Silica fume is Microsilica powder, the main component is silica, is a powder material obtained by cooling the smoke produced by ferrosilicon smelting, widely used in the preparation of various kinds of concrete, so as to improve its performance, in the shotcrete can also improve its performance, the main performance lies in reducing the electric flux of shotcrete, improve its seepage resistance.
The role of silica fume on shotcrete
Through the use of silica fume, the performance of shotcrete and production technology can be improved as follows.
1. In the dry mix of shotcrete to reduce the amount of rebound, thereby improving the economic efficiency of the material.
2. Increased single-layer shotcrete thickness on top and vertical surfaces without the use of set promoters, thus improving production efficiency.
3. When repairing piles and breakwaters in tidal areas, it can improve the cohesion and scouring strength of piles and dikes.
4. Improved freeze-thaw durability due to reduced permeability.
5. Early and late flexural and compressive strength of shotcrete are improved.
6. Increased resistance to chemical attack by chlorides, nitrates, sulfates, acids and alkali-aggregate reactions.
7. In concrete repair work in chloride environment, the high resistivity and low permeability of silica fume shotcrete mitigates reinforcing steel and wire mesh
corrosion.
Silica fume shotcrete construction method
Shotcrete is a mortar or concrete mix of cement and aggregate, sprayed on a surface at high speed with compressed air. There are two basic construction methods for shotcrete, namely the wet-mix method and the dry-mix method. In both construction methods, silica fume admixtures are easily added.
Dry Mixing Method
1. There are cement, aggregate, silica fume of fiber pre-mixed oversized bag mix, the general weight is 1000kg.
2. Dry mix with cement and aggregates in the factory into a delivery mix, and put silica fume and fiber into the delivery mixer at the site.
3. Use the silica fume or mixed cement bagged with water in a standard volume ratio by weight at the construction site.
4. Add the silica fume thin slurry into the nozzle.
Wet Mixing Method
1. Deliver the mix, just like ready-mixed concrete, together with cement, admixtures and aggregates, silica fume is added by volume in the central mixing plant or dry mix plant.
2. Delivering concrete from the ready-mix plant, silica fume is batched by the bag at the site.
3. Thin slurry is added in the batch feeding plant.
Advantages of dry mix shotcrete
1. where the site is remote or difficult to access and providing wet mix shotcrete is difficult, such as in some mining applications and offshore structure repair of offshore structures.
2. where small quantities of shotcrete are required periodically, such as for repairs in heavily trafficked road or rail tunnels.
Advantages of wet mix shotcrete
1. better control of the water-cement ratio through the factory batching, in the dry mix method of construction, the water-cement ratio is controlled by the workers in control of the nozzle.
2. Less rebound, higher injection rate and productivity, thus reducing costs.
3. Less dust and greater uniformity when mixing.
Three different silica fume products are used in wet and dry shotcrete:
- Undensified Silica Fume.
- Low Density Silica Fume.
- High Density Silica Fume.
The silica fume shotcrete mix ratio was designed with an average dose of 13% silica fume (by mass of cement). A sulfonated naphthalene-based superplasticizer was used to control the water-cement ratio of the wet-mix shotcrete. Dry shotcrete does not need superplasticizer, because most of the water in the mix is added in the spray nozzle, water and cement and silica fume reaction contact time is too short, so that the mix is sprayed to the surface before the actual solidification, it is too late to effectively reduce the water effect.
With a shotcrete piston pump to spray the wet mix of shotcrete, dry mix before loading into the rotating cylinder fed into the gun, to be pre-wetted with water to a moisture content of 3% to 4%.
Silica Fume Manufacturer
Henan Superior Abrasives Import & Export Co., Ltd. (HSA), established in 2001, is a leading supplier of Silica Fume and related products in China. Our markets cover USA, Canada, Middle East, Russia, Spain, South Africa, Southeast Asia, etc. If you have demand for micro silica fume , welcome to contact us to get the latest offer of silica fume in 2022.
