Alkali activated fly ash: effect of admixtures on paste rheology

In this paper, an investigation related to the rheological behaviour of alkali-activated fly-ash pastes (AAFA) is described. Those pastes were prepared by mixing the fly ash with an alkaline dissolution containing 85% of a 12.5 M NaOH solution and 15% of waterglass and adding some commercial chemical admixtures usually used in the Portland cement concrete fabrication, like lignosulphonates, melamines (first and second generation products) and polycarboxylates (latest generation). The fly ash rheological data were determined by rotational viscometry measurements as well as by the use of the flow table test. Results indicate that chemicals admixtures used do not work the same in the Portland cement systems than in alkali-activated fly ash systems. As a general rule, it seems that the most efficient admixtures for these new cementitious pastes (AAFA) are those based in polycarboxylates.