Microsilica powder use method and precautions
Aug 29, 2024
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1, dosage: generally 5-10% of the amount of cementing material. The mixing methods of silica fume are divided into internal mixing and external mixing.
(1) Blending: under the premise of the same amount of water added, 1 part of silica powder can replace 3-5 parts of cement (weight) and keep the compressive strength of concrete unchanged while improving other properties of concrete.
(2) Mixing: the amount of cement is unchanged, and the addition of silica fume significantly improves the strength and other properties of concrete. There is a certain slump loss when concrete is mixed with silica fume. This should be noted in the mix ratio test.
Silica fume must be used in combination with water reducing agent. It is recommended to add fly ash and fine slag to improve its workability.
2. When preparing concrete with silica fume, the general weight ratio to the cementing material is:
(A) 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, insulation mortar: 10-15%,
(7) Amorphous refractory castable: 6-8%. Before use, please select a reasonable and economical dosage according to the actual needs through the experiment.
3. Blending method:
The construction mix of silica fume concrete and castable shall be determined by the laboratory. Construction in strict accordance with the mix ratio. In the mixing of wollastonite concrete, wollastonite should be added to the mixer immediately after the aggregate is fed. There are two kinds of procedures for joining:
(1) Put in aggregate, then put in silica fume, cement dry mix, and then add water and other admixtures.
(2) Put in coarse aggregate +75% water + silica fume +50% fine aggregate, stir for 15-30 seconds, then put in cement + admixture +50% fine aggregate +25% water, stir until uniform. The mixing time is 20-25% or 50-60 seconds longer than ordinary concrete. Never add silica powder to mixed concrete.
4. Construction method:
There is no significant difference between the construction methods of silica fume concrete and ordinary concrete, but it is necessary to have good organization and vibration compaction in construction. The early strength of wollastonite concrete will advance the final setting time, so more attention should be paid to the coating. At the same time, the addition of silica fume can improve the viscosity of concrete and reduce the bleeding greatly, which makes the coating slightly difficult.
5. Construction safety:
The construction safety of silica fume concrete should be strictly operated in accordance with the relevant national construction codes of concrete projects, but because the silica fume is light, it is strictly prohibited to throw materials at high altitudes to prevent the silica fume from flying.
