Nanoscale shear cohesion between cement hydrates: The role of water diffusivity under structural and electrostatic confinement

\ua9 2022 The Authors. The calcium silicate hydrate (C-S-H) controls most of the final properties of the cement paste, including its mechanical performance. It is agreed that the nanometer-sized building blocks that compose the C-S-H are the origin of the mechanical properties. In this work, we employ atomistic simulations to investigate the relaxation process of C-S-H nanoparticles subjected to shear stress. In particular, we study the stress relaxation by rearrangement of these nanoparticles via sliding adjacent C-S-H layers separated by a variable interfacial distance. The simulations show that the shear strength has its maximum at the bulk interlayer space, called perfect contact interface, and decreases sharply to low values for very short interfacial distances, coinciding with the transition from 2 to 3 water layers and beginning of the water flow. The evolution of the shear strength as a function of the temperature and ionic confinement confirms that the water diffusion controls the shear strength

Y-System and Deformed Thermodynamic Bethe Ansatz

We introduce a new tool, the Deformed TBA (Deformed Thermodynamic Bethe Ansatz), to analyze the monodromy problem of the cubic oscillator. The Deformed TBA is a system of five coupled nonlinear integral equations, which in a particular case reduces to the Zamolodchikov TBA equation for the 3-state Potts model. Our method generalizes the Dorey-Tateo analysis of the (monomial) cubic oscillator. We introduce a Y-system corresponding to the Deformed TBA and give it an elegant geometric interpretation.Comment: 12 pages. Minor corrections in Section

CASCO: a simulator of load paths in 2D frames during progressive collapse

Modern structural design software can simulate complex collapse dynamics, but the main physical processes driving collapse propagation are often hidden among structure-specific details. As a result, it is still unclear which structural geometries and material properties should be preferred when approaching the design of a damage-tolerant structure. This manuscript presents a new approach to explore the relationships between structural geometry, local mechanical properties, and collapse propagation. The insight comes from a unique ability to trace the evolution of load paths during collapse, achieved by combining energy conservation with local mechanisms of plastic failure and a few simplifying assumptions. The method is implemented in a new simulator of collapse of 2D frames, called CASCO and programmed in MATLAB. Simulation results for reinforced concrete frames predict collapse loads and mechanisms in agreement with fully non-linear, dynamic simulations, while also providing a graphical description of the evolving structural topology during collapse. A first application of CASCO to mechanically homogeneous and heterogeneous frames, indicates certain evolutions in number and density of load paths during collapse that may be targetted to improve collapse resistance

Carbonation and self-healing in concrete: Kinetic Monte Carlo simulations of mineralization

Industrial applications of carbonation such as self-healing and carbon capture and storage have been limited, due to a lack of reliable predictive models linking the chemistry of carbonation at the molecular scale to microstructure development and macroscopic properties. This work proposes a coarse-grained Kinetic Monte Carlo (KMC) approach to simulate microstructural evolution of a model cement paste during carbonation, along with evolution of pore solution chemistry and saturation indexes of solid species involved. The simulations predict the effective rate constants for Ca(OH)2 dissolution and CaCO3 precipitation as kCa(OH)2 = 2.20 × 10−5 kg/m3/s and kCaCO3 = 4.24 × 10−6 kg/m3/s. These values are directly fed to a macroscale reactive transport model to predict carbonate penetration depth. The rate constants from the molecular scale are used in a boundary nucleation and growth model to predict self-healing of cracks. Subsequently these results are compared with experimental data, and provide good agreement. This proposed multiscale approach can help understand and manage the carbonation of both traditional and new concretes, supporting applications in residual lifetime assessment, carbon capture, and self-healing

Advances in biomimetic collagen mineralisation and future approaches to bone tissue engineering

With an ageing world population and ~20% of adults in Europe being affected by bone diseases, there is an urgent need to develop advanced regenerative approaches and biomaterials capable to facilitate tissue regeneration while providing an adequate microenvironment for cells to thrive. As the main components of bone are collagen and apatite mineral, scientists in the tissue engineering field have attempted in combining these materials by using different biomimetic approaches to favour bone repair. Still, an ideal bone analogue capable of mimicking the distinct properties (i.e., mechanical properties, degradation rate, porosity, etc.) of cancellous bone is to be developed. This review seeks to sum up the current understanding of bone tissue mineralisation and structure while providing a critical outlook on the existing biomimetic strategies of mineralising collagen for bone tissue engineering applications, highlighting where gaps in knowledge exist

Century-long expansion of hydrating cement counteracting concrete shrinkage due to humidity drop from selfdesiccation or external drying

A physically based model for auotgenous shrinkage and swelling of portland cement paste is necessary for computation of long-time hydgrothermal effects in concrete structures. The goal is to propose such a model. As known since 1887, the volume of cement hydration products is slightly smaller than the original volume of cement and water (chemical shrinkage). Nevertheless, this does not imply that the hydration reaction results in contraction of the concrete and cement paste. According to the authors’ recently proposed paradigm, the opposite is true for the entire lifetime of porous cement paste as a whole. The hydration process causes permanent volume expansion of the porous cement paste as a whole, due to the growth of C–S–H shells around anhydrous cement grains which pushes the neighbors apart, while the volume reduction of hydration products contributes to porosity. Additional expansion can happen due to the growth of ettringite and portlandite crystals. On the material scale, the expansion always dominates over the contraction, i.e., the hydration per se is, in the bulk, always and permanently expansive, while the source of all of the observed shrinkage, both autogenous and drying, is the compressive elastic or viscoelastic strain in the solid skeleton caused by a decrease of chemical potential of pore water, along with the associated decrease in pore relative humidity. As a result, the selfdesiccation, shrinkage and swelling can all be predicted from one and the same unified model, in which, furthermore, the low-density and high-density C–S–H are distinguished. A new thermodynamic formulation of unsaturated poromechanics with capillarity and adsorption is presented. The recently formulated local continuum model for calculating the evolution of hydration degree and a new formulation of nonlinear desorption isotherm are important for realistic and efficient finite element analysis of shrinkage and swelling. Comparisons with the existing relevant experimental evidence validate the proposed model

Reconstruction and Analysis of the Po River Inundation of 1951

Flood inundation models have become essential tools in flood risk management, being used also in the analysis of historical flood events, which is often needed for a reliable assessment of the potential flood hazard. This study aims at reconstructing the 1951 inundation of the Polesine Region, Italy. The 1951 flooding was a mayor natural catastrophe that caused a large inundated area (1080 km2) and produced devastating social consequences. The reconstruction of the 1951 hydraulic conditions is based on partial knowledge of discharges and water stages at the Pontelagoscuro gauging station (downstream of the 1951 levee breach) using extrapolation of the rating curves beyond the measurement range. This is, even today, something open to uncertainty. We applied a decoupled hybrid approach to the hydraulic modeling: a 1D model is used to simulate the flow into the river and to compute the flow through the levee breach; this result is then adopted as the inflow condition for a 2D model application on the inundated area. A good agreement between the patterns of the observed and reconstructed inundation areas was found, and the timing of the inundation was also found to be close to the information derived from the historical chronicles. The results of the flood inundation modelling exercise provide two practical insight: (i) obstacles in the floodplains increased the flooded area by 40% and prolonged the time to reach the sea from 5 to 15 days, (ii) the peak discharge of the event was overestimated by up to 20

Dual stage resistive transition of MgB2 evidenced by noise analysis

The resistive transition of polycrystalline superconducting MgB2 films is studied by means of an extensive set of stationary noise measurements, going from the very beginning of the transition to its final point, where the normal state is reached, either with and without magnetic field. The experimental results, taken at low current density and close to the critical temperature Tc, show very clearly the existence of two different dissipative processes at the different stages of the transition. An extended analysis proves that, at the beginning of the transition, when the resistance is below ten percent of normal value, the specimen is in a mixed state and dissipation is produced by fluxoid creation and motion. At higher temperature the specimen is in an intermediate state, constituted by a structure of interleaved superconducting and resistive domains. Such a situation occurs in type II superconductor when the transition temperature is very near to Tc and the critical field Hc for fluxoid penetration tends to zero. It is found that in the intermediate state, the power spectrum of the relative resistance fluctuations, is independent of the average resistance value and is unaffected by the magnetic field. As shown in the paper, this means that the noise is generated by density fluctuation of the normal electron gas in the resistive domains, while the contribution of the superconducting ones is negligible. The reduced noise amplitude does not depend on the steepness of the transition curve, thus adding further evidence to the above interpretation. The noise is thus related to the film impurities and can be investigated when the specimen is in the normal state, even at room temperature. The occurrence of a different dissipative process at low resistance is clearly evidenced by the experimental results, which show that the amplitude of the reduced power spectrum of the noise depends on magnetic field and resistance. These results are consistent with the assumption of fluxoid noise as shown by the model for the calculation of the noise developed in the manuscrip

Along-the-net reconstruction of hydropower potential with consideration of anthropic alterations

Even in regions with mature hydropower development, requirements for stable renewable power sources suggest revision of plans of exploitation of water resources, while taking care of the environmental regulations. Mean Annual Flow (MAF) is a key parameter when trying to represent water availability for hydropower purposes. MAF is usually determined in ungauged basins by means of regional statistical analysis. For this study a regional estimation method consistent along-the-river network has been developed for MAF estimation; the method uses a multi-regressive approach based on geomorphoclimatic descriptors, and it is applied on 100 gauged basins located in NW Italy. The method has been designed to keep the estimates of mean annual flow congruent at the confluences, by considering only raster-summable explanatory variables. Also, the influence of human alterations in the regional analysis of MAF has been studied: impact due to the presence of existing hydropower plants has been taken into account, restoring the "natural" value of runoff through analytical corrections. To exemplify the representation of the assessment of residual hydropower potential, the model has been applied extensively to two specific mountain watersheds by mapping the estimated mean flow for the basins draining into each pixel of a the DEM-derived river network. Spatial algorithms were developed using the OpenSource Software GRASS GIS and PostgreSQL/PostGIS. Spatial representation of the hydropower potential was obtained using different mean flow vs hydraulic-head relations for each pixel. Final potential indices have been represented and mapped through the Google Earth platform, providing a complete and interactive picture of the available potential, useful for planning and regulation purpose

Topology optimization using the discrete element method. Part 1: Methodology, validation, and geometric nonlinearity

Structural Topology optimization is attracting increasing attention as a complement to additive manufacturing techniques. The optimization algorithms usually employ continuum-based Finite Element analyses, but some important materials and processes are better described by discrete models, for example granular materials, powder-based 3D printing, or structural collapse. To address these systems, we adapt the established framework of SIMP Topology optimization to address a system modelled with the Discrete Element Method. We consider a typical problem of stiffness maximization for which we define objective function and related sensitivity for the Discrete Element framework. The method is validated for simply supported beams discretized as interacting particles, whose predicted optimum solutions match those from a classical continuum-based algorithm. A parametric study then highlights the effects of mesh dependence and filtering. An advantage of the Discrete Element Method is that geometric nonlinearity is captured without additional complexity; this is illustrated when changing the beam supports from rollers to hinges, which indeed generates different optimum structures. The proposed Discrete Element Topology Optimization method enables future incorporation of nonlinear interactions, as well as discontinuous processes such as during fracture or collapse