At present, the construction process of building engineering puts forward special requirements for concrete materials, such as adjustable setting, high durability and light weight. At the same time, concrete is required to be easy to form and easy to maintain. This promotes the rapid development of concrete admixture.
Concrete admixtures are mainly composed of early strength agent, water reducer, air entraining agent and retarder. Adding a certain amount of admixture to concrete can effectively improve the performance of concrete and is of great significance to improve the overall quality of the project.
Effect of concrete admixture on concrete performance.
Effect of air entraining agent on concrete.
By adding a certain amount of air entraining agent into concrete, a large number of tiny air bubbles can be produced in concrete, so as to improve the workability of concrete and reduce the probability of bleeding and segregation. And the setting time of concrete mixed with air entraining agent will also change greatly, which can effectively improve the strength of concrete.
Effect of superplasticizer on concrete.
By adding appropriate amount of superplasticizer to concrete, the slump of concrete can be increased and the workability of fresh concrete can be improved. In the process of adding superplasticizer to concrete, batch mixing or post-mixing method can be used, which can effectively avoid the slump loss of concrete and save the production cost.
Effect of antifreeze and early strength agent on concrete.
By adding antifreeze, the freezing point of concrete can be effectively reduced, the hydration of cement can be ensured, and the concrete can achieve the expected strength within a certain period of time. However, in the process of specific application of antifreeze, it is necessary to select the antifreeze with suitable composition according to the use of the project. At present, some concrete early strength agents generally contain chloride ion, but chloride ion will have a chemical reaction with the steel bar in the concrete structure, accelerating the corrosion of steel bar, resulting in concrete expansion and cracks. Therefore, when using chlorine-containing admixture, it is necessary to add an appropriate amount of rust inhibitor to the mixed spring soil in time. At the same time, the admixture containing chloride ion should be avoided in the open-air concrete, so as not to have a great impact on the quality of the concrete. Matters needing attention in the application of admixtures 1 correctly select admixtures according to the nature of the project or the use of concrete.
At present, there are many kinds of concrete admixtures, so in the application of concrete admixtures, it is necessary to select suitable admixtures according to the properties of the project and the use of concrete. In the selection of admixtures, it is necessary to meet the requirements of design and construction to ensure economy and rationality. As there are many kinds of concrete admixtures, the concrete admixtures can be selected according to the following categories in the specific selection process:
Modified naphthalene superplasticizer. Because this kind of superplasticizer can optimize the hydration heating capacity of cement, it can be used to configure mass concrete. During the configuration and construction of large volume stick concrete, it will produce a lot of hydration heat, which is not conducive to the construction, and these two kinds of superplasticizer can reduce the thermal effect very well.
Polycarboxylic acid admixtures and air entraining agents. Because of its shrinkage-reducing ability, this superplasticizer can be well used in the preparation of durable concrete.
Polycarboxylic acid series concrete admixture. Because of its large water-reducing rate, it can be used as high-strength concrete, and polycarboxylic acid concrete admixture can enhance the pumpability of concrete, configure pumping concrete, reduce the secondary adsorption of cement in the process of transportation, and reduce slump loss.
Carry on the preparation experiment to determine the amount of admixture will affect the quality of concrete. The mix proportion experiment of concrete is carried out by selecting the raw materials used in construction, the best parameter range of admixture is found out, and the dosage is finally determined according to the principle of economy.
The method of adding admixture.
Mix it first. The powder admixture is mixed with cement, and then mixed with aggregate and water.
Post-mixing method. After mixing the concrete with water for a period of time, and then adding the admixture to further stir, the concentration of the admixture in the liquid phase of the concrete will not decrease quickly.
Co-mixing method. Water agent, powder and concrete material are poured into a mixer, or liquid admixture is mixed with water, and then mixed with other materials. In this method, the admixture is involved in the hydration of concrete at the beginning, and it is immediately absorbed by the surface of cement particles, thus rapidly reducing the concentration in the liquid phase.
Step-by-step addition. In the process of concrete mixing or transportation, the admixture is added to the concrete several times, so that the concentration of the admixture in the liquid phase of concrete can be kept at a certain level.
In the actual construction process, different admixture methods will also have different effects on the quality of concrete. Therefore, the correct admixture method should be selected in the process of preparing concrete. In the specific addition, the use of the first addition method is more conducive to the dispersion of the admixture, so that the adsorption capacity of the aggregate to the admixture will be reduced. Under the same and workable conditions, the post-blending method and co-blending method are beneficial to realize the saving of superplasticizer. Usually, when the admixture is added, it needs to be tested through the laboratory.
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