Problems in the Application of Polycarboxylate Superplasticizers-2

The mud content in concrete raw materials such as sand and gravel can have an irreversible impact on the performance of concrete, reducing the performance of polycarboxylate superplasticizer. The fundamental reason is that when polycarboxylate superplasticizer is adsorbed by a large amount of clay, the part used to disperse cement particles decreases, and the dispersibility deteriorates. When the mud content in sand is high, problems such as a significant reduction in the water reduction rate of polycarboxylate superplasticizer, increased slump loss, decreased fluidity, easy cracking of concrete, and reduced strength and durability may occur. To address the current issue of mud content, several conventional solutions are available:

(1) Increase the dosage or the proportion of retarder-type slump retention agent of polycarboxylate superplasticizer, but control the amount to prevent problems such as yellowing, bleeding, segregation, bottoming out, and excessively long setting time of concrete;

(2) Adjust the sand ratio or increase the dosage of air-entraining agent. Under the premise of ensuring good workability and strength, reduce the sand ratio or increase the air-entraining agent dosage to increase the free water content and slurry volume in the concrete system, thereby adjusting the performance of the concrete;

(3) Add or modify certain components appropriately to solve the problem. Experiments have shown that adding an appropriate amount of sodium metabisulfite, sodium thiosulfate, sodium hexametaphosphate, and sodium sulfate to the polycarboxylate superplasticizer can reduce the impact of mud content on concrete to a certain extent. Of course, the above methods cannot solve all problems related to mud content, and the impact of mud content on the durability of concrete still needs further research. Therefore, the fundamental solution is to reduce the mud content in raw materials.

Selecting appropriate materials and scientifically and reasonably compounding them with polycarboxylate superplasticizers is currently the main measure in China to improve the performance of superplasticizers. Such compounding often achieves a synergistic effect. However, the compounding of polycarboxylate superplasticizers with certain components is highly selective. They should not be compounded with naphthalene-based superplasticizers, sulfonated melamine-based superplasticizers, or sulfonated amines. When compounded with sulfonated fatty acid superplasticizers within a certain proportion range, a mutual enhancement effect can be achieved. It is recommended that the proportion of sulfonated fatty acid superplasticizers does not exceed 7% for better results. When used in combination with cellulose of different viscosities, water-containing flocs and precipitates may occur, affecting the water retention effect of the polycarboxylate superplasticizer and actual production. When compounded with retarders, sometimes odorous flocs and discoloration may occur. The compatibility with other inorganic salt-based admixtures is also generally poor, such as accelerators and antifreeze agents, with poor solubility and difficulty in compounding. During the mixing process, oily substances may float on the surface. Given this, it is recommended that when using polycarboxylate superplasticizers in combination with other components, the compounding effect and actual impact on concrete must be confirmed through experiments before determining whether the polycarboxylate superplasticizer can be compounded with other components. Moreover, the decisive role of the mother liquor in the performance of the superplasticizer must be emphasized. Not only should the synergistic effects of various additives be utilized, but also the multifunctionality of the mother liquor should be enhanced. Different raw materials should be adopted to produce superplasticizers with different components and performance differences, forming a series of multifunctional products. Through the compounding of mother liquors with different functions, a good effect can be achieved.

Polycarboxylate superplasticizer PCE high performance water reducer, as a new generation of water reducer for concrete, has outstanding advantages. However, during its application, many problems have also been exposed. So far, this issue has always been a topic that practitioners pay close attention to and conduct in-depth research on. We hope that the raw materials of concrete can fluctuate within an appropriate range to achieve relative stability. At the same time, it is suggested that when encountering similar problems, one should carefully analyze and conduct systematic experiments. The problem of using polycarboxylate superplasticizer PCE high performance water reducer can still be solved.