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Influence and Control of Raw Materials on Precast Concrete Structures

- May 22, 2018 -

Influence and Control of Raw Materials on Precast Concrete Structures

Raw materials mainly include cement, fine aggregates, and coarse aggregates. Only high-quality raw materials can produce high-quality concrete components that meet the technical requirements. The


(a) Cement

The cements used for the preparation of concrete are usually made of Portland cement, ordinary cement, slag cement, pozzolan cement, and fly ash cement. Ordinary Portland cement concrete mix works better than slag cement and pozzolan cement. The slag cement mixing material has a large mobility, but its cohesiveness is poor, and its bleeding is easy to isolate; the pozzolan cement has a small fluidity, but the cohesiveness is best. The use of slag or pozzolan cement precast concrete small components, easy to cause uneven initial surface moisture, after the removal of the color uneven, slag or volcanic ash mixed in the surface of the concrete is easy to form uneven flower bands, black lines, affecting the appearance of the quality of the components. Therefore, ordinary Portland cement should be used as far as possible when precast concrete components. The


The number of cements used should be adapted to the concrete strength of the components required. If the cement label is selected too high, the amount of cement in the concrete is too low, which affects the workability and durability of the concrete, resulting in rough and dull components. If the cement number is too low, the amount of cement in the concrete is too large to be economical. The purpose is to reduce the technical quality of the concrete components of the coagulation chart, increase the concrete shrinkage, and cause severe cracking of the components. In general, when making concrete, cement strength is 1.5 to 2.0 times that of concrete. The


Aggregate

Fine aggregate should be well-graded, hard texture, clean particles, particle size less than 5mm. Sand with 3% mud content. The sand after entering the site should be inspected and accepted. Unqualified sand is strictly prohibited. Check frequency is 1/100 cubic meters. The


Crude aggregates require a hard, skid-resistant, wear-resistant, clean, and compliant gradation. The stone strength should not be less than Grade 3, the content of needle-like tablets should be ≤25%, the content of sulfides and sulfates should be <1%, and the content of clay should be <2%. The maximum particle size of the gravel must not exceed 1/4 of the minimum edge size of the structure. After entering the site, inspection and acceptance shall be carried out at a frequency of 1/200 cubic meters.