In recent years, concrete admixture technology has developed rapidly. Due to the wide variety of concrete admixtures with different properties, the characteristics of construction projects and the actual engineering environment are different, as well as the materials required for different projects in different regions. They are also different. If the application of admixtures is inappropriate, it will lead to varying degrees of technical accidents or problems related to project quality.
The application of admixtures in concrete is absolutely different from the application of other materials such as cement and aggregates. It not only needs to be tested itself, but also needs to be tested on its adaptability to cement, mortar and other tests. To test the impact on the performance of concrete, in projects using admixtures in concrete, it is first necessary to select a reasonable type of admixture, clarify its dosage and mixing method, and it should be well adapted to cement. sex. Since the performance of concrete and the quality of construction projects are directly affected by the adaptability of admixtures and cement, the adaptability of admixtures and cement in concrete has gradually become an urgent problem in our country.
1. Incompatibility between admixtures and cement
1.1 Abnormal cement setting
When cement uses anhydrite as a setting regulator, because The gypsum has a strong adsorption effect on sugar-calcium water-reducing agents, lignin-based water-reducing agents and polyol water-reducing agents, so it reduces the solubility of gypsum and cannot provide enough sulfate ions and C3A reacts to form ettringite, which will also cause C3A to hydrate rapidly when the C3A content in cement is high (more than 8%). It may cause “false setting” in concrete. In addition, excessive retardation of cement is another manifestation of abnormal setting of cement caused by water reducing agent.
1.2 Workability of concrete Poor
The main manifestations of poor concrete work are: at the beginning of the induction period, its fluidity decreases rapidly; the main manifestations of concrete bleeding and segregation are that the concrete appears relatively unstable during trial mixing. The phenomenon of sticking to the bottom plate increases the friction resistance with the inner wall of the pipeline during pumping, which easily causes pump blockage; the adsorption of carbon to the water-reducing agent will lead to a reduction in dispersion efficiency; insufficient retardation and plastic retention; water-reducing agent and slowing The coagulants are not fused; ordinary air-entraining agents and polycarboxylic acid admixtures have poor adaptability, and sometimes even increase the bleeding and segregation of concrete.
2. Influence of admixtures and cement Factors of adaptability
2.1 Cement
Because cement clinkers are different, their performance in adsorbing water-reducing agents is also different. The main order of action is:
C3A>C4AF>C3S>C2S, after adding the water-reducing agent to the cement slurry system, because C3A has the fastest hydration rate, its adsorption capacity for the water-reducing agent is also the largest, and the water-reducing agent will be absorbed first. A large amount of water-reducing agent is absorbed. Therefore, if cement with a higher content of C3A has the same amount of water-reducing agent, the more water-reducing agent it absorbs, it will definitely affect other minerals in the cement slurry. The amount of water-reducing agent required for the components has an impact, which is mainly manifested in the low fluidity of the concrete. At this time, it is necessary to increase the amount of water-reducing agent appropriately. The alkali content in the cement will affect the effect of the water-reducing agent. It has a great influence. Under normal circumstances, the alkali in cement has a significant early-stage and accelerating effect, so the fluidity of concrete is reduced, which in turn leads to the use of water-reducing agent not having the expected effect. Therefore, it should be used as much as possible Low-alkali cement.
2.2 Water reducing agent
2.2 1 Types of water reducing agent
Most carboxylic acid coagulation admixtures are good for cement The adaptability is relatively good, because carboxylic acid admixtures are mainly formed through graft copolymerization. However, polycarboxylic acid admixtures sometimes have certain restrictions on the range of certain cement dosages. , if it is slightly more, it is very easy to cause serious bleeding and segregation.
2.2 2 Re-mixing of water-reducing agents
Many manufacturers often combine naphthalene-based water-reducing agents with amino-based water-reducing agents. The combined use of sulfonate admixtures can improve and reduce the loss of concrete slump, the ease of construction of concrete containing naphthalene-based water-reducing admixtures, and ensure good construction performance of pumped concrete. However, adding polycarboxylic acid-based admixtures Mixing admixtures with naphthalene-based water-reducing admixtures will cause the strength of the concrete to decrease and the working performance to deteriorate. Therefore, when using different types of admixtures in combination, the impact of compatibility on the performance of the concrete should be taken into consideration. Test before compounding, and the results can only be used if they meet the requirements.
2.3 Adoption of additive addition technology
There are three methods of adding additives: co-doping, first doping, and post-doping. The simultaneous mixing method means that when mixing concrete, water and admixture solution are mixed into the concrete at the same time. First mixing method, that is, first mix the dry powder of the admixture with the cement, and then mix it with sand, stone, and water. The post-mixing method is to add admixtures in batches for mixing after the concrete is mixed. The post-mixing method is divided into water retention method and batch addition. The water retention method is when mixing concrete.During the process, add water first, and then add the admixture 1 to 3 minutes later; batch addition means adding admixtures in batches to restore and compensate for the slump value.
3. Measures to improve the adaptability of admixtures and cement
3.1 Examine the adaptability of concrete admixtures and cement
From the current point of view, my country is facing The main problem is that construction units and concrete production units do not pay enough attention to the adaptability of concrete admixtures and cement. Therefore, we must strengthen publicity and increase the attention paid by construction workers to the adaptability of concrete admixtures and cement so that they can Take proactive steps to address this issue.
3.2 Properly mix admixtures and cement
In the process of using concrete admixtures, the concrete mixing station must conduct quality inspections on each batch of admixtures and cement. According to the raw materials Characteristics, cement is usually mixed with admixtures with good adaptability, which can ensure the quality of the project.
3.3 Cooperation between production units
To improve the adaptability of cement and admixtures in concrete, it is necessary to cooperate with the admixture synthesis factory, cement factory and concrete guidance unit. To put it simply, in the process of making cement, the admixture synthesis plant should continue to carry out technological innovation and improve the production process. The cement plant should use some components with weak adsorption capacity. The concrete mixing station should improve the mixing of cement and admixtures. Use appropriate mixing methods and ratios during the addition process.
3. 4 Complete the adaptability test of admixtures and cement before making concrete
In the actual construction process, a very large amount of concrete is required. Therefore, in large-scale concrete Before manufacturing, the concrete mixing station must conduct adaptability tests of cement and admixtures to ensure that concrete can be manufactured on a large scale. Able to use appropriate admixture dosage and cement type in a timely manner.
3. 5 Pay attention to the usage amount of admixtures in different concretes
There are many types of concrete, and there are many ingredients in it. Different concretes have different requirements. The types of admixtures and the demand for admixtures are also different. Therefore, in the actual production process, these factors must be considered for the use of admixtures. Never ignore these factors in order to save project costs. Pay attention to.
4. Conclusion
The use of concrete admixtures can not only ensure the quality of construction projects, but also change the working performance of concrete. There are many problems faced in the process of using concrete admixtures. Therefore, in the process of using concrete admixtures, measures should be taken to improve the adaptability of concrete and cement. </p
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