Study On The Activated Mechanism Of Fly-ash In Portland Cement Containing C₄A₃(?)

Portland Cement containing C₄A₃ is one of the development directions of high performance cements. It is produced with low Ferrum dosage prescription at low temperature(±1350℃). Its main mineral components are C3S,C2S, C₄A₃, and it also contains some calcined gypsum. As C3S, C₄A₃and calcined gypsum exist, this kind cement has the functions of alkali-activation and sulfur-activation at the same time. Therefore, Portland Cement containing C₄A₃ is advantageous to activate the latent activity of adimixtures(e.g fly-ash, slag).The strength of Portland Cement containing C₄A₃ added with admixtures was high., especially the strength of fly-ash cement containing C₄A₃ was higher than that of slag cement containing C₄A₃. However, this phenomenon is reversed to the traditional verdict "The activity of slag is higher than that of fly-ash in cement system". Therefore, the need to find out the activated mechanism is urgent, which is important to improve the dosage of fly-ash in cement and accelerate the resourceful course of fly-ash. In the research, high calcium fly-ash, the ordinary fly-ash and slag were added to Portland Cement containing C₄A₃ at the same dosage. The results showed that the strength of these two kind of flh-ash cements containing C₄A₃ was higher than that of slag cement containing C₄A₃. The conclusion was drew that the hydration degree of fly-ash cements containing C₄A₃ was higher than that of slag cement containing C₄A₃ by measuring the non-evaporable water content. And the order of reaction degree of admixtures showed as follows: high calcium fly-ash>the ordinary fly-ash > slag.In this dissertation, the activating function of C₄A₃ to fly-ash was investigated. When C₄A₃ was added at the same dosage to the systems of fly-ash-CaO and slag-CaO, the order of reaction degree of admixtures was listed as follows: high calcium fly-ash> the ordinary fly-ash. This showed that C₄A₃ could activate the activity of fly-ash. The f-CaO absorptivity of fly-ash-CaO-CaSO4·2H2O system washigher than that of fly-ash-CaO system, which showed that gypsum could accelerate the pozzolanic reaction of fly-ash in a way. Based on this work, some C₄A₃ was added to Portland Cement. The result showed that the strength of fly-ash cement was higher than that of slag cement. The hydration degree of cements and reaction degree of admixtures also illustrated that C₄A₃ could activate the activity of fly-ash.The hydration products were studied by XRD, DSC－TG, SEM/EDS. The results showed that the contents of AFt and CSH were higher in fly-ash cement containing C₄A₃ than that in slag cement containing C₄A₃. And the crystalline of zeolite in fly-ash cement containing C₄A₃ was better than that in slag cement containing C₄A₃. All these revealed that the condition of fly-ash cement containing C₄A₃ was in favor of the formation of hydration products.The Si-components and Al-constituents were investigated by NMR during hydration process. The finding was that the spectra of Al changed greatly during hydration process. Thus conclusion was drew that Portland Cement containing C₄A₃ could accelerate the dissolution of the active Al2O3 in vitreous body of fly-ash. And the result of heat of hydration also indicated that fly-ash was in favor of strength development.Pore solution was pressed out of hardened cement pastes. The concentrations of Ca2+,AlO2-,SO42-,SiO44- in the aqueous phase were measured by ICP-AES. The results showed that the concentration of SO42- was high, which was advantageous to the dissolution of active Al2O3 and quicken the resolution of vitreous body of admixtures. And all these facts tallied with the results drew by NMR.The cause of the higher activity of fly-ash was that the quantity of heat evolution of fly-ash Cement containing C₄A₃ was much. Therefor the temperature of it was higher than slag Cement containing C₄A₃. And the condition of fly- ash Cement containing C₄A₃ was in favor of the formation of AFt. All these factors accelerated the resolu...