Concrete problem 10, what quality problems are prone to occur after concrete pouring

Cementitious materials include cement, mineral admixtures, etc. The addition of admixtures is generally to save costs, improve the condition of concrete, improve strength, etc. Keep the total amount of rubber unchanged, increase the amount of admixture, and the cement will decrease accordingly, but the water-glue ratio will not change; If the amount of cement remains the same and the amount of admixture increases, the total amount of rubber will also increase, so that the water-glue ratio will be reduced.

Generally speaking, for the same grade of concrete, the total amount of rubber mixed with admixture is a little more than the total amount of rubber without mixing.

It stands to reason that this is what you say. However, it also depends on whether the admixture will participate in the hydration reaction, if it participates, the early strength is still low, but the later strength is similar to that of the unadulterated. According to the 28-year-old period, it is basically necessary to reduce the water-cement ratio.

The amount of mineral admixture increases, (the amount is a percentage of mass), the mineral admixture in the cementitious material increases, but the quality of the cement remains the same, or decreases.

The increase in the content of mineral admixture is generally a percentage of the mass of the cementitious material (the mass of cement plus admixture), and if the water-cement ratio remains unchanged, then the cement will be less. However, to achieve the same strength, it must be a reduction in the water-cement ratio, if the water remains unchanged, it means that the total cementitious material has increased, but the cement should still be less. You'll know when you try it out.

Yes, that's right. Mineral admixtures are part of the cementitious material. Such as mineral powder, silica fume, fly ash, cement are cementitious materials.

The factors that affect the strength of concrete are mainly raw materials and production technology.

Raw materials include: cement strength to water-cement ratio, aggregate type, quality and quantity, admixtures and admixtures.

The production process includes: stirring in vibration, curing temperature and humidity, age.

You can read "The Effect of Mineral Admixture Content on the Performance of Pumped Concrete" directly in the library.

After the concrete is poured, these quality problems are prone to occur: the surface of the concrete is matte.

Phenomenon: The surface of the concrete is rough or has many small pits.

Treatment method: hemp surface mainly affects the appearance of concrete, and the parts that are no longer decorated on the surface should be repaired. That is, the hemp surface part should be washed with water, and then leveled with cement slurry or 1:2 cement mortar after being fully wetted.

Before pouring, the garbage, soil, oil stains and other debris on the steel bar in the formwork should be removed, and the cement mortar cushion block and plastic cushion block of the steel bar should be checked to see if they are well mated. If wooden formwork is used, it should be watered to make the formwork moist. The sweeping port of the column formwork should be closed after removing debris and stagnant water.

Job Conditions:

1. The formwork, steel bars, embedded parts and pipelines of the pouring concrete layer are all installed, and the design requirements are met after inspection, and the hidden and pre-inspection procedures are completed.

2. The frame and horse road for pouring concrete have been erected and passed the inspection.

3. Cement, sand, stone and admixtures have been inspected to meet the requirements of relevant standards, and the laboratory has issued a notice of concrete mix ratio.

4. The scale (or automatic feeding system) is checked and approved for accurate measurement, and the vibrator (rod) is qualified after inspection and trial operation.

5. The foreman has carried out comprehensive construction technical training for the operation team according to the construction plan, and the concrete pouring application has been approved.

a) The sand contains too many pebbles.

Cause analysis. This is due to repeated sand pumping in the river channel, less fine sand, more pebbles, sand pumpers enlarge the sieve holes, resulting in more pebbles.

Handling method or letter reform.

Take a sand sample, use a sieve to screen out the pebbles, calculate the sieving residual rate, as long as the sieving residual rate is not more than 10%, and the excess will be returned immediately. Add the excess pebble screening rate to the sand rate.

2) Concrete mixture slurry.

Cause analysis. This is due to the large dosage of admixtures. If the slurry flows out of the edge within 30, it is slightly segregated, and if the slurry flows out of the edge more than 100, it is severe segregation.

Solution: 1) When severe segregation, the amount of admixture should be reduced before redo;

2) If it is mild or moderately segregated, it is necessary to look at the slump of half an hour, and if the slump is large after half an hour, the segregated slurry will disappear naturally; If the slump is small after half an hour, but the slurry is very slight, look at the slump and workability of 1 hour, if the effect is good, it means that this dosage is available.

3) The wrapping property of the concrete mixture is not good.

Cause analysis. 1) The adaptability of admixtures is poor, and the cement or other concrete raw materials are not adaptable, or the amount of admixtures is too large.

2) The sand fineness modulus is large, the particle content of the particle size is insufficient, and the sand rate is small;

3) The water content of sand and gravel suddenly increases, resulting in high actual water consumption of concrete;

4) The amount of concrete mixture slurry is insufficient.

Solution: 1) Compound air entraining and thickening components in the admixture, and adjust the compatibility of the admixture with concrete raw materials;

2) Compound fine sand, adjust the fineness modulus of fine aggregate, or increase the sand rate;

3) Reduce the amount of admixtures or water used;

4) Increase the amount of mineral admixture and increase the volume of slurry.

Please ask the admixture factory to adjust the formula and try again, or find admixture samples from other manufacturers to try again. If the cement is not suitable for the admixture, you can change the cement or admixture and try again until it is suitable.

4) The slump of the concrete mixture is small.

Cause analysis. 1) The moisture content of sand is small, and the water consumption for production is small;

2) There is a change in the mixture of new cement, and the demand for admixtures increases;

3) The quality of fly ash is poor, which leads to the increase of water demand;

4) The water reduction rate of the new admixture is small;

5) It is the increase of shale content or mud content in the stone.

Solution: 1) Observe the moisture content of the sand, if it is small, you can increase the amount of water jacket by 5 m3; If it is too small, the water consumption can be increased by 10 m3;

2) If the moisture content of the sand is normal, it is the cause of cement or fly ash, and the amount of admixture should be increased;

3) The test determines that the water reduction rate of the admixture is small, and the dosage of the admixture should be increased appropriately;

4) When it is determined that it is the shale of stones or the mud content is too large, the amount of admixture should also be appropriately increased (the increase in the amount should be determined by experiment).

5) The slump of the concrete mixture is too large.

Cause analysis. 1) When the loader is loading, the shovel uses the green sand that has just been pulled, which is caused by excessive moisture content;

2) The concrete truck tank is not discharged from the sewage tank, which is caused by imitation of water.

Problems that are prone to occur in the process of concrete pouring: due to the untimely occurrence of concrete, resulting in the existence of construction joints, the construction personnel do not leave the construction joints in accordance with the specified position or the treatment measures for the construction joints are not in place.

Concrete is not poured evenly on both sides of the opening, resulting in deformation or deviation of the opening.

For some wide windows, the bottom template does not take measures, and it often happens that the pouring under the window sill is not in place.

The reinforcement personnel are not in place to cause the deviation of the reinforcement, and the concrete pouring often leads to the movement of the wall reinforcement, and if there is no reinforcement personnel to adjust the reinforcement in time, it will cause the deviation of the wall reinforcement to be serious.

1.Why is concrete divided into strength grades?

To ask why concrete is divided into strength grades, you should first know what concrete strength grades are. Concrete strength grade.

It is artificially divided according to the compressive strength value of the concrete cube, and it is the characteristic strength of concrete. According to the current relevant standards.

The standard and specification stipulate that the compressive strength of the concrete cube is a cube test of the standard size with a side length of 150mm made according to the standard method.

The compressive strength of the concrete cube measured according to the standard test method under the standard conditions of environment or water with a temperature of 20+3 °C and a relative wet slag and a degree of more than 90%, cured to 28 days of age. According to the provisions of the relevant standards, the strength grade of building materials should be:

The name of the material is expressed along with its strength standard value. Therefore, the concrete strength grade is based on the symbol C (English concrete shrinkage.

The standard value of the compressive strength of the cube written and followed by it is divided into twelve levels: ie.

c10,c15,c20,c25,c30,c35,c40,c45,c50,c55,c60.

Because the load of concrete in different parts of the general project is different, some are large, some are small, and one cannot be completely used.

a strength grade of concrete. For the parts that bear high pressure, it is necessary to use high-strength grade concrete, and for those that bear low pressure.

For the part, it is necessary to use low-strength grade concrete, so the concrete is divided into different strength grades to meet the needs of different projects.

Yes, it is selected through design calculation.

2.Why is concrete divided into strength grades by compressive strength?

Concrete is called artificial stone, and its main performance is to withstand pressure, and its ability to resist tension or breaking is very low, but it is compressive.

The ability is more than ten times higher. For this reason, concrete in engineering structures, if it is to be encouraged. in reinforced concrete.

In the soil structure, the reinforcement is also tried to withstand the tensile force, and the concrete is mainly subjected to the pressure. The main performance of the concrete in the mark.

It is the compressive strength, and the higher the compressive strength, the better the other properties of the concrete. Therefore, concrete also has high compressive strength.

Small to determine the intensity level.

3.Why does the strength of concrete stipulate 28d as the standard strength?

Concrete is gradually hardened by the cementation of cement to improve its compressive strength. The hardening of the cement is not Liang Zhi all at once.

It is finished, but gradually perfected over time. Under normal maintenance conditions, the compressive strength increased significantly in the first seven days.

Fast, the growth is slightly slower between 7d and 14d, and after 28d, the intensity growth is even slower. That is to say, after 28 days, it is compressive.

The strength is the standard strength, which is used as the standard for the quality of design and construction inspection. Obviously, if the intensity of less than 28d is taken as the standard strength.

degree, will make the performance of the concrete can not be fully utilized. If the strength greater than 28d is used as the standard strength, although the nature of the concrete.

It can be fully utilized, but due to the long time to reach the standard strength, the construction progress is affected.