How to prevent concrete “segregation” using Yulong concrete anti-segregation agent

Compared with the pouring construction of ordinary concrete, the pouring construction of pumped concrete has many advantages (such as saving manpower, material resources, shortening the construction period, etc.), and the single cost increase is not much. Therefore, in recent years, pumped concrete pouring has been widely used in high-rise building concrete construction. The extensive use of pumped concrete has promoted the development of commercial concrete. The advancement of science and technology has provided guarantee for the preparation and construction of pumped concrete. However, pumped concrete generally has the characteristics of large slump, which to a certain extent increases the difficulty of concrete quality control. In particular, the segregation and sinking of concrete are very common, which seriously affects the apparent performance and structural function of concrete. . Therefore, how to suppress and solve the segregation problem of concrete is an important issue that needs to be researched in the current development of pumped concrete. In response to the above problems, this article mainly analyzes the causes of concrete segregation from the raw materials used in concrete, and proposes countermeasures.

1. Harm caused by segregation

Segregation refers to the components of the concrete mixture A phenomenon in which the cohesion between aggregates is insufficient to resist the sinking of coarse aggregates. The main manifestations are concrete aggregate separation, delamination, sinking, poor workability, etc. Concrete segregation will seriously affect all aspects of concrete performance.

① Affects the performance of concrete pumping construction, causing sticky tanks, blocked pipes, affecting the construction period, etc., and reducing economic benefits.

② Affects the apparent effect of the concrete structure, such as sand patterns, exposed aggregates, and exposed steel bars on the concrete surface.

③ The strength of concrete will be greatly reduced, which will seriously affect the load-bearing capacity of the concrete structure and destroy the safety performance of the structure. In severe cases, it will cause rework and cause huge economic losses. .

④ The poor homogeneity of concrete results in inconsistent shrinkage of various parts of the concrete, which is prone to shrinkage cracks in the concrete. Especially when constructing concrete floor slabs, due to concrete segregation, the surface cement slurry layer thickens, shrinkage increases sharply, and serious cracks occur.

⑤ Greatly reduces the durability properties of concrete such as concrete impermeability and frost resistance.

2. Causes and countermeasures for concrete segregation

As we all know, ordinary concrete is mainly composed of cement , water, sand and gravel coarse and fine aggregate, admixtures and other materials are mixed; pumped concrete is made by adjusting the sand and gravel coarse and fine aggregate grade, sand rate and adding a certain amount of fly ash on the basis of ordinary concrete . In addition to the mixing method and mixing time, concrete segregation is generally related to the quality of the cementitious materials of the concrete mixture, excessive water consumption, poor gravel gradation, and excessive amount of water-reducing agent. The relationship is closer.

3. Cement. Cement is the most important cementing material in concrete. The stability of cement quality directly affects the stability of concrete quality. Changes in cement quality will cause segregation of concrete, and there are many factors in cement that affect the performance of concrete mixtures.

4. Changes in cement fineness. As we all know, the higher the fineness of the cement, the higher its activity and the greater the water demand of the cement. At the same time, the greater the fineness of the cement, the stronger the adsorption capacity of the cement particles to the concrete water-reducing agent, which greatly weakens the reduction of concrete water-reducing agents. Water reducing effect of aqueous agent. Therefore, in actual production, when the fineness of cement is greatly reduced, the water-reducing effect of concrete admixtures will be enhanced. When the dosage of admixtures remains unchanged, the water consumption of concrete will be greatly reduced. The decrease in cement fineness can easily lead to excessive amounts of concrete admixtures, causing concrete to segregate. And this kind of segregation usually occurs in high-strength concrete grades with higher amounts of water-reducing admixtures.

5. Changes in alkali content in cement. The alkali content has a great influence on the adaptability of cement and admixtures. As the alkali content of cement decreases, the water-reducing effect of the water-reducing agent increases. Therefore, when the alkali content of cement changes significantly, it may cause changes in the viscosity and flow of concrete. have a greater impact.

The influence of cement storage time. Cement is a kind of hydraulic cementitious material. If it is not stored well, it is very susceptible to moisture. After the cement gets damp, the water demand will be reduced. At the same time, the longer the storage time of the cement, the temperature of the cement itself will decrease, and the adsorption between cement fine powder particles will occur. They condense into larger particles, which reduces the surface energy of the cement particles and weakens the adsorption of the water-reducing agent by the cement particles. During the concrete test, the water-reducing effect of the water-reducing agent is often enhanced, and the new concrete mixture appears to ooze slurry. , the phenomenon of sinking to the bottom. In actual production, if cement stored for a long time is used and the mix ratio is not adjusted, it is very easy to cause concrete segregation. Of course, the impact of cement storage time on different types of cement is inconsistent, which needs to be understood through experiments.

In summary, it can be seen that there are many factors in cement that affect the workability of concrete, and they are relatively complex, but no matter what the factors are, , the results shown are the same, namely: (1) changes in cement water demand; (2) adaptability changes of cement and admixtures.

(4) Excessive mud content in sand and gravel will reduce the bonding force between the cement slurry and the aggregate, and the cement slurry's ability to wrap the aggregate will decrease. It leads to the separation of aggregates and concrete segregation.

For the phenomenon of concrete segregation caused by aggregates, the following measures can be taken to adjust.

(1) In order to avoid the problem of concrete segregation due to aggregate problems, we should first focus on prevention and strictly enforce the inspection system for the entry of aggregates to ensure Quality of aggregate.

(2) For the first reason above, the sand rate can be appropriately increased to adjust the concrete mix ratio to solve the segregation problem.

(3) For the segregation problem caused by excessive flake stone chips in the aggregate, adjusting the sand rate alone cannot solve the problem and should be increased. Concrete cementing materials (especially the amount of admixtures), and adjust the amount of admixtures at the same time.

(4) The problem of concrete segregation caused by the problem of aggregate moisture content should be solved by extending the mixing time. Increasing the dosage of admixtures such as fly ash is also very effective in controlling this type of segregation phenomenon.

Others. Many causes of concrete segregation have been analyzed above, but the causes of concrete segregation are far more than these. Issues such as cement dosage, types of cement and admixtures, and measurement are all causes of concrete segregation. In daily work, you should pay attention to accumulation, strengthen the management of details, and solve problems in a timely manner.

Summary

1. The key to preventing concrete segregation is prevention.

2. When segregation occurs in concrete, the quality of various raw materials should be carefully analyzed and checked. It is best to use comparative tests to check and use the elimination method to find out. Reasons, prescribe the right medicine.

3. Segregation is a common quality problem in pumped concrete. When a problem occurs, it should be tested in time. The problem is easy to solve.