Application of amorphous calcium aluminate and microsilica in shotcrete

Application of amorphous calcium aluminate and microsilica in shotcrete

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Amorphous calcium aluminate, microsilica, shotcrete, accelerator, concrete admixture, silica fume

As we all know, shotcrete is mainly used for the lining and support of rock caves, tunnels or underground projects and mine tunnels. In addition to the base material: cement, sand and gravel and other products, shotcrete also requires additional concrete admixtures, such as accelerator, microsilica fume, fly ash, mineral powder, cellulose, etc. These admixtures can improve the performance of concrete. Such as increasing the early strength of concrete, reducing costs, reducing shrinkage and improving durability.

The formula proportion of shotcrete can be adjusted according to the needs of concrete strength. The general proportion is: cement (500kg), fly ash (50-80kg), mineral powder (100-120kg), microsilica powder (30-50kg), super Fine silica powder (50-80kg), cellulose (1-3kg), and appropriate amount of water.
Water and accelerating setting agent: The water-cement ratio is 0.45. The type and amount of accelerating setting agent should be determined according to the specific engineering requirements and site conditions.

The construction methods of shotcrete include dry mix method and wet mix method. The dry mixing method is a method in which cement, sand and stone are mixed evenly in a dry state, and compressed air is used to send the cement and quick-setting agent to the nozzle and mix with pressurized water for sprinkler irrigation. The wet mixing method is a method in which the mixed concrete is delivered to the nozzle through a grouting pump, and then compressed air is used for sprinkler irrigation.

As the core admixture, amorphous calcium aluminate plays a vital role in shotcrete. Its core advantages and properties are as follows:
1.Super quick setting performance
2.Excellent early strength performance
3. Ultra-low shrinkage, little strength loss in the later period, and slight and significant enhancement in compressive strength and flexural resistance.
4. Excellent impermeability and dry shrinkage resistance
5. The density, strength and durability of concrete components are significantly increased
6. Energy saving and efficient

In addition, shotcrete adds microsilica fume, which has good performance advantages and ease of operation.
Reduced springback in dry mix shotcrete
Increases single-layer spray thickness on top and vertical surfaces without the use of coagulants
When repairing piles and breakwaters in tidal areas, the cohesion and anti-scouring strength of piles and breakwaters can be improved;
Improved freeze-thaw durability due to reduced permeability;
The early and late flexural and compressive strengths of shotcrete are improved;
Enhanced resistance to chemical attack by chloride, nitrate, sulfate, acid-base aggregate reaction;
In concrete repair projects in chloride environments, the high resistivity and low permeability of microsilica sprayed concrete mitigates corrosion of steel bars and wire mesh.
The influence and effect of microsilica fume on shotcrete greatly improves the performance of dry-mix and wet-mix shotcrete, and enables it to obtain better performance in rock mass stabilization, tunnel lining and underground structure repair.
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