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  1. Alkali-silica reaction (ASR) is a fatal deterioration that can cause volume expansion, cracking, and premature failure of concrete. In this study, the efficacy of sodium montmorillonite (NaMt) organically functionalized with two non-ionic surfactants (ONaMts) in mitigating ASR is investigated by determining the expansion and cracking behavior of mortars containing reactive aggregates. The underlying mitigation mechanisms were analyzed through the quantification of reaction products and in-situ characterizations of ASR gels. The results revealed that, compared with raw NaMt, ASR-induced expansion and cracking can be more substantially mitigated in the presence of ONaMts, which is supported by the improved consumption of portlandite and reduced formations of both crystalline and amorphous ASR gels. The functionalized ONaMts appeared to further suppress the formation of Q3 polymerization sites, decrease the [K + Na]/Si atomic ratio and increase the Al/Ca in ASR gels. 
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    Free, publicly-accessible full text available December 1, 2024
  2. 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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    Free, publicly-accessible full text available November 1, 2024
  3. Although the high efficiency of coupled lithium and saturated metakaolin in alkali-silica reaction mitigation has been documented, its influence on cement hydration remains uninvestigated. In this study, saturated metakaolin with varying degrees of saturation and its combined influence with lithium on the hydration kinetics, phase evolution, and development of microstructure and molecular structures of hydration products in the blended cement composite was investigated. The experimental and thermodynamic modeling results indicate the synergistic effect between saturated metakaolin and lithium in enhancing the hydration of cement, interaction between metakaolin and cement, incorporation of Al in the silicate chains, and precipitations of Al-rich phases. In the blended cement matrix, the dissolution of metakaolin, formation of calcium silicate hydrates with incorporated aluminum (C-(A)-S-H), and precipitation of strätlingite are improved by 19.6%, 17.6%, and 20.0%, respectively, and the formation of cubic siliceous hydrogarnet was triggered. 
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    Free, publicly-accessible full text available November 1, 2024
  4. 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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    Free, publicly-accessible full text available October 1, 2024
  5. Metakaolin (MK) has been widely used in modifying cement and designing high-performance concrete, while the role of this alumino-silicate mineral has not been fully exploited due to its low reaction degree, especially at high-volume incorporations. To enhance the pozzolanic reactivity, functionalization of MK particles with two non-ionic surfactants, namely polyoxyethylene (9) nonylphenylether (PONPE9) and t-octyl phenoxy poly ethoxyethanol (TX100), are investigated in this study under a hypothesis that the intercalations of the surfactants into MK’s interlayer space can trigger changes in structure and properties. The dry MK particles were mixed with aqueous solutions with two surfactant concentrations to reach two surfactant loadings in MK at its 1.0 and 6.0 cation exchange capacity (CEC). The surfactant uptake behavior of MK and its influence on the hygroscopic swelling, pozzolanic reactivity, and dissolution behavior in simulated cement pore solution were characterized. The results indicate that, compared with TX100, PONPE9 can be absorbed by MK more easily. After functionalization at 1.0 and 6.0 CEC, MK exhibited surfactant mass fractions of 1.85% and 3.81% for TX100, and 1.95% and 5.39% for PONPE9, respectively. The intercalation of surfactants resulted in an up to 28.6% increase in the swell index of MK when absorbing water. A more robust aluminum and silicon dissolution behavior in the simulated cement pore solution was observed from the functionalized MK. Increases in reaction heat and lime consumption capacity were obtained in the MK-lime blends indicating the enhanced pozzolanic reactivity of MK after functionalization and paving a path to enhance the role of MK in future sustainable concrete design. 
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    Free, publicly-accessible full text available October 1, 2024
  6. 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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    Free, publicly-accessible full text available October 1, 2024
  7. A novel internal conditioning (InCon) technique based on saturated sodium montmorillonite (sMT) functionalized with two non-ionic surfactants, polyoxyethylene (9) nonylphenylether and t-octyl phenoxy poly ethoxyethanol, is investigated in this study. With the integration of water for internal curing and pozzolanic reactivity in a single system, the role of InCon in modifying cement hydration kinetics is comprehensively elucidated. The results indicate that, in the presence of InCon, both silicate reaction and secondary aluminate reaction rates are enhanced, and the apparent activation energy (Ea) of cement hydration was decreased from 34.3 KJ/mol to 28.7 KJ/mol indicating a lower temperature sensitivity and threshold of the cement hydration reactions. In addition, decreased CH contents, improved degree of hydration, increased chemical shrinkage, and the formation of additional Csingle bondSsingle bondH and aluminum-containing phases were obtained from the cement with InCon. The autogenous shrinkage of cement and the negative impact of dry sMT on the early age strength of cement can be offset by InCon paving a new path to improve the overall properties of concrete. 
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    Free, publicly-accessible full text available July 1, 2024