The decision on how much the foundation should stand after pouring should be made taking into account a set of factors. The determinants in this case are the structural construction of the base of the building, design features of the structure and the standing time necessary for the full maturation of concrete. It should be remembered that failure to comply with the period during which the foundation structure must be maintained before the construction of the house can lead to partial or complete devaluation of the bearing properties stipulated by the project.
Concrete Maintenance Work
The construction rules of SP 70.13330.2012, in which the text of SNiP 3.03.01–87 is updated, require concrete to withstand the implementation of measures for taking care of it before stripping. Data on how much concrete should be laid laid in the formwork forming the contours of the foundation, concrete is prescribed in paragraph 5.4.1 of the Rules.
All surfaces must be reliably protected from possible evaporation of the water contained in the solution. Freshly laid concrete should also be protected from contact with its surface. precipitation. Such measures should be carried out before construction during the entire period until a set strength of at least 70% of the passport is ensured.
After stripping, it is necessary to create conditions for maintaining temperature and humidity in values \u200b\u200bthat optimally correspond to the increase in the strength of the concrete structure. The rules are not allowed to walk on the surfaces of concrete structures until the concrete gains strength of 2.5 MPa. It is impossible, accordingly, to install overlying formwork, to carry out brickworkto erect wooden walls and perform other construction or auxiliary operations.
Strength Concrete
The concrete mixture dries and obtains the necessary and sufficient strength values \u200b\u200bduring the passage of two successive interconnected stages:
- Setting stage. The preliminary setting of the concrete mortar laid in the formwork in summer at an ambient temperature of about 20 ° C occurs during the day. In cold seasonal periods it is necessary to use available funds heating and apply heat insulating structures. It should be borne in mind that setting processes begin to occur within the first two hours from the moment the concrete mixes with water. That is why the operation of mixing the mixture and laying concrete in the formwork should be as close as possible to each other in time intervals.
- Hardening of concrete. A set of concrete strength occurs in the process of hydration - the formation of molecular bonds of water particles with the substances that make up the mixture. Hydration takes place in a narrow range of temperature and humidity, which should be provided with measures for the care of concrete. The importance of careful monitoring of the progress of the physicochemical process in the mass of the reinforced concrete structure is explained by the complete dependence of the quality of the structure.
It is natural to assume that the period during which the foundation is to be defended is directly related to the set of strength of concrete that forms its basis. Ready-mixed concrete of grades M – 200 and M – 300, which is made on the basis of Portland cement M – 400 and M – 500, respectively, gains 70% of the strength necessary for construction and normalized joint ventures 70.13330.2012 in 28 days at its average daily temperature of 20 ° C . A change in daily average temperature inevitably leads to other indicators of strength. The dependence of the gained strength is clearly visible from the table.
To build a reliable and strong foundation, it is not enough to correctly lay the reinforcement, select and pour the concrete mixture. A strong influence on the quality of work is exerted by how well the set of concrete strength is ensured. To guarantee this, you need to know how much the foundation of the house should stand after pouring.
Concrete is fake diamond, which is obtained from a solution prepared in special proportions. The hardening of the mixture depends on many factors, so there is no exact answer, suitable for all cases, to the question of how much the foundation of the house should be after pouring. The answer is individual for certain conditions.
On average, it is believed that the set of strength takes 28 days, but this value is averaged. The process depends on the following factors:
- what type of cement was used when mixing the concrete solution;
- the ratio of cement and water in the mixture;
- temperature the environment during the hardening of the foundation;
- what weather will be after pouring (sunny, cloudy, windy);
- how compact is the concrete solution.
Each of these factors has an effect. The whole process can be divided into two stages:
- setting;
- hardening.
Grasping
This is the period during which the foundation mix remains mobile. This means that the whole process of transportation, filling and compaction should fit into this framework. When delivered by concrete mixers, setting time is increased due to constant mixing. If the solution is in the mixer for too long, changes occur that adversely affect the quality finished construction. The setting period is inversely proportional to the ambient temperature.
The optimum temperature is 20 ° C. Fast setting at high temperatures can adversely affect the quality of the foundation of the house after pouring.
Hardening
The second stage of curing is hardening. If the time of the first stage dictates the conditions for the work, how much hardening takes will affect the possibility of continuing construction and the transition to the construction of the “box” of the building. The table below shows how much the foundation of the house should stand after pouring, depending on the temperature. For 100% of the set of compressive strength, the value that will be obtained at a temperature of 20 ° C is taken if the foundation is allowed to stand for 28 days. Values \u200b\u200bare given for material of grades M200-300 (class B 15 - B 22.5) made on Portland cement of grades M400-500.
| Average daily air temperature, ᵒС | The hardening period, days. | ||||||
| 1 | 2 | 3 | 5 | 7 | 14 | 28 | |
| -3 | 3% | 6% | 8% | 12% | 15% | 20% | 25% |
| 0 | 5% | 12% | 18% | 28% | 35% | 50% | 65% |
| +5 | 9% | 19% | 27% | 38% | 48% | 62% | 77% |
| +10 | 12% | 25% | 37% | 50% | 58% | 72% | 85% |
| +20 | 23% | 40% | 50% | 65% | 75% | 90% | 98% |
| +30 | 35% | 55% | 65% | 80% | 90% | 98% | — |
The table shows that negative temperatures slow down the process especially strongly.
The graph of the set of concrete strength depending on the temperature.
The stripping strength of concrete is determined by the joint venture "Structural and Enclosing Structures" and is 70% of the brand name (safe start time). This means that it is necessary to remove the formwork after pouring the foundation of the house at least 7 days later for an average daily temperature of + 20 ° C or at least 14 days later for + 10 ° C. With appropriate justification, it is possible to withstand the time until only 50% of the brand compressive strength is reached (a normatively safe period for the commencement of work) before removing the formwork. For self-construction, it is also recommended that you read the “Production Guide concrete work in winter conditionsareas Far East, Siberia and the Far North. "
How much the foundation should stand after performing monolithic works depends on the type of Portland cement for the manufacture of the mixture. There are three types:
- quick hardening;
- normally hardening;
- slow hardening.
The table shows the values \u200b\u200bof compressive strength for concrete on various binders depending on air temperature. All values, as in the previous table, as a percentage of strength at a temperature of 20 ° C, if you let the monolith stand for 28 days.
| The average daily temperature, ᵒС | The time of curing, days | |||||
| 1 | 2 | 3 | 7 | 14 | 28 | |
| On fast-hardening Portland cement | ||||||
| 5 | 16% | 22% | 26% | 33% | 38% | 45% |
| 10 | 26% | 37% | 43% | 54% | 61% | 71% |
| 20 | 42% | 58% | 66% | 82% | 92% | 98% |
| On normally hardening Portland cement | ||||||
| 5 | 12% | 19% | 23% | 31% | 37% | 43% |
| 10 | 21% | 32% | 38% | 51% | 60% | 70% |
| 20 | 34% | 50% | 60% | 78% | 90% | 98% |
| On slow hardening Portland cement | ||||||
| 5 | 6% | 12% | 17% | 27% | 34% | 41% |
| 10 | 11% | 21% | 28% | 44% | 56% | 67% |
| 20 | 19% | 34% | 45% | 68% | 85% | 98% |
The requirements for how much the foundation of the house should stand after monolithic work before removing the formwork remain the same: 70% of the branded compressive strength (50% under special conditions).
Do not forget that the concrete during the first days of hardening requires moisture, for this it is covered with sawdust, burlap or sand (to accumulate and preserve moisture) and watered abundantly with water for the first 7 days.
When to proceed to the next stage of work
After the foundation is erected, it is necessary to proceed to the construction of walls and ceilings. It is important to determine whether the structure should be sufficient time to ensure that after commissioning there are no problems. The answer to the question of how much the foundation should stand before the construction of the "box" of the house depends only on the concrete hardening time.
In private housing construction, the myth of what is necessary after foundation work give the construction of the house to stand and only then proceed with the laying of walls and the installation of ceilings. This is not regulated. normative documents. In addition, if during construction tenement house, the design and construction of which are engaged in by specialists, to give reason to stand, then the work will stretch for a long time. Also in individual construction.
If you let the foundation stand, in addition to increasing the construction time, this can lead to structural damage. This is especially true when building a house on heaving soils. Even the massive tape type of support does not give a high load to the ground. Its value is up to 10% of the mass of the whole house. If you give the foundation to stand in winter period, forces of frost heaving, acting on an unloaded element, can lead to the appearance of cracks and deformations. If in winter reinforced concrete “freezes”, the consequences may not be noticeable immediately, but 1-2 years after construction.
With sufficient compaction of the base, the question of how much the foundation should stand is not relevant. Even if the structure is allowed to stand, shrinkage will be small. No matter how much time passes, if the technology is followed, the changes will be minimal. The load during the construction is not immediately applied, but gradually, building walls, laying ceilings, roofing. Therefore, if deformations do occur, they will not be sharp.
If we summarize all of the above, then the following can be cited against stopping work after a “below zero” cycle:
- increase construction time;
- the meaninglessness of the event with a sufficient compaction of the base;
- the likelihood of cracks and deformations when the construction is stopped for the winter.
Foundation conservation
If, nevertheless, there is a need for “wintering” of the structure, then it is necessary to take care of its competent warming. You can preserve the foundation for the winter or another period, taking care of the following activities:
- waterproofing with bituminous materials;
- thermal insulation with extruded polystyrene foam (foam);
- prevention of damage to the structure by groundwater, especially in the spring.
It is important to note that conservation is a necessary measure when it is impossible to continue work, and not their necessary stage. It often happens that after starting construction, the owner can not finish it for personal reasons. This is probably where the myth of maintaining the support under the building structures came from.
In conclusion, it should be repeated that how much the monolith should stand after pouring depends only on temperature conditions and concrete. After gaining 100% compressive strength, you can safely proceed to the "zero" cycle.
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Foundation drying time - important point during the construction of the house. Although the term "drying" is not entirely appropriate in this case, concrete requires a lot of moisture to gain strength. About how time affects the strength of the foundation, let's try to understand this material.
How does the drying time affect the foundation, you can figure it out only by knowing the characteristics of concrete. Here it is necessary to distinguish between the concepts of "drying" of concrete and the "strength" of concrete.
Concrete drying is the process of moisture loss in concrete. A kind of dehydration. Concrete gains strength within 30 days from the moment of pouring.
Compressive strength is the main characteristic of concrete. And, as already mentioned, concrete is gaining it gradually. Concrete gains the first 70% of its brand strength within 7 days. Therefore, it is recommended to disassemble the formwork no earlier than this time.
The drying time of the foundation can adversely affect the strength of the entire structure. After all, water is actively involved in the processes of building strength. Since the curing process takes long time - up to 30 days, it constantly evaporates. And so that the foundation does not lose strength, it must be watered.
Therefore, it is necessary to prevent the drying of the foundation during the set of strength.
In addition to the direct watering of the foundation with water, it is necessary to make sure that the water does not evaporate from the foundation tape. For this, the foundation is covered with roofing material or plastic wrap.
After what time can the foundation be loaded?
The time after which the foundation can be loaded directly depends on the type of construction, the material from which the walls will be built. But, most importantly, the setting time of concrete.
Due to the fact that concrete is gaining brand strength within 30 days, it is a logical decision to begin to load the foundation no earlier than this time. In practice, for cottage construction, the formwork is removed after 7 days, and walls, that is, load the foundation, begin to be erected no earlier than 21 days after the foundation is poured.
After what time it is possible to overlap the strip foundation with plates?
If you intend to overlap the foundation with floor slabs, then the question - after what time to do this, is directly similar to the question of the foundation load. Therefore, the procedure is the same:
- formwork dismantling - after 7 days;
- overlapping plates - after 21 days.
Particular attention should be paid to the shallow strip foundation built on floating soils. Suppose you filled such a foundation and decided to leave it in the winter.
If such a foundation is left unloaded in winter, then due to winter-spring deformation of soils, a difference in the density of soils under the foundation will appear. And, as a result, load resistance in different parts foundation slab will be different, which can lead to cracks in the foundation.
Therefore, if you leave such a foundation in the winter, it is recommended to load it at least minimally - to remove the base.
What time of year is it better to lay the foundation?
Many people worry about the time of the year when it is better to fill the foundation. As a rule, the foundation is laid in the fall, so that during the winter it can stand. But, strict recommendations on the time of laying the foundation does not exist. The main thing is that the soil is not frozen.
Again, everything has to do with hardening concrete. If in spring and autumn Since there are no problems with this, in winter the water necessary for setting concrete can freeze. Because of this, concrete does not gain the necessary strength. Antifreeze additives, of course, can save the situation, but still best time years for pouring the foundation - summer or autumn.
Any concrete structure or cement mortarbefore you start others construction worksrelated to the load on this structure must be maintained for a certain time in the state of "pouring" without loading.
After pouring, the concrete structure goes through several stages of polymerization: setting, hardening and final curing. At the same time, during the setting time of concrete, further construction processes can be planned: the construction of walls, partitions and the installation of the roof.
What determines the hardening rate of concrete?
Factors that affect the rate of polymerization and hardening of concrete:
- Ambient temperature;
- Humidity of air;
- Direct or sliding sun rays;
- Brand of concrete;
- Additional measures: wetting with water, adding special additives, warming up in winter timecovered with polyethylene, etc .;
The polymerization of concrete can be described as a complex natural process associated with the set of strength and drying, which can be adjusted. The polymerisation of concrete consists of the following steps:
- Grasping. At an ambient temperature of 20 ° C, the volume setting of concrete begins two hours after the preparation and pouring of the mixture will last exactly the same period of time. When the temperature is lowered to 10 ° C or lower, the setting process significantly lengthens and can be from 20 hours or more;
- Hardening. For private concrete structures poured and maintained at a temperature of 15 to 20 ° C and a relative humidity of 75%, the hardening process is at least 3 days or 72 hours, after which you can begin other construction work;
- A set of strength. This is a lengthy process, depending on the "power" of the flooded structure, which can range from several weeks to several years.
How long does concrete dry?
- Seasonality fill. Depending on the specific ambient temperature and relative humidity, the setting time of concrete can be from three days in the summer and one month in the cold;
- Rammer. In this case, the rule applies: “the higher the density of the fill, the faster the hydration (hardening) processes. In construction companies, ramming is carried out with special installations. In private construction, tight "bayonet" shovel or manual ramming.
- The composition of concrete. The more porous fillers (expanded clay granules, slag) in the thickness of concrete, the more slowly hardening occurs. In variants with sand or gravel, the abduction process is much faster;
- To slow down the evaporation of moisture and slow down the hardening process, use special additives or regular liquid soap;
- Drying conditions. In order to avoid cracks in the hot season, they practice regular wetting with water or shelter with plastic wrap. In the cold season, shelter is practiced with special heating mats, introductions into the thickness of concrete heating cables or the construction of greenhouses;
Additives. This is a simple and widely used way to slow down or speed up the drying of concrete. IN wide sale antifrosty, modifying and accelerating are presented
The foundation is fundamental supporting structureperceiving all the loads from the building. Its main task is to support the weight of the building. The foundation must not settle, warp and form cracks. Thus, reliability is a basic requirement for the foundation.
The foundation will not become reliable if it is broken technological rules its manufacture and primary operation. It is recommended to make a concrete foundation at an ambient temperature of at least + 5 ° C. This makes the work seasonal, otherwise there will be no complete setting of concrete. Today we will find out how much the foundation can be loaded in time.
Ripening concrete
The main indicator of concrete characterizing its brand is its strength when tested for compression. After pouring concrete, it does not immediately become durable, it takes four weeks.
The first week for concrete is peak, during this period it receives up to 70% of the strength characteristic of this brand. IN further process hardening does not proceed so intensively, after 28 days from the moment of pouring, it is believed that concrete has matured and gained brand strength.
Until the concrete is fully ripe, do not load the foundation. Installation of walls should be carried out after the concrete has fully matured. The mixture obtains the minimum strength after seven days; a week later, some developers dismantle the formwork.
Laboratory tests showed that while maintaining the temperature + 30 ° С, in 72 hours the mortar gains about 65% of strength, and at 80 ° С, in 20 hours concrete receives already 80% of the brand strength.
In reality, it is impossible for 30 ° C to stand during the day. Therefore, in individual construction, it is more advisable not to rush and give concrete more time to set, and dismantle the formwork a month after pouring, after this time, you can proceed to the construction of walls.
Chemical processes
In the manufacture of concrete, cement is used, which is designed to connect the components of concrete. Cement, entering into a chemical reaction with water, forms a solid rocky substance that combines sand and gravel.
The chemical processes occurring at the initial stage are called setting, while the first bonds between the filler are formed in concrete, and the set of strength is to strengthen these bonds.
For normal flow chemical reactions in concrete, water is required. The ripening process of concrete is long, and the water contained in the solution initially quickly evaporates, so the concrete is protected from quick drying moisture, and for this, cover it with roofing material or plastic wrap, or periodically wet it with plenty. To obtain a quality foundation, it is important to ensure that uniform drying of concrete occurs.
Is it possible to make a foundation in winter?
When pouring the foundation in the winter, the maturation of concrete is suspended, since the water necessary for chemical processes freezes. But this is not all the disadvantages of such installation, the water in the solution, freezing, will expand, and at the same time tear the concrete from the inside. Practice and research show that already at minus 10 ° С chemical processes in concrete slow down, and with them the process of curing slows down.
Therefore, in the manufacture of the foundation in the winter, after pouring, the concrete mixture must be heated during the entire time of maturation. In individual construction, it is difficult to heat the foundation and this will entail additional costs, therefore it is advisable to produce the foundation in summer periodat average temperature air from 20 to 25 ° C.
How to reduce the ripening time of concrete?
Modern materials allow you to change the ripening time of concrete, it is enough to use special additives. The use of additives makes it possible to obtain strong concrete in two weeks. Such additives have one significant minus, which does not allow their use in individual construction. Additives reduce not only the ripening time, but also the setting time, and therefore, when applying them, there is little time for pouring the foundation.
Another way to reduce the ripening period is to increase the ambient temperature, which is also problematic for individual construction.
Compliance with the maturing time of concrete will provide a solid foundation.