The addition of nano SiO2 powder as an admixture to cement-based materials can improve many of the properties of cement-based materials. A large number of research results show that adding appropriate amount of SiO2 nanopowder to cement-based materials, due to the volcanic ash effect of nano SiO2 particle, nucleation effect and micro-filling effect, can significantly improve the early strength of cement-based materials, improve the bleeding of cement-based materials and The pore distribution characteristics improve the durability of the structure.

1. Effect of nano-SiO2 on properties of cement-based materials
1.1The nano-SiO2 has a small particle size, so the specific surface area is large and the surface activity is high, so that a part of the free water of the cement-based material slurry is consumed in the early stage of the cement-based material curing age. In addition, since nano-SiO2 is too small in particle size, it is almost difficult to uniformly disperse in the system, and it is usually present in the form of agglomerates, and these agglomerates have particularly large pores and absorb a large amount of free water. If too much free water is consumed, the slurry will be more viscous and the fluidity of the slurry will be lost, which is unfavorable for some grouting materials that have special requirements for fluidity. Therefore, nano-SiO2 has an optimum dosage, and it is not good if the dosage is too large or too small.
SAT NANO believes that when the particle size of nano-SiO2 is the same, the larger the specific surface area, the lower the fluidity of the cement paste, and when the specific surface area is the same, the particle size is small, and the fluidity loss is more. SAT NANO believes that nano-SiO2 is the best when added as a modified additive of water reducing agent, and the dosage is controlled to be 0.1% of the concentration of the water reducing agent. Mainly because of the plasticizing and water reducing mechanism of nano-SiO2, the fluidity is increased, but the excessive specific surface area increases the water absorption of the particles.

1.2 Effect of SiO2 on mechanical properties of cement-based materials
Since the specific surface area of nano-SiO2 is very large and the surface energy is high, nano-SiO2 can react with the hydrate hydrate Ca(OH)2 of the cement-based material to form a hydrated calcium silicate gel. On the one hand, the progress of the hydration reaction is accelerated, the development of the strength of the cement-based material is promoted, and the early strength is improved. On the other hand, the content of the hydrated calcium silicate gel in the hydration product is increased, so that the cement stone skeleton is more dense, so that the late strength is also appropriately increased. In addition, nano-SiO2 can directly act as a nucleus, providing a point of attachment for the flocculated CSH formed by the reaction. CSH directly adheres to its surface and continuously develops outward to form a cement stone skeleton to form strength, eliminating the need for CSH to form its own crystal. The nuclear process accelerates the development of strength and greatly increases the early strength.

SAT NANO used TGA-DTA method to analyze the mechanism of nano-silica acting on cement mortar. It was found that the degree of orientation of Ca(OH)2 crystal in the interface between cement stone and aggregate decreased after the modification of cement mortar with nano-silica. The grain is refined and in an amorphous state. The hydration product increases, making the structure dense and increasing in strength.
SAT NANO studied the influence of nano-SiO2 on the interfacial transition zone between cement mortar and concrete. The microstructure of the experimental results was analyzed by SEM, XRD and EDM. The results show that cementite is added when adding 3% nano-SiO2. The particle size of Ca(OH)2 crystal between the aggregate and the aggregate is obviously smaller, the arrangement is more regular, the pores are smaller, the structure is tighter, and the early strength is obviously improved.
1.3 Effect of nano-SiO2 on durability of cement-based materials
Nano-SiO2 has a small particle size and can be filled in the voids between the cement particles, just like the cement particles in the concrete fill the voids between the aggregates, making the structure more dense. On the other hand, due to the pozzolanic effect of nano-SiO2, the yield of CSH in the reaction product is increased, and it is filled in some large pores, which effectively reduces the number of macropores in the concrete, makes the pore distribution more uniform, and thus makes the structure impervious. Sex, durability is improved very well.
SAT NANO studied the effect of nano-SiO2 on the strength and durability of hardened cement mortar. It was found that with the increase of nano-SiO2 content, the neutralization depth of mortar gradually decreased, indicating that the anti-Cl-permeability was significantly improved.
SAT NANO is analyzed by various microscopic analysis methods such as XRD, MIP and nanoindentation: double-doped nanomaterials can further improve the properties of the material. Nano-SiO2 can promote cement hydration and increase the content of CSH in hydration products. Nano-CaCO3 mainly exerts its filling effect and nucleation. Under the combined action, the structure is more encrypted and the porosity is further reduced, resulting in uniform and compact microscopic. The structure allows the composite to exhibit excellent mechanical properties at a macroscopic level.

SAT nano Technology Material Co., Ltd. can supply silicon dioxide nanopowder SiO2 powder 20nm for customer to use in concrete, please feel free to contact us.