The influence of concrete admixture amount and mixing process

The optimal amount of concrete admixture admixture should be determined by the recommended amount, use requirements, construction conditions, raw materials and other factors through testing. Use requirements refer to the requirements of the project, such as early strength or slow setting, saving cement or improving performance, etc. Construction conditions refer to the site conditions, such as the prevailing temperature, insulation and maintenance measures, above-ground construction or underground construction, and the level of site management and operation. Concrete raw materials vary greatly, and the effect of changes in raw materials on the admixture is not the same. Changes in the above conditions will affect the effect of the use of admixtures, therefore, the project to determine the use of admixture varieties, should be determined through testing the best amount of admixture. For a certain cement, a ratio of concrete, any concrete admixture there is an optimal amount, that is, in the best amount of admixture, the performance of concrete admixture will appear inflection point.

The amount of admixture is an important factor to obtain the best technical and economic benefits, the best amount of admixture is based on the test, concrete ratio to determine. The most suitable amount of various water reducing agents are not the same. Naphthalene water reducing agent is about 0.5%-1.5% of the mass of cement, when the strength increase of 10%-25%. In the concrete admixture large or low admixture (relative to the best admixture) will often appear very different, unexpected effects. Such as the "slump" loss of speed, the size of the water, slow setting and promotion of condensation, etc.. Different admixtures have their own different appropriate dosing range, less than or greater than the range can not play its essential role. Super admixture will make the setting time is extended, water reduction rate and strength growth is not large, especially calcium wood, super admixture will make the concrete does not set for a long time. High efficiency water reducing agent overmixing will cause serious water secretion, and poor compatibility, technical and economic are not reasonable. The use of high-efficiency water reducing agent due to the water reduction rate is large, generally can reach 12% ~ 20%, so in use must pay attention to control the appropriate amount of admixture, in order to avoid excessive admixture caused by strength decline, excessive fluidity, affecting the quality of the project. Therefore, before the construction unit uses the admixture, it should be verified to determine the best admixture amount according to the actual situation of the project.

Concrete admixture admixture process (first admixture method and after admixture method) to change the concrete admixture admixture admixture process, according to past work experience and the investigation of concrete engineering personnel, after the admixture method of concrete work better than the first admixture method of concrete, and to achieve the same effect. The amount of admixture of the latter method is often smaller, which is related to the adsorption and dispersion of concrete admixture and cement particles. Therefore, in engineering practice, we have to decide whether to use the first admixture method or the latter method according to the test. Tests and practical application of engineering show that: the use of post-mixing method or water stagnation method, or a small number of times the mixing process, the effect of this method is better.

Concrete admixtures contain different functional groups such as: -OH, -SO3, -COOH, -CH2, etc. on the cement particles have different effects, the molecular weight of the admixture, the shape of different will affect the performance of the admixture. Concrete admixtures are anionic surfactants or cationic surfactants. The adsorption and dispersion effects of C3A, CAF and C3S in cement are different, which also directly affect the solubility of SQ42- in cement, thus leading to the problem of concrete admixture and cement adaptability. Most of the admixtures in Taian area are sodium salts of β-naphthalene-sulfuric acid formaldehyde high condensate. In construction, when the admixture is not well adapted to the cement used, and it is impossible to replace the cement, the admixture manufacturer can be asked to adjust the composition of the admixture to achieve good adaptation of the admixture to the cement. High alkali content in concrete admixture is beneficial to the early strength of concrete, but the loss of fresh concrete slump is fast. Some admixtures induce too much air, and the air bubbles are not uniform and closed. Too large air bubbles lead to fast slump loss of fresh concrete, and make the hardened concrete frost resistance, seepage resistance and other durability decreases.