Strength of concrete - the process from the inside

08-05-2018

Building

The most important property for concrete, characterizing its brand, is the strength of the product, which is tested in laboratory conditions. A sample that has reached the age of 28 days (the period for which concrete is being cured depending on temperature may vary) is subjected to a compressive load until the first signs of failure. According to the test results, a concrete grade is assigned under compression conditions in the range from M50 to M800.

Not everyone thinks about whether the product will have the necessary strength, blindly trusting the hired workers or the workflow instructions that the neighbor suggested

Design of construction objects

When designing a building with the use of concrete mixes, a certain class of material is approved for each individual construction.

The use of a brand depends on the application, but we can safely say that brands in the range of 100-500 are considered the most popular in urban planning.

Usually it is the cube that is the result of laboratory research.

Designing structures where the formation of cracks in the supporting elements is unacceptable (dams, water storage tanks, etc.) should be considered tensile strength of the hardened mortar.
The design of pavements and takeoff lines of airfields is of great importance indicator of tensile strength during bending.

All these components of the indicator of the strength of concrete are reflected in the marking of the material.

For understanding, we give the ratio of indicators of grading and classiness of concrete with indicators of the strength of a mixture of classes:

3.5 - an average strength indicator of 46 kgf / cm2 (only numerical values will be shown below) - grade 50.
At 5 - 65 - M 75.
At 7.5-98 - M 100.
B10 and B12.5 - 131 and 164 - M150.
In 15 - 196 - M 200.
In 20 - 262 - M 250.
In 25 - 327 - M 300.
In 30 - 393 - M 450.
C 35 and C 40 - 458 and 524 - M 550.
45 and B 50 - 589 and 655 - M 600.
At 55 - 720 - M 700.
In 60 - 786 - M 800.

It is possible to translate the value of the brand of the mixture into the class according to the formula - B = (M * 0.787) / 10. If you are going to build something with your own hands, that is, is a private developer, then it is best to use the brands 250 - 550.

The presence of many cracks and bubbles indicates a low quality product

Note! The class of concrete reflects the guaranteed strength in MPa. It is possible to change the class of concrete at the construction stage in a section with the project only by agreement with the project organization and approval by the department of architectural supervision. To this resort in exceptional cases.

What affects the strength of concrete

This factor of the finished product is influenced by many factors:

The quality and correct reinforcement cage (in the photo) is another indicator that directly affects the strength of a concrete product.

The activity and content of cement in the mixture.
Water / cement ratio.
Selection of mineral aggregates.
The degree of homogeneity (depending on the quality of mixing).
Subsequent compaction.
Time elapsed after pouring.
Concrete hardening conditions.

To reduce the time of hardening of concrete products using concrete strength accelerators. They are used for technological needs and always in the production of works in the winter. With the introduction of the mixture of special additives, of course, increases the selling cost of concrete.

Note! Additives are relevant only for large construction companies engaged in the construction of apartment buildings, they will not bring particular benefit to private developers.

Achievement of concrete grade strength

The readiness of the mixture, depending on the time intervals, reflects the graph of the strength gain of concrete SNiP. The standard specifies the average time of hardening and the time to build strength of concrete.

Under normal conditions, the mixture matures within 28 days, and:

Horizontal time is indicated (day), vertical strength (percentage)

The first stage of intensive hardening is the first five days.
After seven days after completion of casting, 70% of the design strength of the product is achieved.
The final time of hardening (100%) will have to wait the remaining 21 days and only then you can proceed to further work.

Attention! This is how the strength indicators of concrete solutions change over time according to SNiP. In real conditions, they can vary due to different reasons, this is influenced not only by the temperature, but also by the quality of the solution.

Leaving in the period of aging

Here is a brief guide on how to create optimal conditions for cement ripening:

The first five to seven days are particularly important to carry out activities to ensure comfortable conditions for holding cement poured:

Cover the surface of the solution with a moisture-proof material (regular plastic film will do, its price does not hit the budget very much).
Actively moisturize it about once a day, again covering the protective canvas.
If necessary, organize the heating of concrete with heat guns.

After a week, pay special attention to moisture, if at the initial stage it was allowed to water the hardening solution once every two days, then you should not miss it.

Note! At an outdoor air temperature of 25-30 ° C, the product can be put into operation after 11 days.

In the regulatory documents relating to concrete work, you can find a schedule for the set of strength of concrete B25 or any other class that will help you deal with the construction time.

These are the numbers and calculations you can find in specialized documents.

Conclusion

We hope that the above information was useful to you, we only remind you that the building up of concrete strength over time is guaranteed in ideal conditions. Guided by this information, you should give an amendment to "life", and not to limit the period of hardening in moderate weather 14-15 days, as it can be stated in the documents.

In the presented videos in this article you will find additional information on this topic.