This paper introduces in detail what strength levels of concrete, what are the requirements of concrete for water quality, what factors the durability of concrete is related to, and how concrete is maintained.
Why should concrete be graded in intensity?
To ask why concrete should be graded in strength, you should first know what the strength level of
concrete is. The concrete strength level is artificially divided according to the value of the concrete
cube's anti-pressure strength, which is the characteristic strength of concrete. According to the
current relevant standards and specifications, the concrete cube pressure strength is a standard size
of 150mm of the edge of the standard size of the cube test piece sproducing according to the
standard method, the temperature consistent with the ISO test method is 20 pc 2 degrees C, humidity
is more than 95% of the standard maintenance room, maintenance to 28d age.
The pressure strength of the concrete cube measured according to the standard test method.
According to the relevant standards, building material strength grade should be expressed by the
name of the material plus its strength standard value.
Therefore, the concrete strength grade is divided into the standard valueofs of the symbol C (short for the English concrete Concrete) and the pressure strength of the cube behind it: C10, C15, C20, C25, C30, C35, C40, C45, C50, C55, C60, C65, C70, C75, C80.
Because the general engineering of different parts of the concrete load is not the same, some large,
some small, can not fully use a strength grade of concrete. For the heavy pressure of the site, it is
necessary to use high-strength grade concrete, for the low pressure of the site, the use of low-
strength grade of concrete, therefore, the concrete is divided into different strength levels to meet the
needs of different projects, through the design and calculation of selection.
Why does concrete specify 28d strength as the standard strength?
Concrete is based on the cement bonding action, gradually hardening, and improve the strength of
pressure. Because the cement stiffness is not done at once, but gradually perfected over time.
Under normal maintenance conditions, the first seven days of pressure resistance increased faster,
between 7d and 14d growth slightly slower, and after 28d, the intensity growth is relatively slow.
In other words, after 28d the pressure strength is the standard strength, as the standard for design
and construction inspection quality. Obviously, if the strength of less than 28d as the standard
strength, will make the concrete performance can not be fully exploited. If the strength of greater
than 28d as the standard strength, although the performance of concrete can be fully developed,
but because of the time to reach the standard strength is too long, affecting the construction
progress.
Concrete level leveling on concrete working
Why does concrete had request standard of water?
Industrial wastewater containing fat, vegetable oil, sugar, acid and so on can not be used to mix
concrete. Because the water containing impurities will reduce the cement bonding force, so that the
strength of the concrete decreased, so can not use mineral water contains a large number of salts, so
that cement can not be very resistant to water erosion.
For the chemical composition of mineral water, must meet the indicators set by the family, or
compared with ordinary drinking fresh water test, see the intensity does not decrease before use.
As for the general tap water and drinkable water, can be used to mix concrete.
Concrete level leveling on concrete working
Why are concrete blocks in groups of three?
Concrete test block is the standard to measure the strength of concrete components, that is, the
strength of the test block is destroyed by pressure, as the strength of the component can have.
Therefore, in addition to the test block should be made according to the component, the test block
must also have a certain number. Because although we try to make the concrete of the test block and
the concrete of the component is the same, but after all, there are some differences, if only a test
block to identify the strength of the component, it is difficult to be reliable. So in three groups, the
strength of the three test blocks is used as the strength of the three test blocks (in special cases, some
values need to be removed), that is, the strength of the component symup.
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