Blending amount
Generally 5-10% of the amount of cementitious materials.
The mixing method of silica fume is divided into internal mixing and external mixing.
- Internal blending: under the premise of the same amount of water, 1 part of silica fume can replace 3-5 parts of cement (weight) and keep the compressive strength of concrete unchanged while improving other properties of concrete.
- External mixing: the amount of cement remains unchanged, and the addition of silica fume significantly improves the strength of concrete and other properties. Concrete mixed with silica fume when there is a certain slump loss. This point needs to be noted in the ratio test.
Silica fume must be used in conjunction with water reducing agents, it is recommended to compound fly ash and finely ground slag to improve its constructability.
When formulating concrete with silica fume, the general weight ratio with cementitious materials is:
- high-performance concrete: 5-10%.
- hydraulic concrete: 5-10%
- shotcrete: 5-10%.
- Pumping aid: 2-3%.
- wear-resistant industrial flooring: 6-8%.
- polymer mortar, insulation mortar: 10-15%.
- Indefinite refractory castables: 6-8%. Before use, please select the reasonable and economic mixing amount through experiment according to the actual needs.
Mixing method.
Silica fume concrete and castables should be made by the test room. Strictly follow the construction ratio. Silica fume should be added to the mixer immediately after the aggregates are fed. There are two procedures for adding.
- Into the aggregate, followed by silica fume, cement dry mix, and then add water and other admixtures.
- Put in coarse aggregate + 75% water + silica fume + 50% fine aggregate, mix for 15-30 seconds, then put in cement + admixture + 50% fine aggregate + 25% water, mix until uniform. Mixing time is 20-25% or 50-60 seconds longer than ordinary concrete. Never add silica powder into the already mixed concrete.
Construction method
There is no significant difference between the construction method of silica fume concrete and ordinary concrete, but it is necessary to organize and vibrate densely during construction well. The early strength of silica fume concrete will make the final setting time earlier, which should be paid attention to when plastering; at the same time, the addition of silica fume will improve the viscosity of concrete and significantly reduce water secretion, making plastering slightly difficult.
Construction safety
Silica fume concrete construction safety should be strictly in accordance with the relevant national construction specifications for concrete projects, but because silica fume is light, it is strictly prohibited to throw the material from a height to prevent silica fume from flying.
