Rheology and Setting of High Volume Fly Ash Mixtures
Dale P. Bentz, Chiara F. Ferraris
While high volume fly ash (HVFA) concretes can be designed and produced to meet 28-d strength requirements and often even exceed the durability performance of conventional concretes, a persistent problem is the potentially long delay in setting time that produces concurrently long delays in finishing the concrete in the field. Previously, based on isothermal calorimetry studies, two different powder additions, namely calcium hydroxide and a rapid set cement, have been suggested as potential solutions to mitigating this excessive retardation. In this paper, rheological measurements and conventional Vicat setting time studies are conducted to verify that these powder additions do indeed reduce setting times in paste systems based on both class C and class F fly ashes. The reductions obtained are dependent on the class of fly ash and suggest that trial mixtures would be a necessity to apply these technologies to each specific fly ash/cement/admixture combination being employed in the field. Potentially, for such screening studies, the rheological measurement of yield stress may provide an earlier indication of setting (and finishability) than conventional Vicat needle penetration measurements on pastes.
and Ferraris, C.
Rheology and Setting of High Volume Fly Ash Mixtures, Cement and Concrete Composites, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=904150
(Accessed December 8, 2023)