Like many others, silicate solids dissolve when placed in contact with water. In a given aqueous environment, the dissolution rate depends highly on the composition and the structure of the solid, and can span several orders of magnitude. Although the kinetics of dissolution depends on the complexities of both the dissolving solid and the solvent, a clear understanding of which critical structural descriptors of the solid control its dissolution rate is lacking. Through pioneering dissolution experiments and atomistic simulations, we correlate the dissolution rates -ranging over four orders of magnitude -of a selection of silicate glasses and crystals, to the number of chemical topological constraints acting between the atoms of the dissolving solid. The number of such constraints serves as an indicator of the effective activation energy, which arises from steric effects, and prevents the network from reorganizing locally to accommodate intermediate units forming over the course of the dissolution.

Fly ash which encompasses a mixture of glassy and crystalline aluminosilicates is an abundant supplementary cementitious material (SCM), valuable for replacing ordinary portland cement (OPC) in the binder fraction in concrete. Because higher OPC replacement levels are desired, it is critically important to better understand and quantify fly ash reactivity. By combining molecular dynamics (MD) simulations and vertical scanning interferometry (VSI), this study establishes that the reactivity of the glassy fractions in a fly ash with water (i.e., their aqueous dissolution rate) is controlled by the number of constraints placed on atoms within the disordered aluminosilicate network. More precisely, an Arrhenius‐like dependence of dissolution rates on the atomic network topology is observed. Such topological controls on fly ash reactivity are highlighted for a range of U.S. commercial fly ashes spanning CaO‐enriched and SiO2‐enriched compositions. The structure‐property relationships reported herein establish an improved framework to control and estimate fly ash‐cement interactions in concrete.

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Although quartz (α-form) is a mineral used in numerous applications wherein radiation exposure is an issue, the nature of the atomistic defects formed during radiation-induced damage have not been fully clarified. Especially, the extent of oxygen vacancy formation is still debated, which is an issue of primary importance as optical techniques based on charged oxygen vacancies have been utilized to assess the level of radiation damage in quartz. In this paper, molecular dynamics (MD) simulations are applied to study the effects of ballistic impacts on the atomic network of quartz. We show that the defects that are formed mainly consist of over-coordinated Si and O, as well as Si-O connectivity defects, e.g., small Si-O rings and edge-sharing Si tetrahedra. Oxygen vacancies, on the contrary, are found in relatively low abundance, suggesting that characterizations based on E centers do not adequately capture radiation-induced structural damage in quartz. Finally, we evaluate the dependence on the incident energy, of the amount of each type of the point defects formed, and quantify unambiguously the threshold displacement energies for both O and Si atoms. These results provide a comprehensive basis to assess the nature and extent of radiation damage in quartz.

Concrete, used in the construction of nuclear power plants (NPPs), may be exposed to radiation emanating from the reactor core. Until recently, concrete has been assumed immune to radiation exposure. Direct evidence acquired on Ar+-ion irradiated calcite and quartz indicates, on the contrary, that, such minerals, which constitute aggregates in concrete, may be significantly altered by irradiation. More specifically, while quartz undergoes disordering of its atomic structure resulting in a near complete lack of periodicity, calcite only experiences random rotations, and distortions of its carbonate groups. As a result, irradiated quartz shows a reduction in density of around 15%, and an increase in chemical reactivity, described by its dissolution rate, similar to a glassy silica. Calcite however, shows little change in dissolution rate - although its density noted to reduce by ≈9%. These differences are correlated with the nature of bonds in these minerals, i.e., being dominantly ionic or covalent, and the rigidity of the mineral’s atomic network that is characterized by the number of topological constraints (nc) that are imposed on the atoms in the network. The outcomes have major implications on the durability of concrete structural elements formed with calcite or quartz bearing aggregates in nuclear power plants.

We report a petrographic and mineralogical survey of tochilinite/cronstedtite intergrowths (TCIs) in Paris, a new CM chondrite considered to be the least altered CM identified to date. Our results indicate that type‐I TCIs consist of compact tochilinite/cronstedtite rims surrounding Fe‐Ni metal beads, thus confirming kamacite as the precursor of type‐I TCIs. In contrast, type‐II TCIs are characterized by complex compositional zoning composed of three different Fe‐bearing secondary minerals: from the outside inwards, tochilinite, cronstedtite, and amakinite. Type‐II TCIs present well‐developed faces that allow a detailed morphological analysis to be performed in order to identify the precursors. The results demonstrate that type‐II TCIs formed by pseudomorphism of the anhydrous silicates, olivine, and pyroxene. Hence, there is no apparent genetic relationship between type‐I and type‐II TCIs. In addition, the complex chemical zoning observed within type‐II TCIs suggests that the alteration conditions evolved dramatically over time. At least three stages of alteration can be proposed, characterized by alteration fluids with varying compositions (1) Fe‐ and S‐rich fluids; (2) S‐poor and Fe‐ and Si‐rich fluids; and (3) S‐ and Si‐poor, Fe‐rich fluids. The presence of unaltered silicates in close association with euhedral type‐II TCIs suggests the existence of microenvironments during the first alteration stages of CM chondrites. In addition, the absence of Mg‐bearing secondary minerals in Paris TCIs suggests that the Mg content increases during the course of alteration.

By invoking analogies to lime mortars of times past, this study examines the carbonation of portlandite (Ca­(OH)2) by carbon dioxide (CO2) in the liquid and supercritical states as a potential route toward CO2-neutral cementation. Portlandite carbonation is noted to be rapid; e.g., >80% carbonation of Ca­(OH)2 is achieved in 2 h upon contact with liquid CO2 at ambient temperatures, and it is only slightly sensitive to the effects of temperature, pressure, and the state of CO2 over the range of 6 MPa ≤ p ≤ 10 MPa and 8 °C ≤ T ≤ 42 °C. Additional studies suggest that the carbonation of anhydrous ordinary portland cement is slower and far less reliable than that of portlandite. Although cementation is not directly assessed, detailed scanning electron microscopy (SEM) examinations of carbonated microstructures indicate that the carbonation products formed encircle and embed sand grains similar to that observed in lime mortars. The outcomes suggest innovative directions for “carbon-neutral cementation.”

Long--term creep (i.e., deformation under sustained load) is a significant material response that needs to be accounted for in concrete structural design. However, the nature and origin of creep remains poorly understood, and controversial. Here, we propose that concrete creep at RH (relative humidity) ≥ 50%, but fixed moisture--contents (i.e., basic creep), arises from a dissolution--precipitation mechanism, active at nanoscale grain contacts, as is often observed in a geological context, e.g., when rocks are exposed to sustained loads, in moist environments. Based on micro--indentation and vertical scanning interferometry experiments, and molecular dynamics simulations carried out on calcium-silicate-hydrates (C-S-H's), the major binding phase in concrete, of different compositions, we show that creep rates are well correlated to dissolution rates -an observation which supports the dissolution--precipitation mechanism as the origin of concrete creep. C-S-H compositions featuring high resistance to dissolution, and hence creep are identified -analysis of which, using topological constraint theory, indicates that these compositions present limited relaxation modes on account of their optimally connected (i.e., constrained) atomic networks.