Alkali-Equivalent-Dependent Dual Role of Sodium Chloride in Alkali-Activated Slag Cement: From Synergistic Activator to Competitive Inhibitor
Nan Ding, Zhenyun Cheng, Hua Lei, Bo Fu
TL;DR
Sodium chloride can either enhance or hinder the performance of eco-friendly cement, depending on the level of alkali used.
Contribution
This study reveals the dual role of NaCl as a synergistic activator or competitive inhibitor in alkali-activated slag cement, depending on alkali-equivalent levels.
Findings
At low alkali-equivalent (2% Na2O), ≤4 wt% NaCl increased 28-day compressive strength by up to 21%.
At high alkali-equivalent (4% Na2O), 10 wt% NaCl reduced strength by up to 18% due to competitive Cl− binding.
Microstructural analyses confirmed Friedel’s salt formation and alkalinity-dependent effects on gel phases.
Abstract
The cement industry is a major contributor to global CO2 emissions, necessitating the development of low-carbon alternatives, such as alkali-activated slag cement (AAS). This study investigates the feasibility of using NaCl and NaOH as co-activators for granulated blast furnace slag (GBFS), focusing on the alkali-equivalent-dependent role of NaCl. At a low-alkali equivalent (2% Na2O), incorporation of ≤4 wt% NaCl enhanced ionic strength, promoted slag dissolution, and accelerated C-(A)-S-H gel formation, increasing 28-day compressive strength by up to 21%. In contrast, at a high-alkali equivalent (4% Na2O), NaCl addition induced competitive binding of Cl− with aluminate species, inhibiting C-(A)-S-H formation and reducing strength by up to 18% at 10 wt% NaCl. The optimal NaCl dosage for strength improvement was 1–4 wt% under low alkalinity and 1–2 wt% under high alkalinity.…
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Taxonomy
TopicsConcrete and Cement Materials Research · CO2 Sequestration and Geologic Interactions · Smart Materials for Construction