Analysis of the deterioration phenomenon of Polycarboxylate superplasticizer

What is Polycarboxylate superplasticizer?

Polycarboxylate superplasticizer is the third generation of high-performance water-reducing agent after ordinary water-reducing agent and high-efficiency water-reducing agent. Compared with other types of superplasticizers, it has the advantages of strong molecular designability, high water reduction rate, good slump retention, low chloride ion and alkaline substance content, and pollution-free production and use. In practical applications, polycarboxylate superplasticizers are often compounded with a small amount of defoaming components, retarding components, air-entraining components, and viscosity-modifying components to meet different technical performance requirements of concrete.

The combination of sodium gluconate or sucrose as a retarding component with a polycarboxylate superplasticizer can increase the water reduction rate to a certain extent, slow down the loss of concrete slump, and improve the adaptability of the superplasticizer to cement. However, at the same time, the polycarboxylate superplasticizer products are often deteriorated quickly due to the addition of sodium gluconate, ranging from reduced performance to complete loss of efficacy, which brings many uncertain factors to engineering use or directly leads to engineering accidents. This problem is even worse in hot weather.

Phenomenon and causes of deterioration of polycarboxylate superplasticizers

1.In the early stage of deterioration of polycarboxylate superplasticizer, there are light-colored fluffy or cotton-wool plaques on the liquid surface, and then develop into discrete block-shaped floating objects, and string-shaped bubbles emerge from time to time;

2. When the deterioration is serious, the bacterial plaque will cover the entire liquid surface, and the solution will appear dense green, brown and black suspended matter, accompanied by the generation of rotten sour gas. This deterioration is mainly caused by mildew.

The mildew of polycarboxylate superplasticizer is also related to its storage environment. Improper storage conditions, such as severe temperature rise in the storage space, lack of ventilation, and humidity, lead to the melting of the large monomer and the local temperature of the monomer is too high. Higher temperature will intensify the movement of macromolecular chains. Once the dissociation energy of chemical bonds is exceeded, chain decomposition, random fracture and thermal decomposition will occur, resulting in accelerated degradation of polymers. Similarly, the higher the temperature, the greater the activity of microorganisms, and the faster the mildew rate of the superplasticizer.

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