Concrete raw material proportioning is a crucial part of concrete engineering, which directly affects the performance, quality and project cost of concrete. The following four aspects from the basic principles, common ratios, influencing factors and design standards are explained in detail.

I, the basic principles of concrete raw material proportioning

Concrete ratio design needs to take into account the project requirements, structural forms, construction conditions and raw material conditions to ensure that the concrete not only meet the requirements of workability, strength and durability, but also economical and reasonable. Specific principles include:

Meet engineering needs: according to the concrete strength level (such as C20, C25, C30, etc.) and workability requirements for the design of the proportion.

Economic rationality: minimize material cost under the premise of meeting performance requirements.

Control of water-cement ratio: water-cement ratio is the key parameter to determine the strength, durability and workability of concrete. The higher the strength, the lower the water-cement ratio should be.

Optimize sand rate: Select the optimal sand rate to ensure that the concrete mixture has good cohesion and workability.

Aggregate selection: choose larger particle size, gradation with reasonable aggregates to improve the compactness and strength of concrete.

II, Key Components

Cement:

Cement accounts for 12%-15%, and the grade matches the project requirements.

C30 requires 32.5 grade cement, and C50 uses 42.5 grade cement.

Cement quality affects strength. High-quality cement has moderate hydration heat and reduces crack wind.

Water-cement ratio:

Water-cement ratio of 0.4-0.6 is the key to durability. Low water-cement ratio improves impermeability. If the water-cement ratio is too low, the fluidity is poor and the construction is difficult, which requires reasonable control.

Admixture:

Admixture accounts for 1%-2%, water reducer reduces water consumption, and retarder prolongs setting time.

Admixtures have poor compatibility with cement and may affect strength. It is necessary to test and determine the optimal dosage.

Aggregate:

Aggregate accounts for 60%-75%, and the sand and gravel grading is optimized to reduce the void ratio and improve the density. Aggregate particle size 0-5mm sand, 5-10 small stones, 10-20 medium stones, 25-30 large stones mixed ratio. Coarse aggregate particle size is too large, easy to segregate, affecting the quality.

III, Common concrete proportioning ratios

The proportion of different strength levels of concrete is different, the following is a common example of proportion (unit: kg/m³):

C20 cement dosage 260-300kg/m³, sand rate 38%-42%, gravel particle size 5-31.5mm.

C20 water-cement ratio 0.55,

Suitable for foundation cushion layer, good construction and workability.

C30 cement dosage 320-380kg/m³, sand rate 35%-40%, gravel particle size 5-25mm.

C30 water-cement ratio 0.45, suitable for high-rise building structure, moderate strength.

C50 cement dosage is 420-480kg/m³, sand content is 30%-35%, and gravel particle size is 5-20mm.

C50 water-cement ratio is 0.35, suitable for bridge piers, with high strength and good durability.

IV, Common concrete grades and applicable projects

Low-grade concrete (C15-C30)

Technical characteristics: high fluidity for easy construction, low shrinkage to reduce cracks.

High fluidity is achieved by optimizing aggregate grading and admixtures, and low shrinkage depends on cement quality.

Application scenarios

Low-grade concrete is used for foundation cushion and road base, with low bearing requirements.

The foundation cushion requires good flatness, and the road base requires compressive resistance, and low-grade concrete meets the requirements.

Medium-high grade concrete (C35-C50)

Technical characteristics: early strength and fast hardening shorten the construction period, and pumping performance optimization facilitates construction.

Early strength and fast hardening are achieved by optimizing cement and admixtures, and pumping performance optimization depends on equipment.

Application scenarios

Medium-high grade concrete is used for high-rise building structures and bridge piers, with high load-bearing requirements.

High-rise buildings require high strength, bridge piers require durability, and medium-high grade concrete is suitable.

Special concrete (C60+)

Technical characteristics: good self-compacting performance, high durability design, and adaptability to complex environments.

Self-compacting performance is achieved by optimizing aggregates and admixtures, and high durability depends on materials.

Application scenarios

Special concrete is used for super-high-rise core tubes and nuclear power projects, with extremely high requirements.

Super-high-rise core tubes require high strength, and nuclear power projects require high durability, which special concrete meets.