In concrete, when does the 28 day age of cement start to be calculated?

The 28-day age of cement has nothing to do with concrete, the age of cement is mainly calculated from the kiln, and the strength value of the early age of the kiln cement will be tested, that is, the strength value of the 3-day age period, and then the strength value of the 28-day age period will be tested, so that the stability and strength of the cement can be determined whether it meets the requirements of the specification, and can only leave the factory after meeting the requirements of the specification. After the cement enters the construction site, it needs to be retested, and the retest is mainly to detect the strength value of the cement at the age of 28 days, and it can be used only after meeting the requirements of the specification. The cement used in the concrete is the cement that has passed the retest, so there is no need for a strength test.

The concrete needs to be tested for the strength of the test block, and there is a standard 28-day age here, but this age is the concrete test block.

age.

For example, the time of pouring cement into the mixing pot is 10:30 on May 1, then the 28-day age is 10:30 on May 29, and the 28-day test can be 8 hours.

If it is calculated by date, from the day the concrete is poured, plus 28 days is its age, if it is directly calculated by the number of days, that is, the day is not counted, the next day is 1 day, until 28 days.

The 28-day age of cement is calculated from the time of adding water.

The standard curing age is 28 days from the start of stirring and adding water, and the hydration is basically over.

The demoulding time of the specimen under the same condition can be the same as the demoulding time of the actual component, and the specimen still needs to be cured under the same condition after demoulding!

Under the conditions of normal maintenance, the strength of concrete will continue to develop with the growth of age, the strength develops faster in the initial 7 14d, and then gradually slows down, 28d reaches the design strength, and determines the strength grade of concrete according to the compressive strength of 28d. After 28 days, the intensity is still developing, and its growth process can continue for decades.

Cement has an initial setting time and a final setting time. Generally, the initial setting time shall not be earlier than 45min, the final setting time of Portland cement shall not be longer, and the final setting time of the other five types of cement shall not be longer than 10h.

For the part that bears high pressure, it is necessary to use high-strength grade concrete, and for the part that bears low pressure, it is necessary to use low-strength rolling grade concrete, therefore, the concrete is divided into different strength grades to meet the needs of different projects, and is selected through design calculation.