Molecular dynamics simulation in concrete research: A systematic review of techniques, models and future directions

This paper presents a comprehensive review of the application of molecular dynamics simulation in concrete research. The study addresses the background and significance of the topic, providing an overview of the principles, applications, and types of molecular dynamics simulation, with a particular focus on its role in enhancing the understanding of concrete properties. Moreover, it critically examines existing research studies that employ molecular dynamics simulation in concrete research, highlighting the associated benefits and limitations. The paper further investigates various simulation techniques and models employed in concrete research, offering a comparative analysis of their effectiveness. Additionally, the study explores future directions and identifies research needs in the field of molecular dynamics simulation in concrete, while also discussing the potential impact of this approach on the sustainability of the construction industry. By providing a comprehensive overview and critical analysis, this review serves as a valuable resource for researchers and practitioners interested in leveraging molecular dynamics simulation for advancing concrete science and engineering

Enhancement of Heat-Cured Cement Paste with Tannic Acid

The Improvement of Cement-Based Materials\u27 Performance by Natural Organic Compounds Can Greatly Promote the Green and Sustainable Development of the Construction Industry. However, Such Compounds Are Not Widely Used Yet Because of their Retarding Effect on Cement. in This Study, the Retardation Effect of Tannic Acid (TA, a Well-Known Retarding Compound) is overcome and the Enhancing Effect is Achieved by Adding Less Than 0.1% Content and Curing Samples in Thermal Regime. Then the Mechanism of TA Enhancing Heat-Cured Cement Pastes is Studied Systematically. Mechanical Properties Results Suggest that Addition of 0.025% TA Can Reduce the Compressive and Flexural Strengths of Cement Pastes by Up to 3.4% and 17.1% under Normal Curing Regime at 3 Days, But Enhance These Two Strengths by More Than 11.4% and 34.6% after Thermal Curing, Respectively. XRD Patterns and TGA Analysis Indicate that, under Thermal Curing Regime, 0.025% TA Can Improve the Hydration Degree of Cement Where the Bound Water Content is Increased by 21.4%. SEM Observations and MIP Results Show that TA Can Compact the Microstructure and the Porosity is Decreased by More Than 7.0%. Furthermore, FTIR Spectrums Prove that TA Can Bond with Hydration Products. Molecular Dynamics Simulation Demonstrates that TA Cross-Links with Calcium Silicate Hydrates (C–S–H) through Ionic and Hydrogen Bonds, Which Could Increase the Tensile Strength by 12.5% and the Ultimate Strain by 100%

Nano-Scale Investigation of Mechanical Characteristics of Main Phases of Hydrated Cement Paste

Hydrated cement paste (HCP), which is present in various cement-based materials, includes a number of constituents with distinct nano-structures. The elastic properties of the HCP crystals are calculated using molecular dynamics (MD) methods. The accuracy of estimated values is verified by comparing them with the results from experimental tests and other atomistic simulation methods. The outcome of MD simulations is then extended to predict the elastic properties of the C-S-H gel by rescaling the values calculated for the individual crystals. To take into account the contribution of porosity, a detailed microporomechanics study is conducted on low- and high-density types of C-S-H. The obtained results are verified by comparing the rescaled values with the predictions from nanoindentation tests. Moreover, the mechanical behavior of the HCP crystals is examined under uniaxial tensile strains. From the stress-strain curves obtained in the three orthogonal directions, elastic and plastic responses of the HCP crystals are investigated. A comprehensive chemical bond and structural damage analysis is also performed to characterize the failure mechanisms of the HCP crystals under high tensile strains. The outcome of this study provides detailed information about the nonlinear behavior, plastic deformation, and structural failure of the HCP phases and similar atomic structures

Atomistic Simulation of Na+ and Cl- Ions Binding Mechanisms to Tobermorite 14Å as a Model for Alkali Activated Cements

The production of ordinary Portland cement (OPC) is responsible for ~8% of all man-made CO2 emissions. Unfortunately, due to the continuous increase in the number of construction projects, and since virtually all projects depend on hardened cement from the hydration of OPC as the main binding material, the production of OPC is not expected to decrease. Alkali-activated cement produced from the alkaline activation of byproducts of industries, such as iron and coal industries, or processed clays represents a potential substitute for OPC. However, the interaction of the reaction products of AAC with corrosive ions from the environment, such as Cl-, remains largely unexamined. In this study, we present the details of preparing undoped and 5% Na-doped tobermorite 14Å structures as molecular models for the disordered alkali-doped calcium-alumino-silicate-hydrate (C-(N)-A-S-H, where N represents sodium and A represents aluminum) structure, which is the main reaction product in Ca-rich AAC. Moreover, we examined the ability of these structures to hinder the ingress of solvated Na+ and Cl- ions using molecular dynamics simulations. We adopted a core-shell model for these simulations to represent the polarizability of oxygen ions and a flexible model to represent water molecules. The combined interatomic interactions adopted in this work accurately predicted lattice parameters and basic mechanical properties similar to those obtained from different experimental and computational studies for the tobermorite 14Å structure. Moreover, these interactions could predict lattice parameters similar to those predicted by the ClayFF force field, a widely used force field to describe cementitious materials. By examining the structural, energetic, and dynamic properties of interfacial water molecules and solvated Na+ and Cl- ions, we showed that introducing Na+ ions as dopants to the bulk tobermorite 14Å structure had a positive impact on enhancing the adsorption of solvated Cl- ions. This positive impact is twofold; first, new and stable adsorption sites have been introduced on the surface of the 5% Na-doped system because of the charge balancing mechanism taking place while substituting Ca2+ ions with Na+ ions. Second, introducing the 5% Na+ ions led to slower dynamics for all species in this system. The slow dynamics originated from the excess Na+ ions in this system, and that NaCl is a structure-making salt. These results suggest that the presence of Na in Ca-rich AAC results in more resistance to chloride-induced corrosion due to an increased ability to hinder the movement of Cl- ions. In addition to the effectiveness of these types of cement to resist Cl- ions diffusivity, these results from molecular-scale simulations also encourage the usage of sustainable AACs, which directly reduce the immense volume of greenhouse emissions produced annually from the OPC industry

Atomistic simulation studies of the cement paste components

230 p.El cemento y sus derivados, como los morteros o el hormigón, son generalmente considerados materiales de bajo nivel tecnológico. A pesar de ser el material manufacturado más empleado en el mundo, otros como los plásticos, los metales, el algodón, la lana, la madera e incluso las piedras, se valoran más en el día a día. De hecho, el cemento es comúnmente considerado como una pasta gris, con la única característica de endurecerse cuando se seca, y que se empleada para construir edificios. Probablemente, el hecho de que sea barato, disponible, común y haya sido empleado satisfactoriamente durante siglos, contribuye a su percepción como material de bajo perfíl tecnológico. Sin embargo, esa visión se aleja de la realidad. La pasta de cemento es un compuesto complejo y heterogéneo, con diferentes características a diferentes escalas de tamaño. El mecanismo por el cual el clínker al entrar en contacto con el agua se convierte en una pasta endurecida incluye cientos de reacciones químicas y procesos físicos. El componente principal de la pasta de cemento, el gel C-S-H, es una fase amorfa con una determinada porosidad intrínseca, y su nanoestructura aún se desconoce. Curiosamente, el gel C-S-H presenta claras similitudes con otros sistemas de interés tecnológico. Por ejemplo, la estructura del gel es habitualmente descrita en términos de minerales naturales tobermorita y jennita. Estos minerales presentan una estructura laminar similar al de las arcillas montmorillonita-esmectita, que son utilizadas con objetivos catalíticos, como parte de los nano- y bio-composites, o como absorbentes de residuos contaminantes. La morfología del gel C-S-H en la microescala se parece también a la de la hidroxiapatita, que es el principal componente de los huesos. Tal semejanza proviene de su composición análoga: silicato-calcico-hidratado (C-S-H) en la matriz de cemento, y fosfato-calcico-hidratado (C-P-H) en hidroxiapatita. De hecho, tanto el gel C-S-H como la hidroxiapatita sufren un proceso de descalcificación, conocida como lixiviación de calcio en el cemento y osteoporosis en los huesos. Pero hay analogías adicionales con otros sistemas biológicos. La posición y el papel del agua en el gel C-S-H y en ciertas proteínas cristalinas son similares. Las moléculas de agua pueden estar en diferentes posiciones y asociadas con fuerzas diferentes, actuando como una parte estructural o como una solución en los poros. Estos ejemplos ilustran porque el interés de la estructura y las propiedades del gel C-S-H son comparables a los de otros materiales. La investigación en cemento incluye muchos aspectos diferentes, desde la reducción de los gases de efecto invernadero emitidos durante el proceso de fabricación, a la investigación de la nanoestructura del material, incluyendo el desarrollo de nuevos cementos que utilizan desechos como materias primas, o la modificación y mejora de las propiedades del cemento Portland ordinario. Debido a su naturaleza heterogénea, la pasta de cemento es un material multiescalar. El cemento presenta diferentes rasgos y características a escalas nano-, micro- y macro-, y su comportamiento en dichas escalas dista de ser el mismo, Además, la investigación del cemento es un campo multidisciplinar en el que están implicados ingenieros, químicos, físicos y geólogos. Ese ambiente cooperativo, así como la naturaleza de multiescalar de los problemas a estudiar, implican el uso de numerosas técnicas experimentales en la investigación del material. La evolución de las técnicas experimentales en los últimos años nos permite estudiar la pasta de cemento a escalas cada vez más pequeñas, con la apertura al cemento de un campo como la nanotecnología. En nanotecnología, los métodos de simulación atomística han demostrado ser un instrumento numérico indispensable. Estos métodos nos permiten estudiar la nanoescala de un material o molécula con gran detalle. Sin embargo, los métodos de simulación atomística apenas se han aplicado en la investigación de aspectos relacionados con el cemento. La misma complejidad que dificulta las investigaciones experimentales de los materiales en base cemento en la nanoescala, como su naturaleza amorfa y heterogénea, es un problema en la simulación atomística, ya que la posición exacta de los átomos es información necesaria para los cálculos. No obstante este problema ha sido parcialmente solucionado por el incremento de la capacidad computacional y el desarrollo de nuevas técnicas y métodos de cálculo. En esta Tesis, se han empleado métodos de simulación atomísticos para estudiar diversos aspectos de los componentes de pasta de cemento, como son sus propiedades elásticas, reactividad, estructura y formación, prestando una atención especial al gel C-S-H

Cementitious materials subjected to mechanical and environmental stressors: A computational framework

Despite the significant amount of concrete produced worldwide, there are long-standing issues with the long-term performance of concrete structures and facilities subjected to the mechanical and environmental stressors. To settle these issues, it is first imperative to understand the structural hierarchies and heterogeneous characteristics of concrete. While the structure of concrete at large length scales have been widely investigated in the literature, little knowledge is available about the structure, composition, and properties of the smallest building blocks of concrete, i.e., hydrated cement paste (HCP). This is mainly due to the complexities involved in the atomic structure of HCP phases that are often difficult to be characterized using conventional experimental methods. Atomistic simulations, however, can offer a promising solution, which not only plays a critical role to further interpret the experimental test results, but also advances the fundamental knowledge that is not accessible otherwise. In this dissertation, a robust bottom-up computational framework supported with experimental test data is established to address three categories of research needs. These research needs seamlessly connect the atomic structure of cement-based systems to the long-term performance of concrete structures at the macroscale. The first category of research needs attempts to understand the interplay between the structure and properties of the crystalline HCP phases, including portlandite, and the AFt and AFm phases. The second category of research needs deals with the characterization of the magnitude, sign, and directionality of the mechanical stresses produced as a result of the formation of the secondary sulfate-bearing minerals during the chemical sulfate attack reactions. Lastly, the third category of research needs is associated with the identification of the atomistic processes underlying the diffusion of water molecules and chloride ions at the interfaces of the main aluminum-rich phases in HCP. The outcome of this study (1) will extend the fundamental knowledge about the structure, dynamics, and properties of the HCP phases at the nanoscale, (2) will offer an invaluable addition to the existing experimental test data, and (3) can directly contribute to understanding and controlling the long-standing issues due to the deterioration of concrete structures subjected to the mechanical and environmental stressors

Physical Origins of Thermal Properties of Cement Paste

Despite the ever-increasing interest in multiscale porous materials, the chemophysical origin of their thermal properties at the nanoscale and its connection to the macroscale properties still remain rather obscure. In this paper, we link the atomic- and macroscopic-level thermal properties by combining tools of statistical physics and mean-field homogenization theory. We begin with analyzing the vibrational density of states of several calcium-silicate materials in the cement paste. Unlike crystalline phases, we indicate that calcium silicate hydrates (CSH) exhibit extra vibrational states at low frequencies (<2  THz) compared to the vibrational states predicted by the Debye model. This anomaly is commonly referred to as the boson peak in glass physics. In addition, the specific-heat capacity of CSH in both dry and saturated states scales linearly with the calcium-to-silicon ratio. We show that the nanoscale-confining environment of CSH decreases the apparent heat capacity of water by a factor of 4. Furthermore, full thermal conductivity tensors for all phases are calculated via the Green-Kubo formalism. We estimate the mean free path of phonons in calcium silicates to be on the order of interatomic bonds. This satisfies the scale separability condition and justifies the use of mean-field homogenization theories for upscaling purposes. Upscaling schemes yield a good estimate of the macroscopic specific-heat capacity and thermal conductivity of cement paste during the hydration process, independent of fitting parameters.Portland Cement AssociationNational Ready Mixed Concrete Association (Research and Education Foundation

Computational Material Modeling For Mechanical Properties Prediction And A Methodology For Mie Gruneisen Equation Of State Characterization Via Molecular/Nano Scale Cementitious Material Constituents

Cementitious materials have complex hierarchical structures with random features that range from nanometer (nm) to millimeter (mm) scale. Processes occurring at the nanometer scale affect the performance at larger length scales. The present work employs molecular dynamics (MD) simulations as the computational modeling methodology to predict mechanical properties for both hydrated and unhydrated cementitious materials at the molecular/nano scale level. A detailed study on the effect of increasing MD simulation cell size, dynamics time duration on the predicted mechanical properties was performed. Further studies focused on understanding the effect of higher thermodynamic pressure states on predicted mechanical properties using MD based material modeling. High strain rate behavior of materials undergoing shocks, detonations and other dynamic failure modes are characterized via an Equation of State (EOS) and Hugoniot curves to account for the associated adiabatic effects. A MD modeling methodology for the characterization of Mie Gruneisen EOS and Hugoniot curves based on molecular structures is developed and presented. This method is demonstrated for cement hydrated product (C-S-H Jennite) and the associated adiabatic longitudinal stress -- specific volume relationship is developed. This method is based on the assumption that cementitious molecular constituents are confined and subjected to plane longitudinal shock waves. This allows their response to be investigated based on the estimation of shock Hugoniot curves

A comprehensive review of C-S-H empirical and computational models, their applications, and practical aspects

[EN] The C-S-H gel is an elusive material. Its variable composition and disordered nature complicate a complete characterization of its atomic structure, and the elaboration of models is key to understanding it. This work aims to review those proposed models, dividing them into empirical and computational models. After a brief description of related crystalline calcium silicate hydrates, empirical C-S-H models based on interpretation of experimental data are presented. Then, we focus on the historic development of atomistic models to study the C-S-H, until the current state of the art. We describe current computational C-S-H models built from the empirical models and computer simulations. We review common applications of these computational models: the aluminum incorporation, the elastic and mechanical properties, the diffusion of water and ions in nanopores, and C-S-H/organic composites. Finally, we discuss some practical aspects of the computational models and their interpretation, as well as possible future directions.The authors would like to acknowledge funding from “Departamento de Educación, Política Lingüística y Cultura del Gobierno Vasco” (Grant No. IT912-16 and IT1639-22) and the technical and human support provided by the Scientific Computing Service of SGIker (UPV/EHU/ ERDF, EU). E.D.-R. also acknowledges the postdoctoral fellowship from “Programa Posdoctoral de Perfeccionamiento de Personal Investigador Doctor” of the Basque Government

Enhancement of Cement Paste with Carboxylated Carbon Nanotubes and Poly(Vinyl Alcohol)

Cement has been a major consumable material for construction in the world since its invention, but its low flexural strength is the main defect affecting the service life of structures. To adapt cement-based materials to a more stringent environment, carboxylated carbon nanotubes (CNTs-COOH) and poly(vinyl alcohol) (PVA) are proposed to enhance the mechanical properties of cement paste. This study systematically verifies the synergistic effect of CNTs-COOH/PVA on the performance of cement paste. First, UV-Vis spectroscopy and FTIR spectroscopy prove that CNTs-COOH can provide attachment sites for PVA and PVA can improve the dispersion and stability of CNTs-COOH in water, which demonstrates the feasibility of synergistically enhancing cement paste. When a 0.015% CNTs-COOH suspension with 0.1% PVA is added, the flexural strength of the cement paste increases by 73, 32, and 42% compared with control specimens at curing ages of 3, 7, and 28 days, respectively. The strength enhancement mechanism is revealed from the aspects of cement matrix enhancement and interface enhancement. Thermogravimetric (TG) analysis and mercury intrusion porosimetry (MIP) prove that CNTs-COOH can enhance the hydration degree of the cement matrix and fill the pores introduced by PVA. Based on the fact that PVA can improve the dispersibility and the nucleation site effect of CNTs-COOH in cement paste, molecular dynamics simulation confirms that PVA can bridge CNTs-COOH and C-S-H to enhance the interfacial bonding by 64.1%