Document Type
Extended Abstract
Abstract
Calcium nitrate (Ca(NO₃)₂, CN) has demonstrated strong potential as an additive to suppress alkali–silica reaction (ASR) in concrete. Its effectiveness is attributed to the formation of precipitates (i.e., barrier or passivation layer) that hinder the dissolution of reactive aggregates. This study investigates the ASR mitigation performance of CN across two cement types—ordinary Type I/II and Portland Limestone Cement (PLC)—in combination with aggregates of varying reactivity and several supplementary cementitious materials (SCMs), including amorphous steel slag and both Class C and Class F fly ashes. Accelerated mortar bar tests, following ASTM C1260 and C1567, show that CN substantially reduces expansion in a dose-dependent manner across all mixtures. Microstructural characterization, chemical dissolution analysis, and thermodynamic modeling reveal that CN promotes the precipitation of calcium-silicate-hydrate (C-S-H), portlandite (Ca(OH)₂), and calcite (CaCO₃) mixtures on aggregate surfaces. These phases thermodynamically hinder the formation of typical ASR gels and create a protective layer that suppresses silica dissolution and alkali-induced degradation The mitigation is effective in both SCM-free and SCM-containing systems, demonstrating the reliable performance of CN in varied mix designs. Considering the cost-effectiveness of CN (~$250–$600 per tonne) relative to lithium-based alternatives (>$12,000 per tonne) and the declining availability of fly ash, CN presents a viable and scalable strategy for controlling ASR in modern concrete infrastructure. This work highlights the importance of aggregate surface passivation in mitigating ASR and provides insight into the practical application of CN across diverse concrete formulations.
Keywords
Alkali-silica Reaction, Cement, Dissolution, Calcium Nitrate.
DOI
10.5703/1288284317976
Calcium Nitrate Effectively Mitigates Alkali-silica Reaction by Surface Passivation of Reactive Aggregates
Calcium nitrate (Ca(NO₃)₂, CN) has demonstrated strong potential as an additive to suppress alkali–silica reaction (ASR) in concrete. Its effectiveness is attributed to the formation of precipitates (i.e., barrier or passivation layer) that hinder the dissolution of reactive aggregates. This study investigates the ASR mitigation performance of CN across two cement types—ordinary Type I/II and Portland Limestone Cement (PLC)—in combination with aggregates of varying reactivity and several supplementary cementitious materials (SCMs), including amorphous steel slag and both Class C and Class F fly ashes. Accelerated mortar bar tests, following ASTM C1260 and C1567, show that CN substantially reduces expansion in a dose-dependent manner across all mixtures. Microstructural characterization, chemical dissolution analysis, and thermodynamic modeling reveal that CN promotes the precipitation of calcium-silicate-hydrate (C-S-H), portlandite (Ca(OH)₂), and calcite (CaCO₃) mixtures on aggregate surfaces. These phases thermodynamically hinder the formation of typical ASR gels and create a protective layer that suppresses silica dissolution and alkali-induced degradation The mitigation is effective in both SCM-free and SCM-containing systems, demonstrating the reliable performance of CN in varied mix designs. Considering the cost-effectiveness of CN (~$250–$600 per tonne) relative to lithium-based alternatives (>$12,000 per tonne) and the declining availability of fly ash, CN presents a viable and scalable strategy for controlling ASR in modern concrete infrastructure. This work highlights the importance of aggregate surface passivation in mitigating ASR and provides insight into the practical application of CN across diverse concrete formulations.