Abstract
This paper deals with the possibility of partial replacement of blast furnace slag with fly ash and fly ash after denitrification by SNCR method in alkali-activated materials based on granulated blast furnace slag. The aim of this paper is to verify the effect of fly ash on properties of alkali-activated materials based on blast furnace granulated slag. Frost resistance and resistance to aggressive environments, represented by demineralized water were tested. The reference mixture was based on blast furnace granulated slag activated by sodium water glass with silicate modulus of 2. Mixtures with an ash content of 10, 20, and 30% were then compared with the reference mixture. The influence of the denitrification process on fly ash and its use in mixed alkali activated materials was also compared. As a part of the experiment, alkali-activated pastes were also prepared. Infrared spectroscopy with Furier transformation was subsequently determined on these pastes. The reference mixture achieved the highest compressive strength in the experiment and the strength decreased with increasing amount of fly ash. In terms of flexural strength, the highest values were reached for mixtures with 10% slag replacement by fly ash. In the case of frost resistance, the significant increase of flexural strength, which was 50% for the reference mixture, is particularly interesting. For compressive strength, the frost resistance coefficient ranged from 0.95 to 1.00. In the case of resistance to aggressive environments, no differences were observed in the compressive strength, on the other hand, flexural strength decrease of up to 20% was detected for 10 and 20 percent replacement of slag with fly ash that did not undergo denitrification. Monitored properties did not show any negative effect of the denitrification process on fly ash properties. Infrared spectroscopy identified the main hydration product in the region of 945 cm-1which is a C-(A)-S-H gel and in combined mixtures with fly ash also N-A-S-H gel. Doi: 10.28991/esj-2020-01247 Full Text: PDF
Highlights
This paper deals with the possibility of using fly ash, including fly ash after denitrification by the SNCR method, as an additive to alkali-activated materials based on finely ground granulated blast furnace slag activated by sodium water glass with silicate modulus of 2
As the fly ash dose increased, the strengths dropped below the reference mixture (BFS)
In the frost resistance determination, only minimal strength decreases were found within the standard deviations for compressive strength
Summary
This paper deals with the possibility of using fly ash, including fly ash after denitrification by the SNCR method, as an additive to alkali-activated materials based on finely ground granulated blast furnace slag activated by sodium water glass with silicate modulus of 2. Various precursors are used for alkaline activation, such as finely ground blast furnace granulated slag, fly ash, metakaolin and others. Blast furnace granulated slag rapidly solidifies and achieves high strengths in the initial stages of maturation, but it has the possibility of high shrinkage cracking. The possibilities of reducing its disadvantages, including the use of mixed binders and fibers, are being explored. These efforts focus primarily on composites, where the binder and activator are dosed separately [1]
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