Research On The Glass Phase Of Slag, High Calcium Fly Ash And Low Calcium Fly Ash And Their Hydration Mechanism

The glass phase of aluminosilicate melts was studied comprehensively.Blast furnace slag from Beijing Shougang Group, high calcium fly ash fromGaobeidian power plant and low calcium fly ash from Shijingshan power plantwere used as raw materials. Although there are many researches focused on slagand fly ashes, however, the studies of glass phase contained in slag and fly ashesare very few. In order to comprehensively understand the properties of glassphase, the paper presents a series of investigation on glass phase content,composition and structure. Moreover, the dissolution properties, hydrationproperties, mechanical and hydration properties of blended systems were alsostudied.Different methods were used to analyze the content and composition ofglass phase according to the phase characteristics of each raw material, such asXRD crystallinity calculation method for slag, X-ray diffraction combined withRietveld method and chemical analysis with HF solution for low calcium fly ash,and whole pattern simulation by PDF2cards group combined with TG analysisfor high calcium fly ash.The glass phase structures of these three kinds of materials were studied byIR, NMR, SEM-HRTEM and devitrification XRD analysis methods. The resultsshow that they have very different polymerized structure, and phase separationwas observed in slag and low calcium fly ash glass phase, meanwhile the glassphase structure models of them were established. On the basis of these analyses,the relationship between the activity of raw material and glass phase wasinvestigated by different evaluation methods, and the basis of glass phaseactivity was described.The dissolution properties of them were studied, and the experimentconditions included different pH solutions, different concentrations of NaOHsolution and different reaction time. The dissolution behaviors of main glassphase elements (Ca, Si, Al) in alkali solution were studied and the dissolutionmechanisms were discussed. Furthermore, the hydration properties of slag, highcalcium and low calcium fly ash activated by NaOH were studied. The resultsobtained show that the main hydration products were CSH, hydrated calcium aluminate and hydrated magnesium aluminate. The hydration products of highcalcium fly ash were CSH, NASH and AFt. However, low calcium fly ash wasnot fully hydrated, but some zeolite phase was formed. In the meanwhile, thehydration mechanisms of them in alkali system were discussed.These three kinds of materials were compounded homogeneously in theform of binary and ternary, and the mechanical and hydration properties of thesefour blended systems were studied. It was found that the high activity assistedcementitious component (such as slag or high calcium fly ash) and low activityassisted cementitious component (low calcium fly ash) compounded in the formof binary and ternary would have good final mechanical properties. In addition,the compound cementitious effect was found by the analysis of hydrationprocess, which provided a theoretical basis of preparation of blendedcementitious materials.