Reactivity of fly ash in the presence of chemical activators

Author(s): Frank Winnefeld, Salaheddine Alahrache, Jean-Baptiste Champenois,Frank Hesselbarth, Barbara Lothenbach
Paper category: Proceedings
Book title: Proceedings of the International RILEM Conference
Materials, Systems and Structures in Civil Engineering 2016
Segment on Concrete with Supplementary Cementitious Materials
Editor(s): Ole M. Jensen, Konstantin Kovler and Nele De Belie
ISBN:978-2-35158-178-0
e-ISBN: 978-2-35158-179-7
Publisher: RILEM Publications SARL
Publication year: 2016
Pages: 54-63
Total Pages: 10
Language : English

Abstract: The hydration of a fly ash - Portland cement blend (70/30 by mass) without and with the addition of activators (potassium sodium silicate, sodium carbonate, sodium oxalate and potassium citrate) was examined. Measurements of setting time and strength were performed
as well as analyses of the hydrate assemblages and of the composition of the pore solution. The influence of the activators on fly ash reactivity was determined using a pozzolanity test in combination with thermodynamic modelling, which allowed the calculation of the reaction degree of the fly ash. The activators enhanced compressive strength at early age, but decreased strength at late age. All activators increased pH and decreased thus the calcium concentrations in the pore solution. Higher undersaturation with respect to alite led to a faster reaction of alite and thus to early setting and a high early strength. On the long term, the high alkali concentrations lowered compressive strength. Thermodynamic modelling indicated that the high pH values due to the high alkali concentrations destabilized ettringite. The pozzolanic reaction of the fly ash could be enhanced by some of the activators, which seems to be mainly an influence of the increased pH values.

Online publication : 2016
Publication type : full_text
Public price (Euros) : 0.00