Common Problems and Countermeasures in the Use of Polycarboxylate Superplasticizers
Release Time:
2016-08-01
Source:
Common Problems and Countermeasures in the Use of Polycarboxylate Superplasticizers
Currently, the commonly used admixtures in the concrete industry include: Polycarboxylate superplasticizer These include naphthalene-based admixtures, naphthalene–amine composite admixtures, naphthalene–aliphatic composite admixtures, and aliphatic-based admixtures. Each type of admixture has its own advantages and disadvantages. With the continuous advancement of polycarboxylate admixture technology and the corresponding reduction in manufacturing costs, their application scope is expanding rapidly. As a representative of China’s third-generation water-reducing agents, polycarboxylate high-efficiency pumping admixtures offer superior performance compared with first-generation lignosulfonate-based water reducers and second-generation naphthalene-based water reducers, including higher water-reduction rates, better slump retention, and greater strength enhancement. They are particularly well suited for producing high-durability concrete with high workability, excellent slump retention, high strength, and plain-concrete applications. However, they impose relatively stringent requirements on the quality of concrete raw materials and on the production process; in particular, they are highly sensitive to the silt content of aggregates and the temperature of cementitious materials. Therefore, careful attention must be paid during actual field application.
Polycarboxylate-based pumping admixtures still face challenges in compatibility with cement; in some cases, they may exhibit low water-reducing efficiency and significant slump loss. Therefore, when the admixture shows poor compatibility with a particular cement, its formulation should be trial-mixed and its constituent ratios adjusted to achieve optimal performance. In addition, cement fineness, temperature, and storage duration can also influence the effectiveness of polycarboxylate pumping admixtures.
Polycarboxylate-based pumping admixtures are highly sensitive to variations in raw materials. Significant changes in the quality of sand, coarse aggregate, and supplementary cementitious materials such as fly ash and mineral powder can markedly affect the performance of concrete containing polycarboxylate pumping admixtures; therefore, trial mixes should be conducted using the altered raw materials to optimize the admixture dosage for achieving the best performance.
Polycarboxylate-based pumping admixtures exhibit a high water-reducing efficiency, making the concrete slump highly sensitive to the water content. Therefore, during application, it is essential to strictly control both the dosage of the polycarboxylate pumping admixture and the concrete’s water content. Exceeding these limits can lead to undesirable phenomena such as segregation, bleeding, surface hardening with bottom-set, and excessive air content.
