Problems in the Application of Polycarboxylate Superplasticizers-1

Polycarboxylate superplasticizers, as a new generation of concrete admixtures, have the advantages of low dosage, high water reduction rate, and good slump retention. They give concrete excellent workability and durability. Their application in engineering is increasing day by day and has been widely recognized. Due to the significant differences in molecular structure, action principle, and practical application of polycarboxylate superplasticizers compared to the previous two generations of superplasticizers, several problems have arisen during application:

(1) Significant slump loss under high-temperature conditions;
(2) Poor compatibility with other materials;
(3) Strong sensitivity to the mud content of sand and gravel aggregates;
(4) High viscosity, more obvious in low water-cement ratio concrete, which is not conducive to construction;
(5) Strong sensitivity to dosage and water usage, prone to causing concrete segregation, bleeding, and poor system stability problems;
(6) There is strong selectivity when polycarboxylate-based superplasticizers are compounded with other components.

1.1 Adaptation Issues of Polycarboxylate Superplasticizers High Performance Water Reducing Agent to Cementitious Materials

The mineral composition of cement in China is rather complex. In addition, the extensive use of admixtures, especially the instability of fly ash performance, still poses adaptation problems for polycarboxylate water reducing agents to cement and admixtures. These problems are mostly reflected in:

The saturation point of polycarboxylate Superplasticizers High Performance water reducing agents for different cements varies, the water reducing rate decreases, the slump of concrete increases, the appearance of "puddles" in concrete due to insufficient cement paste, leakage, sedimentation and separation, and difficulty in pumping. There are problems such as inability to open the concrete or excessive release of the concrete due to sensitivity to dosage. The reasons for this are quite complex. The freshness of cement, fineness, the types and dosages of admixtures in cement, the proportion of several mineral components especially tricalcium aluminate, the types and dosages of gypsum, the carbon content and water requirement of fly ash, and other properties will all affect the adaptability of the water reducing agent to cementitious materials.

Regarding the current adaptability of polycarboxylate Superplasticizers High Performance water reducing agents, the solutions include the following:

(1) Under the premise of ensuring the strength of concrete, adjust the sand ratio, the proportion of coarse aggregate, increase the amount of slurry in the concrete system, and increase the amount of fly ash;

(2) Use ether and ester compounds for the mother polycarboxylate Superplasticizers liquid and appropriately increase the dosage. Generally, a ratio of 5:5 for ether and ester is recommended, and the dosage should be increased by 0.2% increments. Increasing the dosage too much easily leads to overmixing and is not conducive to accurately grasping the essence of the problem; too little also has no obvious effect.

(3) Appropriately add or modify the components, use admixtures such as SJ, Degussa DY, air-entraining agent AR, K12, etc., increase the proportion of retention agent, use compound retarders such as sodium gluconate, white sugar, phosphate, ATMP, citric acid, modified starch, etc., use soluble cellulose, xanthan gum, dextrin, modified soluble thickening agent, or add "sulfur" or "alkali" to the concrete, which can generally improve the situation;

(4) Change the composition of the polymer. During the synthesis process, adjust certain components to adjust its adaptability. Under current conditions, the problems of concrete water reducers are mostly solved by the first three methods, which are relatively simple and effective. With the in-depth research on polycarboxylate water reducers, the fourth method will gradually become a reality.

The further problems of Polycarboxylate Superplasticizers will show in my next textile, please kindly noted. 

Shanxi Jiankai Fine Chemicals Co., Ltd. is a professional manufacturer of building materials additives integrating production, sales, research and development and technical service. The company mainly produces high-performance polycarboxylate superplasticizers water reducer, sodium naphthalene sulfonate formaldehyde water reducer, melamine-based water reducer, gypsum retarder and defoamer as its core products, forming a complete one-stop procurement supply chain. Warmly welcome your inquiry at anytime.