Classification and application of concrete admixtures
Concrete admixtures are called admixtures. In the process of disposing and mixing concrete, it is necessary to add some products according to the city design requirements and test results to enhance or change the performance of concrete. This part of the added substances is called admixture, plus The use of the agent should be strictly controlled, and the total amount required should be 5% by weight of the regional cement. Admixture quality, type selection, dosage and ratio have a significant impact on the quality and performance of concrete. In the actual construction process, concrete processing, addition and use of admixtures should be carried out in strict accordance with the relevant standards set by the State.
Taking high-performance concrete configuration as an example, in order to improve the performance of concrete, the following admixtures are added: (1) Water reducing agent. The water reducing agent has a high water reducing rate, the water reducing agent is added mainly to reduce the loss of concrete slump, and the second is to maintain the concrete pumping and filling property, and maintain the concrete during the construction process. Stability, reducing mechanical and operational impact. (2) Retarder. Retarded soil is mainly to prolong the solidification time of concrete, inhibit the rate of induration, and also reduce the loss of concrete slump and reduce the number of cracks. The defect lies in the fact that the incorporation of concrete reduces the early strength of concrete and increases its plastic shrinkage. Therefore, in practical applications, it is necessary to strictly analyze the ratio of retarder to water reducer, and the two are matched and used together with cement. Compatibility, after testing, determine the final reasonable amount. (3) Air entraining agent. The use of air entraining agent reduces the bubbles in the concrete, which makes the pouring quality of the concrete more uniform and avoids inconsistent quality inside and outside. The use of air entraining agents enhances the workability and durability of the concrete and prolongs the service life of the concrete. However, the use of the admixture has strict requirements. In general, the air entraining agent is added only when the engineering has impermeability and antifreeze requirements.
Analysis of the role of concrete admixtures in construction engineering: (1) affecting, changing or improving the performance of concrete: the processing and mixing of concrete requires the use of a large amount of water, which not only causes an increase in construction costs, but also wastes resources. The use of admixture can reduce the amount of water, ensure the concrete has suitable fluidity in the case of low water consumption; adjust the setting time to meet the construction needs of the project; delay the initial hydration heat; greatly reduce the segregation and secretion Water problem, optimize concrete workability and water washability; improve pumping; reduce concrete slump loss; avoid rapid rise of concrete temperature, reduce the occurrence of cracks; reduce concrete viscosity coefficient. (2) Affecting concrete strength: changing the concrete shrinkage or compensating for shrinkage; improving its early strength to avoid freezing, and also optimizing its antifreeze, corrosion resistance, impermeability and wear resistance. (3) Affect the durability of concrete: improve the controllability of alkali-aggregate reaction, avoid the corrosion and corrosion of steel bars during condensation, reduce the diffusion of chloride ions; improve the internal compactness of concrete, reduce the occurrence of air bubbles and internal voids . (4) Other influences: The use of admixtures can also give concrete some special properties and use it for construction in special locations, such as construction in acidic environments, pouring of high-pressure bearing surface concrete, and mass concrete. The construction of the location has special requirements for concrete and can be achieved with admixtures.