It is also known as micro silica, silica fume, has a huge surface area. Since the beginning of this century in Norway in the 50 years of its application in cement concrete research, since the 70's, European and American countries on this material widely, carried out a lot of research work. Due to the introduction of this material, the porosity and permeability of mortar and concrete can be greatly reduced, and the strength and durability of mortar are improved obviously, so it is widely used.
Micro silica fume particles with the average particle size is generally 0.1 0.3um. Specific surface area of 2.0 - 3.5 million square meters / kg, approximately fly ash is 50 times bigger, than the cement particle large diameter of more than 100 times, the incorporation of cement concrete, can increase concrete mixing toughening soft sticky poly and hardened concrete filling density, with significant of the super fine aggregate effect. Micro silica fume in the rapid condensation of gas, liquid and solid phase change process, the formation of different sizes, spherical particles with smooth surface in cement concrete can reducing the lubrication between the particles friction role, to diffusion filling of micro pore, enhanced densification, fine particles morphology effect should be obvious. Due to the condensed silica fume process is very rapid, resulting in silica will not form a crystal. The crystal structure is amorphous silica, high activity of volcanic material, mixed in cement concrete can significantly improve the anti impact grinding, anti erosion, anti permeability and anti freeze properties, pozzolanic effect significantly.
In the whole development process in the application of micro silica, our micro silica powder on how best to use accumulated rich experience. Here are some summary:
Micro silica fume is not suitable for all occasions. Formulate concrete technology personnel must be carefully analyzed the special occasions, and confirmed using micro silica fume can get the expected results.
Micro silica fume must use in the appropriate composition (with the ratio of concrete, for low water binder ratio (w / cm) and water, reducing concrete water. The earlier study found, mix in concrete with silica fume, water cement ratio is 0.6 or higher, unreasonable.
And the combination of micro silica and other auxiliary cementitious materials use is growing. At first, these materials were considered to be competing with each other, but it is now being increasingly widely recognized that the best concrete is often the result of a combination of these materials.
Micro silicon amount per unit volume of concrete is reduced, especially exposed to chloride environment of concrete. Initial bridge deck concrete containing 12% ~ 15% silica fume (by weight of cement), and then a few years micro silica fume is reduced to about 8%. At present, if used with fly ash or slag composition, micro silica fume content decreased to about 5%.
And there is no with silica fume concrete than the method of experience design and performance prediction, but can reference the existing guidelines and with specific examples. Laboratory and field tests must be carried out in order to determine the final mix.
And the silica fume concrete on plastic shrinkage cracking of sensitive, but this problem is easily overcome.
- concrete plane structure, especially the surface cracks, once was a problem.
Wet curing at least 7 days can solve or mitigate the problem of crack. However, some cracks on some long span bridges are not explained or prevented by construction procedures. Such cracks in the concrete without silica fume also appear, therefore may need to consider more from the structure, rather than the material. The research is being conducted in this area.
- silica fume concrete must be properly maintained. If there is no maintenance, bring the advantages of micro silica fume concrete cannot be achieved. If not proper maintenance requirements into technical standard of concrete and not in the project implementation of the maintenance requirements, it is best not to use the silica fume concrete.
Use of micro silica fume concrete, must pay attention to every aspect of the construction of concrete production. The mixing process, micro silica powder is well dispersed in relation to the concrete performance of the key. Mixing is not good and the poor dispersion of silica fume, may not get the desired concrete properties.
It may be a suitable method for determining the performance of the concrete. However, to determine the performance must be cautious and fully understand its occasions and conditions. With the same strength of concrete, the test of other performance parameters, the performance is not necessarily the same.
Many plane concrete structure too much precausions. Plaster of silica fume concrete experience shows that were least plaster work can get more durable concrete, while preventing the plastic shrinkage cracks.
In chloride environment, silica fume concrete has the desired resistance to chloride ion permeability. So far, some of the actual structure of the test, the performance of silica fume concrete is good. One of the reports showed that the rate of chloride penetration was significantly decreased with the extension of time. Now, the actual number of silica fume concrete structure has enough, exposure time is long enough, it is able to describe the problem. A project is USA silicon Association, namely in the actual bridge, parking building and marine structure sampling.
And the type of product change of micro silicon powder. Now, the product formula and slurry of silica fume has disappeared from the market. Almost all commercial concrete and precast concrete enterprises are using densification type micro silicon powder.
From the aspects of construction performance, concrete in the fresh state (plastic) the performance has become more and more important. These advantages include: improve the jet concrete adhesion properties and the hardened properties, reduce the planar structure of the construction of the finishing work, improve the self compacting concrete stability and
