Application scope of micro silica fume (silica fume) for building concrete
1. For water conservancy and hydropower projects: after adding micro silica fume to the anti-seepage and anti abrasion parts, the anti-seepage, anti cracking, anti abrasion and anti cavitation properties can be greatly improved, and the service life of buildings can be extended.
Such as dam anti-seepage concrete panel, intake gate, tunnel, channel, main powerhouse substructure and other hydraulic structures. Traditional abrasion resistant materials mostly use polymer materials epoxy mortar. Although such materials have good abrasion resistance, their linear expansion coefficient is several times higher than that of the base ordinary concrete, and they are not well adapted to the temperature of the base concrete. They are easy to crack and fall off under natural climate conditions. Moreover, they are complex in construction, toxic, expensive in cost, and cannot be widely used. Using silica fume concrete, and the erosion resistance can be increased by about one time, and the abrasion resistance of 48m/s flow rate can be increased by more than three times.
2. For harbor engineering and salt water construction engineering: adding silica fume into concrete can improve the abrasion resistance and impermeability of concrete, prevent electrochemical corrosion of reinforcement, and prolong the service life.
In underwater engineering, chloride ions penetrate into concrete, causing rapid corrosion of reinforcement, delamination of concrete, short service life and serious damage. The tremie method is generally used for underwater concrete pouring. Due to the loss of cement slurry, it cannot bond well with the base course, and the strength of the part in contact with water is reduced. After adding micro silica fume into underwater concrete, these problems can be obviously improved.
3. For industrial and civil construction projects: micro silica fume concrete has the characteristics of early strength and high strength, and is widely used in industrial plants and high-rise buildings.
Such as Liaoning Anshan International Hotel C50 concrete, Beijing Finance and Taxation Building C110 concrete, etc. It can not only increase the strength, reduce the section size of members, shorten the construction period, but also save the project cost.
4. For traffic engineering: silica fume concrete can be used in highway pavement and aircraft runway, greatly improve the early strength and wear resistance of concrete. In the maintenance and emergency repair of highway pavement, it can be early opening time and increase economic benefits.
5. For prepare high-strength and high-performance concrete: micro silica fume powder is used as an admixture to prepare high-strength concrete, and its strength can be more than 100Mpa in practical application.
The high-grade concrete mixed with silica fume can be used in offshore oil drilling platforms, long-span bridges, high-rise buildings, tunnels, abrasion resistant pavement and sluice chamber floor of hydraulic buildings.
6. For shotcrete: after adding microsilica into the concrete, the adhesive property and cohesiveness of soil concrete are significantly improved, the resilience is greatly reduced, the one-time forming thickness of shotcrete is increased, the construction period is shortened, and the project cost is saved.
In European and American countries, 75% of shotcrete is mixed with silica fume, while in Norway and Sweden, micro silica fume is an essential material for shotcrete.
7. For fair faced concrete and pumping concrete: due to the fineness and activity of silica fume, the workability of concrete is enhanced, and its concrete surface is also very smooth and beautiful.
There is no significant difference between the construction method of silica fume concrete and ordinary concrete, but it is necessary to organize and vibrate well during construction. The early strength of micro silica fume concrete will advance the final setting time, so attention should be paid to plastering; At the same time, adding microsilica fume will improve the viscosity of concrete and greatly reduce bleeding, making plastering slightly difficult.
Generally 5-10% of the cementitious material.
The method of adding silica fume includes internal mixing and external mixing.
(1) Internal mixing: on the premise of constant water content, one part of silica fume can replace 3-5 parts of cement (weight) and keep the compressive strength of concrete unchanged and improve other properties of concrete.
(2) External mixing: The strength and other properties of concrete will be significantly improved by adding silica fume without changing the amount of cement. There is a certain slump loss when concrete is mixed with silica fume. This should be noted during the mix proportion test.
When preparing concrete with silica fume, the weight ratio between silica fume and cementitious material is generally:
（1）High performance concrete: 5-10%;
（2）Hydraulic concrete: 5-10%
（3）Shotcrete: 5-10%;
（4）Pump aid: 2-3%;
（5）Wear resistant industrial floor: 6-8%;
（6）Polymer mortar, thermal insulation mortar: 10-15%;
（7）Unshaped refractory castable: 6-8%. Before use, please select a reasonable and economical dosage through experiments according to the actual needs.
The construction mix proportion of micro silica fume concrete and castable shall be made by the laboratory. The construction shall be carried out in strict accordance with the mix proportion. In the mixing of silica fume concrete, silica fume shall be added to the mixer immediately after the aggregate is fed. There are two procedures for adding:
(1) Add aggregate, then add silica fume and cement for dry mixing, and then add water and other additives.
(2) Add coarse aggregate +75% water+ silica fume + 50% fine aggregate, mix for 15-30 seconds, then add cement + admixture + 50% fine aggregate + 25% water, and mix until uniform. The mixing time is 20-25% or 50-60 seconds longer than that of ordinary concrete. Do not add silica fume to the mixed concrete.