Supply sand-free concrete

No greater than the British Standard Screening pass rate no greater than.
The mass ratio of aggregate to cement should not be less than and should not be greater than.
The cement content should be appropriate so that each particle of the aggregate is surrounded by cement slurry but the dense concrete should have pores so that water can flow in the pores of the hardened concrete.
Standard Analysis
The technical requirements place certain restrictions on the raw materials and mix proportions of sand-free concrete.
Raw materials
The cement requires ordinary Portland cement or fly ash Portland cement commonly used in Hong Kong. The aggregate particle size is required to be single, generally between ~ 0.0% of large particles and 0.0% of small particles are allowed. The singleness of particles determines the characteristics of low pore volume inside sand-free concrete and difficulty in segregation during pouring. When the aggregate specific gravity is certain, the bulk density of concrete prepared with aggregates of a single particle size is approximately lower than that of concrete prepared with well-graded aggregates. In addition, the size of the aggregate has a relatively large impact on the strength of concrete. The smaller the aggregate particles are, the shorter and thicker the shape, the greater the strength. This is because the contact points between the aggregates increase.
Ash ratio
The value of the bone ash ratio of sand-free concrete depends on the strength of the concrete to be prepared. The lower the strength of sand-free concrete, the greater the bone-to-ash ratio. Generally speaking, the ashes ratio is between ∶～∶. The structure of road and bridge projects generally does not have high requirements for the strength of sand-free concrete, so the ashes in the technical requirements are relatively large.
Water-cement ratio
To ensure that each particle of the aggregate is wrapped with cement slurry and to ensure that there are pores inside the sand-free concrete, it is mainly achieved by controlling the bone-ash ratio and water-cement ratio. There is a narrow optimal water-cement ratio for a given aggregate and ash ratio. If the water-cement ratio is lower than the optimal value, the cement slurry cannot be evenly wrapped around the coarse aggregate. If the water-cement ratio is too high, the cement slurry will flow away from the aggregate particles. A representative water-cement ratio is between ~. To determine the optimal water-cement ratio it can be determined through a compressive strength test. In the actual construction process, it is generally judged based on experience whether the water-cement ratio is appropriate. For example, take out some mixed mixture and observe it. If the cement is evenly wrapped on the surface of the aggregate and there is no cement slurry dripping down, and the particles have a metallic luster, it means that the water-cement ratio is relatively good. as appropriate.