Effect of Superplasticizer On Long-Term Performance of Concrete

1 Influence on compressive strength of concrete

Different water reducing agents have certain effects on the strength and late strength of the hardened cement paste.The high-efficiency water reducing agent can effectively reduce the mixing water consumption of the concrete mixture, and has a significant improvement effect on the hydration degree of the cement, and effectively improves the strength of the concrete at various ages.Compared with blank concrete, the incorporation of high-efficiency water reducer can effectively improve the compressive strength, flexural strength and static modulus of concrete.Among them, the polycarboxylate superplasticizer has the strongest compressive strength in the early stage of concrete, and the compressive strength is the best after 28d.

2 Influence on shrinkage and creep of concrete

The application of high-efficiency water reducer in concrete can effectively reduce the water consumption, increase the strength of concrete, save cement, and the concrete with high-efficiency water reducer has lower shrinkage value than blank concrete.When used to enhance concrete slump and improve cement workability, the shrinkage value is greater than or equal to blank concrete.

The effect of high-efficiency water reducer on concrete creep is the same as that of shrinkage. When the compressive strength is increased, the creep is significantly reduced.

3 Influence on the freeze-thaw property of concrete

Under other conditions, the water-cement ratio and gas content are two important factors affecting the freeze-thaw resistance of concrete.The smaller the concrete water-cement ratio is, the stronger the freeze-thaw resistance is. The concrete is mixed with the water-reducing agent with air-entraining effect, which can greatly improve its freeze-thaw resistance.At this stage, the high-efficiency water reducing agent widely used in China has a high water-reducing rate and a small amount of bleed air, which greatly improves the freeze-thaw resistance of concrete.

4 Influence on concrete impermeability

The water-cement ratio is the biggest factor affecting the impermeability of concrete.When the water-cement ratio of concrete is >0.55, the amount of water used for mixing concrete at this time far exceeds the water requirement for cement hydration.The original pores left by hydrated residual water, early evaporated water, and bleeding channels in the concrete greatly increase the water permeability of the concrete.However, if the water-cement ratio of the concrete is too low, the concrete structure is not sufficiently dense in view of the poor workability of the concrete, and the impermeability of the concrete cannot be improved.In the case of the same workability, the addition of a water reducing agent and an air-entraining water reducing agent can greatly reduce the water reducing agent required for concrete mixing.If a proper amount of microbubble water reducing agent is added, in view of the reduction of the bleeding passage, not only the impermeability of the concrete can be greatly improved, but also the antifreeze performance of the concrete is better.

5 Influence on the performance of reinforced concrete

Concrete carbonization is closely related to the durability of reinforced concrete structures.

The concrete structure starts from the surface by the action of carbon dioxide, and the calcium hydrate, the hydration product of the concrete, slowly changes to calcium carbonate and loses its alkalinity.The addition of the admixture, because it contains a large amount of chloride ions, further exacerbates the electrochemical corrosion of the steel bars,Therefore, it is necessary to strictly control the chloride ion content in reinforced concrete.The use of superplasticizers, the carbonization rate of concrete is slower than that of blank concrete.It can effectively compensate for the defects of low carbonation resistance of slag cement, inhibit the corrosion of steel bars, and significantly reduce the corrosion damage of the total steel reinforcement.

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