1, concrete expansive agent is a kind of concrete admixture developed on the basis of expansive cement. It can be mixed with portland cement on site to make expansive concrete. Its main function is to improve the crack resistance, impermeability and durability of concrete. 1936, American scientists first used ettringite (calcium sulphoaluminate) expansion agent to prepare self-stressing concrete.
2. Japan is the first country to develop expansive agent. 1962, Japan Dacheng Building Technology Research Institute purchased the patent of K-type expansive cement from American A.Klein Company, and on this basis, successfully developed a calcium sulphoaluminate expansive agent (CSA), the main expansion source of which is ettringite (C3A 3CaSO4 32H2O).
3. 1970, Onota cement company has successfully developed lime expansive agent, and its expansive source is mainly Ca(OH)2. 8% ~ 10% (equivalent to the weight of cement) of these two expansive agents can be mixed with shrinkage compensating concrete, and 15% ~ 20% can be mixed with self-stressing concrete.
4. China began to develop expansive agent on 1975. A calcium sulphoaluminate expansion agent similar to Japanese CSA has been successfully developed by You et al. of China Institute of Building Materials Science. Different from the electric melting method in Japan, CSA clinker is sintered in a rotary kiln and ground to a specific surface area of (200-300)m2/kg. Due to the small demand in the construction market at that time, it was not put into production.
4. During the period of1979, Anhui Academy of Building Research successfully developed alunite expansive agent on the basis of alunite expansive cement in our hospital, but it was later eliminated because of its low expansion efficiency and high alkali content.
5. After1988, China Building Materials Research Institute successively developed UEA, AEA and CEA expansive agents, and mixed 10% ~ 12% into cement to make shrinkage-compensating concrete. Subsequently, Tongji University, Changjiang Academy of Sciences, Shandong Academy of Building Sciences and Zhejiang University have also successfully developed calcium sulphoaluminate expansion agent.
During the period of 6. 1992, China formulated the industrial standard of concrete expansive agent (JC476), which unified the test methods and technical indicators. Subsequently, the standard was revised from 1998 to 200 1. Through the upgrading of expansive agents, especially the emergence of two efficient expansive agents, HSCA and ZY, and large-scale engineering practice.
7. In 2009, the state promulgated and implemented two core standards in this industry: one is the first national product standard GB23439-2009 "Concrete Expansive Agent", and the other is the first technical standard for the application of shrinkage compensating concrete in China (JGJ/T 178-2009 "Technical Specification for the Application of Shrinkage Compensating Concrete"). These two standards have played an important role in standardizing and improving the application technology level of expansive agent concrete in China.
Extended data:
I. Overview of concrete expansion agent
The concrete expansion agent belongs to calcium sulphoaluminate concrete expansion agent, which contains no sodium salt and should not cause alkali-aggregate reaction of concrete. However, it has good durability, stable expansion performance and continuously rising strength. Ordinary concrete often leaks due to shrinkage and cracking, which reduces its use function and durability.
Adding 8%- 12% expansive agent to cement can prepare shrinkage-compensating concrete, which greatly improves the crack resistance and waterproof ability of concrete structure. The external waterproof operation can be cancelled, the spacing of post-pouring zone can be extended, and the temperature difference crack between mass concrete and high-strength concrete can be prevented.
Second, the concrete expansion agent use method:
1. When using this product, the recommended dosage is 8 ~ 12%. After preparation, the dosage of joint pouring and post-pouring reinforced concrete should be appropriately increased.
2. The concrete prepared by this product can adopt structural self-waterproofing technology, so that the building structure and waterproof function are integrated, and the external waterproof is cancelled, making the building structure simpler.
3. The concrete prepared with this product can adopt the seamless design and construction technology of super-long reinforced concrete, which reduces the construction process, makes the construction simpler and greatly shortens the construction period. No post-cast strip is left, and large-area continuous concrete pouring is carried out. It can also be used for the post-pouring zone treatment of ordinary concrete.
References:
Baidu encyclopedia-concrete expansion agent