Study On Digesting Of F-CaO From HFA And Cement Workability With Digested HFA

High-calcium fly ash（HFA）from CFB has a high content of f-CaO, so it is limitedto use in cement industry. In order to make use of HFA, it’s necessary to find effectivemeasures to digesting in advance. HFA from a power plant is researched. Variousf-CaO digesting methods and workability of digested HFA cement were investigated.The results are:Morphology of HFA is irregular, the surface is uneven, and particle sizedistribution is unreasonable. Residue on sieve at45μm is15.8%, and d50is14.88μm.The content of CaO is44.50%and the content of f-CaO is26.09%which is main reasonof Volume stability.The factors influencing f-CaO digesting are water content, dispersant, digestingtime and grinding. When water content is30%, after one day’s digesting, the content off-CaO is11.4%. When dispersant content is1%and water content is30%, the contentof f-CaO is reduced to9.0%after1day. In the case of adding dispersant, grinding havea negative effect on the digestion. When water content is10%, digesting time andgrinding is important to digesting. Digesting without dispersant, HFA particle iscovered with Ca(OH)2which has a typical hexagonal plate with sharp edges. Digestingwith dispersant, fine Ca(OH)2clusters with round edges are grown from the particles.Adding dispersant, HFA digestion generated a mesh material, which is related to glassphase of HFA.The standard consistency of Cement adding digested HFA is reduced to22.9%. The setting time is shortened. The strength development of cement with digested HFAis faster than which without. The ratio of compressive strength is developed from73.8%at the3rdday to88.1%at28thday. For cement with digested HFA, it can be observedfrom SEM that hydration rate is faster, the forming time of AFt is earlier and more. Inall the hydration time, there are not big CH existed. At the4thday of hydration, AFt istightly coupled with gel.