Preparation skills of extra-fine sand concrete
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Preparation of extra-fine sand concrete.
When using ultra-fine sand to prepare concrete, we should choose clean sand with low mud content and low impurity content. at the same time, we can refer to or follow the following basic principles.
1. Reduce the sand rate appropriately.
The sand ratio has an important influence on the workability of concrete mixture, and the sand ratio decreases with the decrease of fineness modulus.
When the fineness modulus decreases, the sand particles become smaller, the smaller particles are easier to fill the gap between coarse aggregate particles, and less sand can be filled effectively. Therefore, the fineness modulus becomes smaller and the sand ratio should be reduced appropriately.
In addition, the sand fineness modulus becomes smaller and the specific surface area increases. If the sand ratio remains unchanged, the viscosity of the mixture increases, the fluidity slows down, the flow rate decreases, and the shrinkage of concrete becomes larger, which greatly increases the probability of cracking.
When the fineness modulus of sand is 1.4, the sand ratio is 7% to 13% lower than that of medium sand with a sand ratio of 2.6.
2. Increase the amount of cementitious material appropriately.
The disadvantage of ultra-fine sand is that the specific surface area is larger and the mud content is higher. Compared with the concrete prepared with medium sand, the amount of cement and cementitious material is higher.
Generally speaking, the amount of cement should be increased by 20kg/m ³.
3. Reduce the slump of concrete as much as possible.
There are many fine particles and large specific surface area of ultra-fine sand. When the paste is unchanged, the cohesion of concrete is poor, and the phenomenon of bleeding and anti-sand is easy to occur after concrete pouring and vibration, which affects the construction quality of concrete.
There are few coarse particles in ultra-fine sand, and when mixed with coarse aggregate, the intermediate gradation is missing, the rheological property of concrete is poor, and it is easy to cause slurry-stone separation when the slump is large.
In addition, with the increase of concrete slump, the amount of cementitious material will increase, the shrinkage of concrete will increase, and the risk of cracking will increase.
Therefore, the principle of low sand rate should be followed when using ultra-fine sand.
4. appropriately increase the amount of admixture to control water consumption.
There are many fine particles and large specific surface area of ultra-fine sand. When mixing concrete, the water consumption of the same slump is higher than that of medium-coarse sand, so it is easy to cause the strength of fine-sand concrete to be lower than that of medium-coarse sand concrete.
When using ultra-fine sand, the amount of admixture should be increased appropriately to keep the water consumption of concrete unchanged.
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Fine sand screening machine reduces the loss rate of fine sand in the process of sand washing.
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