First, the dosage is less than or equal to 5% of the weight of cement. This means that the dosage of concrete admixtures must not be greater than 5% of the weight of cement. Based on this definition, other mineral admixtures whose content is greater than 5% by weight of cement cannot be treated with admixture concrete. Two other points need to be explained. First, although the dosage of expansion agent and antifreeze is greater than 5% of the weight of cement, they have been included in the classification of admixtures in GB8076-87 as a special case. Second, according to my country's current "Ordinary Concrete Mix Proportion Design Regulations" - JGJ55-2000, mineral admixtures are used to replace part of the cement dosage, and the dosage of admixtures should be calculated based on the overall dosage of cementing materials.
Second, what is the true meaning of a product that can modify the normal properties of concrete as required? Why should normal concrete properties be modified? There is only one conclusion. Normal concrete performance may not necessarily meet the design or construction technical requirements, which requires or relies on the modification of concrete by admixtures. For example, if a road needs to be opened to traffic 24 hours after pouring, the performance of ordinary concrete cannot be met, but it can be achieved by adding a retarder. For another example, the original mix ratio of a C30 concrete uses 400kg of cement per m3, 200kg of water, 0.5 water-cement ratio, and 100mm slump. Now, 0.6% of high-efficiency water reducing agent is added to maintain the water-cement ratio of 0.5. Under the same technical conditions as the slump of 100mm, the water consumption is reduced to 160kg, and the cement consumption is reduced to 320kg. Each m3 of concrete can save 80kg of cement, and greatly reduces the hydration heat index of concrete. By studying and understanding the definition, we should grasp one key point. The main function of concrete admixtures is to change the normal properties of concrete as required through its incorporation. This modification includes both technical performance and economic performance. aspect.
The production of concrete admixtures is due to the inevitable needs of concrete. The development history of concrete admixtures is closely related to the development history of concrete. To a certain extent, in the process of pursuing its own development, concrete admixtures also promote the development of concrete technology. The birth of high-strength concrete, which is generally recognized internationally as the third technical revolution in concrete, is based on a major breakthrough in high-efficiency water-reducing admixtures. The earliest concrete admixtures in the world were hydrophobic agents and plasticizers in 1898, but they did not become industrial products until 1910. Large-scale development began in the 1830s. At that time, the United States first developed an AE air-entraining agent using rosin resin as raw material. It became popular for a while because it solved the anti-freeze problem of highway pavement. In the 1830s, foreign countries developed M series water-reducing admixtures based on pulp waste liquid as the main material. This admixture improved the plasticity of concrete to a great extent and was hailed as the main modern concrete water-reducing agent. start. In the 1860s, Japan and the Federal Republic of Germany successively launched naphthalene sulfonate and melamine high-efficiency water-reducing admixtures. Since then, the technology of modifying concrete with additives has entered a landmark era. So far, in order to meet the needs of new concrete preparation with high strength, large flow state and good plastic retention, a variety of products called high-performance water-reducing agents have gradually come to the fore. Such as hydroxycarboxylate composite high-performance water-reducing agent, high-efficiency collapse-preserving water-reducing agent, and polymer collapse-preserving water-reducing agent. These new water-reducing agents generally have water reduction rates greater than 20% and have good plastic retention effects. But in essence, the main material is still naphthalene sulfonate or melamine resin. </p
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