At present, the special requirements of adjustable setting, high durability and light weight for concrete materials are put forward in the process of construction engineering.This promotes the rapid development of concrete admixtures.Generally, concrete admixtures are mainly composed of early strength agent, water reducing agent, air entrainment agent and retarding agent.Adding a certain amount of admixture into concrete can effectively improve the performance of concrete, and it is of great significance to improve the overall quality of the project.
Influence of concrete admixtures on concrete properties
1. Influence of aerating agent
By adding a certain amount of air entraining agent in concrete, a large number of tiny bubbles can be produced in concrete, so as to improve the workability of concrete and reduce the probability of bleeding segregation.Moreover, the setting time of concrete mixed with aeration agent also changes greatly, which effectively improves the strength of concrete.
2.Effect of water reducer on concrete
The slump of concrete can be increased and the workability of fresh concrete can be improved by adding a proper amount of water reducing agent.In the process of adding water-reducing agent to concrete, batch component incorporation or post-incorporation can be adopted, which can effectively avoid the problem of concrete slump loss and realize the saving of production cost.
3.Effect of antifreeze and early strength agent
By adding antifreeze agent, the freezing point of concrete can be effectively reduced, the hydration of cement can be guaranteed, and the concrete can reach the expected strength within a certain time.However, in the specific application process of antifreeze, it is necessary to select the appropriate components of antifreeze for engineering purposes.
At present, some concrete early strength agents generally contain chloride ions, but chloride ions will react with the steel bars in the concrete structure, accelerate the corrosion of steel bars, and thus lead to concrete expansion and crack.Therefore, when using the additive containing chlorine, it is necessary to add an appropriate amount of rust inhibitor to the mixed spring soil in time.At the same time in the open air concrete to avoid adding additives containing chloride ion, so as not to bring greater impact on the quality of concrete.
The matters needing attention when applying admixture
1.According to the nature of the project or the use of concrete, the right choice of admixture
There are many kinds of admixtures in concrete at present, so it is necessary to select suitable admixtures by combining the properties of engineering and concrete use when concrete admixtures are applied.In the selection of admixtures, it is necessary to comply with the design and construction requirements on the basis of ensuring the economy and rationality.Since concrete admixtures have many types, the following types can be selected in the specific selection process:
(1) modified naphthalene series water reducer.Because this kind of water reducer can optimize the heat capacity of cement hydration, it can be used to configure mass concrete.In the configuration and construction of large volume clays, a large amount of heat of hydration will be generated, which is not conducive to construction.
(2) polycarboxylic acid admixtures and air entraining agents.This water reducer can be well used in the preparation of durable concrete due to its shrinkage capacity.
(3) polycarboxylic acid concrete admixtures.Due to its large water reduction rate, can be used as high strength concrete, at the same time polycarboxylic acid type concrete admixtures can enhance the pumping of concrete, can be configured to pump concrete, reduce the cement in the transport process of secondary adsorption phenomenon, reduce slump loss.
2.Conduct preparation experiments to determine the amount of admixture
The amount of admixtures will affect the quality of concrete, too much or too little can not best play its role, so we must carry out the experiment of admixture, determine the amount of admixture.The raw materials used in the construction are selected for the concrete mixture ratio experiment, the optimum parameter range of admixture is found out, and the admixture quantity is finally determined according to the principle of economy.
3. Methods for adding admixtures
(1) blending first.Powder admixture mixed with cement, then add aggregate and water mixing.
(2) after doping.Concrete mixed with water for a period of time, then add admixture further mixing, maintaining the concrete liquid admixture concentration will not soon reduce.
(3) co-doping.Water, powder and concrete materials into a blender, or liquid admixtures mixed with water, and then mixed with other materials.This method of concrete in the beginning of hydration when the admixture into the immediate cement particle surface adsorption, thus rapidly reducing the concentration of the liquid phase.
(4) fractional addition method.In the process of concrete mixing or transportation, admixtures are added into concrete several times to keep the concentration of admixtures in the liquid phase of concrete at a certain level.
In the actual construction process, different admixtures will also have different effects on the quality of concrete.Therefore, it is necessary to select the right admixture method in the process of preparing concrete.In the specific admixture, the use of admixture first is more conducive to the dispersion of admixture, so that the aggregate of admixture adsorption will be reduced.In the case of the same workability, it is beneficial to realize the saving of water reducer when the admixture method and the admixture method are used.Usually, when the admixture is added, it needs to go through the laboratory.