Influence Of Sand Rate On Concrete Strength

When the water-binder ratio is greater than 0.4, the compression failure of concrete mainly occurs in the cement stone itself and its bonding interface with aggregate, and the strength of cement stone and its bonding interface mainly depends on the strength of cement and water-binder ratio. Therefore, when the water-binder ratio is large, the influence of sand rate on concrete strength is not obvious. However, when the water-binder ratio is less than 0.40, the cement stone and the bond strength are greatly improved. Besides the cement stone itself and the bonding surface with aggregate, the compressive failure of concrete also includes the failure of aggregate itself. In the design of mix ratio, the sand rate is large, which increases the total surface area of coarse and fine aggregate, so that the cohesiveness of concrete mix is seriously deteriorated, and even the phenomenon of collapse occurs. As a result, the binding force between the various components of concrete decreases, and the strength of concrete will be reduced after hardening. However, if the sand rate is too small, the slurry is too abundant, and in the process of concrete forming, under the condition of dead weight and strong vibration, it is more likely to appear bleeding phenomenon. If the concrete mix bleeding seriously, it will cause the following adverse effects: first, the formation of a large number of bleeding channels, increase the porosity of the concrete, thereby reducing the strength of the concrete; Second, at the lower edge of coarse aggregate and horizontal steel bar, water film appears due to bleeding action, which will form a gap after evaporation, reducing the strength of concrete and the binding force between concrete and steel bar. Thirdly, bleeding increases the water-binder ratio of the surface concrete, forming the so-called floating slurry layer, which has very low strength after hardening. Fourth, bleeding will also lead to uneven concrete inside, increase the shrinkage of concrete during the hardening process, will also reduce the strength of concrete. When the sand rate is reasonable, the concrete mixture can obtain good working performance and improve the strength of concrete after hardening.