Effects Of Microfines On The Dispersibility Of Polycarboxylate Superplasticizer

Polycarboxylate superplasticizer is an important component in high performanceconcrete. In recent decades, superplasticizer shows rapid development because of itslow content, high water reduction, strong dispersing force, good workability, themolecular structure and variability, environmental protection and other excellentperformance. However, as consistently indicated by lab studies and engineeringapplication, microfines in aggregates have negative influence on the dispersionproperties of Polycarboxylate superplasticizer.Most of the existing researches focus on the effect of microfines from differentregions or different size on the workability and mechanical properties of concrete usingPolycarboxylate superplasticizer. This article focus on the different kinds of clays inmicrofines on the dispersing performance of Polycarboxylate superplasticizer.Meanwhile, combined with a variety of different physical and chemical properties of theclays to explore the impact mechanism, measureing the main component of clays whichaffect the dispersion properties. The paper also explained from the perspective ofinter-layer adsorption, there is a high reference value for research additives to shieldmicrofines on the the Polycarboxylate negative effects.Montmorillonite, erie, kaolin were Selected as the research object and dependingon the cation, montmorillonite is divided into calcium montmorillonite and sodiummontmorillonite. The fluidity of cement paste mixed with PC is adopted as aperformance index to study the effect of different clays on the dispersion properties ofPC. The results show that the fluidity of cement paste that added with PC lost muchmore than that of Ca-Montmorillonite and Na-Montmorillonite incorporation of1%,buterie and kaolin have little effect on the fluidity of cement paste added PC.Recommended choice of aggregates should consider not only the microfines content onthe surface of the aggregate, but also from the clay minerals contained the microfines tocontrol the quality of aggregate.The mechanism of the clays affect the dispersion properties of PC was studiedfrom the electrical properties, water absorption properties and characteristics of theadsorbed polymer of the calcium montmorillonite, sodium montmorillonite, erie andkaolin. The experiment showed that the presence of clay does not impact on theelectrical properties of the surface of cement particles in the water reducing agent solution. In other words, clay has little effect on the electrostatic repulsion in the system.However, a variety of clay minerals are adsorbed on a certain amount of water in theconcrete mixing process, the sodium montmorillonite have the maximum amount ofadsorption.It showed that water absorption properties of clay is not the most importantreason to affect the dispersion properties of PC by study the influence of saturatedabsorbent clay on the fluidity of cement paste added PC. So we focused on thePolycarboxylate adsorption characteristics of clays, and found that there is a bigdifference in the amount of adsorption of Polycarboxylate of a variety of clay. Theadsorption amount of montmorillonite is3times of the cement particles, the adsorptionamount of kaolin and erie is quite slightly higher than the cement particles.The adsorption type of montmorillonite,Erie and kaolin to PC was studied by usingdifferential thermal-thermogravimetric analyzer，infra-red spectrophotometer (IR)，XRDsmall angle diffract meter. Results demonstrate that polycarboxylate superplasticizer hasbeen absorpted into the lamellar structure of montmorillonite and the adsorption the PCentered the interlayer space can not play the role of water-reducing dispersion.yet,polycarboxylate superplasticizer has not been absorpted into the lamellar structure oferie or kaolin and the adsorption the PC on the surface of particles can play the role ofwater-reducing dispersion. It indicatates that inter-layer adsorption of clay should betaken full account when researching additives to shield microfines on the thePolycarboxylate negative effects or new water-reducing agent.