Concrete with a strength grade greater than or equal to C50 is called high-strength concrete; concrete with good construction workability and excellent durability, and uniform and compact is called high-performance concrete; concrete with the above properties is called high-strength and high-performance concrete. The performance of high-strength and high-performance concrete is so superior, and there must be strict requirements on the selection of raw materials. The following Zhengzhou Changli will introduce you one by one.
1. Cement
The types of cement are usually Portland cement and ordinary cement, and slag cement can also be used. The strength grade selection is generally: C50 ~ C80. Concrete should use strength grade 42.5, and higher strength cement should be used above C80. The amount of cement in 1m3 concrete should be controlled within 500kg, and the amount of cement should be reduced as much as possible. The total amount of cement and mineral admixtures should not be greater than 600kg/m3.
2. Admixtures
①Silicon powder
The active SiO2 content 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 voids of cement, thereby greatly improving the density and strength of concrete. The suitable dosage of silica fume is 5% to 10% of the cement dosage. The research results show that silica fume is very significant in improving the strength of concrete. When adding 6% to 8% of silica fume, the strength of concrete can generally be increased by more than 20%, and the impermeability, frost resistance, wear resistance and resistance of concrete can be improved at the same time. Durability such as alkali-aggregate reaction. 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, and accelerating the slump loss of concrete.
② Grinding slag
The slag is usually ground to a specific surface area of more than 350m2/kg, resulting in excellent early strength and durability. The dosage is generally controlled between 20% and 50%. The greater the fineness of the mineral powder, the higher its activity and the more significant the enhancement effect, but the grinding cost is also greatly increased. Compared with silicon powder, the enhancement effect is slightly inferior, but other properties are better than silicon powder.
③High-quality fly ash
Generally, grade I ash is selected, and the lubricating effect of glass beads contained in it is used to reduce the water-cement ratio, as well as the filling effect of fine powder and the effect of pozzolanic activity, so as to improve the strength of concrete and improve the overall performance. The dosage is generally controlled between 20% and 30%. The effect of Class I fly ash is similar to that of mineral powder, and its crack resistance is better than that of mineral powder.
④ Zeolite powder
Natural zeolite contains a large amount of active SiO2 and micropores. After being finely ground, it can be used as a concrete admixture to play the active function of micropowder and pozzolan. The specific surface area is over 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% to 15%.
⑤Metakaolin
Metakaolin is a white powder obtained by dehydrating kaolin at 700-800 ℃. The average particle size is 1-2 μm, and the content of SiO2 and Al2O3 is more than 90%, especially Al2O3 is high. The results show that adding metakaolin can significantly improve the early strength, long-term compressive strength, flexural strength and splitting tensile strength of concrete.
3. Admixtures
Superplasticizer (or pumping agent) is a commonly used type of admixture for high-strength and high-performance concrete. The water-reducing rate is generally required to be greater than 20% to minimize the water-cement ratio and improve the strength. In order to improve the construction workability of concrete and provide other special properties, air-entraining agents, retarders, waterproofing agents, expansion agents, antifreeze agents, etc. can also be added at the same time. The dosage can be selected according to different varieties and requirements.
4. Sand, stone
Generally, medium sand with good gradation should be selected, and the fineness modulus should be greater than 2.6. The mud content should not be greater than 1.5%. When preparing concrete above C70, the mud content should not be greater than 1.0%. Harmful impurities are controlled within the national standard.
The gravel should be selected as the stone, the particle size of the large aggregate should not be larger than 25mm, and the strength should be greater than 1.20 times that of the concrete. For concrete with strength grade greater than C80, the maximum particle size should not be greater than 20mm. The needle flake content should not be greater than 5%, and the mud content should not be greater than 1.0%. For concrete with a strength grade greater than C100, the mud content should not be greater than 0.5%.
The selection of raw materials for high-strength and high-performance concrete is introduced here, and I hope it can help you.
