Investigation On The Efficient Dispersion Of Agglomerate Metakaolin Particles

Metakaolin, which has the pozzolanic effect, alkali activated effect and the filling effect, has been considered a high-quality concrete admixtures. Because its huge specific surface area and high activity, metakaolin particles are prone to reunite. Based on such theory, this paper focuses on trying to disperse agglomerate metakaolin particles and mixing the dispersed particles with concrete materials, to test its macro performance and micro-structural changes to provide a theoretical support for the preparation of high performance concrete materials.To explore the optimum dispersion program of the agglomerate metakaolin particles, this paper carries on a large mount of comparative tests in for dispersing metakaolin particles, using three kinds of common chemical dispersant such as AZN-1, AZN-2and AZN-3, combining with manual physical methods such as grinding and mechanical polishing. Then, the degree of fineness of metakaolin particles is evaluated through the field emission scanning electron microscopy and laser particle size analyzer, etc. On this basis, through Microsoft Windows "Programs-Accessories-Paint "application, the curves obtained by the laser particle size analyzer are studied by coloring processing, the curves are analyzed by the image analyzer. After finding the quantitative relationship of the relative area of various colored areas, the concept of Theoretical dispersion efficiency is brought forward in order to give a quantitative assessment of the variety of dispersion mechanism for agglomerate metakaolin particles. Lastly, both of the dispersed and undispersed metakaolin particles are mixed into the mortar to comparatively study the impact on its compressive strength, and to evaluate the impact on its micro-structure through micro-testing method such as SEM and XRD, etc. The main conclusions are as following:The effect of complex doped dispersant for the agglomerate metakaolin particles is generally better than the single-doped dispersant. Among them, the complex doped dispersant which consists of0.88%of AZN-1and1.44%of AZN-2is the best. A large number of particles are dispersed to below1μm, even the minimum size of0.25μm. According to the results of field emission scanning electron microscope, there are particles below100nm in the dispersed metakaolin.The concept of "Theoretical dispersing efficiency" can reflect the dispersing situation of agglomerate metakaolin particles to a certain extent. Using the complex doped dispersant which consists of0.88%of AZN-1and1.44%of AZN-2is the best way, whose theoretical dispersing efficiency is the highest, more than96.43%.The compressive strength of the mortar mixed with the dispersed metakaolin is totally higher than that mixed with undispersed metakaolin. When the content of the dispersed metakaolin is at the middle level(10%), the early and late strength of the mortar are comparatively largely increased. If the content of the dispersed metakaolin is higher or lower, the impact to the strength of the mortar is not clear. Through the phase analysis and microstructure analysis, using dispersed metakaolin can even lower the content of Ca(OH)2and promote the formation of ettringite, which leads to even less pores in the mortar materials, even denser inner structure and better mechanical properties.