If these three basic parameters can be correctly determined in the mix design, the concrete can meet the four basic requirements of the mix design.
The basic principle for determining these three parameters is; on the basis of the strength and durability of concrete, determine the water-cement ratio. The unit water consumption of concrete is determined on the basis of meeting the requirements of concrete construction and workability; the amount of sand should be based on the principle that there is a little surplus after filling the stone voids.
When specifically determining the water-cement ratio, from the perspective of strength, the water-cement ratio should be smaller; from the perspective of durability, the smaller the water-cement ratio, the more the amount of cement, the higher the density of the concrete, and the better the durability. Control the maximum water-cement ratio and the minimum cement dosage to meet. The water-cement ratio determined by strength and durability is often different, and the smaller value should be taken at this time. However, under the premise of both strength and durability, the water-cement ratio should be larger to obtain higher fluidity.
Determining the sand ratio should mainly be considered from the two aspects of satisfying workability and saving cement. Under the premise that the water-cement ratio and the amount of cement (that is, the amount of cement slurry) remain unchanged, the sand rate should be the largest slump, and the sand rate with good cohesion and water retention, that is, the reasonable sand rate can be preliminarily calculated from (Table 5). The decision is determined by trial mixing and adjustment. When the workability is satisfied, the sand rate should be as small as possible to achieve the purpose of saving cement.
The unit water consumption actually reflects the proportional relationship between the amount of cement slurry and the aggregate under the condition that the water-cement ratio and the amount of cement are constant. The amount of cement slurry should meet the requirements of covering the surface of coarse and fine aggregates and maintaining sufficient fluidity, but excessive water consumption will reduce the durability of concrete.
