The Effect of Blast Furnace Slag/Fly Ash Ratio on Setting, Strength, and Shrinkage of Alkali-Activated Pastes and Concretes

Abstract

The aim of this study was to determine the effects of partial fly ash substitution in to a series of alkali-activated concrete based on a high-MgO blast furnace slag BFS. Mixes were activated with various amounts of sodium silicate at alkali modulus (mass ratio SiO 2 /Na 2 O) values of 1.0, 0.5, and 0.25. The results showed that, an increase in the fly ash content extended the initial setting time but had very little effect on the final setting time, although the early age compressive strength was decreased. The fly ash addition had no effect on the drying shrinkage but lowered the autogenous shrinkage. The mixes activated with sodium silicate at a lower alkali modulus showed a significantly higher autogenous shrinkage but lower drying shrinkage values. Severe micro cracking of the binder matrix was observed only for mixes without fly ash, activated with sodium silicate solution at higher alkali modulus. Decreasing the alkali modulus resulted in a higher autogenous shrinkage, less micro cracking and a more homogenous structure due to more extensive formation of sodium-aluminate-silicate-hydrate gel (N-AS -H), promoted by the addition, and more extensive reaction of the fly ash.

Fundamental studies for high temperature processing of tungsten leaching residues for alloy formation

“…The Fe-Mn-W alloy formed can be used directly for the production of white cast iron [16][17][18][19]. The slag generated can be used as additives for cement or concrete [22][23][24][25].…”

“…After reduction of FeO, MnO and WO 3 , the remaining slag contains mainly Al 2 O 3 -CaO-MgO-SiO 2 -MnO which has the similar compositions as the iron blast furnace slag and steelmaking slags. The iron blast furnace slag and steelmaking slags have been extensively used in production of concrete and cement [22][23][24][25].…”

Effects of Curing Conditions on Shrinkage of Alkali-Activated High-MgO Swedish Slag Concrete

“…For example exposure to the relative humidity (RH) between 50 and 70% was indicated as especially unfavorable (Douglas et al, 1992;Bakharev et al, 1999;Krizan and Zivanovic, 2002;Provis and Van Deventer, 2014;Ye et al, 2017). A partial replacement of BFS with FA tended to lower the drying shrinkage (Wallah and Rangan, 2006;Singh et al, 2016;Humad et al, 2019). Decrease of the NaO to SiO 2 molar ratio of the SS alkali activation reduced the drying shrinkage values, but increased the autogenous shrinkage (Krizan and Zivanovic, 2002;Atiş et al, 2009;Humad et al, 2019).…”

“…A partial replacement of BFS with FA tended to lower the drying shrinkage (Wallah and Rangan, 2006;Singh et al, 2016;Humad et al, 2019). Decrease of the NaO to SiO 2 molar ratio of the SS alkali activation reduced the drying shrinkage values, but increased the autogenous shrinkage (Krizan and Zivanovic, 2002;Atiş et al, 2009;Humad et al, 2019).…”

Effect of Admixtures on Durability Characteristics of Fly Ash Alkali-activated Material

“…At the same time, these mixtures achieve better homogeneity and the formation of microcracks is reduced. The development of short-term strength is mainly associated with the reactions of blast furnace granulated slag, while the reactions of fly ash are manifested in longer-term strength [8]. Ye (2018) and Ye et al (2019) [9,10] state that in addition to the main hydration product in alkali-activated slags in the form of a C-(A)-S H gel, phases of the hydrotalcite type are also formed, regardless of the chemical composition and source of reactants.…”