Analysis on the Application of Polycarboxylate Superplasticizer
Analysis on the Application of Polycarboxylate Superplasticizer
With the rapid development of the construction industry, the concrete superplasticizer has put forward new and higher requirements. The polycarboxylate superplasticizer has emerged to tackle such needs, and its application scope and scale are increasing. Its advantages are obvious, but it has its drawbacks. With the deepening of practical application, we have a deeper and more accurate understanding of its performance.
- The Adaptability of Polycarboxylate Superplasticizer and Cement
Polycarboxylate superplasticizer is formed by copolymerization of unsaturated monomers containing carboxyl and other monomers, making the mixed concrete have excellent water reduction effect, slump loss control, strength improvement, and environmental protection, and the like. However, the adaptability of a polycarboxylate superplasticizer is relatively better than that of an ordinary superplasticizer. If the variety of cement changes, the adaptability of polycarboxylate superplasticizer and cement will also change. This change is mainly manifested in the fact that when used with some cement, there may be mortar bleeding and water bleeding of concrete, low cohesion, easy collapse, low fluidity of concrete construction, fast slump loss in the construction process, short setting, and hardening time, and inability to improve construction effect and quality, and the like. The causes of all these problems are not only the superplasticizer itself but also closely related to the characteristics of various cement themselves. The fineness and storage time of cement will also affect the performance of the polycarboxylate superplasticizer. Therefore, during the application, we should try to match the mixture ratio in advance, check the adaptability of superplasticizer and cement, and then choose the appropriate cement superplasticizer varieties to achieve economic and reasonable concrete construction.
- The Effects of Aggregate on Polycarboxylate Superplasticizer
Polycarboxylate superplasticizer has many active parts in its molecular chain and great freedom of molecular structure, so it is essentially a surfactant. In actual engineering construction, the aggregates used all contain mud, chloride ions, light substances, and the like. These substances will absorb some of the superplasticizer’s active parts and reduce the superplasticizer’s actual effect. At this time, if the builder wants to keep the original working performance of concrete, it is generally realized by adequately adjusting the amount of superplasticizer. Our experiments found that the content of mud, chloride ions, and light substances in aggregate seriously affects the superplasticizer in concrete. In this case, the amount increase of superplasticizer will increase the construction cost. The gradation of aggregate used in concrete and the needle-like particle content of coarse aggregate will also significantly influence the water reducing effect and volume of the superplasticizers. If other factors are unchanged and the aggregate gradation is worsened, the gap between aggregate particles becomes larger. If the builder wants to achieve the ideal working performance, the builder must add fine particles to fill these gaps, and the surface area will increase accordingly, causing the increase of the adsorption of additives. If the blending number of additives is unchanged at this time, segregation and water bleeding will occur.
- The Influence of Polycarboxylate Superplasticizer on Air Content of Concrete
Most polycarboxylate superplasticizers are air-entraining superplasticizers. It has specific air-entraining properties, and the air content of concrete will generally increase by about 2~5% after being thoroughly mixed with concrete. This phenomenon is due to a polycarboxylate superplasticizer containing a surface-active component that can reduce concrete surface tension. However, the proper increase of air content is beneficial to improve the durability and workability of concrete. However, if these bubbles are not handled properly in the construction process or enhance concrete workability and increase the blending number of superplasticizers, it will harm hardened concrete properties. Therefore, in the construction process, it is critical to strictly control the vibration-blending of concrete and the blending amount of polycarboxylate superplasticizer. Also, the builders will release many bubbles through the gap between concrete and formwork in the work process of vibrated blending. However, the improper use of mold-release agents will seriously hinder bubbles’ discharge, causing bubbles to accumulate on the concrete surface, significantly reducing the apparent quality of concrete. Therefore, it is recommended to use a special concrete mold-release agent with lower viscosity.
- The Influence of the Blending Amount of Polycarboxylate Superplasticizer on the Quality of Concrete
Polycarboxylate superplasticizer has the advantages of low dosage and good water reducing effect. At present, the blending amount of polycarboxylate superplasticizer sold in the market is generally about 1% (accounting for cementitious materials), while the blending amount for minute quantity and low-concentration specifications can reach about 2% (accounting for cementitious materials). Among them, the water reduction rate is generally over 20%, even over 30%. When the polycarboxylate superplasticizer leaves the factory, the manufacturer will provide a recommended dosage, and the builders need to control the actual dosage within this range. If the dosage is too small, the superplasticizer’s effect will not be pragmatically worthwhile, i.e., it is neither economical nor practical. When the blending amount is too large, it will quickly lead to a series of problems, such as concrete segregation, water bleeding, harmful bubbles increasing significantly, and the like. When it is indispensable to adjust the dosage, it must be tested and verified in the laboratory according to various indicators and put into production after meeting the requirements.
Application Notes: –
(1) When using a polycarboxylate superplasticizer, it is necessary to do a good adaptability test with cement. The builders should choose cement with good adaptability, which is economical and easy to apply.
(2) The amount of mud in sand and gravel has a significant influence on the effect of polycarboxylate superplasticizer. In the construction, the constructor tries to choose sand and stone containing mud settled at the bottom.
(3) With the concrete already blended with polycarboxylate superplasticizer in the construction process, the constructor should pay special attention to strengthen the work of vibrated blending while using a special concrete mold-release agent.
(4) The builders should control the dosage of polycarboxylate superplasticizer within the manufacturer’s recommended range, and when the dosage needs to be adjusted, it ought to be verified by test.