The multi-scale approach of masonry, paradigm of clay brick

Recent progress in nanoscience and engineering allows advanced characterization of materials. This type of characterization includes investigations revealing the scale dependent microstructure and mechanical as well physical properties of each component incorporated in the heterogeneous material. Its applicability and efficiency is confirmed in the field of cement based materials where the paradigm of these materials is solved, and universal buildings blocks and the multi-scale nature are well described. As a consequence, material researchers and engineers have knowledge about the impact of basic constituents and microstructure on macro behaviour of cement based materials. In the masonry field, a quite diverse situation is found. Although clay brick is among the oldest building materials, the main building blocks are still unknown. This knowledge gap is apparent in structural masonry, since the present homogenization and upscaling techniques consider only mortar joints, brick units and interface as a basic units. Here, the mechanical properties and elementary arrangement of these three components in the representative volume element (RVE) are assumed to govern the behaviour of masonry as a composite. But, it is understood that mortar may be broken down to lower scales, and its macro mechanical properties considered in the already developed approaches are governed by the lover scale components and its microstructure. Similarly, as it is shown by the authors in this contribution the brick unit may be broken down to lower scales, in which the basic material components and theirs properties are inherent. Therefore, the macro behaviour of composite masonry wall and its durability is considered to be ruled by the phenomena from the much lower scales present in the mortar, clay brick and the interface of these two

Multitechnique investigation of extruded clay brick microstructure

Despite the omnipresence of clay brick as construction material since thousands of years, fundamental knowledge about the link between composition, microstructure and mechanical performance is still scarce. In this paper, we employ a variety of advanced techniques of experimental mechanics and material characterization for extruded clay brick for masonry, that range from Scanning Electron Microscopy (SEM) coupled with Energy-dispersive X–ray Spectroscopy (EDX), Mercury Intrusion Porosimetry (MIP), to Instrumented Nanoindentation and macroscopic strength and durability tests. We find that extruded clay brick possesses a hierarchical microstructure: depending on the firing temperature, a “glassy” matrix phase, which manifests itself at sub-micrometer scales in form of neo-crystals of mullite, spinel-type phase and other accessory minerals, forms either a granular or a continuum matrix phase that hosts at sub-millimeter scale the porosity. This porous composite forms the backbone for macroscopic material performance of extruded brick, including anisotropic strength, elasticity and water absorption behavior.Authors gratefully acknowledge Portuguese Foundation for Science and Technology (FCT) for providing doctoral scholarship under the reference SFRH/BD/39232/2007 for Konrad J. Krakowiak. Special thanks to Dr. J. P. Castro Gomes, Centre of Materials and Building Technologies (C-MADE), University of Beira Interior for making feasible Mercury Intrusion measurements, as well as Dr. G. P. Souza for helpful guidance and advices related to this work

Precise Experimental Investigation of Eigenmodes in a Planar Ion Crystal

The accurate characterization of eigenmodes and eigenfrequencies of two-dimensional ion crystals provides the foundation for the use of such structures for quantum simulation purposes. We present a combined experimental and theoretical study of two-dimensional ion crystals. We demonstrate that standard pseudopotential theory accurately predicts the positions of the ions and the location of structural transitions between different crystal configurations. However, pseudopotential theory is insufficient to determine eigenfrequencies of the two-dimensional ion crystals accurately but shows significant deviations from the experimental data obtained from resolved sideband spectroscopy. Agreement at the level of 2.5 x 10^(-3) is found with the full time-dependent Coulomb theory using the Floquet-Lyapunov approach and the effect is understood from the dynamics of two-dimensional ion crystals in the Paul trap. The results represent initial steps towards an exploitation of these structures for quantum simulation schemes.Comment: 5 pages, 4 figures, supplemental material (mathematica and matlab files) available upon reques

Topological Origin of Fracture Toughening in Complex Solids: the Viewpoint of Rigidity Theory

In order to design tougher materials, it is crucial to understand the relationship between their composition and their resistance to fracture. To this end, we investigate the fracture toughness of usual sodium silicate glasses (NS) and complex calcium--silicate--hydrates (CSH), the binding phase of cement. Their atomistic structure is described in the framework of the topological constraints theory, or rigidity theory. We report an analogous rigidity transition, driven by pressure in NS and by composition in CSH. Relying both on simulated and available experimental results, we show that optimally constrained isostatic systems show improved fracture toughness. The flexible to stressed--rigid transition is shown to be correlated to a ductile-to-brittle transition, with a local minimum of the brittleness for isostatic system. This fracture toughening arises from a reversible molecular network, allowing optimal stress relaxation and crack blunting behaviors. This opens the way to the discovery of high-performance materials, designed at the molecular scale

Order and disorder in calcium–silicate–hydrate

Despite advances in the characterization and modeling of cement hydrates, the atomic order in Calcium–Silicate–Hydrate (C–S–H), the binding phase of cement, remains an open question. Indeed, in contrast to the former crystalline model, recent molecular models suggest that the nanoscale structure of C–S–H is amorphous. To elucidate this issue, we analyzed the structure of a realistic simulated model of C–S–H, and compared the latter to crystalline tobermorite, a natural analogue of C–S–H, and to an artificial ideal glass. The results clearly indicate that C–S–H appears as amorphous, when averaged on all atoms. However, an analysis of the order around each atomic species reveals that its structure shows an intermediate degree of order, retaining some characteristics of the crystal while acquiring an overall glass-like disorder. Thanks to a detailed quantification of order and disorder, we show that, while C–S–H retains some signatures of a tobermorite-like layered structure, hydrated species are completely amorphous.ICoME2 Labex (ANR-11-LABX-0053)A*MIDEX projects (ANR-11-IDEX-0001-02)Program “Investissements d’Avenir

Feedback-Optimized Operations with Linear Ion Crystals

We report on transport operations with linear crystals of 40Ca+ ions by applying complex electric time-dependent potentials. For their control we use the information obtained from the ions' fluorescence. We demonstrate that by means of this feedback technique, we can transport a predefined number of ions and also split and unify ion crystals. The feedback control allows for a robust scheme, compensating for experimental errors as it does not rely on a precisely known electrical modeling of the electric potentials in the ion trap beforehand. Our method allows us to generate a self-learning voltage ramp for the required process. With an experimental demonstration of a transport with more than 99.8 % success probability, this technique may facilitate the operation of a future ion based quantum processor

Mesoscale texture of cement hydrates

Strength and other mechanical properties of cement and concrete rely upon the formation of calcium-silicate-hydrates (C-S-H) during cement hydration. Controlling structure and properties of the C-S-H phase is a challenge, due to the complexity of this hydration product and of the mechanisms that drive its precipitation from the ionic solution upon dissolution of cement grains in water. Departing from traditional models mostly focused on length scales above the micrometer, recent research addressed the molecular structure of C-S-H. However, small-angle neutron scattering, electron- microscopy imaging, and nanoindentation experiments suggest that its mesoscale organization, extending over hundreds of nanometers, may be more important. Here we unveil the C-S-H mesoscale texture, a crucial step to connect the fundamental scales to the macroscale of engineering properties. We use simulations that combine information of the nanoscale building units of C-S-H and their effective interactions, obtained from atomistic simulations and experiments, into a statistical physics framework for aggregating nanoparticles. We compute small-angle scattering intensities, pore size distributions, specific surface area, local densities, indentation modulus, and hardness of the material, providing quantitative understanding of different experimental investigations. Our results provide insight into how the heterogeneities developed during the early stages of hydration persist in the structure of C-S-H and impact the mechanical performance of the hardened cement paste. Unraveling such links in cement hydrates can be groundbreaking and controlling them can be the key to smarter mix designs of cementitious materials