The 28 day strength value of concrete is 10

Is it to be qualified or unqualified?

About 120% is a relatively normal and common value. The specimens made on the same plate are usually lower than those of standard maintenance. More than 200% of the standard breeding can be said to be in the past.

Compression or bending? The size of the specimen and the requirements for the use of concrete are different, and the strength value requirements will be correspondingly different.

It also depends on whether you have added admixtures, how much is the curing temperature, the conditions during curing, and what part is used.

We can discuss this issue when we have time, hehe.

It is not certain, this is related to the production of the test piece, the conditions of health preservation, the mix ratio and a certain deviation rate. It may be higher or lower.

Theoretically speaking, it should be lower than the strength of C25, because the conditions of natural watering are of course not as good as the conditions of the health room, but in fact, a certain safety factor will be reserved in advance when doing the C25 concrete mix ratio, that is, when doing the mix ratio test, the strength should be greater than C25, otherwise the mix ratio is unsuccessful, so in general, as long as the concrete component strength is higher than C25 as long as the mix ratio report issued by the regular laboratory.

Of course, it is necessary to achieve resistance above C25, and there is no one in the standard maintenance that can be cured by water, only soaked in water.

Should be C25 and above.

It's too low, and if it's not qualified, it has to be rebounded.

It's too high to say that you do a fake test block, and our side is no more than 170% qualified.

In a humid environment at room temperature, concrete strength.

It is a continuous development process, but the intensity development rate is high in the early stage (14 days ago), and the intensity growth rate gradually decreases in the later stage. This consists of the mineral composition of cement, cementitious material.

Composition, water addition, environmental humidity and other factors are determined. In the spring of the laboratory environment, there are tests that prove that the strength of concrete will increase slightly after 10 years. Therefore, it is normal to have a large increase in intensity after 28 days.

General rule: use pure silicate.

Fast-hardening cement, mixed with silica fume.

or ultra-fine mineral powder, the early strength of concrete is developed into a block, and the strength growth potential in the later stage is small. The use of mineral admixtures such as fly ash and mineral powder will have a slower strength development in the early stage, but there will be a greater strength increase in the later stage, because the hydration process of fly ash and ordinary fineness mineral powder is slower. Therefore, some projects set the standard strength test age of fly ash concrete as 56 days, and even set the test age as 90 days for large amount of fly ash concrete.

The aim is to make the most of the actual strength of the fly ash concrete, as the structure is not put into use after 28 days, and it often takes three months or more for the load to actually bear the load.

In addition, the strength of concrete may also shrink, mostly in concrete structures that are not scattered. For example, internal destruction such as alkali-aggregate reactions, delayed aluminite formation, etc., has occurred. For example, by the action of damaging factors in the environment, high temperature dehydration (above 100 degrees), freeze-thaw, chemical corrosion, sulfate.

erosion, etc.

The strength of concrete can basically reach about 50% of the design value in 3 days, 70-80% in 7 days, and about 100% in 28 days, or even higher.

Concrete has the characteristics of abundant raw materials and simple production process, so that the amount of concrete is getting larger and larger, and concrete has the characteristics of high compressive strength, good durability and wide range of strength grades.

These characteristics make it widely used, not only in various civil engineering projects, but also in shipbuilding, machinery industry, marine development, geothermal engineering, etc., concrete is also an important material.

Precautions for beating concrete:

1. When putting concrete into the mold, do not inject a large amount of concrete into the impact formwork or steel frame. If the height of the concrete pouring is more than 2m, the tandem pipe and slide pipe should be used for cutting, and the drop height between the discharge nozzle and the pouring layer should be kept within it.

2. If you plan to pour concrete twice, the interval should usually not exceed 1 hour and 30 minutes, and the vibrator must be continuously stirred at the handover position.

3. In the process of pouring concrete, when the concrete surface floats, there are no bubbles and will not sink, the vibrating rod should always be used to vibrate. When using a vibrator, it is necessary to carry out continuous movements in a determined order, and the position of each movement should not exceed 40 cm to avoid leakage or excessive vibration.

4. After a rough estimate of the remaining amount of concrete and the remaining amount of concrete, the required quantity should be discussed with the construction manager of the batching plant and a reasonable schedule should be formulated.

Hello, I'm glad to answer your questions, please wait a minute, oh kiss and ask a question, my cement pavement has been poured for 5 days, and there are a few days to pass the heavy-duty car, because in the curing process of cement, in the time intensity curve, 3 days, 7 days, 28 days, these three time periods are obviously representative. Within 3 days, the strength of cement is growing rapidly. Generally, it can reach more than 75% of the maximum strength, and can be used basically.

Within 3 to 7 days, the strength growth of cement slows down, and generally reaches more than 95% of the maximum strength, which can be used completely. After 7 days, the cement strength increases more slowly, and by 28 days, the cement strength reaches its maximum. 14 days is a median value, and it will not increase after 28 days.

Therefore, the national standard regards these few days as several basic time points to measure the strength of cement.

Question: Can I pass for 10 days?

Depending on the level of your pouring, if you maintain it properly, it will take seven days to pass the small car, and at least 14 days to pass the large car, generally about 28 days.

Hope it can help you kiss it.

Question: PC425 cement, thickness 20 cm, is there an 8 mm steel bar in the middle?

Yes, please wait a minute.

Purely in terms of pressure, there should be no problem, but it is difficult to guarantee that it will not crack, and it will take at least 12 days to kiss.

There is a battlefield to ask questions, and I am afraid of being crushed by a cart.

At least 12 days to pass the heavy vehicle.

Question: Is the temperature 10 not guaranteed now?

There is no provision for this, because for the strength of concrete, the strength growth has slowed down by 28 days, and the difference between the beginning of the 28th day and the end of the 28th day is very small, and it can be considered to be within the error range and cannot be distinguished. So there is no specific time requested.

The concrete strength is generally based on 28 days. However, there are also structures in the specification that take the 90-day age as the standard for the loading speed and slow search. The strength growth process of concrete is the process of hydration of chemical components (silicate, aluminate, etc.) in cement.

Under the 28-day standard condition, its intensity is about 97% of its 90-day intensity and about 99% of its 180-day intensity. After 180 days, although it is still growing in intensity, it is small and very slow.