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1. Hydration and phase evolution of blended cement composites containing lithium and saturated metakaolin

   https://doi.org/10.1016/j.cemconcomp.2023.105268  

   Luo, Dayou; Wei, Jianqiang (November 2023, Cement and Concrete Composites)

   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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2. Effects of shear on the rheological property development of alkali-activated metakaolin geopolymers with implications for ISRU in lunar construction

   https://doi.org/10.1122/8.0001050  

   Egnaczyk, Thaddeus M; Wagner, Norman J (January 2026, Journal of Rheology)

   Alkali-activated materials (AAMs) are candidates for high-strength lunar construction materials via in- situ resource utilization (ISRU) of aluminosilicate lunar regolith. To inform processing strategies for lunar AAMs, the shear-dependent rheological properties of a model AAM comprised of a sodium silicate activated metakaolin are measured from synthesis through gelation along with the compressive strength at longer reaction times. A combination of steady-shear, small amplitude oscillatory shear (SAOS), and Optimally Windowed Chirp (OWCh) techniques characterize the viscosity and shear moduli from initial slurry through the critical gel time. The critical gel point defines the processing time window regardless of the applied shear duration. Shearing prior to the critical gel point does not affect the critical gel time or viscoelastic properties of the material after the set point, or the 7-day compressive strength. However, the dynamic moduli prior to the critical gel time vary significantly based on the shear duration, and the critical gel exponent (n) increases with the duration of applied shear. These results demonstrate how to process without compromising final material properties. Metakaolin geopolymers exposed to low earth orbit (LEO) conditions on the Multi-purpose International Space Station Experiment Flight Facility (MISSE-FF) test station on the International Space Station (ISS) for six months of durability testing retain their compressive strength, furthering the technology readiness of aluminosilicate-derived construction material for future lunar construction. This study provides practical guidance for AAM processing protocols and insight into the effect of shear on the binder structural network valuable for both terrestrial and lunar ISRU 

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3. Evolution of the pore structure during the early stages of the alkali-activation reaction: an in situ small-angle neutron scattering investigation

   https://doi.org/10.1107/S1600576716018331  

   White, Claire E.; Olds, Daniel P.; Hartl, Monika; Hjelm, Rex P.; Page, Katharine (February 2017, Journal of Applied Crystallography)

   null (Ed.)

   The long-term durability of cement-based materials is influenced by the pore structure and associated permeability at the sub-micrometre length scale. With the emergence of new types of sustainable cements in recent decades, there is a pressing need to be able to predict the durability of these new materials, and therefore nondestructive experimental techniques capable of characterizing the evolution of the pore structure are increasingly crucial for investigating cement durability. Here, small-angle neutron scattering is used to analyze the evolution of the pore structure in alkali-activated materials over the initial 24 h of reaction in order to assess the characteristic pore sizes that emerge during these short time scales. By using a unified fitting approach for data modeling, information on the pore size and surface roughness is obtained for a variety of precursor chemistries and morphologies (metakaolin- and slag-based pastes). Furthermore, the impact of activator chemistry is elucidated via the analysis of pastes synthesized using hydroxide- and silicate-based activators. It is found that the main aspect influencing the size of pores that are accessible using small-angle neutron scattering analysis (approximately 10–500 Å in diameter) is the availability of free silica in the activating solution, which leads to a more refined pore structure with smaller average pore size. Moreover, as the reaction progresses the gel pores visible using this scattering technique are seen to increase in size. 

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4. 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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5. Relating the early‐age reaction kinetics and material property development in a model metakaolin geopolymer

   https://doi.org/10.1111/jace.20531  

   Egnaczyk, Thaddeus_M; Quinn, Caitlin_M; Wagner, Norman_J (April 2025, Journal of the American Ceramic Society)

   Abstract Geopolymers, a class of alkali‐activated binders, are studied as sustainable alternatives to Ordinary Portland Cement due to their potential for CO₂emission reduction. However, the critical relationship between early‐age reaction kinetics, the development of material properties, and evolving chemical structure remains insufficiently explored, primarily because of the complexity of the underlying chemical reactions and the wide variety of geopolymer chemistries. To address this, we investigate the mechanism of early‐age (<72 h) strength development of a model metakaolin geopolymer by measuring curing kinetics using isothermal calorimetry, material property development via rheology, and chemical coordination at distinct extents of reaction via²⁹Si and²⁷Al NMR. A novel approach of collecting solid‐state²⁹Si and²⁷Al NMR spectra at low temperature (−17°C) successfully quenches the geopolymer reaction, allowing for spectrum collection at a desired extent of reaction despite long²⁹Si NMR spectrum collection times. Applying the Avrami kinetic model to deconvoluted calorimetry data enables independent analysis of dissolution and polycondensation/crosslinking reactions. From these data, the gel reaction product mass fraction is estimated, revealing an exponential relationship with the storage modulus in the activated metakaolin slurry. This study provides new insights into the interconnected dynamics of molecular chemistry, reaction kinetics, rheology, and strength development, offering a semi‐empirical framework for understanding property evolution in geopolymers more broadly. 

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