Portland cement and ordinary cement are usually selected as cement varieties, and slag cement can also be used. The strength grade is generally C50 ~ C80. The strength grade of concrete should be 42.5, and the cement with higher strength should be selected above C80. The amount of cement in 1m3 concrete shall be controlled within 500kg, and the amount of cement shall be reduced as much as possible. The total amount of cement and mineral admixtures shall not be greater than 600kg / m3. Self mixing concrete mixer
① Silica fume
The content of active SiO2 in silica fume is more than 90%, the specific surface area is more than 15000m2 / kg, the pozzolanic activity is high, and it can fill the gap of cement, so as to greatly improve the compactness and strength of concrete. The appropriate content of silica fume is 5% ~ 10% of cement. The results show that silica fume can significantly improve the strength of concrete. When 6% ~ 8% silica fume is added, the strength of concrete can be improved by more than 20%, and the durability of concrete such as impermeability, frost resistance, wear resistance and alkali aggregate reaction can be improved. However, silica fume also has adverse effects on concrete, such as increasing the shrinkage value of concrete, reducing the crack resistance of concrete, reducing the fluidity of concrete, accelerating the slump loss of concrete and so on. Self mixing concrete mixer
② Ground slag
Self mixing concrete mixer. The slag is usually ground to a specific surface area of more than 350m2 / kg, so it has excellent early strength and durability. The dosage is generally controlled between 20% ~ 50%. The greater the fineness of mineral powder, the higher its activity and the more obvious its enhancement effect, but the grinding cost also increases greatly. Compared with silicon powder, the reinforcing effect is slightly inferior, but other properties are better than silicon powder.
③ High quality fly ash
Grade I ash is generally selected, and the lubrication of glass beads contained in it is used to reduce the water cement ratio, fine powder filling effect and pozzolanic activity effect, so as to improve the strength and comprehensive performance of concrete. The content is generally controlled between 20% ~ 30%. The effect of grade I fly ash is similar to that of mineral powder, and the crack resistance is better than that of mineral powder. Self mixing concrete mixer
④ Zeolite powder
Natural zeolite contains a large amount of active SiO2 and micropores. As a concrete admixture after grinding, it can play the function of micro powder and pozzolanic activity. The specific surface area is more than 500m2 / kg, which can effectively improve the cohesion and water retention of concrete, and enhance the internal curing, so as to improve the later strength and durability of concrete. The dosage is generally 5% ~ 15%.
Metakaolin is a white powder prepared by dehydration of kaolin at 700 ~ 800 ℃, with an average particle size of 1 ~ 2 μ m. The content of SiO2 and Al2O3 is more than 90%, especially Al2O3. The results show that the early strength, long-term compressive strength, flexural strength and splitting tensile strength of concrete can be significantly improved by adding metakaolin.
Superplasticizer (or pumping agent) is a common admixture for high-strength and high-performance concrete. The water reduction rate is generally required to be greater than 20% to greatly reduce the water cement ratio and improve the strength. In order to improve the workability of concrete and provide other special properties, air entraining agent, retarder, waterproof agent, expansion agent, antifreeze, etc. can also be added at the same time. The dosage can be selected according to different varieties and requirements. Self mixing concrete mixer
4. Sand and stone
Generally, medium sand with good grading should be selected, and the fineness modulus should be greater than 2.6. The mud content shall not be greater than 1.5%. When preparing concrete above C70, the mud content shall not be greater than 1.0%. Harmful impurities shall be controlled within national standards. Gravel should be selected, the particle size of large aggregate should not be greater than 25mm, and the strength should be greater than 1.20 times of the concrete strength. For concrete with strength grade greater than C80, the large particle size shall not be greater than 20mm. Self mixing