Effect of sand rate on concrete properties

The sand rate refers to the percentage of the mass of sand in concrete to the total mass of concrete, that is: SP = amount of sand S / (amount of sand S + amount of gravel G) × 100%. In the preparation process of concrete, the sand rate is a key parameter in the concrete mix design, which determines the consistency of the mortar and the gradation of aggregates in the concrete. At the same time, （stone crusher）the choice of the sand rate will directly affect the fluidity and cohesion of the concrete. durability, strength and durability.

Because in the concrete system, sand and cementitious material slurry form a mortar that fills the pores between the stones and wraps them on the surface for lubrication. Compared with the stones, the sand has a larger specific surface area, so changes in the sand rate will cause bone The total surface area of the material changes, which also causes changes in the aggregate void ratio and the relative content of coarse aggregate, which in turn affects the workability of the concrete mixture and the strength and durability of the hardened concrete.

  fluidity(xingaonai)

The mortar composed of sand and cement slurry can lubricate between coarse aggregates and reduce the friction between coarse aggregates, so changes in sand rate have a direct impact on the fluidity of concrete. When the sand rate is too small, the mortar in the concrete is not enough to fill the gaps between the coarse aggregates and wrap their surfaces, which will lead to poor fluidity of the concrete and affect its workability. As the sand rate increases, the gaps between the coarse aggregates will The friction force is reduced and the fluidity of concrete will be improved. However, when the sand rate exceeds a certain range and the total surface area of the aggregate increases, the friction between the aggregates cannot be effectively reduced, and the fluidity of concrete will decrease as the sand rate increases.

Cohesiveness and water retention

If the sand rate is too small, the total surface area of the aggregate will be reduced, and the ability of the surface to absorb water will be significantly reduced, which will make the cohesion and water retention of the concrete mixture worse, and prone to bleeding, segregation and slurry. As the sand rate increases, the specific surface area of the aggregate increases, and the cohesion and water retention of the concrete mixture will be improved. However, when the sand rate is too large and a certain amount of cement slurry is not enough to cover the aggregate surface, then On the contrary, the cohesion becomes worse, and the concrete mixture is prone to collapse and divergence.

Strength

If the sand rate is too low, there will be insufficient mortar between the aggregates, which will not provide lubrication, leading to a weak interface and reducing the strength of the concrete. If the sand rate is too high, the proportion of coarse aggregate in the concrete will increase, which will also reduce the strength of the concrete. Strength, therefore, choosing the right sand rate is critical to balancing the strength and toughness of concrete.

Durability

There seems to be no direct relationship between the sand rate and the durability of concrete, because the sand rate often affects the workability of the concrete mixture, thereby affecting the durability of the concrete after hardening. If the sand rate is too small, the water retention of the concrete will decrease, making it difficult for the concrete to be vibrated and compacted during the pouring process. After pouring, honeycombs and cavities are easily formed inside the concrete and on the inside of the formwork, and pitted surfaces are also easily formed on the surface, increasing the size of the concrete. The porosity inside hardened concrete reduces the impermeability of the concrete, thereby increasing the risk of erosion by moisture and harmful substances. If the sand rate is too high, the concrete may be too dry and prone to shrinkage cracks. Therefore, a reasonable sand rate can improve Durability of concrete.

Economy

The sand rate also has an impact on the economy of concrete, because if the sand rate is too small, more materials will be needed to make up for the defects, which will increase the cost of concrete; while if the sand rate is too high, the quality of the concrete may be unstable, requiring additional processing and Reinforcement, thereby increasing costs. Therefore, choosing the right sand rate can balance the cost and quality of the concrete.

In summary, changes in the sand rate not only change the filling effect of the aggregate voids, but also change the specific surface area of the aggregate. If the sand rate is too high or too low, it may lead to a decrease in the working performance of the concrete. Only a moderate sand rate Only then can the concrete have good fluidity, plasticity and stability, and be easy to construct and pour. Therefore, the sand rate is of great significance to the performance of concrete. In actual projects, the appropriate sand rate should be selected based on comprehensive considerations such as design requirements, raw material characteristics, construction conditions, and engineering requirements to ensure that the concrete has good performance and economic benefits. .

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