Hydration study of mechanically activated mixtures of Portland cement and fly ash

• Published in: Journal of the Serbian Chemical Society 2007, Vol.72 (6), p.591-604
• Main Authors: Stefanovic, Gordana, Cojbasic, Ljubica, Sekulic, Zivko, Matijasevic, Srdjan
• Format: Article
• Language: English
• Subjects: activity; cement; fly ash; mechanical activation
• ISSN: 0352-5139; 1820-7421
• DOI: 10.2298/JSC0706591S

Fly ash (FA) can be used in cement mixtures with certain limitations. The problem of the mentioned mixtures lies in the insufficient activity of the particles of FA in the reactions which are important for the establishment of the mechanical characteristics of cement. This is particularly true for the hydration reactions. As a result of this, cement pastes formed by mixing ash and clinker have worse characteristics compared to those of pure Portland cement (PC), especially in the early period of setting. As is well known, FA can be a good solution for the neutralization of the negative effects generated due to the creation of free Ca(OH)2 during the hydration of PC, provided that the problems with the low activity of FAare overcome. For the experiments in this study, a mixture of Portland cement and fly ash was used, the content of ash in the mixture being 30 % and 50 %. Mechanical activation was performed in a vibrating ring mill. The goal of this study was to demonstrate, through experimental results, that during the mechanical activation of a PC and FA mixture, the components in the mixture which mostly affect the direction, rate and range of hydration reactions occurring in the mixture had been activated. The values of the compressive strength of the activated and non-activated mixtures and the changes of their specific surface area proved that during the grinding process, the mixture PC+FA had been mechanically activated. The highest increase of compressive strength was achieved in the early period of setting, which indicates an improvement in the early hydration of the mixture. XRD, DTA and TG analyses showed that the alite (C3S) and belite (C2S) from the PC and a part of the fly ash were activated. . Leteci pepeo se moze koristiti u cementnim smesama uz odredjena ogranicenja. Problem navedenih smesa ogleda se u nedovoljnoj aktivnosti cestica LP u reakcijama koje su znacajne za uspostavljanje mehanickih karakteristika cementa. To se posebno odnosi na reakcije hidratacije. Usled toga, cementne paste nastale mesanjem pepela i Portland cementa imaju losije karakteristike u odnosu na cist PC, pogotovu u ranijem periodu ocvrscivanja. Za eksperimente u ovom radu upotrebljena je smesa Porland cementa (PC) i leteceg pepela (LP) sa ucescem pepela od 30% i 50%. Mehanicka aktivacija izvedena je vibro-mlinu sa prstenovima. Cilj ovog rada je da se eksperimentalnim rezultatima pokaze da je tokom procesa mehanicke aktivacije smese PC i LP doslo do aktivacije onih k