Factors affecting the effect of concrete superplasticizer

What is concrete superplasticizer?

Admixtures that can greatly reduce the amount of mixing water under the condition that the slump of concrete is basically the same are called superplasticizers.

Factors affecting the effect of concrete superplasticizer

Different cements have different clinker components. The higher the content of MgO in the clinker component, the greater the influence of the water reducer on the performance of concrete, and the easier it is to cause micro-cracks in the concrete.

Superplasticizer has the property of selective adsorption to mineral clinker. When C3A is in contact with water, it has enough adsorption layer immediately. less. This uneven adsorption will make the dispersion of superplasticizers not the same. The higher the C3A content, the worse the compatibility between cement and water reducing agent, which will cause the superplasticizer to have insufficient water reduction or no water reducing effect at all.

Experiments show that the setting time of concrete with water reducing agent is longer than that of concrete without water reducing agent.

In the concrete with superplasticizer added, the concrete system characterized by low water-cement ratio, its setting and rheology are very different from the cement mortar without superplasticizer.

1.Reduced water consumption. The amount of gypsum dissolved in the cement slurry is very small, and its concentration is not enough to control the hydration of C3A, resulting in rapid setting and rapid slump loss;

2. The addition of superplasticizer interferes with the power of cement hydration, reduces the solubility of gypsum, and makes the concentration of gypsum in the liquid phase lower. At the same time, due to the lack of sulfate ions, the sulfonate group on the superplasticizer molecule will combine with C3A, so that the dosage of superplasticizer in the liquid phase is reduced, the dispersing effect on cement is lost, and the slump loss is accelerated.

The specific surface area and particle gradation of cement affect the dispersion effect of superplasticizer. Generally speaking, cement with larger specific surface area, when mixed with the same superplasticizer, has obvious effect and greatly improves fluidity.

A lot of data show that the alkali content obviously affects the fluidity of the cement system of the superplasticizer. The higher the alkali content, the smaller the fluidity of the cement. Experiments show that the use of high-efficiency superplasticizer in high-alkali cement will reduce the water reduction rate. 

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