What are the preventive measures for air bubbles on the surface of precast concrete members?
(1) Check the label, variety and performance of the cement used in strict accordance with the requirements. If there are many cement suppliers for precast concrete manufacturers, cement with low alkali content and less surface foaming should be preferred. The label of cement should be compatible with the label of precast concrete mixture ratio. In addition, the use of additives should be strictly controlled to ensure that the air content of concrete does not exceed 4%. At present, there are many brands of additives on the market, so manufacturers should choose several additives with high chemical composition for testing.
(2) Within the scope permitted by the specification, large-size aggregate can be used to prepare concrete. This is because the increase of aggregate particle size can effectively reduce the water consumption of concrete, and then reduce the shrinkage and shrinkage of concrete. However, if the aggregate size is too large, it is easy to cause concrete segregation. Therefore, it is necessary to reasonably choose aggregate chicken embryo, and the ratio of coarse aggregate to fine aggregate is moderate. The specifications of the stone can be selected according to the specific construction conditions, and the stones with good gradation and large particle size should be selected as far as possible to reduce the consumption of cement and water, reduce the wettability and shrinkage of concrete, and also effectively reduce the heat generated during cement hydration.
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