Effect of slag chemistry on the hydration of alkali-activated blast-furnace slag

Abstract

This paper presents results of detailed investigations about the alkaline activation of ground granulated blast furnace slags whose chemical composition were modified. Sodium hydroxide and potassium silicates were used as alkaline activators. The influence of the CaO/SiO 2 ratio, the Al 2 O 3 and TiO 2 content of the slag composition on the hydration reaction was analyzed utilizing isothermal heat flow calorimetry, compressive strength development of binder samples, 29 Si MAS NMR spectroscopy and molybdate method. It could be shown that the TiO 2 content of the slag has only minor influence on the hydraulic reactivity and compressive strength of the alkaline activated binders.The variation of the Al 2 O 3 content of the slag leads to different results. A rise in Al 2 O 3 content enhanced the strength if activating with NaOH but resulted in a lower strength if activating with potassium silicate. The results of the 29 Si MAS NMR spectroscopy verify the decrease in the reaction degree with increase of Al 2 O 3 content. This is associated with the rise of the chain length of the C-(A)-S-H phases by incorporation of Al-O tetrahedrons resulting in a lower Si/Al-ratio. A decrease in the C/S-ratio yielded to a lower heat evolution, whereas the reaction was delayed if activated with potassium silicate with higher silicate content. The increase of the C/S-ratio caused in less condensed slag glass and therefore an enhancement of the reaction degree with a simultaneous decrease of silicate chain length, as seen by 29 Si NMR. These outcomes fit well with the results measured by the molybdate method.

Reactivation of a Retarded Suspension of Ground Granulated Blast-Furnace Slag

“…According to Langenfeld et al [ 2 ], the calcium complexes with the retarder are destroyed by the increase of the pH-value and the setting can occur. With the alkaline activation, the pH-value is not the only influencing factor, but also the composition and the concentration of the activator has an effect [ 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 ]. The results of some studies [ 32 , 33 , 35 , 36 , 37 ] show an increase in strength and a higher degree of hydration of the binder due to an increase of the activator concentration.…”

Activated slag as an additive to rubberized unsaturated polyester composite: Thermal and mechanical study

“…The amount of slag added to the UPE/NBR composite was 20 phr of the polymer composite. The components were intensively mixed by spinning using electrical mixer for 3 min, at the end of the mixing stage, the peroxide was added and mixed for 30 s. The paste solution was cast into a plastic molds and left to solidify for 24 h at room temperature . The following designation was adopted throughout this study, the unfilled sample was “R‐UPE,” with the unmodified slag is “R‐UPE/S,” with stearic acid only modified slag is “R‐UPE/NS,” the formula with H 2 SO 4 modified slag was “R‐UPE/AS.”…”

“…Furthermore, few studies on the use slag in polymeric foams for high‐voltage insulation are available and polyurethane foams seem to be a good candidate for this application . Recall that the degree of interaction between the fillers and the polymer fillers is dependent on the active functional groups and on both sides; thus surface modification can improve the wettability of the filler surfaces by promoting the formation of hydrophilic groups, which increase the degree of interactions . To achieve this target, it is intended in this work to expose the mechanically treated slag powder to various polar strong acids and organic chemical surface treatment to introduce surface functional groups onto the slag surfaces to increase the activity of which to polymers.…”

Fungistatic Properties of Granulated Blastfurnace Slag and Related Slag-Containing Cements

“…The glassy phase content in GGBS was determined by light microscopy [18,19], which was supplemented by X-ray diffraction method [20]. Therefore the crystalline and glassy components of 1000 slag grains (fraction 40 -63 μm) were counted as well as they were analysed by X-ray diffraction.…”