Study On The Effect Of Metakaolin-based Mineral Paste On Performance Of Concrete

Domestic and international numerous studies have shown that metakaolin is akind of excellent mineral admixture, it can significantly increase the strength anddurability of concrete, but metakaolin is difficult to disperse in concrete duringmixing, addition of metakaolin powders in concrete will lead to degradation ofworkability, and the price is higher, so it has not been widely used. The research isfocus on developing a kind of metakaolin-based mineral paste, it does not affect thefluidity of concrete under the premise that it can improve the concrete performanceexcellently. At the same time it can reduce costs, promoting the wide application ofmetakaolin.In this paper, based on the physical and chemical characteristics of metakaolin,influence of paste prepared by a combination of metakaolin and water on theperformance of metakaolin using in cement mortars was investigated. Then puttingthe metakaolin mixed with fly ash will reduce the negative impact on fluidity withusing of fly ash ball water reducing effect, a kind of metakaolin-based mineral pastecan be made through adjusting the proportion of metakaolin and fly ash which can notinfluence the fluidity of cement mortar but have significantly improving onstrength.Emphasis are given on the analysis that the influence of metakaolin-basedmineral paste for basic properties of cement such as the setting time, the consistencyof cement and high efficiency water reducing agent. Finally apply it to the concrete,the influence of metakaolin-based mineral paste for the durability and microscopicproperties of concrete were focused in this study, testing technolog of X-raydiffraction (XRD), scanning electron microscope (SEM), thermogravimetricanalysis(TG-DSC), interfacial transition zone (ITZ), energy dispersive spectrometer(EDS) and the heat of hydration, non-evaporable water content are applied to explainthe hydration mechanism of the influence of metakaolin-based mineral paste forconcrete. Experimental results show that:1). Adding metakaolin in paste form to concrete will slightly reduce the negativeimpact on fluidity but have little influence on strength. A kind ofmetakaolin-based mineral paste can be made through adjusting the proportion ofmetakaolin and fly ash in paste form which can not influence the fluidity of cement mortar but have significantly improving on strength, and with theincrease of addition content, mortar strength showed a trend of decrease afterincrease, the optimum addition content was controlled between10%and20%and the strength appears as highest when dosage was20%.2). Early hydration heat of cementing material will increase after joiningmetakaolin-based mineral paste, but compared with the metakaolin powder earlyhydration heat of cementing material was reduced. Composite paste will reducethe cement setting time. And the composite paste has promoting the consistencyof cement and high efficiency water reducing agent with the saturation dosage ofwater reducing agent was relatively lower, the loss of cement paste fluidity after60min was reduced when the dosage of water reducing agent had reached thesaturation.3). Metakaolin-based mineral paste can improve the accumulation of cementingmaterial that accumulation curve of cementing material was closed to the mostdense accumulation curve of Dinger-Funk theory.4). The interfacial transition zone of concrete become more dense with the additionof metakaolin-based mineral paste, which enhance the combination between thecement paste and aggregate and the pore fracture was reduced. The content ofCa(OH)2at the interfacial transition zone was reduced through the analysis ofenergy dispersive spectrometer after the addition of metakaolin-based mineralpaste, that the ratio of Ca/Si in C-S-H gel was reduced are applied to explain thepolymerization degree of silicon oxygen tetrahedron in C-S-H gel become better,the silicon oxygen tetrahedron chain is relatively longer and the gel structurebecome more dense.5). The performance of the resistance of chloride ion penetration and carbonationbecome better, also it can reduce the early and late shrinkage and improve thevolume stability of concrete through inhibition of the internal stress and microcrack caused by shrinkage of concrete.