The Influence Of The Ultra-fine Fly Ash During The Hydration And Hardening Process Of Complex Binders

At present,Fly Ash has been widely used as a kind of mineral admixture in the production of cement and concrete. As a matter of fact, the excitation of its chemical activity is still worth studying. With the method of mechanical grinding,a large part of vitreous has been ground up. Thus the ultra-fine fly ash(UFA) has been got, of whose specific surface area is 651m2/ kg, and particle size distribution is mainly under 7μm. Although the chemical composition of ultra-fine fly ash and the ordinary fly ash are the same, the particle size distribution and morphology of ultra-fine fly ash have been greatly changed, so as to the physical and chemical function of ultra-fine fly ash. As a result, the performance of ultra fly ash is different from the ordinary fly ash during the hydration process of the complex binders.The cement-based mortar and paste were set as the research object in this paper. Through the study of the hydration performance of composite gelled material in the early time, the mineral composition, microstructure, pore structure of cement-based paste and the pore structure were studied, so the influence of the ultra-fly ash and ordinary fly ash during the hydration were compared. The results are as followings:The ultra-fly ash helps to improve the mechanical properties of composite cement mortar. The physical filling effect of ultra-fine fly ash helps to increase the flexural strength 3 days before; the activity of the ultra-fine fly ash began to emerge 3 days later. The flexural strength after 14 days and compressive strength after 60 days improved significantly; compared with the compressive strength, the ultra-fly ash helps to increase the flexural strength, the more dosage, the greater the flexural strength increased; compared with the ordinary fly ash, the activity of the ultra-fly ash is greater, the pozzolanic reaction started earlier, the ultra-fine fly ash contributes a lot to the strength of the middle and later time.The ultra-fine fly ash promotes the hydration of the composite gel materials, in the early stage, the ultra-fine fly ash makes the second moment of exothermic peak appeared slightly ahead of time, the bigger the dosage is, the more obvious in advance; the activity of ultra-fine fly ash appeared at 3 days, it also can be proved through the result of XRD and the content of the CH, the first hydration dominants 28 days before, the reaction of fly ash increases. 28 days later, then the second hydration reaction dominants.The ultra-fine ash improves the microstructure of the hardened pastes, the ultra-fine fly ash helps to decreases the threshold aperture and most probable aperture of the hardened pastes, the most probable aperture of the hardened paste is about 100 nm because of the ultra-fine fly ash, which is near that of the pure cement system. As the curing time going, the most probable aperture of each group decreases, the holes whose diameter is above 200 nm decreases.