What is silica fume concrete
Industrial silicon and ferrosilicon in the process of high-temperature melting, with the exhaust gas escapes the dust for silica dust or silicon powder, its main component is active SiO2 (content of about 90%, which contains about 10% of the free state SiO2). The particles are very small, one hundredth of the cement particle size, small capacity and large specific surface area, inherently known as micro-silica powder, which can directly enter the human alveoli through breathing and is extremely harmful to human health.
Silica Fume Application
Silica Fume powder is widely used in construction, chemical industry, metallurgy and other industries. It is mainly used as an active admixture in the concrete set, used to improve the performance of cement or concrete, to formulate special concrete with ultra-high strength, wear resistance, scouring resistance, corrosion resistance, anti-permeability and anti-freeze, early strength, and can be used in large hydropower, harbor terminals, railroad bridges, highways, airport runways, tunnels and urban high-rise construction projects.
Why need to add silica fume in concrete?
Due to the fine particles of silica powder, large specific area, high purity of active SiO2 and strong volcanic ash activity and other physical and chemical characteristics, the silica powder as an admixture into the concrete to improve the performance of concrete in many aspects.
1. Improve the early strength and final strength of concrete
Research shows that when the replacement rate of silica fume to cement is 30% or less, the steam temperature is 80 ℃, the compressive strength of mortar one day for not mixed with silica fume 2 times, if the use of steam curing, it is almost 3 times; using standard curing, the compressive strength of mortar is also significantly increased.
2. Increase the compactness
Concrete mixed with silica powder increases the silicon content of the reaction, observed under the electron microscope, there are crystals growing in the cement stone voids of concrete mixed with silica powder. In addition, the silica powder particles are very small, uniformly fill the concrete micropores, micro-aggregate filling effect is obvious.
3. Improve the concrete segregation and water secretion performance
After pouring concrete, often produce the phenomenon of water separation from the concrete, that is, the formation of water film in the surface layer, also known as floating slurry, so that the upper layer of concrete distribution is not uniform, affecting the quality of construction. Foreign research has proved that the amount of silica fume, that is, the substitution rate Si / (Si + C) the more, the more difficult it is for concrete materials to segregate and secrete water. When the replacement rate of 15%, the concrete slump even up to 15 ~ 20cm also almost no segregation and water secretion. When the replacement rate of 20% to 30%, the concrete directly into the water is not easy to produce segregation. Due to the improvement of silica powder on the concrete segregation and secretion performance, so that the concrete doped with silica powder can be used in ports, tunnels and other underwater projects.
4. Improve the permeability, chemical resistance and specific resistance of concrete
Micro-silica powder used in concrete, on the one hand, fill in the cement particles around the slurry more dense; on the other hand, it is combined with calcium hydroxide generated by hydration of cement to generate hydrated calcium silicate gel, these gels plugged in the capillary tubes, so that the capillary pores become smaller and discontinuous, greatly improving the denseness of concrete, effectively improving the ability to resist the penetration of chloride ions, greatly enhancing its rust resistance. Foreign research has proved that when the replacement rate of silica powder in concrete is 10% to 20%, significantly improved the permeability of concrete, chemical corrosion resistance, and corrosion resistance of reinforcing steel has also improved. This is due to the improvement of compactness and the increase of SiO2 content, which effectively prevents the intrusion of acid ions and corrosion effects. In addition, because of the high specific resistance of silicon powder, so the concrete specific resistance can be increased by more than 1 times.
5. Improve the anti-abrasion ability of the project
Traditional anti-abrasion materials mostly used epoxy mortar and other polymer materials, such materials anti-abrasion ability is good, but because of its own linear expansion coefficient of several times based on the bottom of ordinary concrete, and the substrate concrete temperature is not well adapted to the natural climate conditions are prone to cracking off. And construction is complicated, toxic, expensive, can not be widely used. Micro-silica powder as anti-abrasive materials mixed into the concrete, its anti-abrasive capacity can be increased by about double.
6. Improve the anti-cracking performance of the project
Silica fume concrete crack resistance is improved thanks to its high increase in concrete compactness, but the crack resistance of silica fume concrete must pay attention to the disadvantages of increased concrete shrinkage due to silica fume admixture, and grasp the choice of admixture amount in the actual use process.
