Nanotechnology in concrete – A review

Concrete, bone and shale have one thing in common: their load-bearing mineral phase is a hydrated nanocomposite. Yet the link between material genesis, microstructure, and mechanical performance for these materials is still an enigma that has deceived many decoding attempts. In this article, we advance statistical indentation analysis techniques that make it possible to assess, in situ, the nanomechanical properties, packing density distributions, and morphology of hydrated nanocomposites. These techniques are applied to identify intrinsic and structural sources of anisotropy of hydrated nanoparticles: calcium–silicate–hydrate (C–S–H), apatite, and clay. It is shown that C–S–H and apatite, the binding phase in, respectively, cement-based materials and bone, are intrinsically isotropic; this is most probably due to a random precipitation and growth process of particles in calcium oversaturated pore solutions, which can also explain the nonnegligible internanoparticle friction. In contrast, the load-bearing clay phase in shale, the sealing formation of most hydrocarbon reservoirs, is found to be intrinsically anisotropic and frictionless. This is indicative of a ‘smooth’ deposition and compaction history, which, in contrast to mineral growth in confined spaces, minimizes nanoparticle interlocking. In all cases, the nanomechanical behavior is governed by packing density distributions of elementary particles delimitating macroscopic diversity.

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Statistical indentation techniques for hydrated nanocomposites: concrete, bone, and shale

https://www.gci.ulaval.ca/fileadmin/gci/documents/3.pdf

The nano-mechanical signature of Ultra High Performance Concrete by statistical nanoindentation techniques

Surface Roughness Criteria for Cement Paste Nanoindentation

Since its inception 30 years ago perhaps no innovation in radar technology has made such a tremendous impact on the field as that of radar interferometry. Radar interferometry uses two or more observations separated in either time or space to measure fraction of a wavelength scale range differences between the two observations. Radar interferometry is used by scientific, commercial and government institutions for numerous applications including topographic map generation, surface deformation mapping, landslide monitoring, current velocity measurement, vegetation structure determination and change detection. Radar interferometers can be flown on either spaceborne or airborne platforms or be fixed observing systems. This course is designed to provide an overview of the basic concepts of radar interferometry and an introduction to some of its applications. The course will cover basic radar imaging principles, a geometric and imaging signal perspective of the interferometric phase, interferometric correlation, basic sensitivity equations, phase unwrapping, topographic mapping and repeat pass interferometry for deformation measurements. The principles will be illustrated with examples from both spaceborne and airborne interferometric data sets. An overview of some of the major applications of radar interferometry will be presented with an emphasis on topographic and deformation mapping. The course will also briefly touch upon permanent scatter methods and polarimetric interferometry.

Radar interferometry

The nanogranular behavior of C-S-H at elevated temperatures (up to 700 °C)

In this paper, the dynamic response of the rocking block subjected to base excitation is revisited. The goal is to offer new closed-form solutions and original similarity laws that shed light on the fundamental aspects of the rocking block. The focus is on the transient dynamics of the rocking block under finite-duration excitations. An alternative way to describe the response of the rocking block, informative of the behaviour of rocking structures under excitations of different intensity, is offered. In the process, limitations of standard dimensional analysis, related to the orientations of the involved physical quantities, are revealed. The proposed dimensionless and orientationless groups condense the response and offer a lucid depiction of the rocking phenomenon. When expressed in the appropriate dimensionless–orientationless groups, the rocking response becomes perfectly self-similar for slender blocks (within the small rotations range) and practically self-similar for non-slender blocks (larger rotations). Using this formulation, the nonlinear and non-smooth rocking response to pulse-type ground motion can be directly determined, and need only be scaled by the intensity and frequency of the excitation.

https://royalsocietypublishing.org/doi/pdf/10.1098/rspa.2012.0026

Revisiting the rocking block: closed-form solutions and similarity laws

In 1675, English scientist Robert Hooke discovered “the true... ...manner of arches for building,” which he summarized with a single phrase: “As hangs the flexible line, so but inverted will stand the rigid arch.” In the centuries that followed, Hooke’s simple idea has been used to understand and design numerous important works. Recent research at MIT on the interactive analysis of structural forces provides new graphical tools for the understanding of arch behavior, which are useful for relating the forces and geometry of masonry structures. The key mathematical principle is the use of graphical analysis to determine possible equilibrium states.

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As Hangs the Flexible Line: Equilibrium of Masonry Arches

SUMMARY Recent seismic events have caused damage or collapse of invaluable historical buildings, further proving 7 the vulnerability of unreinforced masonry (URM) structures to earthquakes. This study aims to understand failure of masonry arches—typical components of URM historic structures—subjected to horizontal ground 9 acceleration impulses. An analytical model is developed to describe the dynamic behaviour of the arch and is used to predict the combinations of impulse magnitudes and durations which lead to its collapse. The 11 model considers impact of the rigid blocks through several cycles of motion, illustrating that failure can occur at lower ground accelerations than previously believed. The resulting failure domains are of potential 13 use for design and assessment purposes. Predictions of the analytical model are compared with results of numerical modelling by the distinct element method, and the good agreement between results validates 15 the analytical model and at the same time confirms the potential of the distinct element framework as a method of evaluating complex URM structures under dynamic loading. Copyright q 2007 John Wiley & 17 Sons, Ltd.

Failure of masonry arches under impulse base motion

Numerous structures uplift under the influence of strong ground motion. Although many researchers have investigated the effects of base uplift on very stiff (ideally rigid) structures, the rocking response of flexible structures has received less attention. Related practical analysis methods treat these structures with simplified 'equivalent' oscillators without directly addressing the interaction between elasticity and rocking. This paper addresses the fundamental dynamics of flexible rocking structures. The nonlinear equations of motion, derived using a Lagrangian formulation for large rotations, are presented for an idealized structural model. Particular attention is devoted to the transition between successive phases; a physically consistent classical impact framework is utilized alongside an energy approach. The fundamental dynamic properties of the flexible rocking system are compared with those of similar linear elastic oscillators and rigid rocking structures, revealing the distinct characteristics of flexible rocking structures. In particular, parametric analysis is performed to quantify the effect of elasticity on uplift, overturning instability, and harmonic response, from which an uplifted resonance emerges. The contribution of stability and strength to the collapse of flexible rocking structures is discussed. © 2012 John Wiley & Sons, Ltd.

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Matthew J. DeJong

Papers

The nanogranular behavior of C-S-H at elevated temperatures (up to 700 °C)

Revisiting the rocking block: closed-form solutions and similarity laws

As Hangs the Flexible Line: Equilibrium of Masonry Arches

Failure of masonry arches under impulse base motion

The interaction of elasticity and rocking in flexible structures allowed to uplift