Prediction of Hydration Heat for Diverse Cementitious Composites through a Machine Learning-Based Approach.

Hydration plays a crucial role in cement composites, but the traditional methods for measuring hydration heat face several limitations. In this study, we propose a machine learning-based approach to predict hydration heat at specific time points for three types of cement composites: ordinary Portland cement pastes, fly ash cement pastes, and fly ash-metakaolin cement composites. By adjusting the model architecture and analyzing the datasets, we demonstrate that the optimized artificial neural network model not only performs well during the learning process but also accurately predicts hydration heat for various cement composites from an extra dataset. This approach offers a more efficient way to measure hydration heat for cement composites, reducing the need for labor- and time-intensive sample preparation and testing. Furthermore, it opens up possibilities for applying similar machine learning approaches to predict other properties of cement composites, contributing to efficient cement research and production.

Reconstruction of degraded image transmitting through ocean turbulence via deep learning.

When a laser carrying image information is transmitted in seawater, the presence of ocean turbulence leads to significant degradation of the received information due to the effect of interference. To address this issue, we propose a deep-learning-based method to retrieve the original information from a degraded pattern. To simulate the propagation of laser beams in ocean turbulence, a model of an ocean turbulence phase screen based on the power spectrum inversion method is used. The degraded images with different turbulence conditions are produced based on the model. A Pix2Pix network architecture is built to acquire the original image information. The results indicate that the network can realize high-fidelity image recovery under various turbulence conditions based on the degraded patterns. However, as turbulence strength and transmission distance increase, the reconstruction accuracy of the Pix2Pix network decreases. To further improve the image reconstruction ability of neural network architectures, we established three networks (U-Net, Pix2Pix, and Deep-Pix2Pix) and compared their performance in retrieving the degraded patterns. Overall, the Pix2Pix network showed the best performance for image reconstruction.

Unveiling the complexity of nanodiamond structures.

Understanding nanodiamond structures is of great scientific and practical interest. It has been a long-standing challenge to unravel the complexity underlying nanodiamond structures and to resolve the controversies surrounding their polymorphic forms. Here, we use transmission electron microscopy with high-resolution imaging, electron diffraction, multislice simulations, and other supplementary techniques to study the impacts of small sizes and defects on cubic diamond nanostructures. The experimental results show that common cubic diamond nanoparticles display the (200) forbidden reflections in their electron diffraction patterns, which makes them indistinguishable from new diamond (n-diamond). The multislice simulations demonstrate that cubic nanodiamonds smaller than 5 nm can present the d-spacing at 1.78 Å corresponding to the (200) forbidden reflections, and the relative intensity of these reflections increases as the particle size decreases. Our simulation results also reveal that defects, such as surface distortions, internal dislocations, and grain boundaries can also make the (200) forbidden reflections visible. These findings provide valuable insights into the diamond structural complexity at nanoscale, the impact of defects on nanodiamond structures, and the discovery of novel diamond structures.

Novel 3D Printing Phase Change Aggregate Concrete: Mechanical and Thermal Properties Analysis.

The use of phase change materials (PCMs) in concrete is a double-edged sword that improves the thermal inertia but degrades the mechanical properties of concrete. It has been an essential but unsolved issue to enhance the thermal capacity of PCMs while non-decreasing their mechanical strength. To this end, this work designs a novel 3D printing phase change aggregate to prepare concrete with prominent thermal capacity and ductility. The work investigated the effects of 3D printing phase change aggregate on the compressive strength and splitting tensile strength of concrete. The compressive strength of phase change aggregate concrete is 21.18 MPa, but the ductility of concrete improves. The splitting tensile strength was 1.45 MPa. The peak strain is 11.69 × 10-3, nearly 13 times that of basalt aggregate concrete. Moreover, using 3D printing phase change aggregate reduced concrete's early peak hydration temperature by 7.1%. The thermal insulation capacity of the experiment cube model with phase change concrete has been improved. The results show that the novel 3D printing change aggregate concrete has good mechanical properties and latent heat storage, providing a guideline for applying PCMs in building materials.

An Approach of Producing Ultra-High-Performance Concrete with High Elastic Modulus by Nano-Al2O3: A Preliminary Study.

Ultra-high-performance concrete (UHPC) has promising applications in civil engineering. However, the elastic modulus of UHPC is relatively low compared with its compressive strength, which may result in insufficient stiffness in service. This work was carried out to explore the feasibility of producing UHPC with high elastic modulus by nano-Al2O3 (NA). Based on particle densely packing theory, the initial mixture of UHPC was designed via the modified Andreasen and Andersen model. An experimental investigation was conducted to systematically examine the effects of NA on different properties of UHPC, including its fluidity, mechanical properties, durability, and microstructure. It was found that: (1) Compared with UHPC without NA, the flexural strength, compressive strength, and elastic modulus of UHPC were improved by 7.38-16.87%, 4.08-20.58%, and 2.89-14.08%, respectively, because of the incorporation of NA; (2) the addition of NA had a prohibiting impact on the threshold pore diameter and porosity of UHPC, which suggested that NA could be conducive to its pore structure; (3) the incorporation of NA led to a decline of 2.9-11.76% in the dry shrinkage of UHPC, which suggested that incorporating NA in a proper amount could reduce the risk of cracking and alleviate the dry shrinkage of UHPC; (4) the optimal amount of NA in UHPC was 1.0%, considering the effects of NA on workability, mechanical properties, microstructure, and the durability of UHPC.

The manner and extent to which the hydration shell impacts interactions between hydrated species.

The hydration shell (HS) has a critical impact on every contact between hydrated species, which is a prerequisite for a great many physical and chemical processes, such as ion adsorption at the solution-solid interface. This paper reveals the extent and manner to which the HS interferes with ion adsorption utilizing molecular dynamics. The single-layer HS is the smallest unit that maintains the ionic hydration structure and the force on it. The energy penalty incurred by partial dehydration upon adsorption is one of the approaches through which HS influences ion adsorption, yet the collision of water molecules in HS may be the critical one. The repulsive force during dehydration is, to great extent, neutralized by HS collision. The index for estimating the extent of the influence of the HS is not the hydration energy, but the quantification of the contest between HS' collision and the binding of adsorption sites. The hydration energy is larger for charged functional groups, but the HS' impact is much smaller, as compared with electroneutral group cases. As a result, the order of the adsorption capacity for different ionic species may be quite different between charged and electroneutral cases.

Observation of Surface Ligands-Controlled Etching of Palladium Nanocrystals.

Selective adsorption of ligands on nanocrystal surfaces can affect oxidative etching. Here, we report the etching of palladium nanocrystals imaged using liquid cell transmission electron microscopy. The adsorption of surface ligands (i.e., iron acetylacetonate and its derivatives) and their role as inhibitor molecules on the etching process were investigated. Our observations revealed that the etching was dominated by the interplay between palladium facets and ligands and that the etching exhibited different pathways at different concentrations of ligands. At a low concentration of iron acetylacetonate (0.1 mM), rapid etching primarily at {100} facets led to a concave structure. At a high concentration (1.0 mM), the etch rate was decreased owing to a protective film of iron acetylacetonate on the {100} facets and a round nanoparticle was achieved. Ab initio calculations showed that the differences in adsorption energy of inhibitor molecules on palladium facets were responsible for the etching behavior.

A Novel Heterostructure Based on RuMo Nanoalloys and N-doped Carbon as an Efficient Electrocatalyst for the Hydrogen Evolution Reaction.

Heterostructures exhibit considerable potential in the field of energy conversion due to their excellent interfacial charge states in tuning the electronic properties of different components to promote catalytic activity. However, the rational preparation of heterostructures with highly active heterosurfaces remains a challenge because of the difficulty in component tuning, morphology control, and active site determination. Herein, a novel heterostructure based on a combination of RuMo nanoalloys and hexagonal N-doped carbon nanosheets is designed and synthesized. In this protocol, metal-containing anions and layered double hydroxides are employed to control the components and morphology of heterostructures, respectively. Accordingly, the as-made RuMo-nanoalloys-embedded hexagonal porous carbon nanosheets are promising for the hydrogen evolution reaction (HER), resulting in an extremely small overpotential (18 mV), an ultralow Tafel slope (25 mV dec-1 ), and a high turnover frequency (3.57 H2 s-1 ) in alkaline media, outperforming current Ru-based electrocatalysts. First-principle calculations based on typical 2D N-doped carbon/RuMo nanoalloys heterostructures demonstrate that introducing N and Mo atoms into C and Ru lattices, respectively, triggers electron accumulation/depletion regions at the heterosurface and consequently reduces the energy barrier for the HER. This work presents a convenient method for rational fabrication of carbon-metal heterostructures for highly efficient electrocatalysis.

Highly tunable anisotropic co-deformation of black phosphorene superlattices.

Controlling mechanical deformation is one of the state-of-the-art approaches to tune the electronic properties of 2D materials. We report a new mechanism for tuning a phosphorene superlattice with intercalated amphiphiles by its strong anisotropic co-deformation. Anisotropic co-deformation of a phosphorene superlattice is found to follow tunable sinusoidal and Gaussian functions, which exhibit adjustable mechanical actuation, curvature and layer separations. We analysed the controlling mechanism and tuning strategy of co-deformation as a function of amphiphile assembly topology, van der Waals interactions, interlayer separation and global deformation based on Euler-beam theory. Our first-principles calculations demonstrate that the co-deformation mechanism can be used to achieve a theoretical bandgap tunability of 0.7 eV and a transition between direct and indirect bandgaps. The reported tuning mechanisms pave new ways for designing a wide range of tunable functional electronics, sensors and actuators.

Nanoengineering Microstructure of Hybrid C-S-H/Silicene Gel.

Two-dimensional (2D) materials have been incorporated into calcium silicate hydrate (C-S-H) gel to enhance its mechanical performance for decades, while the modified C-S-H gel exhibits poor toughness, tensile strength, and ductility. In this work, we report a new design strategy and synthesis route to strengthen C-S-H interface by intercalating a silicene sheet of one atom thickness. The hybrid C-S-H/Silicene gel shows superb mechanical properties, with a remarkable enhancement in strength and other functional properties. By using density functional theory (DFT) and molecular dynamics (MD) simulations, we have demonstrated that Si-O bonds between silicene and C-S-H are stable and covalent, and the interaction energy of this bilayer gel nearly doubles by forming a 3D covalent network with a strong bridging effect. Owing to its better crystallinity enrichment and its induced dislocation dissipation mechanism, the hybrid C-S-H/Silicene gel possesses a higher tensile ductility (∼118% average enhancement and ∼228% in the c direction) and a much smaller elastic stiffness (59.04 GPa for average Young's modulus). This work offers an ingenuous route in turning brittle C-S-H gel into a soft gel, which provides opportunities for fabricating ultrahigh performance cementitious materials.

Effect of Inhibitor on Adsorption Behavior and Mechanism of Micro-Zone Corrosion on Carbon Steel.

A new type of inhibitor is studied in this paper. Inhibition efficiency and adsorption behavior of an inhibitor film on the steel surface is tested via the electrochemical method and theoretical calculation to establish the adsorption model. Test results confirm that inhibition efficiency is improved with the addition of an inhibitor, and the inhibitor film is formed firmly by comparing the characteristic peaks of S and N. Moreover, the micro-zone corrosion progress of Fe in 3.5% invasive NaCl-simulated seawater environment is studied. The results further show that corrosion is initiated under the zone without the inhibitor film, while it is prevented under the protection of the film. By the experiments, it is shown that inhibitor can be adsorbed on the surface of steel stably and has excellent protection performance for reinforced rebar, which can be widely used in concrete structure.

Feasibility of manufacturing ultra-high performance cement-based composites (UHPCCs) with recycled sand: A preliminary study.

Due to the excellent mechanical and durability properties, ultra-high performance cement-based composites (UHPCCs) have attracted a lot of attention during the past decades. It is noted that most existing UHPCCs are manufactured from raw materials with high quality, for instance, well-graded river sands. However, the huge consumption of river sands as construction materials has inevitably resulted in some serious ecological impacts, as reported around the world. In this regard, it shall be much beneficial if some substitutes, such as recycled sands produced through processing of construction and demolition waste (CDW), could be used to replace natural sands to manufacture the qualified UHPCCs. This paper presents such a preliminary study on the feasibility of manufacturing UHPCCs with recycled sands. A total of five UHPCCs are designed and cast with different replacement percentages of recycled sand, i.e., 0%, 30% 50%, 70% and 100% (in mass). The associated packing density of the mixed sands is estimated based on the linear packing model. The fresh and hardened properties of the UHPCCs, including the workability, strength and shrinkage, are experimentally examined. The test results indicate that it is possible to use recycled sand to replace natural river sand in the manufacture of UHPCCs; however, the amount of the recycled sand needs to be limited. In the case when the replacement percentage of the recycled sand is lower than 50% (in mass), the properties of the UHPCCs with the recycled sand are comparable with those containing river sand only.

Molecular structure, dynamics, and mechanical behavior of sodium aluminosilicate hydrate (NASH) gel at elevated temperature: a molecular dynamics study.

Sodium aluminosilicate hydrate (NASH) gel is the primary adhesive constituent in environmentally friendly geopolymer. In this study, to understand the thermal behavior of the material, molecular dynamics was utilized to investigate the molecular structure, dynamic property, and mechanical behavior of NASH gel subjected to temperature elevation from 300 K to 1500 K. The aluminosilicate skeleton in NASH gel provides plenty of oxygen sites to accept H-bond from the invading water molecules. Upon heating, around 18.2% of water molecules are decomposed and produce silicate and aluminate hydroxyls. About 87% of hydroxyls are associated with the aluminate skeleton, which weakens the Al-O bonds and disturbs the O-Al-O angle and the local structure, transforming it from an aluminate tetrahedron to a pentahedron and octahedron. With increasing temperature, both Al-O-Si and Si-O-Si bonds are stretched to be broken and the network structure of the NASH gel is gradually transformed into a branch and chain structure. Furthermore, the self-diffusivity of water molecules and sodium dramatically increases with the elevation of temperature, because the decrease in connectivity of the aluminosilicate network reduces the chemical and geometric restriction on the water and ions in NASH gel under higher temperatures. The high temperature also contributes to around 63% of the water molecules further dissociating and hydroxyl groups forming; meanwhile proton exchange between the water molecules and aluminosilicate network frequently takes place. In addition, a uniaxial tensile test was utilized to study the mechanical behavior of the NASH gel at different temperatures. During the tensile test, the aluminosilicate network was found to depolymerize into a branch or chain structure which plays a critical role in resisting the tensile loading. In this process, the breakage of the aluminosilicate skeleton is accompanied with hydrolytic reactions that further deteriorate the structure. Due to the reduction of the chemical bond stability at elevated temperature, both the tensile strength and stiffness of the NASH gel are weakened significantly. However, the ductility of the NASH gel is improved because of the higher extent of structural arrangement at the yield stage and partly due to the lower water attack. Hopefully, the present study can provide valuable molecular insights on the design of alkali-activated materials with high sustainability and durability.

Insights on magnesium and sulfate ions' adsorption on the surface of sodium alumino-silicate hydrate (NASH) gel: a molecular dynamics study.

The movement of water and ions in sodium alumino-silicate hydrate gel (NASH) influences the physical and chemical properties of the geopolymer material. In this paper, in order to better understand the structure and dynamics of water and ions in the interfacial region of the NASH gel, molecular dynamics was utilized to model Na2SO4 and MgSO4 solutions (both at 0.44 mol L-1) near the NASH surface. The broken silicate-aluminate surface network, with predominant percentage of randomly connected Q1 and Q2 silicate and aluminate species, provides plenty of non-bridging oxygen sites to accept the H bond from the surface water molecules, contributing toward a strongly adsorbed hydration layer with a thickness of around 5 Å. Consequently, the water molecule in the hydration layer exhibits increased density, increased dipole moment magnitude, orientation preference, and slow diffusivity. In contrast, up to 36.4% of the counter sodium ions, originally caged in the vacancies on the NASH surface, gradually dissociate from the silicate-aluminate skeleton and migrate into the bulk solution, which is consistent with the experimentally observed leaching process of alkali ions in the geopolymer material. In the MgSO4 solution, the magnesium ions-with a smaller ionic radius-penetrate into the silicate-aluminate skeleton vacancy, have 1.8 to 2.5 coordinated solid oxygen atoms, and remain on the NASH surface for a fairly longer time due to the stable Mg-O bonds. Mg species adsorbed on the inner sphere got rooted onto the hydroxyl layer, healing the damaged silicate-aluminate structures and stabilizing the network by inhibiting Na ion immigration into the solution. Mg ions in the outer layer, on average, associated with around one neighboring SO4 ion, forming ionic pairs and accumulating into large Mg-SO4 clusters, to help the immobilization of sulfate ions on the NASH surface.

Understanding the deformation mechanism and mechanical characteristics of cementitious mineral analogues from first principles and reactive force field molecular dynamics.

In this paper, first principles and reactive force field molecular dynamics were utilized to study the mechanical properties of tobermorite 9 Å, tobermorite 11 Å and jennite. These are essential minerals in cement chemistry. The mechanical properties calculated by the first-principle method match well with previous experimental results, pointing to the introduction of vdW dispersion-type forces as able to improve the precision. The calculated elastic constants of the three minerals confirm anisotropic mechanical behavior of the layered structures. The crystals jennite and tobermorite 9 demonstrate stronger mechanical behavior in the ab plane than the interlayer direction due to the presence of stable covalent "dreierketten" silicate chains. For tobermorite 11 Å, the Q3 silicate tetrahedrons bridging the neighboring calcium silicate sheets heal the weak interlayer structure and enhance the c-direction stiffness and cohesive strength. Furthermore, analysis of uniaxial tension by reactive force MD elucidated the chemical and mechanical responses of the atomic structures in loading resistance. The stress-strain relation of the layered mineral tensioned along b direction, showing the "strain hardening" region, where stress continues to increase past the yield stage. The strain hardening and ductility enhancement for the minerals is largely due to the ability of the silicate chains to first de-polymerize into short chains or separate tetrahedrons before the broken Q species re-polymerize to form branched networks and ring structures which are able to resist loading. For all three minerals, protons transfer to oxygen and water, resulting in the formation of Si-OH and Ca-OH groups during the strain hardening stage as Si-O-Si or Si-O-Ca bonds start to break and the calcium atoms and silicate morphology is rearranged. Hydrolysis therefore accelerates structural damage and contributes to weakening of mechanical properties in the interlayer direction. Increased tensile stress level in the tobermorite 11 Å can contribute to a greater extent of water damage.

Calcite crystallization in the cement system: morphological diversity, growth mechanism and shape evolution.

Carbonation plays an indispensable role in engineering construction, embracing mineralization, CO2 sequestration and low pH induced corrosion, but the essential mechanism of carbonation occurring in calcium silicate hydrate or portlandite can hardly be interpreted. Observation on how carbonation proceeds at the nano scale is thus critical for a better understanding of its dynamics. Here, using electron microscopy combined with first-principles calculation, a new view on carbonation in the cement system is revealed, considering morphological diversity, growth mechanism and shape evolution. Two types of crystalline forms of calcium carbonate (i.e. cubic and spindle) under room conditions were observed and determined to be calcite, both experimentally and theoretically. The mechanism of morphological evolution of calcite in a cement system was demonstrated based on the theory of aqueous chemistry. The [Ca2+] to [CO3] ratio was the principle cause for the diversity in crystal morphology instead of the types of reactants (i.e. portlandite or calcium silicate hydrates). Excess calcium species in the solution could selectively adsorb on surfaces, resulting in an inhibitive effect on the growth of specific crystal faces, (1 0 4)calcite and (2 1 1[combining macron])calcite in this case. Furthermore, a relationship between relative ionic concentration and the length to diameter ratio was established to predict the shape transformation. This work makes it possible to explore the chemical nature of carbonation from a nano scope rather than being confined to the macroscopic carbonation of concrete.

Insights into the interfacial strengthening mechanisms of calcium-silicate-hydrate/polymer nanocomposites.

The mechanical properties of organic/inorganic composites can be highly dependent on the interfacial interactions. In this work, with organic polymers intercalated into the interlayer of inorganic calcium silicate hydrate (C-S-H), the primary binding phase of Portland cement, great ductility improvement is obtained for the nanocomposites. Employing reactive molecular dynamics, the simulation results indicate that strong interfacial interactions between the polymers and the substrate contribute greatly to strengthening the materials, when C-S-H/poly ethylene glycol (PEG), C-S-H/poly acrylic acid (PAA), and C-S-H/poly vinyl alcohol (PVA) were subject to uniaxial tension along different lattice directions. In the x and z direction tensile processes, the Si-OCa bonds of the C-S-H gel, which were elongated and broken to form Si-OH and Ca-OH, play a critical role in loading resistance, while the incorporation of polymers bridged the neighboring silicate sheets, and activated more the hydrolytic reactions at the interfaces to avoid strain localization, thus increasing the tensile strength and postponing the fracture. On the other hand, Si-O-Si bonds of C-S-H mainly take the load when tension was applied along the y direction. During the post-yield stage, rearrangements of silicate tetrahedra occurred to prevent rapid damage. The polymer intercalation further elongates this post-yield period by forming interfacial Si-O-C bonds, which promote rearrangements and improve the connectivity of the defective silicate morphology, significantly improving the ductility. Among the polymers, PEG exhibits the strongest interaction with C-S-H, and thus C-S-H/PEG possesses the highest ductility. We expect that the molecular-scale mechanisms interpreted here will shed new light on the stress-activated chemical interactions at the organic/inorganic interfaces, and help eliminate the brittleness of cement-based materials on a genetic level.

Galvanic corrosion of duplex corrosion-resistant steel rebars under carbonated concrete conditions.

Galvanic corrosion between two different kinds of steel rebars is usually the case in practical engineering. Open circuit potential (OCP), linear polarization resistance (LPR), Tafel polarization, scanning vibrating electrode technique (SVET), scanning electron microscopy (SEM) and reflection digital holographic microscopy (DHM) were used to study the galvanic corrosion of a novel corrosion-resistant steel bar (CR) and low-carbon steel bar (LC) in simulated concrete pore solutions with different pH values and a chloride ion concentration of 5 mol L-1. The pH of the simulated concrete pore solution had a significant impact on the corrosion behaviour of CR and LC when they were in contact and were attacked by chloride ions. As the pH increased, the potential between CR and LC decreased and the driving force for the galvanic corrosion decreased. When the pH was 9.0, galvanic corrosion occurred on CR and LC at a high rate. CR developed local pitting corrosion, while LC mainly developed uniform corrosion, each with an apparent accumulation of corrosion products on the sample's surfaces. When the pH was 11.3, galvanic corrosion occurred when CR and LC were in contact. CR showed a relatively smooth surface, with only a small amount of pitting corrosion. In contrast, LC developed both pitting corrosion and uniform corrosion, and both apparent pitting corrosion and an accumulation of corrosion products on the sample surface were observed. When the pH was 13.6, there was no galvanic corrosion when CR and LC were in contact; the corrosion of CR and LC was mainly pitting corrosion. Therefore, for regions with chloride ion corrosion and severe carbonization, the galvanic corrosion between CR and LC cannot be ignored.

Molecule adsorption and corrosion mechanism of steel under protection of inhibitor in a simulated concrete solution with 3.5% NaCl.

Herein, the protective performance of a new triazole inhibitor for carbon steel was studied by electrochemical methods. Potentiodynamic polarization curves showed that the anti-corrosion efficiency improved with increasing concentrations of the inhibitor and the results show that it is 22 times corrosion resistance efficiency for inhibitor compared to bare aggressive solution. X-ray photoelectron spectroscopy showed that the film adsorbed well on the carbon steel surface. The scanning vibrating electrode technique demonstrated the corrosion process of carbon steel with and without the protection of inhibitor. Thus, a mechanism for the corrosion process was proposed and the behavior of carbon steel under the protection of the inhibitor was discussed.

The mechanism of cesium ions immobilization in the nanometer channel of calcium silicate hydrate: a molecular dynamics study.

The cement-based matrices are preferred candidates in disposing nuclear waste due to the immobilization role of the calcium-silicate-hydrate (C-S-H) gel. To better understand the immobilization mechanism of cementitious materials, molecular dynamics was utilized to investigate the intensity distribution, local structure and dynamics properties of Cs+ ions in the vicinity of the calcium silicate surface. The strong inner-sphere adsorbed cesium ions were restricted by coordinated oxygen atoms in bridging and pair silicate tetrahedron and water molecules were fixed in the silicate channel by H-bonds network. On the other hand, the adsorption of chloride ion, repulsed by the negatively charged silicate surface, is mainly attributed to the formation of the cation-anion ionic pair near the interface. As compared with those of the solvated ions in the solution, the relaxation time of water in the hydration shell of adsorbed Cs+ is significantly increased and the diffusion coefficient of adsorbed Cs+ is dramatically reduced. Furthermore, based on the intensity profile and resident-time analysis, the adsorption capacities of monovalent cations on the C-S-H surface increase with decrease in the ionic radius, following the sequence of Na+ ≫ K+ > Cs+. This study provides a molecular-level understanding of the immobilization mechanism of different ions in the C-S-H gel pores.