Self-compacting concrete is a special type of concrete with high fluidity and good filling properties, which can self-compact without the need for vibration. The ratio design of this concrete is the key, which directly affects the mechanical properties and construction performance of concrete. This article will introduce the proportional design of self-compacting concrete.
First, the selection of raw materials.
1.Cement: should choose a stable quality, strength grade not less than 42Grade 5 Portland cement or ordinary Portland cement.
2.Aggregate: medium sand should be used for fine aggregate, and continuous graded gravel with a particle size of 5-25mm should be used for coarse aggregate, and the mud content should not be greater than 1%.
3.Admixtures: Pumping agents or superplasticizers with the functions of water reduction, plasticization, retarding, and air bleing should be selected.
4.Admixture: high-quality fly ash, slag powder, etc. can be selected to improve the working performance and durability of concrete.
Second, the mix ratio design.
1.Determine the water-glue ratio: The water-glue ratio should be determined according to the design strength grade, durability requirements and the performance of raw materials of concrete, and is generally controlled at 03-0.between 5.
2.Determine the sand rate: The sand rate should be determined according to the maximum particle size and type of coarse aggregate, which is generally controlled between 38% and 45%.
3.Determine the unit water consumption: the unit water consumption should be determined according to the maximum particle size of the coarse aggregate, the slump requirements and the water reduction rate of the admixture, which is generally controlled between 160-200kg m.
4.Determine the amount of cement per unit: The amount of cement per unit should be determined according to the design strength grade and durability requirements of concrete, which is generally controlled between 250-400kg m.
5.Determine the amount of admixture: the amount of admixture should be determined according to the design requirements of concrete and the performance of the admixture, which is generally controlled between 50-100kg m.
3. Preparation method.
1.Raw materials such as cement, aggregates, admixtures and admixtures are weighed proportionally and mixed evenly.
2.Gradually add an appropriate amount of water during the mixing process to keep the slump of the concrete within the specified range.
3.Adjust the mix ratio of the concrete until the required strength level, durability and workability are achieved.
4.After laboratory trial, the final mix ratio is determined, and the production is carried out according to the mix ratio.
4. Precautions.
1.The fluidity of self-compacting concrete is large, so the sand rate and water consumption should be strictly controlled when formulating, so as to avoid segregation or water leakage of concrete.
2.The strength grade of self-compacting concrete is higher, so the quality requirements for raw materials are also higher, and raw materials with stable quality and good performance should be selected.
3.The preparation of self-compacting concrete should be carried out according to the requirements of specific projects, and the mix ratio required for different projects is different, so the targeted mix ratio design should be carried out.
4.Attention should be paid to preventing segregation and water leakage during the transportation and construction of self-compacting concrete, so as to ensure the quality and construction performance of concrete.