According to "technical specification for high strength concrete structures" (CECS104:99), thestrength grade of concrete is greater than or equal to C50 for high strength concrete; with goodworkability and excellent durability, uniform and dense concrete is known as the high performance concrete; at the same time, with the performance of the concrete is known as the high strength and high performance concrete; and the "ordinary concrete mix design specification" (JGJ552000) isgreater than or equal to C60 strength grade of concrete for high strength concrete; "code for design of concrete structures" (GB500102002) is not clearly distinguish between ordinary concreteand high strength concrete, only the provisions of the strength grade of concrete in reinforced concrete structures shall not be less than C15, the strength of concrete scope from C15 to C80.Research and application of high strength concrete at home and abroad, and the development of modern concrete technology, the concrete will be greater than or equal to C60 is called the highstrength concrete is more reasonable.
The most effective way to obtain high strength and high performance concrete mixer with high performance concrete admixture and admixture, and at the same time by using high strength gradecement and fine aggregate. For the special requirements of concrete, also can be mixed with fibermaterials to improve the tensile, flexural and impact properties and toughness; also can be mixed with polymers to improve the density and wear resistance. Commonly used additives withsuperplasticizer, efficient pumping agent, high performance of air entraining agent, waterproofing agent and other special admixture. The activity of the mixed materials are commonly used fly ashand pulverized fly ash, slag, zeolite powder, metakaolin, silica fume, sometimes adding ultra-fine grinding limestone powder or quartz powder. Fiber materials are commonly used steel fiber,polyester fiber and glass fiber.
Raw materials, high strength and high performance concrete
(a) cement
The varieties of cement Portland cement and ordinary portland cement is usually used, but also can be used for slag cement etc.. The strength grade selection: C50 ~ C80 concrete strength grade of C80 should be used more than 42.5; selection of high strength concrete. The amount of cement in concrete to control 1m3 within 500kg, and as much as possible to reduce the amount of cement. The total amount of cement and mineral admixtures should not be greater than 600kg/m3.
(two) admixture
1: it is the production of ferrosilicon powder of ash, therefore it is also called silica fume is a kind of high strength concrete, mixing with the earliest, the most mature technology, applied materials. The content of active SiO2 powder was more than 90%, the specific surface area is more than 15000m2/kg, volcano activity is high, and can fill the void of cement, thus greatly improving the density and strength of concrete. Appropriate dosage of silica fume cement content is 5% ~ 10%.
The results of the study show that, silica fume is very significant to improve the strength of concrete, when mixed with 6 ~ 8% silica fume, the strength of concrete can be increased by more than 20%, and can improve the durability of concrete anti permeability, frost resistance, wear resistance, alkali - aggregate reaction. But also bring disadvantageous influence of silica fume onconcrete, such as increasing the concrete shrinkage, reduce the crack resistance of concrete,reduce the fluidity of concrete, concrete slump loss accelerated.
2 ground granulated blast furnace slag slag: usually will grind to a specific surface area over 350m2/kg, which has the early strength and excellent durability. Content general control in 20% ~ 50%. The fineness of slag is greater, the higher activity, enhance the effect more obvious, but alsogreatly increase the cost of grinding. Compared with that of silica fume, enhanced slightly, but the other is better than silica fume.
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