In order to meet the demand for concrete due to my country's economic development, concrete admixtures were born. Admixtures have become indispensable raw materials in concrete, which can significantly reduce concrete water consumption and improve the working performance of concrete mixtures. Concrete admixture is a material added before or during mixing to improve the properties of fresh concrete and hardened concrete. The dosage of admixture is not much more than 5% of the cement mass. However, in practice, due to various reasons, the method of appropriately increasing the dosage of admixture is adopted to increase the initial slump of fresh concrete and increase fluidity. Meet your pumping needs.
This article analyzes the performance of concrete admixtures, the application of admixtures in concrete construction, and the selection of admixtures to conduct research on the impact of concrete admixtures on concrete properties in building construction.
The sustained development of my country's national economy has brought about an increase in the demand for concrete, cement and products in basic industrial construction and the construction industry, thus promoting the development of the cement, product industry and concrete industry. However, with the continuous advancement of technology in the construction industry, people's requirements for cement concrete are getting higher and higher. This is reflected in the fact that it not only requires concrete to have early strength, adjustable setting, large fluidity, high durability, light weight, etc., but also requires easy molding, low preparation cost, simple maintenance, etc. In order to meet people's needs, concrete admixtures were born.
Concrete admixtures are generally divided into early strength agents, water reducing agents, air entraining agents, and retarders. Admixtures are characterized by low dosage and various varieties, which can improve or improve the hardened concrete. It is very important to study the impact of concrete admixtures on concrete properties and the adaptability of concrete admixtures to cement to make better use of concrete admixtures and give full play to the role of concrete in construction projects.
1 Performance analysis of concrete admixtures
1. The impact of the compatibility of admixtures and cement on concrete
(1) Each type of concrete admixture Each additive has its own unique function. Adding this kind of admixture can improve the performance of concrete in one or more aspects. For example, adding water reducing agent can increase the fluidity of concrete while maintaining the same water consumption, or reduce the unit water consumption while maintaining the same fluidity, thereby increasing the strength of concrete and improving the durability of concrete. From this, the concept of adaptability and unsuitability of concrete admixtures and cement can be understood in this way: according to the technical specifications for the application of concrete admixtures, a certain admixture that has been tested to meet the relevant standards is added to the application. This variety can be used according to regulations. In concrete prepared with cement with admixtures, if it can produce the desired effect, the cement is compatible with the admixture; on the contrary, if it cannot produce the desired effect, there is a gap between the cement and the admixture. Unadaptable. For example, several ordinary Portland cements are used and mixed with a certain high-efficiency water-reducing agent (which has been tested to meet the quality standards of high-efficiency water-reducing agents) to prepare concrete. When the preparation conditions are the same, the concrete prepared by one kind of cement is in There is a serious deficiency in water reduction rate, which means that this cement is not suitable for the high-efficiency water-reducing agent, while other cements are suitable for the high-efficiency water-reducing agent. For another example, when an accelerating setting agent that has been tested and meets the requirements of relevant quality standards is added to the concrete prepared by a certain cement but no quick setting effect is obtained, or a retarder is added but a false setting effect is obtained, it can be considered as Due to the incompatibility between admixtures and cement. There are adaptability problems between almost all kinds of admixtures and cement. However, water reducing agents are currently the most commonly used, and when they are not compatible with cement, they can be responded to intuitively and quickly (such as poor fluidity, The water reduction rate is low, or the mixture is hardened and heated, and the fluidity is lost too quickly, etc.).
(2) A certain project used shaft kiln cement from a cement factory and high-efficiency composite water-reducing admixture from an admixture factory. The effect was good at first. Later, a batch of concrete was mixed with the same admixtures. Rapid setting occurred, causing the concrete structure to become loose, and in the end all 800m3 of concrete that had been poured had to be smashed. After investigating the reason, we found that the cement passed the inspection according to the cement standards and the water-reducing agent also passed the inspection according to the standards. However, the concrete produced by the combination of the two had serious quality problems. In order to find out the cause, the researchers conducted tests with the accidental cement and water-reducing agent. It was found that there was indeed a rapid setting phenomenon. However, after adding 0.5% to 1.0% (dihydrate gypsum) into the cement, good working performance and Strength concrete. It is proved that the cement is incompatible with the water reducing agent due to insufficient gypsum content (but reaches the standard performance of cement).
(3) In short, the adaptability between admixtures and cement The problem is a complicated and practical problem that is unavoidable in engineering. It affects its application effect and sometimes leads to serious engineering accidents and immeasurable economic losses.
Cement and admixtures The compatibility of concrete is a very meaningful scientific issue, and it is also a practical engineering issue. This issue comes from engineering accidents. Therefore, it must be paid great attention by production units and engineering application departments.
2. Concrete The role of admixtures
The role of admixtures varies depending on the type of concrete additives. The general role is to increase the relative water consumption per cubic meter of concrete or when the cement content does not change.�The fluidity of concrete; when the cement dosage remains unchanged or the concrete slump remains unchanged, the water consumption can be reduced, and the concrete strength is also increased, and the durability of the concrete is improved; when the design strength remains unchanged and the concrete slump remains unchanged, the water consumption can be reduced. Under the condition that the drop degree remains unchanged, the cement consumption can be saved, the cost can be reduced, etc. Early-strength agents are used to improve the early strength of concrete and are mostly used in emergency repair projects and winter construction of concrete; water-reducing agents have the effect of reducing water while maintaining the consistency of concrete; air-entraining agents are mainly used to reduce the amount of water produced during concrete mixing. Bleeding segregation caused by bubbles improves the workability of concrete; retarder can delay the setting time of concrete and has both retarding and water-reducing effects. It is mainly used for large-volume concrete, concrete constructed under hot weather conditions, or long-distance construction. Transporting concrete.
3. Analysis of the impact of admixture water-reducing agents on concrete properties
Concrete admixture water-reducing agents are mainly composed of surfactants. This surfactant is an anionic surfactant. In essence, concrete alkaline water agent does not play a chemical role with cement. Its role in concrete mainly reflects the plasticization of fresh concrete. Plasticization is a wetting, adsorption, dispersion, and lubrication effect.
The admixture water-reducing agent has adsorption, dispersion, lubrication and wetting effects, so it is easy to mix the concrete evenly with only a small amount of water, which improves the workability of freshly mixed concrete. This is the plasticizing effect of the admixture water-reducing agent on fresh concrete.
4. Analysis of the impact of admixture air-entraining agents on concrete properties
Admixture air-entraining agents can introduce a large number of tiny and independent small bubbles into concrete, which can make The workability of concrete is greatly improved. Regarding the impact of air-entraining agents on the performance of hardened concrete, from the perspective of water reduction efficiency, the strength of concrete will also increase accordingly; but from the perspective of air-entrainment, the strength of concrete generally decreases. Therefore, the elastic modulus of concrete mixed with air-entraining agent or air-entraining water-reducing agent is lower than that of concrete without air-entraining agent, and the decrease is greater than the change in strength. The reason is that there are a large number of tiny bubbles in the cement slurry, which reduces the elastic modulus of the slurry.
2 Concrete admixtures and concrete construction
Concrete is a necessary building material in modern society. Its variety, large production volume, and wide range of applications are among the highest in the world today. However, the development of concrete construction technology requires admixtures. It can be said that the emergence and development of admixtures have promoted the development of concrete construction technology, allowing concrete technology to develop from plastic concrete to fluidized concrete, dry-hard concrete, and high-performance concrete. For example, the new high-efficiency water-reducing agent currently developed combines the high construction performance, high strength, and high durability of concrete, improves the water reduction rate under low water-cement ratio, and satisfies certain concrete projects. Not only high performance is proposed, but also high functionality requirements are required. And it can also produce high-performance non-vibration concrete with high flow performance, low water consumption, and good performance of not separating and penetrating the steel mesh. These are the positive effects of concrete admixtures on concrete construction.
3 Selection of concrete admixtures
According to the problems encountered in the use of concrete admixtures in Zhangjiabao high-rise residential and Changying East Road dilapidated building renovation projects, the use of concrete admixtures Before use, you should understand the performance of different admixtures, the corresponding conditions of use, and consult the factory product instructions. The type and dosage of admixtures must be based on the concrete performance requirements, construction and climatic conditions, and strictly follow the current specifications. Admixtures The quality meets the relevant national standards. Choose corresponding admixtures that are compatible with cement and can meet design and construction requirements. Admixtures of different types, different production processes or dosages and formulas also have different adaptability to concrete and cement. Therefore, it should be determined through an experiment and the admixture with good adaptability and stable quality should be selected; at the same time, the corresponding admixture should be selected according to the different designs and construction requirements. Combined with the actual use of materials on site for trial mixing, the appropriate dosage of admixtures and reasonable construction coordination are determined.
With the widespread application of pumping technology and high-strength concrete, due to the increase in pouring work and the increased work requirements during pouring, these cannot meet the construction requirements for long-distance transportation. Therefore, there is a need for high-efficiency additional concrete. The dosage requirements of water reducing agent are gradually increasing. Research has also shown that a large amount of high-efficiency water-reducing admixture can make concrete have greater fluidity even when the water-cement ratio is very low, and can form a dense, high-performance and high-strength concrete with good strength and durability. . At the same time, under the condition of using large amounts of high-efficiency water agents, the loss rate of fresh concrete is also reduced. The reason is that in fresh concrete, the form of the cement and the calcium sulfate content affect the concentration of SO4 in the liquid phase. Since the SO4 ion water produced by sulfate in the dissolution of low-water glue is relatively small, the amount of C3A that needs to be controlled is also large, and a large amount of C3A needs to be hydrated. There is a combination of sulfonate gene and C3A on the molecule of high-efficiency external water-reducing agent, and the dosage of high-efficiency water-reducing agent in the liquid phase also decreases, gradually losing its effect on cement dispersion and increasing losses. For this reason, the amount of high-efficiency external water-reducing agent should be increased, so that the amount of SO4 ions in the liquid phase will also increase, and the loss rate caused during work will also be reduced.
4 Conclusion
In short, the use of concrete admixtures should be based on different construction purposes and environmental characteristics, and the appropriate admixture should be selected while considering economic benefits, and during use Pay attention to the proportion and matching, which will help the admixtures to improve the performance of concrete.
4 Conclusion
In short, the use of concrete admixtures should be based on different construction purposes and environmental characteristics, and the appropriate admixture should be selected while considering economic benefits, and during use Pay attention to the proportion and matching, which will help the admixtures to improve the performance of concrete.
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