In order to effectively improve the workability, strength, and durability of concrete and reduce the deformation of concrete, sometimes in order to make the concrete condense quickly or delay the agglomeration, an appropriate amount of concrete admixtures can be added to improve the working performance of the concrete. Meet construction requirements.
1. When constructing concrete in high-rise buildings, admixtures must be added to the concrete to retard setting and improve the workability of the concrete, without affecting the strength of the concrete.
2. When pouring concrete for basement slab walls, crack-resistant fiber materials and impermeability agents are generally added to the concrete.
3. During the construction of concrete in water conservancy, anti-chloride ion admixtures must be added to the concrete, which is what we often call offshore concrete.
Concrete admixtures are increasingly commonly used and are an objective requirement for the development of construction engineering structures and technologies. In recent years, high-rise, long-span and various new structural systems have appeared in the overall cast-in-situ concrete structure. Many large-scale, thin-walled and other new component types have appeared in the prefabricated concrete components. In concrete construction, New construction technologies such as mass concrete, sprayed concrete, vacuum water-absorbing concrete, and slip-form construction concrete have proposed for concrete high fluidity, early strength, high strength, rapid setting, retarded setting, low heat of hydration, frost resistance, and resistance to According to various performance requirements such as permeability and permeability, the use of admixtures is precisely to improve the performance of concrete, improve project quality, reduce project costs, and promote new technology requirements.
The properties of concrete are determined by the proportion of cement, sand, gravel and water. In order to improve a certain property of concrete, the proportion of raw materials can be adjusted. But this often causes losses on the other hand. For example, in order to increase the fluidity of concrete, you can increase the amount of water, but this will reduce the strength of the concrete. In order to improve the early strength of concrete, the amount of cement can be increased, but in addition to increasing the cost, this may also increase the shrinkage and creep of concrete. The use of admixtures can avoid the above-mentioned defects. When it has little effect on other properties of concrete, the use of concrete admixtures can greatly improve certain properties of concrete. For example, as long as 0.2% to 0.3% calcium lignosulfonate water-reducing agent is mixed into concrete, the slump of concrete can be more than doubled without increasing the amount of water; as long as 2% is mixed into concrete ~4% sodium sugar calcium sulfate (NC) composite agent can increase the early strength of concrete by 60% to 70% without increasing the amount of cement, and can also improve the later strength of concrete.
Rational selection and use of concrete admixtures
(1) The variety of admixtures should be selected according to engineering design and construction requirements, and determined through experiments and technical and economic comparisons.
(2) Admixtures mixed into concrete must not cause harm to the human body or cause pollution to the environment.
(3) The cement used in concrete mixed with admixtures should be Portland cement, ordinary Portland cement, slag Portland cement, pozzolanic Portland cement, fly ash Portland cement and composite Portland cement, and the adaptability of the admixture to cement should be tested and used only after meeting the requirements.
(4) The materials used in concrete mixed with admixtures, such as cement, sand, stone, admixtures, and admixtures, should comply with the requirements of the current relevant national standards. When trial-mixing concrete with admixtures, the raw materials used in the project, the mix proportions, and the same environmental conditions as those used in construction should be used. The test items should be determined based on the design and construction requirements, such as slump, change in slump over time, setting time, strength, Air content, shrinkage rate, expansion rate, etc., when the raw materials used in the project or the performance requirements of the concrete change, the trial fitting test should be carried out again.
(5) When different types of admixtures are used in combination, attention should be paid to their compatibility and impact on concrete properties. Tests should be conducted before use to ensure that the requirements are met before use. Concrete admixtures are materials that are added during the concrete mixing process and can improve the properties of concrete as required. The selection of the type of admixture should be determined based on the main purpose of using the admixture and through technical and economic comparison. The dosage of admixtures should be determined through experiments according to their varieties and based on factors such as usage requirements, construction conditions, concrete raw materials, etc. The amount of admixture (calculated on a solid basis) should be expressed as a percentage of cement weight, and the weighing error should not exceed 2% of the specified measurement. The coarse and fine aggregate used should comply with the current relevant national standards. The production and use of concrete mixed with admixtures should also comply with the current national quality standards for concrete admixtures and relevant standards and specifications.
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