m/s and the wavelength 0.76-1,000 microns. Very often, tubes made of quartz and metal are used as a generator.

The main feature of the presented technology is the ability to supply energy from conventional alternating current. When infrared heating of concrete, the power parameter may change. It depends on the required heating temperature.

Thanks to the rays, energy can penetrate into deeper layers. To achieve the required efficiency, the heating process must be carried out smoothly and gradually. It is forbidden to work here at high power levels, otherwise the top layer will have a high temperature, which will ultimately lead to a loss of strength. It is necessary to use this method in cases where it is necessary to heat up thin layers of the structure, as well as prepare a solution to speed up the adhesion time.

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Induction method

To implement this method, it is necessary to use alternating current energy, which will be converted into heat in formwork or reinforcement made of steel.

The converted thermal energy will then be distributed to the material. It is advisable to use the induction heating method when heating reinforced concrete frame structures. These can be crossbars, beams, columns.

If you use induction heating of concrete on the outer surfaces of the formwork, then it is necessary to install successive turns that are isolated from the inductors by wire, and the number and pitch are determined by calculation. Taking into account the results obtained, it is possible to produce templates with grooves.

When the inductor has been installed, it is possible to heat the reinforcement frame or joint. This is done in order to remove ice before concreting occurs. Now the open surfaces of the formwork and structure can be covered with thermal insulation material. Only after the wells have been constructed can the actual work begin.

When the mixture reaches the required temperature, the heating procedure is stopped. Make sure that the experimental indicators differ from the calculated ones by at least 5 degrees. The cooling rate can maintain its limits of 5-15 C/h.

Application of transformers

To increase the temperature in concrete, you can use such an inexpensive and simple method as the PNSV heating wire.

The design of this cable includes two elements:

• round single-wire conductor made of steel;
• insulation, for which you can use PVC plastic or polyethylene.

If you need to heat a mixture of 40-80 m3, then it will be enough to install just one transformer substation. This method is used when the air temperature outside has reached -30 degrees. It is advisable to use transformers for heating monolithic structures. For 1 m of weight, a 60 m wire will be enough.

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This manipulation is performed according to the following instructions:

1. A heating wire is laid inside the concrete. It is connected to the station or transformer terminals.
2. With the help of an electric current, the array begins to gain temperature, as a result of which it manages to harden.
3. Since the material has excellent thermal energy conductivity properties, heat begins to move at high speed throughout the entire mass.

Table 1 – Characteristics of PNSV brand wires

The heating wire, which is laid inside the concrete, should heat the structure up to 80 degrees. Electrical heating occurs using transformer substations KPT TO-80. This installation is characterized by the presence of several low voltage stages. Thanks to this, it becomes possible to adjust the power of the heating cables, and also adjust it according to the changed air temperature.

Using the cable

Using this heating option does not require large amounts of electricity or additional equipment.

The whole process proceeds according to the following scheme:

1. The cable is being installed on the concrete base before the mortar is poured.
2. Secure everything using fasteners.
3. Be careful during cable installation and operation to ensure that its surface does not become damaged.
4. Connect the cable to the low-voltage electrical cabinet.

Antifreeze additives

With the addition of antifreeze additives, concrete is able to withstand the most aggressive precipitation. The components included in such a mixture can be very different, but the main role is assigned to antifreeze. This is a liquid that prevents water from freezing.

If it is necessary to cock reinforced concrete structures, the mixture must contain sodium nitrite and sodium format. The main feature of antifreeze mixtures remains the preservation of anti-corrosion and physico-chemical properties at low temperatures.

When constructing ready-mixed concrete or producing curbs, it is necessary to use a mixture that contains calcium chloride. This component allows you to achieve fast hardening speed and resistance to low temperatures.

The ideal antifreeze additive remains a chemical such as potash. It dissolves very quickly in water, and there is no corrosion. If you use potash when heating concrete in winter, you will be able to save on building materials.

If you use antifreeze additives, it is very important to adhere to all safety standards. For example, you should not use concrete with such components when the structure is under tension and monolithic chimneys are being erected.

SNiP

All installation and construction activities must be carried out in accordance with established standards. The concreting process in winter is no exception. Warming up of a concrete structure at low air temperatures occurs in accordance with the following documents:

• SNiP 3.03.01-87 – Load-bearing and enclosing structures
• SNiP 3.06.04-91 – Bridges and pipes

The video shows concrete heating in winter, technological map:

Despite the fact that the presented documentation only indirectly touches on the topic related to heating concrete, it contains certain sections in which there is a technology for pouring concrete mortar in the frosty season.

Mixture composition

• cement (after mixing, it connects the elements of concrete);
• water;
• aggregate (sand, crushed stone or gravel).

It is possible to improve the operational and technical performance of a structure with the help of special additives (mineral or organic).

Beginners do not always understand for what purpose it is necessary to water concrete after pouring, because they do not know the features of this material. The main active components are water and binder, which envelop the aggregate (which is passive in the mixture).

Water plays an important role in cement mortar. It takes part in physical and chemical processes that lead to its neutralization. Gradually, moisture evaporates and the binder hardens. As a result of binding aggregate grains, concrete (durable artificial stone) is obtained from the mixture.

Fillers occupy up to 85% of the total volume. Their properties influence the physical and mechanical properties of concrete. The share of water in the mixture is about 7% of the volume, cement - 13%.

The top layer loses moisture faster (compared to the bottom layer and middle), so cracks may appear in the concrete. When the surface overdries, the strength of the product decreases and the design will not be able to meet the required grade.

Need for hydration

Often, those new to construction pour concrete into the foundation with their own hands and are sure that the work ends there. However, it takes time (up to 4 weeks) for concrete to gain the required strength.

Strength is influenced by ambient temperature and precipitation. Only after this period has expired is it possible to begin building walls (if we are talking about building a house).

If the ambient temperature is high and a strong wind is blowing, the process of evaporation of water from the outer layer will occur more intensely. And due to rapid drying, depending on its speed, precipitation will occur faster. This causes areas with numerous small cracks to appear on the surface of the structure.

When the hardening process is completed, under the influence of negative environmental conditions, cracks will contribute to the destruction of the concrete structure. In winter, water that gets into cracks freezes and can tear the structure apart.

When the foundation of a building is subjected to such destruction, cracks may appear on the facade, and their size will gradually increase. If the top layer is overdried, the process of cement hydration stops. Because of this, strength is gained slowly and is lower than the planned grade.

Maintenance of concrete structures

The main goals of surface care after pouring the foundation:

• reduction of plastic shrinkage;
• increase in strength;
• preventing drying out;
• neutralization of the influence of temperature changes;
• increase in service life;
• preventing the influence of chemical and mechanical forces.

To understand how much concrete needs to be watered, you need to know about the existing rules. Methods of care after pouring the foundation are influenced by:

• type of cement;
• type of construction;
• climatic conditions, etc.

The maintenance period is affected by the hardening speed of the cement in the mixture:

• structures made of cement, which hardens gradually, need to be wetted for 4 weeks;
• structures based on Portland cement - from 2 to 3 weeks;
• on quick-hardening cement - 8 days.

In hot and dry weather, longer maintenance is required. To slow the evaporation of moisture and to protect against overheating after pouring, it is recommended to cover the foundation with moistened sawdust, matting, and roofing felt.

In hot weather or strong winds, it is recommended to start irrigating the surface 2-3 hours after finishing work. Not everyone understands how to water correctly.

Watering should be carried out throughout the day so that the structure is constantly wet. You can understand how often you need to irrigate the surface by paying attention to the temperature and humidity of the air.

It matters how much time should pass between waterings. In extreme heat, breaks between moisturizing should not be more than 2 hours, in other cases - every 3 hours during the day, and up to 3 times at night. The appearance of hissing during irrigation indicates an insufficient amount of water.

• must be clean flowing;
• it should not contain impurities that can have an aggressive effect on the surface;
• groundwater located close to the surface cannot be used;
• recommended pH level = 7 (permissible deviation - 1);
• must not contain pesticides or organic deposits;
• There should not be a large amount of calcium, magnesium, sodium.

On the foundation, which is in the formwork, moisture is retained longer, so irrigation is allowed less often. After removing the formwork, it is necessary to begin watering, paying more attention to the edges of the structure, since they are more susceptible to the influence of wind and temperature, so moisture loss occurs faster.

Concrete work at sub-zero temperatures

11.1

When the average daily outside air temperature is below 5 °C and the minimum daily temperature is below 0 °C, it is necessary to take special measures to maintain the laid concrete in structures and structures.

11.2

The preparation of the concrete mixture at the construction site should be carried out in heated concrete mixing plants, using heated water, thawed or heated aggregates, ensuring the production of a concrete mixture with a temperature not lower than that required by calculation. It is allowed to use unheated dry aggregates that do not contain ice on the grains and frozen lumps. In this case, it is recommended to increase the duration of mixing the concrete mixture by at least 25% compared to summer conditions.

11.3

Methods and means of transportation must ensure that the temperature of the concrete mixture does not drop below that required by calculation when it is placed in the structure.

11.4

The condition of the base on which the concrete mixture is laid, as well as the temperature of the base and the method of laying must exclude the possibility of freezing of the concrete mixture in the area of ​​contact with the base. When curing concrete in a structure using the thermos method, when preheating the concrete mixture, as well as when using concrete with antifreeze additives, it is allowed to lay the mixture on an unheated, non-heaving base or old concrete, if, according to calculations, freezing will not occur in the contact zone during the estimated period of curing the concrete. At air temperatures below minus 10 °C, concreting of densely reinforced structures with reinforcement with a diameter greater than 24 mm, reinforcement made of rigid rolled sections or with large metal embedded parts should be carried out with preliminary heating of the metal to a positive temperature or local vibration of the mixture in the reinforcement and formwork areas, with the exception of cases of laying preheated concrete mixtures (at a mixture temperature above 45 ° C).

11.5

When concreting elements of frame and frame structures in structures with rigid coupling of nodes (supports), the need to create gaps in the spans depending on the heat treatment temperature, taking into account the resulting temperature stresses, must be indicated in the PPR. Unformed surfaces of concreted structures should be covered with steam and heat insulating materials immediately after concreting is completed.

Reinforcement outlets of concrete structures must be covered or insulated to a height (length) of at least 0.5 m.

11.6

Before laying the concrete mixture, cavities after installing reinforcement and formwork must be covered with a tarpaulin or some other material to prevent snow, rain and foreign objects from entering them. If the cavities are not closed and ice has formed on the reinforcement and formwork, it should be removed before laying the concrete mixture by blowing with hot air. It is not allowed to use steam for this purpose.

11.7

Temperature and humidity curing of concrete in winter conditions is carried out (Appendix P):

• thermos method;
• using antifreeze additives;
• with electrical heat treatment of concrete;
• with heating of concrete with hot air, in greenhouses.

Curing of concrete is carried out according to specially developed technological maps in the PPR, which must contain:

• method and temperature and humidity conditions for curing concrete;
• data on the formwork material taking into account the required thermal insulation indicators;
• data on vapor barrier and thermal insulation covering of open surfaces;
• diagram of the placement of points at which the concrete temperature should be measured and the name of the devices for measuring them;
• standardized strength values ​​of concrete;
• timing and procedure for stripping and loading structures.

In the case of using electrical heat treatment of concrete, the technological maps additionally indicate:

• diagrams of placement and connection of electrodes or electric heaters;
• required electrical power, voltage, current;
• type of step-down transformer, cross-section and length of wires.

The choice of method for carrying out concrete and reinforced concrete work in winter conditions should be made taking into account the recommendations given in Appendix P.

11.8

The thermos method should be used by ensuring the initial temperature of the laid concrete in the range from 5 to 10 ° C and then maintaining the average temperature of the concrete in this range for 5 to 7 days.

11.9

Contact heating of laid concrete in thermoactive formwork should be used when concreting structures with a surface modulus of 6 or more.

After compaction, exposed concrete surfaces and adjacent areas of thermosetting formwork panels must be protected from moisture and heat loss from the concrete.

11.10

When electrode heating of concrete, it is prohibited to use reinforcement of the concrete structure as electrodes.

Electrode heating should be carried out until the concrete reaches no more than 50% of its design strength. If the required concrete strength exceeds this value, then further curing of the concrete should be ensured using the thermos method.

To protect concrete from drying out during electrode heating and increase the uniformity of the temperature field in concrete with minimal energy consumption, reliable thermal and moisture insulation of the concrete surface must be ensured.

11.11

The use of concrete with antifreeze additives is prohibited in structures: prestressed reinforced concrete; reinforced concrete, located in the area of ​​stray currents or located closer than 100 m from high voltage direct current sources; reinforced concrete, intended for use in aggressive environments; in parts of structures located in an area of ​​variable water level.

11.12

The type and amount of antifreeze additive is prescribed depending on the ambient temperature. For structures of medium massiveness (with a surface modulus from 3 to 6), the average value of the outside air temperature according to the forecast for the first 20 days is taken as the design temperature. from the moment of concrete laying. For massive structures (with a surface modulus of less than 3), the average outside air temperature for the first 20 days is also taken as the calculated one. hardening with an increase in temperature by 5 °C.

For structures with a surface modulus of more than 6, the minimum average daily outside air temperature forecast for the first 20 days is taken as the calculated one. concrete hardening.

11.13

At negative ambient temperatures, structures should be covered with hydrothermal insulation or heated. The thickness of the thermal insulation is determined taking into account the outside temperature. When heating concrete with an anti-frost additive, the possibility of local heating of the surface layers of concrete above 25 °C must be excluded.

To protect against freezing of moisture, the exposed surfaces of freshly laid concrete, together with the adjacent surfaces of the formwork, must be reliably covered.

11.14

When monolithing structures with curing concrete with antifreeze additives, the surface layers of concrete of the monolithic structures may not be heated, but it is necessary to remove ice, snow and construction debris from the surfaces of concrete, reinforcement and embedded parts.

11.15

The exposed surfaces of the laid concrete at the joints of the grouting must be reliably protected from freezing of moisture. If cracks appear in the joints, they must be opened only at a stable positive air temperature.

11.16

Requirements for work at subzero air temperatures are given in Table 5.7.

Table 5.7. SP 70.13330.2012

Load-bearing and enclosing structures. Updated version of SNiP 3.03.01-87

11.17

When the average daily outdoor temperature is below 5 °C, a concrete temperature control log must be kept. Temperature measurements are made in the most and least heated parts of the structure. The number of temperature measurement points is determined by the dimensions and configuration of the structure and is indicated in technological regulations and PPR.

Temperature measurement frequency:

a) when concreting using the thermos method (including concrete with anti-frost additives) - twice a day until the end of curing; b) when warming up - in the first 8 hours after 2 hours, in the next 16 hours - after 4 hours, and the rest of the time at least three times a day; c) with electric heating - in the first 3 hours - every hour, and the rest of the time after 2 hours.

In the log, the persons responsible for heating the concrete fill in the shift delivery and acceptance columns. The method of heating concrete is established in the PPR and is indicated for each structural element.

Concrete maintenance times

How many days concrete care should continue depends on environmental conditions. If the temperature:

• above +15°C, it takes 7-15 days to moisturize;
• above +10°C, the watering period is reduced to 5-10 days;
• below +5°C, irrigation can be stopped.

Wetting should continue until the structure reaches its design strength of 70%. On average, this takes 10 days. If you pour concrete longer, the effect may be the opposite: due to excess moisture, strength will increase more slowly.

Caring for concrete: necessary measures and rules for their implementation

The construction of a concrete structure is a complex process and the quality of the result depends on a number of factors - the correct selection of materials, compliance with the proportions of the components of the mixture, compliance with the technology of its preparation and installation. A special place in obtaining high-quality concrete is the organization of measures to care for the hardening mixture.

The need for maintenance of freshly laid concrete

The main goal of caring for a hardening concrete mixture is to create optimal thermal and humidity conditions, on compliance with which the normal increase in the strength of the material depends.

Hardening of concrete is a long physical and chemical process and requires a certain time period for its complete completion. Especially at the beginning of the mixture’s hardening period, for the hydration reaction to occur—the combination of cement grains with water—it is necessary to ensure a sufficient amount of moisture in the concrete. Premature removal or freezing of water in the concrete mixture leads to deterioration of its structure and strength characteristics.

In many ways, the increase in concrete strength depends on the temperature at which the hardening process occurs. Temperature +18-+22oС and relative humidity within 80% are considered normal. At low temperatures above zero, the hardening of the mixture slows down; if it drops below zero, if appropriate measures are not taken, it will stop completely.

Freshly laid concrete requires the most careful care in the first days - during the period of the fastest increase in strength. When normal conditions are created, Portland cement concretes in the first two weeks of drying gain about 70% of the planned strength, which is inherent in 28 days of age.

Rules for caring for concrete in summer

During the warm season, the main goal of concrete care measures is to protect the surface from drying out.

The basic rules for creating an optimal humidity regime are simple, but the main thing is to observe them regularly:

• All exposed surfaces must be carefully protected from wind and direct sunlight. For this purpose, the concrete structure is covered with moisture-absorbing coverings - burlap or tarpaulin. Polyethylene film can serve as protection against drying out.

If such materials are not available, then 2-4 hours after concreting, the surface can be sprinkled with sawdust or sand and watered. The frequency of watering is determined by climatic conditions and should be such that the coating is constantly wet. The duration of moistening is until the concrete reaches 70% of the designed strength. The concrete is watered using a hose with a spray tip.

• At very high ambient temperatures, the formwork itself is also moistened before concreting. If the formwork is removed before the end of the concrete maintenance period, then the vertical stripped surfaces are also watered. In dry, hot climates, a system of pipes with small holes is installed to water steeply inclined and vertical surfaces.
• Freshly laid concrete needs protection not only from heat, but also from the effects of groundwater, especially aggressive ones. This can be achieved by drainage or by installing an insulating layer. For aluminous cements, these measures are relevant for three days, and for all other types - for two weeks.

Watering freshly laid concrete can be difficult due to the presence of large amounts of salts in the water. After the liquid evaporates, salts remain on the concrete and can cause some deterioration in the strength properties of the surface layer. In this case, the covering materials are placed several inches above the surface of the concrete, and only the covering is watered. The mixture is moistened with steam without contact with salts.

Covering and watering freshly laid concrete are labor-intensive activities. Therefore, for areas of significant size that are not subsequently intended for contact with concrete, instead of watering, special painting compounds, protective polymer films, tar or bitumen emulsions are used.

Structures made of lightweight concrete with porous aggregates require a special humidity regime. To care for such concrete, special paint and film coatings are used to protect the surface from moisture.

Freshly laid concrete must be protected from mechanical influences - shocks and shocks.

Caring for concrete at low temperatures

If you have a choice of concreting time, it is certainly better to prefer the warm season. If it is necessary to carry out concrete work in winter, then special measures will help to do this to protect the mixture from freezing until it reaches its design strength.

If you prepare the solution yourself without using antifreeze modifiers, use heated water. Laying the mixture must be done continuously. If the top layer has frozen, it must be treated with steam and the frozen area removed, immediately continuing concreting.

Types of winter concreting technologies:

• The use of concrete with antifreeze components, which are supplied ready-made.
• Heating of hardening concrete using powerful transformers.
• When concreting at borderline temperatures, the structure can be insulated using insulating materials.
• One of the options for creating a normal thermal regime is to install a “low tent” in combination with heating using a heat gun.
• When concreting thin-walled structures, it is undesirable to use electric heating, since it can cause overdrying. In this case, the rational solution is to use infrared heaters or steam heating.

When using steam heating in the first eight hours after laying the mixture, the steam temperature must be monitored every two hours. In the next 16 hours - once every 4 hours, then once per shift is enough. When using infrared heaters, you must maintain a distance between them and the concrete structure - at least 1.2 meters. You can heat both the concrete element itself and the formwork, which is coated on the outside with a matte black paint and varnish composition for better heat absorption. Before heating with infrared radiation, the concrete surface must be protected from drying out with a film.

When concreting at temperatures around -20oC, thermoactive formwork is used, which is a structure consisting of steel plates with heating elements mounted on them and a layer of external thermal insulation. At the end of heating, the formwork is removed, and then the concrete cools under the cover. The shelter is made of slag felt blankets, tarpaulin fabric and plastic film. The cooling of the concrete structure must be carried out under constant control.

Concrete care products after pouring

The modern chemical industry offers many products that can effectively help care for concrete as it reaches its design strength.

• Novapor - used to care for the unprotected surface of a concrete structure. Protects the hardening mixture from low air humidity, intense exposure to direct sunlight, high temperatures and strong winds. The use of this product helps prevent the appearance of shrinkage cracks, shedding of cement that has not undergone the hydration process, and aggregate. The product is an aqueous paraffin emulsion.
• Ecofob is a product used for impregnation of mixtures. Increases the resistance of the concrete mixture to frost, as well as chemical defrosting agents. This substance is used mainly for the maintenance of concrete road surfaces on highways, runways, industrial, utility and warehouse facilities. Ecofob is used in the construction of bridge structures, garages and concrete supports.
• Antisol E20 is a white liquid that does not contain components that provoke corrosive processes, is fireproof and does not contain chlorine. Applying a thin layer of this product helps protect the concrete from drying out too quickly and prevents a decrease in the strength characteristics of the hardening mortar. This composition is also used to care for hardened concrete. Antisol E20 fills the pores, increasing the frost resistance and water resistance of the material. The product retains its positive qualities even under conditions of intensive use of concrete pavements.

Determining the order of concrete care measures and monitoring their implementation

In the conditions of capital construction, measures for the care of the hardening concrete mixture are established by the laboratory and approved by the technical managers of the facility construction.

When constructing massive hydraulic structures, all methods of regulating thermal and humidity conditions are determined by the design of the facility and the work. Such events are regulated by SNiP.

To continuously monitor the accuracy of concrete maintenance work, all activities are recorded in a special “Concrete Work Log”. The concrete maintenance log must be filled out daily.

A sample concrete maintenance journal can be downloaded here (opens in a new tab).

Regular maintenance of freshly laid concrete will help avoid loss of concrete strength characteristics and create a durable structure that can last for many years.

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How to water concrete products

To moisten the structure it is recommended:

• use a hose with a sprayer;
• pay more attention to nodes and edges (in such places water evaporates faster, for this reason cracks or chips may occur);
• to prevent evaporation from the surface of a large area, cover it with film;
• distribute water evenly;
• Irrigate the base, in addition to the top layer.

In the first 2 weeks, the surface should be constantly wet; watering should be done regularly, not allowing the moisture to evaporate completely. If the surface is not moistened, premature dehydration occurs and the fragility of the material increases.

Concrete care in summer: SNIP

When starting the construction of monolithic concrete structures, you should familiarize yourself with all the rules for caring for them in advance. They are necessary for the concrete to gain its original strength and serve for many years. Otherwise, cracks will begin to appear on its surface, which will lead to shrinkage of the building and loss of its functionality. SNIP provides for concrete maintenance at any time of the year, but if you can choose a construction season, it is better to choose the summer option.

At this time of year, it is necessary to provide the concrete with optimal hydration conditions in order to achieve maximum structural strength. All protective measures take place in two stages.

Stages of concrete protection

1. Initially, an analysis of the environmental impact on the concrete pavement should be carried out. It is its insufficient resistance to this that affects the subsequent strength of the entire structure. After the design is completed, the first stage begins. It includes the preparation of the optimal composition of the concrete mixture, which will withstand external influences. To do this, various impurities are added to improve density, frost resistance, crack resistance and water resistance.
2. The second stage is to protect the already laid coating. To do this, it is necessary to cover the surface of the concrete with a special coating that will prevent or limit its contact with the environment. This is done to control the moisture content of the concrete mixture and protect it from destruction. It is also important to maintain an optimal temperature on its surface, which does not always coincide with natural temperature. Therefore, shelter is required.

Methods for caring for concrete

Complete hardening of concrete takes about a month, of which the first two weeks the concrete gains almost eighty percent, so the maintenance process takes a long time. If the moment is missed, cracks will appear on the surface of the concrete, which will lead to a significant loss of strength and functionality. Maintenance of concrete in the summer SNIP provides for all this. Their main requirement is to maintain the level of humidity on the surface of the structure. It is achieved by preventing evaporation or regularly maintaining the level of humidity by replenishing it. The required amount of water is added to the mixture that is still being prepared, which should be kept until it hardens completely, that is, for a month.

The speed of drying is also affected by the ambient temperature. When large monolithic structures are heated unevenly, large cracks appear on them, and when foundations or floor coverings dry out, microcracks form. All this leads to a large loss of strength and shrinkage of the building. Drying slows down, and sometimes even stops, the hardening process. At this time, the volume occupied by concrete also changes. All this should be taken into account when choosing cement for preparing the mixture.

In different temperature conditions, the hardening period also varies. For example, at temperatures above ten degrees Celsius and air humidity of more than eighty percent, the full hardening time increases. This is because under these conditions, water will penetrate into the concrete slowly. Surface maintenance will take about two weeks, as with other slowly hardening cement mixtures. Portland cement will require a moistening period that is half as long.

All methods of maintaining the required moisture content of concrete can be divided into three:

• watering;
• coating with a protective composition (allows you to retain moisture and avoid negative environmental influences);
• aging with salts (used in winter).

All work to moisten the surface with water must be carried out from a sprayer, otherwise a strong jet can wash away the concrete. The first watering is carried out after a couple of hours in very hot weather and after ten hours in average temperatures. Subsequent wetting depends on environmental conditions and the composition of the cement itself. For example, low-heat grades will require care for a couple of weeks, aluminous (quickly hardening) grades should be moistened for only a day, of which the first eight hours should be heavily saturated with moisture, and the remaining time should be completely moistened. In any case, the regularity of this process significantly reduces the risk of cracks. But do not forget that during watering the concrete cools.

Factors affecting the strength of concrete

In fact, the rate of strength gain and final characteristics depend on several important nuances:

• Cement, which is used to prepare concrete. Its different types have different periods of gaining primary strength; it is worth using Portland cement. It is best suited for use due to its excellent characteristics and the shortest curing period.
• Humidity, the reliability of the structure directly depends on this indicator. Its ideal indicator for a set of high properties is 90 percent. It needs to be maintained constantly; the easiest way to do this is with a sprayer.

Caring for freshly laid concrete primarily involves constantly moistening the surface and preventing it from drying out.

• Air temperature: the best conditions for achieving optimal properties of the solution are created at +20 degrees. At zero temperature, the solidification process stops, and at negative values, the water in the structure freezes and, expanding, damages the material, reducing its strength.

Care rules during the warm season

During this period, the air temperature rises significantly, which means that caring for concrete in the summer will have its own characteristics. It all comes down to maintaining a temperature on its surface no higher than twenty-five degrees Celsius and an optimal level of humidity throughout the entire hardening period. To do this, concrete must be covered immediately after pouring to reduce moisture evaporation, which will lead to cracking. Straw, sheets of tin, burlap and any other materials will do. Sometimes, when moisture evaporates, traces of salts remain on the concrete surface, which destroy the surface layer. To prevent their interaction, it is recommended to cover the concrete so that the materials do not come into contact with its surface. To do this, it will be enough to maintain a distance of a couple of centimeters. All subsequent moistening occurs directly through the shelter, which retains salts and allows moisture to pass through. The entire process of laying and maintaining concrete in hot weather is based on certain rules:

• regularly maintaining the level of humidity on the surface;
• at elevated temperatures, moisten the formwork;
• protection of the surface from the sun and wind;
• avoid contact with rain and melt water;
• exclude the possibility of mechanical impact on the surface.

In addition to the rules for protecting the surface, you should also adhere to the rules when pouring concrete. To do this, it is necessary to carry out the main work in the morning or evening, when the air temperature is not too high. It takes no more than an hour to deliver the material to the site or prepare it on site. Immediately after laying, protect the concrete surface from the sun and moisten it regularly throughout the curing period. The frequency of watering, as well as its intensity, depends on the air temperature. In forty-degree heat, not only the concrete, but also its formwork and shelter should be moistened. Particular attention must be paid to the nodes and edges, and it is advisable to water the plant from a sprayer.

If these standards are ignored, the strength of the concrete coating is reduced by half due to rapid drying. And the full period for gaining brand strength of concrete depends on temperature, which has been proven by scientific research, so you need to take weather conditions into account when drawing up a schedule.

Features of care depending on external conditions

As noted above, the activities carried out as part of the maintenance of concrete primarily depend on temperature and humidity. If these indicators are optimal, then this greatly simplifies the work, but in practice ideal conditions practically never occur and, nevertheless, you can create them yourself. Let's consider the main options for work depending on environmental conditions (read also the article “Concrete balusters - a simple way to refine a staircase”).

Summer period

Anyone can make a reliable foundation with their own hands, but any violations of technology can reduce the strength

Most often, work is carried out in the summer, since this is the most favorable period in the sense that temperature changes are insignificant and the working conditions are quite comfortable.

But high temperatures also create a lot of difficulties, because drying out the surface is contraindicated for a number of reasons:

• Termination of the hydration process in the surface layer, due to which its strength is significantly reduced.
• Also, due to too rapid evaporation of moisture, surface cracks form, which over time can cause more significant damage.

This is what happens when a concrete base quickly loses moisture

• Drying can cause a decrease in strength, and this figure can be even 40%, that is, the final reliability of concrete will be only 60% of what was planned.
• When dried prematurely, the surface structure becomes more porous, which reduces its moisture resistance and frost resistance. In addition, deformation resistance decreases.

How to protect concrete and create the most favorable conditions for its maturation? All measures are quite simple, but they must be followed carefully.

The simplified instructions look something like this:

• In sunny weather, it is very important to protect the freshly poured structure from exposure to the sun and wind. For this purpose, any shields or canopies from awnings can be used. At temperatures above 25 degrees, it is better to use reflective film, although this is not necessary for small objects.

Advice! Among private developers, when pouring strip foundations and small screeds, the simplest option is polyethylene film; it will protect the surface from moisture evaporation and weathering.

Regular transparent film is ideal when working indoors

• The first moistening is carried out after a few hours, it is very easy to find out that this is necessary: ​​the surface will become much drier, but it is important that it does not dry out, this can have irreversible consequences for the final result.
• The frequency of moistening is 2-3 hours during the day; at night, a single treatment can be carried out - the temperature during this period is lower, and this is usually sufficient.
• Moistening is carried out in this way for the first few days, then this process is carried out as necessary, but the condition of the concrete must be constantly monitored.

Important! If the surfaces are open and there is no way to protect them, then they should be coated with either bitumen emulsion or Etinol varnish, this will prevent moisture loss.

The emulsion protects the surface from moisture loss

• After finishing the moistening, the covering materials should not be removed for another 3-4 days, so that the humidity returns to normal and cracks do not form on the surface due to sudden drying.

It is worth noting that when pouring large planes, in order to avoid cracks, you will need to cut reinforced concrete with diamond wheels - the grooves will perform a compensating function.

Winter period

There is a SNiP for the care of concrete in winter, it is called 3.03.01-87 “Load-bearing and enclosing structures.”

According to it, the following features of concrete care can be distinguished:

• At temperatures below +5 degrees, humidification is not required.
• When pouring the foundation, additional insulation of the formwork with polystyrene foam or mineral wool is necessary.
• If temperatures are negative, then special additives are needed to protect the composition from freezing. Electric heating can also be used, but it will require more financial investments, in addition, the cost of this option is much higher.

Additives can improve the properties of concrete

As for work in the autumn and spring, it all depends on the temperature conditions, in accordance with them you choose one of the two options above. As you can see, even such a durable material as concrete requires a maintenance process; this will ensure strength and reliability.

If you have to pass pipes or other communications through the concrete surface, foresee this before starting work - diamond drilling of holes in concrete is a difficult and expensive process.

Additional protections

To increase the strength of the concrete coating, various protective mixtures are sprayed onto its surface. They are white, black and colorless.

Black protects well from wind and direct sun, but its surface, on the contrary, increases heat absorption and overheats the concrete. Black bituminous mastic acts even worse; it evaporates a large amount of moisture during the wind. White additives, due to their color, reduce heat absorption, while colorless additives do not affect the appearance of concrete. Modern technologies have made it possible to obtain a product that creates a transparent film on the surface. This type of coating can be found on the floors of large hypermarkets. It involves improving the durability of concrete at average temperatures and humidity. But even when using such additives, one should not forget about the need to regularly moisten the coating.

Rules for caring for monolithic structures

Large surfaces lose moisture much faster, so they should be moistened more often. To ensure sufficient watering, you can build a continuous irrigation system, it is important to use galvanized pipes for this. The fact is that tap water contains a lot of iron, which will settle on the surface of the concrete, and galvanized pipes will prevent this. If the structure is being erected using concrete blocks, then each of them must be watered from all sides and must be covered with film or a protective compound.

What you need to know about concrete

To understand how important it is to care for freshly poured concrete structures, let’s get acquainted with the main features of the hardening of this material:

• The strength of the material is due to a rather complex chemical process called hydration . The bottom line is that water molecules gradually penetrate into the cement particles, as a result of which new super-strong compounds are formed.

The photo shows cement, which, when combined with water, forms a very strong and durable connection.

• The hydration process is quite long, which determines the long period of concrete gaining strength characteristics . Water penetrates the cement gradually and reaches the center of the cement particles only after several months.
• Despite the fact that the development of strength takes a long time, the structures can be used after 28 days, when the material becomes sufficiently reliable and resistant to deformation.
• During the curing process, the volume of the composition decreases, that is, it shrinks . This is normal, moreover, by monitoring shrinkage rates, you can roughly calculate the strength of concrete, although this method is most often used by professionals, since a simple developer is unlikely to have special equipment - its price is quite high.
• It is known that concrete structures that dry in a humid environment gain much higher strength than in the open air . This property is very important to always remember, because there is nothing worse than drying out the surface.