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1. Phase Evolution and Property Development of Alkali-Silica Reaction Gel in Carbonation

   Sinha, Arkabrata; Wei, Jianqiang (October 2023, International Congress on the Chemistry of Cement 2023 (ICCC2023))

   The formation and swelling of alkali-silica reaction (ASR) gels, products of the reaction between amorphous silica from aggregates and alkalis from cement capable of absorbing moisture, are considered the primary mechanism of ASR-induced deteriorations in concrete. To date, the ASR mitigation approaches mainly focus on the incorporation of supplementary cementitious materials and the use of lithium-based admixtures. These traditional approaches possess limitations in the extent of ASR suppression and might compromise concrete performance. Effective ASR mitigation under carbonation has been recently documented but the underlying mechanisms still remain unclear. To fill this knowledge gap, phase evolution and property development of ASR gels under carbonation are investigated in this study A synthetic ASR gel with a calcium-to-silica ratio of 0.3 and an alkali-to-silica ratio of 1.0 was synthesized and conditioned under 20% CO2 concentration, 75% relative humidity, and 25oC. The extent of carbonation and phase evolutions were characterized and quantified through X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). The modulus of elasticity and hardness of the carbonated ASR gels were measured using nanoindentation, and the moisture uptake capacity was evaluated using dynamic vapor sorption in stepwise relative humidity levels. The results indicate complete conversion of ASR gels into stable carbonates (nahcolite, vaterite, calcite and silica gel) with increased mechanical properties and suppressed hygroscopicity. 

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2. Phase Evolution and Property Development of Alkali-Silica Reaction Gel in Carbonation

   Sinha, Arkabrata; Wei, Jianqiang (October 2023, International Congress on the Chemistry of Cement 2023 (ICCC2023))

   The formation and swelling of alkali-silica reaction (ASR) gels, products of the reaction between amorphous silica from aggregates and alkalis from cement capable of absorbing moisture, are considered the primary mechanism of ASR-induced deteriorations in concrete. To date, the ASR mitigation approaches mainly focus on the incorporation of supplementary cementitious materials and the use of lithium-based admixtures. These traditional approaches possess limitations in the extent of ASR suppression and might compromise concrete performance. Effective ASR mitigation under carbonation has been recently documented but the underlying mechanisms still remain unclear. To fill this knowledge gap, phase evolution and property development of ASR gels under carbonation are investigated in this study A synthetic ASR gel with a calcium-to-silica ratio of 0.3 and an alkali-to-silica ratio of 1.0 was synthesized and conditioned under 20% CO2 concentration, 75% relative humidity, and 25oC. The extent of carbonation and phase evolutions were characterized and quantified through X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). The modulus of elasticity and hardness of the carbonated ASR gels were measured using nanoindentation, and the moisture uptake capacity was evaluated using dynamic vapor sorption in stepwise relative humidity levels. The results indicate complete conversion of ASR gels into stable carbonates (nahcolite, vaterite, calcite and silica gel) with increased mechanical properties and suppressed hygroscopicity. 

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3. Phase evolution and mechanical-hydroscopic properties of alkali-silica reaction gels modified by magnesium nitrate

   https://doi.org/10.1016/j.cemconcomp.2023.105283  

   Sinha, Arkabrata; Wei, Jianqiang (November 2023, Cement and Concrete Composites)

   Alkali-silica reaction (ASR)'s destructiveness is governed by the compositions and properties of ASR products, while methods of converting these hygroscopic-expansive gel-like products into innocuous phases remain unexploited. In this study, the influence of magnesium nitrate on the evolutions of phase, molecular structure, hydroscopic and mechanical properties of ASR gels with varying Mg/Si ratios from 0.1 to 1.1 was investigated. The results indicate that the primary phases of ASR products, tobermorite-type calcium silicate hydrate (C–S–H) and alkali kanemites, can be suppressed into brucite and eventually converted into magnesium-silicate-hydrate (M-S-H) in the presence of increasing Mg/Si ratios and the consequent decreasing pH. The Si–O–Si bridging bonds and Si–O symmetric stretching in the Q3 sites of ASR products can be suppressed. The phase and structure modifications resulted in a 93.5% reduction in hydroscopic swelling, a 94.7% decrease in strength, and a 152.3% drop in modulus of elasticity rendering the ASR products less destructive. 

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4. The alkali-silica reaction in belitic calcium sulfoaluminate (BCSA) cement concrete

   https://doi.org/10.1016/j.conbuildmat.2025.140726  

   Adnan, Tayyab; Thomas, Robert J (April 2025, Construction and Building Materials)

   This paper studies the alkali-silica reaction (ASR) in rapid-strength belitic calcium sulfoaluminate (BCSA) cement systems. Theoretically, its low alkalinity and high alumina content should make BCSA less prone to ASR than portland cement (PC), but little experimental evidence has been published, and the theorized mechanisms have not been examined critically. We examine this problem using expansion tests, microstructural analysis, and pore solution analysis. Accelerated expansion tests show increased expansion in BCSA mortars with reactive aggregates, but we argue that the test conditions are unsuitable for the cement. Long-term expansion tests show a significant reduction in expansion in BCSA mortars with reactive aggregates, but later-age measurements still exceed ASTM C1778 limits and microstructural investigations indicate ASR damage. Curiously, BCSA mortars with nonreactive aggregates also expanded significantly, but no ASR damage was observed. BCSA pore solutions had ten times more aluminum than PC and one-tenth as much calcium. While the pH was sufficiently high to initiate ASR, the alkali reserves can be half or less than in PC. Overall, BCSA cement is not immune to ASR, but it is more resistant than PC. This is mostly related to the lower alkalinity of the cement and, to a lesser degree, to the abundance of alumina and shortage of soluble calcium. 

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5. Suppressing alkali-silica reaction through incorporation of calcined kaolinite–montmorillonite clay blends

   Wei, Jianqiang (September 2019, 15th International Congress on the Chemistry of Cement)

   Cement substitution with calcined kaolinite–montmorillonite clay blends as an effective way to suppress alkali-silica reaction in cement composites containing reactive aggregates is investigated. Expansion, cracking behavior, mechanical properties and microstructure of the cement composites were investigated. Hydration of the ternary cement blends was also characterized. The results indicate that cement modification with a combination of calcined kaolinite–montmorillonite clays can effectively mitigate alkali-silica reaction-induced deteriorations. By incorporating 30% clays, the volume expansion of the cement composites was decreased from deleterious to innocuous level. Amount of cracks was decreased with increasing clay incorporations. In the presence of combined calcined clays, the strength gain of the cement composites is more significant the strength loss caused by alkali-silica reaction indicating the effective mitigation of this virulent reaction in concrete. 

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