Calcium nitrate: A chemical admixture to inhibit aggregate dissolution and mitigate expansion caused by alkali-silica reaction - ScienceDirect

The Nugget

Calcium nitrate proves to be an effective and cost-efficient chemical admixture for mitigating alkali-silica reaction (ASR) in concrete, by preventing aggregate dissolution and reducing expansion.

Key quotes

"Despite the prevalence of ASR, so far only lithium-based chemical admixtures have been shown to be successful in mitigating its deleterious effects."
"This study reveals a new and cost-effective pathway to suppress aggregate dissolution and ASR in concrete based on the dosage of soluble alkaline-earth additives."
"Calcium nitrate additions effectively inhibit aggregate dissolution and, in turn, mortar bar expansion."
"The study has shown, for the first time, that calcium nitrate additions effectively inhibit aggregate dissolution and, in turn, mortar bar expansion."
"The significance of reductions of NBS-glass dissolution and mortar-bar expansion rates is discussed, with special focus on highlighting the mechanism by which calcium nitrate mitigates ASR."

Utilized sodium borosilicate (NBS) glass as a model reactive aggregate in a mortar bar setting, observing effects of calcium nitrate on dissolution and expansion rates.
Applied ASTM C150 compliant Type I/II ordinary Portland cement (OPC) with compositions recorded through X-ray fluorescence and X-ray diffraction.
Conducted experiments detailed aggregate dissolution and expansion kinetics, with specific concentrations and conditions outlined.
Limitation and Strength: The usage of a model reactive aggregate (NBS glass) in a controlled laboratory environment provides a focused insight into the chemical interactions and efficiency of calcium nitrate as an inhibitor. However, real-world applications in diverse concrete formulations and environmental conditions warrant further study.

Alkali-silica reaction (ASR): A chemical reaction in concrete between alkaline cement paste and reactive silica found in some aggregates, causing expansion and cracking over time.
Calcium nitrate (Ca(NO3)2): A chemical compound used as an admixture in concrete to inhibit ASR by reducing aggregate dissolution.
Sodium borosilicate glass (NBS): A type of glass with sodium oxide, boron oxide, and silica, used as a model reactive aggregate in this study.
Mortar bar expansion: A measure of volume increase in a mortar bar due to internal reactions, such as ASR, over time.

Calcium nitrate mitigates ASR by inhibiting the dissolution of reactive aggregates, essentially preventing the foundational chemical reaction that leads to destructive gel formation and expansion.
The effectiveness of calcium nitrate was quantifiably demonstrated through reduced dissolution rates of NBS-glass and subsequent mortar bar expansions, underscoring a preventative mechanism against ASR.

The study positions calcium nitrate as a viable and cost-efficient alternative to lithium-based admixtures, historically seen as the primary solution for ASR mitigation.
Through chemical analysis and experimental validation, calcium nitrate showed to significantly reduce the deleterious effects of ASR with potential implications for improving the longevity and durability of concrete structures.

💡 Calcium nitrate acts like a "shield" preventing damage in concrete by stopping harmful reactions before they start.
🌉 The long battle against concrete cancer (ASR) finds a new ally in calcium nitrate, offering a simpler and cost-friendly way to keep structures standing strong.
🔬 By focusing on preventing aggregate dissolution, researchers have opened a new pathway to extend the life of concrete without relying solely on lithium-based solutions.

This summary contains AI-generated information and may have important inaccuracies or omissions.