1.What is concrete admixture
Concrete additive is an admixture added in the process of concrete mixing, which is mainly to improve the performance of concrete.From the additive proportion, generally do not exceed 5%.Although the content is relatively small, but has played a positive role in improving the performance of concrete, concrete development has become an indispensable part.Additives used in concrete mainly refer to different types of water reducer.The wide spread of concrete admixtures has greatly improved the disadvantages of concrete, such as poor strength, strong brittleness and large weight, and improved the applicability of concrete construction.
2.Performance analysis of water reducer commonly used in concrete
Water-reducing agent is mainly to ensure the concrete and the workability on the basis of ensuring the reduction of water consumption.Or improve the workability of concrete without changing the amount of water used.Water reducer can improve the strength and deformation capacity of concrete, at the same time is conducive to the improvement of anti-seepage capacity, and will not produce corrosion of steel reinforcement, is conducive to the anti-rust treatment of steel reinforcement.Water reducer can be divided into ordinary water reducer and high efficiency water reducer.
2.1 Common water reducer
Ordinary water reducer can make concrete achieve at least 5% water reduction.For concrete aged 3-7 days, the compressive strength of concrete can be increased by 10%, and the strength of concrete aged around 28 days can be increased by at least 5%.The common water reducer is calcium lignosulfonate water reducer.Calcium lignosulfonate water reducer belongs to anionic surface active agent.When concrete is mixed in, the amount is 0.2-0.3% of the cement content, and the water reduction rate is about 5%-15%.When the water consumption remains unchanged, the concrete strength can be increased by about 10% to 15%.
2.2 Efficient water-reducing agent
The influence of high-efficiency water-reducing agent on concrete performance mainly includes the following aspects:
(1) Performance of freshly mixed concrete.For the water-reducing effect of the high-efficiency water-reducing agent, the molecular size and specific structure type of the water-reducing agent should also be taken into account.The aeration effect of water reducing agent is affected by the surface tension of its aqueous solution.In terms of concrete setting time, naphthalene series and melamine can advance the setting time of concrete, and amino sulfonate superplasticizer can slow down the setting time.Although the high-efficiency water-reducing agent is not strong adaptability to different cement, but through the use of high-efficiency water-reducing agent, segregation and bleeding phenomenon can be reduced.Through the addition of high-efficiency water-reducing agent.The slump of concrete can be improved.The specific collapse time and degree are determined by the type and quantity of water reducer used.
(2) Influence on the hardening performance of concrete.The degree of hydration of cement can be improved by adding high-efficiency water-reducing agent.The compressive and flexural strength of concrete can be improved comprehensively.The high-efficiency water-reducing agent can also reduce the amount of cement by changing the shrinkage value of concrete.
(3) Influence on durability of concrete.High efficiency water reducer can effectively improve the frost and thaw resistance of concrete due to its high water reduction rate and small amount of air entrainment.And the high-efficiency water-reducing agent can effectively improve the ability of concrete to resist sulfuric acid corrosion.The experimental results show that the corrosion resistance of sulfuric acid is no worse than that of blank concrete.
(4) Influence on corrosion protection of steel reinforcement.Concrete added with high-efficiency water-reducing agent can bond well with steel bars, and the bonding force between straight sliding steel bars and concrete for 7 days can be improved from 1.2mpa to 8.5mpa.The bonding force between bent steel bars and concrete can be increased from 15 MPa to 27.5 MPa within 7D.The experiment shows that the plasticized reinforced concrete with high-efficiency water-reducing agent can hardly corrode the steel bar after 4 years of static treatment. Therefore, the high-efficiency water-reducing agent can effectively protect the steel bar in the concrete.
3.Water-reducing agent is used to improve the performance of concrete
Water reducing agent used in concrete mixing can change the gas content of concrete and greatly reduce the gap rate of concrete.The influence of water reducer on the fluidity of concrete is usually reflected by the numerical value of collapse degree.When the proportion of water and cement used in concrete remains unchanged, the collapse degree of concrete can be greatly improved by adding water reducing agent.Through the use of water reducer, the setting time of concrete can be extended appropriately.But the dosage of water reducer should be controlled reasonably.Maintain reasonableness to avoid excessive increase in concrete that does not condense for a long time.By adding the scientific proportion of water reducing agent, the performance and strength of the whole concrete structure can be improved and the proportion of water and ash in concrete can be reduced.As for the requirement of concrete hardness improvement, water reducer can be appropriately added under the condition of keeping cement content and collapse degree constant.At the same time, water reducing agent can effectively prevent the occurrence of rust problem of steel bar in concrete.Because it can reduce the carbonization of concrete.Therefore, many properties of concrete can be improved by adding water reducer to concrete.