One of the important indicators of concrete quality is strength. If you familiarize yourself with the requirements of state standards, you can find information that the strength can vary from M50 to 800. However, concrete brands from M100 to 500 are among the most popular.
Strength Chart
A solution of concrete for a certain time after pouring will acquire the desired performance properties. This time interval is called the aging period, after which you can apply a protective layer. The graph of the set of concrete strength reflects the time during which the material will reach the highest level of strength. If normal conditions are maintained, then it will take 28 days.
The first five days is the time during which intense hardening will occur. But 7 days after completion of work, the material will reach 70% strength. Further construction work is recommended to begin after reaching one hundred percent strength, which will happen in 28 days. The time schedule for concrete strength may vary for individual cases. In order to determine the timing, control tests on the samples are carried out.
What else you need to know
If work on monolithic housing construction is carried out in warm time, then to optimize the process of maintaining the mixture and gaining its physical and mechanical properties, it will be necessary to maintain the structure in the formwork and leave to ripen after dismantling the fence. The schedule for setting concrete strength in cold weather will be different. In order to achieve brand strength, it is necessary to provide concrete heating and waterproofing. This is due to the fact that lower temperatures contribute to the slowdown of polymerization.
In order for the set of strength to occur as quickly as possible, and the concrete exposure to time was minimized, it is necessary to add sand concrete to the ingredients, in which the water percentage is minimal. If cement and water are added in a proportion of four to one, then the terms will be halved. To obtain such a result, the composition should be supplemented with plasticizers. The mixture can ripen faster if its temperature is artificially raised.
Strength control
In order for the concrete curing schedule to be observed, for some time - up to a week - it is necessary to carry out activities that provide conditions for the exposure of the mortar. It must be heated, moistened, and also covered with moisture and heat insulating materials.
For this, heat guns are often used. Specialists recommend paying special attention to wetting the surface. 7 days after completion of pouring under such conditions, if the temperature of the external environment varies from 25 to 30 ° C, the structure can be loaded.
Concrete classification
If cement and traditional dense aggregates are used in the process of mixing the mortar, which make it possible to obtain heavy compositions, then these mixtures are classified as M50-M800. If you have concrete of the M50-M450 brand, then porous aggregates were used to prepare it, allowing to obtain light compositions. Concrete has a brand name within M50-M150, if it is particularly light or light, as well as cellular.
Design concrete grade should be determined at the stage of preparation of documentation for the construction of the object. This characteristic is given based on the axial compression resistance in the sample cubes. In constructions under construction, axial tension is the main one, the brand of cement is determined by it.
The set of concrete strength (set graph for tensile time) will last longer when the compressive strength mark rises. But in the case of high-strength materials, the growth of tensile strength slows down. Depending on the composition and area of use of the mixture, the strength and grade are determined.
The most durable are materials with the following brands:
They are used in the construction of critical structures. When constructions and buildings are being built that require high strength, concrete of the M300 brand is used. But when arranging the screed, it is best to use the composition of the M200 brand. The strongest are cements, the brand of which begins with the M500.
The dependence of the set of strength on temperature
If you are going to use the mortar in construction, then you should know the graph of the temperature dependence of the set of concrete strengths. As mentioned above, setting occurs within the first few days after mixing the solution. But to complete the first stage, time will be needed, which is affected by the temperature of the environment.
For example, when the thermometer is held at 20 ° C or higher, it takes an hour to set. The process begins 2 hours after the mixture is cooked, and ends after 3 hours. The time and completion of the stage during cooling will shift; more than a day will be necessary for setting. When the thermometer column is kept at zero, the process starts 6-10 hours after the solution is prepared, and it lasts up to 20 hours after pouring.
It is also important to know about viscosity reduction. In the first stage, the solution remains mobile. During this period, it can be mechanically influenced, giving the structure the desired shape. The setting stage can be extended using the thixotropy mechanism, exerting a mechanical effect on the mixture. Mixing the mortar in a concrete mixer ensures the extension of the first stage.
Percentage of concrete strength versus grade depending on temperature and time
Beginner builders are usually interested in a graph of concrete strength set at 25 ° . In this case, everything will depend on the brand of concrete and the curing time. If you use Portland cement grades within the range of M 400 to 500 when kneading, you will eventually be able to obtain concrete M200-300. In a day at the indicated temperature, its percentage of compressive strength from the vintage will be 23. In two, three days, this figure will increase to 40 and 50%, respectively.
After 5, 7 and 14 days, the percentage of brand strength will be 65, 75 and 90%, respectively. The graph of concrete strength set at 30 ° changes slightly. In a day and two, the strength will be 35 and 55% of the brand, respectively. After three, five and seven days, the strength will be 65, 80 and 90%, respectively. It is important to remember that a normative-safe period is 50%, while work can only be started when the concrete strength has reached 72% of the brand value.
The critical strength of concrete depending on the brand: an overview
Immediately after pouring, the solution will gain strength due to heat generation, but after freezing water, the process will stop. If the work is supposed to be done in winter or autumn, it is important to add antifreeze mixtures to the solution. After laying, alumina cement generates 7 times more heat than regular Portland cement. This indicates that the mixture prepared on its basis will gain strength at low temperatures.
The brand also affects the speed of the process. The lower it is, the higher is the critical strength. The graph of the set of concrete strength, an overview of which is presented in the article, indicates that the critical strength for concrete grades from M15 to 150 is 50%. For prestressed structures made of concrete brand M200 to 300, this value is 40% of the brand. Concrete grades from M400 to 500 have a critical strength of 30%.
Concrete hardening in perspective
The schedule for building concrete strength (SNiP 52-01-2003) is not limited to a month. It may take several years to complete the curing process. But you can determine the brand of concrete after 4 weeks. Strength design will gain at different speeds. This process proceeds most intensively in the first week. After 3 months, the strength will increase by 20%, after the process slows down, but does not stop. The indicator can double in three years, this process will be affected by:
- time;
- humidity;
- temperature;
- brand of concrete.
Quite often, novice builders ask themselves the question in which GOST the concrete strength curing schedule can be found. If you look at GOST 18105-2010, then you can learn more about this. These documents mention that temperature directly affects the duration of the process. For example, at 40 ° C, the brand value is reached in a week. Therefore, in winter, work is not recommended. After all, it is problematic to heat concrete on its own, for this you need to use special equipment and first familiarize yourself with the technology. But heating the mixture by more than 90 ° C is completely unacceptable.
Conclusion
Having familiarized with the graph of strength gain, you will be able to understand that formwork is carried out when the structural strength exceeds 50% of the brand value. But if the temperature of the environment dropped below 10 ° C, then the brand value will not be reached after 2 weeks. Such weather conditions require the need to heat the poured solution.