Study on the Effect of Superplasticizer in Concrete

1.What is superplasticizer?

Chất siêu dẻo ,is a kind of concrete admixture which can reduce the amount of water used for mixing under the condition of keeping the slump of concreteunchanged.Most of them are anionic surfactants, such as lignin sulfonate, naphthalene sulfonate formaldehyde polymer, etc.After adding concrete mixture, it can disperse cement particles, improve its workability, reduce unit water consumption and improve the fluidity of concrete mixture.Or reduce the amount of unit cement, but concrete superplasticizer too much, not only can not improve the mobility, but will lead to sand slurry segregation and bleeding water.

2.How does superplasticizer work?

Chất siêu dẻo thực chất là một loại vật liệu xây dựng, in use will produce foam and bubble and other sol bubbles, và chúng có những đặc điểm và cơ chế hình thành khác nhau, is caused by ionic superplasticizer.After adding the superplasticizer to the concrete, the superplasticizer will be adsorbed on the surface of cement particles. Nói chung là, Về 80% of the superplasticizer will be adsorbed by cement particles, which can keep the aggregation state without diffusion for a long time.Without superplasticizer in concrete , concrete will have a certain amount of air (2% or so), the size of the bubbles formed is uneven, and the distribution is very uneven.When superplasticizer is added to concrete, việc phân phối các thông số bê tông có thể duy trì các đặc tính tốt và cải thiện hiệu suất làm việc của bê tông, such as tensile strength of concrete.

Ngoài ra, adding superplasticizer in concrete mixing can help reduce the water consumption in concrete mixing, and the tiny sol air bubbles generated can help fill in the micro pores inside concrete, significantly improve the impermeability of concrete, and enhance its chemical corrosion resistance and aging resistance.The water-reducing agent can be integrated into the free water migration of internal materials, which is helpful to ease hydrostatic pressure and enhance the ability of concrete to resist repeated freezing-thawing cycle.Water-reducing agent can slow down the hydration reaction rate of cement in the middle and late stage, improve the strength of cement and enhance its anti-expansion performance.Therefore, khi trộn bê tông, ngoài việc xem xét cát, cục đá, xi măng và các vật liệu thông thường khác, appropriate addition of a certain amount of water reducer to improve the performance of concrete.

1. Influence of superplasticizer dosage in concrete

(1) Influence of water-reducing agent on slump of fresh mixed concrete

In the analysis of concrete workability and fluidity, a very key index is slump, the higher the value, the better the fluidity of concrete.Slump loss refers to the difference between slump and initial slump measured by concrete after a specific time. Các yếu tố ảnh hưởng bao gồm xi măng, đặc tính cốt liệu và tỷ lệ nước-xi măng, vân vân. The type of water-reducing agent is also the key influencing factor.

2) Influence of water reducer on compressive strength of fresh mixed concrete

The concrete strength formed by different types of superplasticizer has different effects.By applying superplasticizer can significantly reduce the mixing of concrete mixing water consumption, cải thiện mức độ hydrat hóa của xi măng, cải thiện bê tông theo từng độ tuổi (3 d, 7 d và 28 d) cường độ, có thể từ ba loại phụ gia siêu dẻo hiệu quả cao, cường độ nén của bê tông cao hơn đáng kể so với cường độ nén của bê tông trắng, 3 d, 7 d và 28 d tốc độ tăng cường độ nén cao bằng 15%, 20% Và 30% respectively.In addition, the type of concrete with the highest compressive strength in the early stage is the concrete mixed with polyhydroxyacid superplasticizer, which has the highest compressive strength after 28 days.However, bê tông bao gồm chất siêu dẻo dòng naphthalene có cường độ nén tương đối thấp ở giai đoạn đầu, điều này cho thấy hiệu suất cường độ ban đầu của nó tương đối kém.

3) Influence of superplasticizer on early cracking performance of fresh mixed concrete

Physical and chemical reactions may occur between cement and concrete with admixtures.One kind of superplasticizer has a relatively small slump in concrete made up of one kind of cement, while in another kind of cement, a relatively large slump loss may occur, so there is no superplasticizer that has a good effect on any kind of cement.In the actual concrete quality evaluation, the commonly used evaluation index mainly includes concrete slump and strength, but it is easy to ignore the concrete volume stability, easy to induce early shrinkage crack, may accelerate the concrete crack, affect the durability and safety of the building structure.From the point of view of the factors affecting the early cracking of concrete, apart from wind speed and ambient temperature, the types and amount of additives are also the key factors.

4) Influence of superplasticizer on the durability of fresh mixed concrete

Superplasticizer has a greater impact on the durability of concrete, mainly for: (1) the impact of concrete frost resistance.Considering that the smaller the water-cement ratio is, the better the freezing-thawing resistance of concrete will be. By adding water reducing agent with air-entraining effect, the freezing-thawing resistance can be significantly improved.The induced air volume should be controlled at about 2%, và mức tối đa không được vượt quá 6%, otherwise it will adversely affect the strength and durability of concrete.Effect of concrete impermeability.Water-cement ratio is the main factor affecting the impermeability of concrete. If its value is greater than 0.55, it will exceed the hydration water consumption of cement to form many bleeding holes in concrete and increase the permeability of concrete.If the water-cement ratio is too small, it will affect the workability of concrete, and is not conducive to the permeability of concrete.(3) concrete resistance to steel corrosion and the impact of carbonization performance through the selection of superplasticizer, can significantly slow down the carbonization rate of concrete, help to improve the carbonization performance of concrete, reduce the damage of steel corrosion.

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