Construction of silica fume concrete

(2) The fineness of silica fume is extremely fine and requires a large amount of water. When adding silica fume to high-strength concrete, various water reducing agents should be used simultaneously to reduce the unit water consumption.

(3) Silica fume concrete should not only meet the strengthening effect, but also meet the workability requirements during the construction operation period. It is advisable to mix plasticizers or retarders for slump loss control.

(5) The vibration time of silica fume concrete should be appropriately extended, the vibration spacing should be reduced, and after the vibration is compacted, the surface should be immediately repaired and plastered.

(6) After the plastering and finishing of silica fume concrete, if the surface becomes dry, spray curing should be carried out, and heat dissipation and moisture retention should be strengthened. It is advisable to use water pipe spraying, water storage, watering for health preservation, or cover with moisturizing film, geotextile, hemp bag, and straw bag to spray water for moisture preservation and heat dissipation for health preservation. The short curing time of silica fume concrete should not be less than 7 days. Due to its low water cement ratio, high heat generation, high water demand, and self drying properties, silica fume mixed concrete is prone to early cracks caused by plastic shrinkage before initial setting. Therefore, it is necessary to attach great importance to moisturizing and curing before final setting. After final setting, it can be covered with moisturizing film, wet jute bag, wet straw bag, etc., or stored in water, sprayed with water for health preservation, with a duration of up to 7 days. This is to ensure strength, durability, and meet the requirements of crack prevention

(7) When silica fume is used in hot weather construction, high strength concrete under dry conditions, or large volume medium strength concrete structures, the following effective measures can be taken to control temperature rise, dry shrinkage, and self shrinkage cracking:

1) Hydration temperature rise monitoring should be carried out during construction to avoid temperature cracks.

2) In medium and low strength large volume concrete, in order to reduce the amount of cement and reduce the adiabatic temperature rise, the multi generation cement method can be used. 1kg silica fume replaces 3-5 kg cement. Compared to increasing the amount of cement, achieving the same strength requirement, the hydration heat of concrete with multi generation silica fume cement will be reduced

3) Through early spray, timely watering, moisturizing and covering and other strengthening curing measures, the problem of large self shrinkage and dry shrinkage of silica fume high-strength and high-performance concrete is solved. Practice has proven that it can be achieved without cracking

4) In arid areas, special attention should be paid to moisturizing and health preservation to prevent the surface of concrete structures from drying and whitening, and to prevent cracking.