Alkali-activation potential of biomass-coal co-fired fly ash

Co-fired fly ash, derived from the co-combustion of coal and biomass, is examined as a potential precursor for geopolymers. Compared to a coal fly ash, two co-fired fly ashes have a lower vitreous content and higher carbon content, primarily due to differing combustion processing variables. As a result, binders produced with these co-fired fly ashes have reduced reaction potential. Nevertheless, compressive strengths are generally highest for all ashes activated with solutions with a molar ratio of SiO₂/(Na₂O + K₂O) = 1, and these mixes reach the highest extent of reaction among those studied. Activation with sodium hydroxide solution forms zeolitic phases for all ashes. The thermal and dilatometric behavior of the coal and co-fired fly ash geopolymers is similar between equivalent mix designs. These results indicate that co-fired fly ashes can be viably used to form alkali-activated geopolymers, which is a new beneficial end-use for these emerging waste materials

Evaluation of hydration of cement pastes containing high volume of mineral additions

Available ahead of print 2017.The use of mineral additions is a common practice in the production of cementitious materials. Recently proposed usage of high amounts of cement replaced by mineral additions requires the study of the chemical interaction of these additions with the cement. This study intends to evaluate, by means of TG/DTG techniques, XRD and compressive strength, the effect of high volume of mineral additions in the hydration of cementitious pastes. Pastes with 50?70% of cement replaced by mineral addition and with different combinations of fly ash and metakaolin were evaluated, two pastes without mineral addition and two other pastes with lime addition. Results showed TG/DTG and XRD techniques are more suitable for evaluating kinetics of reactions of hydration, making it possible to quantify the substantial reduction in the levels of portlandite in hydrated pastes containing high volumes of mineral additions. These techniques allowed to find important differences in the evaluation of calcium hydroxide, because its morphology can change in the presence of additions. Also showed that it is possible to achieve, enhanced or even high compressive strength (50?80 MPa) in concretes containing reduced cement contents. As well as more resistance against harmful agents and carbonation attack.(undefined)info:eu-repo/semantics/publishedVersio