Impact of activator chemistry on permeability of alkali‐activated slags

Abstract

Durability of alkali-activated slags has been assessed by measuring the permeability using the beam-bending technique. This nondestructive technique obtains permeability values by measuring the hydrodynamic load relaxation curve of a saturated slender beam of solid paste placed in three-point bending. The impact of activator selection on the permeability of alkali-activated slags has been assessed together with the effects of water-to-precursor ratio, revealing that free silica in the activating solution is the dominant factor controlling permeability.The permeability results have been correlated with nitrogen sorption and mercury intrusion porosimetry to elucidate the percolated pore size controlling permeability. Comparison with existing beam-bending results for ordinary portland cement (OPC) paste shows that alkali-activated slags can be synthesized with permeability having the same order of magnitude as for OPC, indicating that certain alkaliactivated slags are as resistant as OPC to ingress of solutions associated with deterioration processes. K E Y W O R D SAlkali-activated slag, beam bending, durability, mercury intrusion porosimetry, nitrogen sorption, permeability

Alkali-activated materials: the role of molecular-scale research and lessons from the energy transition to combat climate change

“…It has been previously shown that the percolated pore network in Portland cement paste (with w/c ratio of 0.5) is made up of pore entries-exits that are ~3nm in size, which was also found to be the case for silicate-activated slag in our previous study [4], as measured using nitrogen desorption analysis (for samples synthesized using 7 wt. % Na 2 O relative to slag, SiO 2 /Na 2 O molar ratio of 1 for the activator, and water/slag wt.…”

“…Another early-age behavior known to influence long-term performance is pore structure development. Concrete is a porous material, and the pore size controlling transport properties will dictate resistance to certain forms of degradation (often related to steel corrosion), where larger pores making up the percolated pore network lead to faster degradation rates [4].…”

“…Nitrogen adsorption leads to slightly different results, since this approach probes the pore interiors, which tend to be larger than the corresponding pore entries-exits. For silicate-activated slag, nitrogen adsorption has revealed that the pore interiors are initially ~10 nm in diameter (up to ~20 days), after which their amount decreases across all pore sizes accessible using nitrogen sorption indicating a depercolation of the pore network [4]. In contrast to the relatively small pore sizes making up the pore network in silicate-activated slag, hydroxide-activated slag consists of pores of ~30 nm in diameter (at ~20 days, for sodium hydroxide activator with 7 wt.…”

“…In contrast to the relatively small pore sizes making up the pore network in silicate-activated slag, hydroxide-activated slag consists of pores of ~30 nm in diameter (at ~20 days, for sodium hydroxide activator with 7 wt. % Na 2 O relative to slag), as measured using mercury intrusion porosimetry [4]. Hence, it is clear that the presence of free silica in the activator has a significant impact on the resultant pore structure of AAS paste.…”

Drying-induced atomic structural rearrangements in sodium-based calcium-alumino-silicate-hydrate gel and the mitigating effects of ZrO2 nanoparticles

“…6,11 Furthermore, given correct mix designs, AAMs have comparable mechanical performance 12 and cost 7 to OPC, and can be tuned to have superior properties via specific chemical compositions, such as high thermal performance 13 and low permeability. 14 Nevertheless, questions remain regarding the long-term durability of AAMs, with the underlying degradation mechanisms often founded at the atomic/nanoscale, such as carbonation-induced chemical reactions [15][16][17][18] (from atmospheric and accelerated CO 2 conditions) and sulfate attack of the binder gel. 19,20 Progress is being made to elucidate the mechanisms responsible for chemical degradation of different types of AAMs, with the aim to pinpoint which mix designs are most resistant to different forms of degradation.…”