Concrete admixtures refer to substances added to improve and adjust the properties of concrete. The application of concrete admixtures in engineering has attracted more and more attention. The addition of admixtures plays a certain role in improving the performance of concrete, but the selection, addition method and adaptability of admixtures will seriously affect its development.
Concrete admixture is a substance other than cement, sand, stone and water that is added in a controlled amount before or during the mixing of concrete to make the concrete produce desired changes. .
Concrete admixtures are characterized by many varieties and small quantities, and they play an important role in concrete modification. Therefore, its quality control, application technology, and variety selection are more important than other engineering materials. . Fourteen chemical admixtures that have formulated national or industry standards: ordinary water-reducing agent, air-entraining agent, air-entraining water-reducing agent, high-efficiency water-reducing agent, antifreeze, expanding agent, retarding high-efficiency water-reducing agent, waterproofing agent agent, pumping agent, early strength agent, retardant water reducing agent, early strength water reducing agent, quick setting agent. 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.
my country’s concrete additives started late. In 1950, the North China Kiln Industry Company Research Institute produced my country’s first additive product, the Great Wall brand air-entraining agent. This product was first used on the runway of Tianjin Airport to improve the frost resistance and corrosion resistance of concrete, and was also used in the Wuhan Yangtze River Bridge and other water conservancy projects. In the next two decades, the development of admixtures in my country was still very slow. Except for other units that used pulp waste liquid to produce low-grade plasticizers, most projects did not use water-reducing agents, that is, antifreeze for winter construction. They are also made of chlorine salt as the main material. It was not until 1973 that, influenced by international construction technology and new concrete technology, the development and production of high-efficiency water-reducing agents was promoted in my country. Since the diffusion agent in the dye industry was successfully transplanted into the ranks of concrete water-reducing agents, it has since affected the rapid development of water-reducing agents produced from various fractions of coal char, especially naphthalene and its homologues, as the main raw materials. From 1974 to 1976, the National Institute of Building Materials developed two high-efficiency water-reducing agents, MF and Jian 1, which used methylnaphthalene and naphthalene residual oil as the main raw materials. Tsinghua University developed NF superplasticizer using naphthalene as raw material, Tianjin Building Materials Institute developed UNF, and Wuhan Metallurgical Construction developed FDN. In view of the lack of naphthalene raw materials, the Building Materials Institute developed AF superplasticizer using anthracene oil as raw material. The Second Bureau of Communications and Aviation has developed CRS using coumaron resin as raw material. At the same time, ordinary water reducing agents have also made great progress. In 1975, Jilin Kaishantun Chemical Fiber Factory developed calcium lignosulfonate, and Guangdong Chemical Factory also produced similar products. The widespread production of ordinary water-reducing agents and high-efficiency water-reducing agents has led to the emergence of composite admixtures.
In terms of changing the properties of concrete, composite admixtures have a broader market background. The different technical requirements of various types of projects give composite manufacturers a lot to do. According to incomplete statistics, in the fourteen years from 1973 to 1987, my country’s admixture factories have grown from few to more than 150, of which more than 80% are composite manufacturers. The variety of admixtures has also grown from a few to more than 16 to more than 300 brands, which indicates that my country’s admixture industry has begun to take shape and mature. In order to further strengthen technical management and standardize the market, my country promulgated its own “Concrete Admixture Standards” (GB8076-87) for the first time in 1987; at the same time, it also promulgated the “Classification, Destination and Definition of Concrete Admixtures” (GB8075-87) ; “Test Method for Homogeneity of Concrete Admixtures” (GB8077-87). These three standards respectively make specific provisions on the types, technical indicators and inspection methods of concrete admixtures: now GB8076-87 has been replaced by GB8076-97. In the following years, our country successively promulgated the “Technical Specifications for the Application of Concrete Admixtures” (GBJ119-88); “Concrete Antifreeze Standard” (JC472-92); “Concrete Pumping Agent Standard” (JC473-92); “Concrete Expansion Agent” (JC476-98) and other series of admixture standards.
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