Silicon powder is able to greatly improve the hardened cement paste and the performance of concrete, mainly because of silicon powder with strong tephros activity and its smaller particle size and larger surface area.
First, silicon has a strong tephros activity. According to metal powder supplier, silicon powder directly added to the water does not react with water hydration, but the silicon powder and cement are added simultaneously to the water, and when the cement hydration reaction occurs, silicon and cement hydration product of Ca (OH) occurs secondary hydration reaction to generate CSH gel body, it not only consume the Ca (OH) 2 in hydration of cement paste, also increased the CSH gel, and silicon powder also can react with another hydration product CSH gel in hydration cement paste, generate new low Ca / Si ratio CSH gel. Tephros CSH gel with the traditional CSH gel in composition and properties are not the same, it can polymerize with the hydroxide ion, aluminum ion, and quite stable after polymerize. Newly generated CSH gel can not decompose in acidic solution, this are the reasons for hardened cement paste is using silicon powder formulated on the acidic media has some resistance, for dialyzed, salt rust, carbornize has a strong resistance.
In addition, in concrete interfacial transition zone, Ca (OH) 2 and ettringite orientation, and interfacial transition zone crystal is more bulky than the hardened cement paste in the crystal, has more porosity and cement paste is relatively secrete large water volume, the upward migration of moisture in the cement paste will form aqueous film under aggregate, weaken the bonding of the interface, form the micro-cracks of the interfacial transition zone. Gel soil mixed with silicon powder, due to the reaction consumes most of the Ca (OH) 2, and make the traditional CSH coagulation body into ash CSH gel body, At the same time, the silicon powder specific surface is pretty large, a large amount of free water can be adsorbed and reduce bleeding, reducing the aggregation of the free water on the aggregate interface, so that make the dense structure of the interface region, while the crystal growth of Ca (OH) 2 is also restricted, grain refinement, ordering orientation reduced, so that the micro-structure of the interfacial transition zone improving. Secondly, because of the smaller particle size of silicon powder, the average particle diameter is about 0.1¼m, about 1/100 of portland cement particle size, while the silicon powder with a very large specific surface area, measured with nitrogen adsorption method, the silicon powder specific surface area is 20m2 / g, silicon powder is very easily to be a group, so it can serve as the nuclei of cement hydration in the cement hydration, thus speeding up the cement hydration. At the same time, since fine particles of silicon powder, which can be filled with small pores in the hardening cement slurry, thereby reducing the porosity of the cement paste, further enabling the hardened cement paste and concrete is more compact, higher strength, while enhancing the harden cement paste and the performance of concrete resist deformation of the external force, so that the hardened cement paste and concrete creep and shrinkage reduce.
The mechanism of silicon powder for hardened cement paste microstructure is mainly reflected in the following aspects: improve the degree of hydration of cement, occurs secondary hydration reaction with Ca (OH) 2, increasing the number of CSH gel in hardened cement paste, and improve the performance of traditional CSH gel, therefore improve the performance of the hardened cement paste.
Silicon powder and its secondary hydration products fill the harmful holes in the hardened cement paste, the macro large hole in the cement paste and the capillary porosity decreases, while increasing the gel pores and transitional pores, pore size distribution has greatly changed, reduce the large hole, increase small holes, and uniform distribution, thus changing the pore structure of hardened cement paste.
Adding silicon powder can consume the Ca (OH) 2 in cement paste, improving the interfacial properties of the hardened cement paste and aggregate. For these reasons, making the performance of hardened cement paste and concrete mixed with silicon powder, in particular, its durability have been greatly improved.
Source:http://www.mhcmp.com
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