Rheological State Research Articles

Gravity flows: Types, definitions, origins, identification markers, and problems

Abstract This review covers 135 years of research on gravity flows since the first reporting of density plumes in the Lake Geneva, Switzerland, by Forel (1885). Six basic types of gravity flows have been identified in subaerial and suaqueous environments. They are: (1) hyperpycnal flows, (2) turbidity currents, (3) debris flows, (4) liquefied/fluidized flows, (5) grain flows, and (6) thermohaline contour currents. The first five types are flows in which the density is caused by sediment in the flow, whereas in the sixth type, the density is caused by variations in temperature and salinity. Although all six types originate initially as downslope gravity flows, only the first five types are truly downslope processes, whereas the sixth type eventually becomes an alongslope process. (1) Hyperpycnal flows are triggered by river floods in which density of incoming river water is greater than the basin water. These flows are confined to proximity of the shoreline. They transport mud, and they do not transport sand into the deep sea. There are no sedimentological criteria yet to identify hyperpycnites in the ancient sedimentary record. (2) A turbidity current is a sediment-gravity flow with Newtonian rheology and turbulent state in which sediment is supported by flow turbulence and from which deposition occurs through suspension settling. Typical turbidity currents can function as truly turbulent suspensions only when their sediment concentration by volume is below 9% or C < 9%. This requirement firmly excludes the existence of 'high-density turbidity currents'. Turbidites are recognized by their distinct normal grading in deep-water deposits. (3) A debris flow (C: 25-100%) is a sediment-gravity flow with plastic rheology and laminar state from which deposition occurs through freezing en masse. The terms debris flow and mass flow are used interchangeably. General characteristics of muddy and sandy debrites are floating clasts, planar clast fabric, inverse grading, etc. Most sandy deep-water deposits are sandy debrites and they comprise important petroleum reservoirs worldwide. (4) A liquefied/fluidized low (>25%) is a sediment-gravity flow in which sediment is supported by upward-moving intergranular fluid. They are commonly triggered by seismicity. Water-escape structures, dish and pillar structures, and SSDS are common. (5) A grain flow (C: 50-100%) is a sediment-gravity flow in which grains are supported by dispersive pressure caused by grain collision. These flows are common on the slip face of aeolian dunes. Massive sand and inverse grading are potential identification markers. (6) Thermohaline contour currents originate in the Antarctic region due to shelf freezing and the related increase in the density of cold saline (i.e., thermohaline) water. Although they begin their journey as downslope gravity flows, they eventually flow alongslope as contour currents. Hybridites are deposits that result from intersection of downslope gravity flows and alongslope contour currents. Hybridites mimic the "Bouma Sequence" with traction structures (Tb and Tc). Facies models of hyperpycnites, turbidites, and contourites are obsolete. Of the six types of density flows, hyperpycnal flows and their deposits are the least understood.

Correlating ultra‐toughening of bio‐based polyamide 410 with melt rheological and solid state relaxation dynamics by gelation rheology approach

AbstractThe sol–gel or viscous‐elastic transitions of the bio‐based polyamide 410/POE‐g‐MA (polyethylene‐co‐octene copolymer grafted with maleic anhydride) blends have been systematically discussed in the framework of melt rheology as assessed on a parallel plate rheometer set‐up in small amplitude oscillatory shear mode and solid state dynamic mechanical relaxation measurements. The viscous response dominated enhancement in elastic moduli of the blends that was characterized by the phase transitions across the composition range of 10–15 wt% of POE‐g‐MA. A direct correlation between the gel point (estimated from the cross‐over of frequency‐independent loss tangent curves) and the ultra‐toughness (maximized to an extent of ~15‐fold increase in notched Izod impact strength) could be established vis‐a‐vis its corroboration from the morphology of the impact‐failed surfaces. The extent of maleic anhydride (−MA) content induced phase interaction with polyamide 410 via the formation of a polyamide‐co‐(polyoctene‐co‐ethylene) type copolymer linkage in solid‐state and its subsequent impact on solid‐state damping was analyzed. The study establishes qualitative correlation between ultra‐toughening of polyamide 410 to that parameters based on relaxation dynamics measurements using melt rheology and solid‐state dynamic responses conforming to the principles of gelation rheology.

The quartz α↔β phase transition: Does it drive damage and reaction in continental crust?

The α↔β phase transition in quartz is accompanied by relatively large, anisotropic changes in cell volume and elastic stiffness properties. Because quartz is among the most abundant minerals in Earth's continental crust, these changes have the potential to profoundly influence the state of stress, mechanical properties, metamorphism, and rheology of crustal rocks. Laboratory experiments confirm strongly enhanced microcracking as rocks cross the transition. In addition, limited seismological studies suggest that the α↔β transition may cause extensive microcracking in the crust. However, the micromechanical basis for potential transition-induced damage has not been quantitatively explored. Here we use numerical methods to show that elastic stresses arising from the transition can greatly exceed the brittle tensile and shear strengths of common crustal rocks and minerals at various confining pressures. In particular, we show that contraction during the down-temperature β→α transition is far more effective than expansion during the up-temperature α→β transition at promoting possible brittle failure and/or recrystallization (damage). Our results suggest that the α↔β transition may play an important role in damaging the continental crust, particularly in rock volumes that experience geologically rapid changes in temperature or pressure. In these environments, the transition may weaken rocks, establish transient permeability, facilitate advective mass transport and metamorphic reactions, and potentially nucleate earthquakes.

From Caledonian Collapse to North Sea Rift: The Extended History of a Metamorphic Core Complex

AbstractExtensional systems evolve through different stages due to changes in the rheological state of the lithosphere. It is crucial to distinguish ductile structures formed before and during rifting, as both cases have important but contrasting bearings on the structural evolution. To address this issue, we present the illustrative ductile‐to‐brittle structural history of a metamorphic core complex (MCC) onshore and offshore western Norway. Combining geological field mapping with newly acquired 3‐D seismic reflection data, we correlate two distinct onshore basement units (BU1 and BU2) to corresponding offshore basement seismic facies (SF1 and SF2). Our interpretation reveals two 40 km wide domes (one onshore and one offshore), which both show characteristic kilometer‐scale, westward plunging upright folds. The gneiss domes fill antiformal culminations in the footwall of a >100 km long, shallowly west dipping, extensional detachment. Overlying Caledonian nappes and Devonian supradetachment basins occupy saddles of the hyperbolic detachment surface. Devonian collapse of the Caledonian orogen formed dome and detachment geometries. During North Sea rifting, brittle reactivation of the MCC resulted in complex fault patterns deviating from N‐S strike dominant at the eastern margin of the rift. Around 61°N, only minor N‐S faults (<100 m throw) cut through the core of the MCC. Major rift faults (≤5 km throw), on the other hand, reactivated the detachment and follow the steep flanks of the MCC. This highlights that inherited ductile structures can locally alter the orientation of brittle faults formed during rifting.

Thermal maturation of a complete magmatic plumbing system at the Sierra de Velasco, Northwestern Argentina

AbstractThe formation of magmatic plumbing systems in the crust involves mass and heat transfer from deep to shallow levels. This process modifies the local geotherm and increases the thermal maturation of the crust, affecting the rheological state of the host rock and the composition of magma. Here, we report a petrological, geochemical, isotopic and geochronological integrated study of the Huaco (354 Ma) and Sanagasta (353 Ma, from a new U–Pb zircon age) units from the Carboniferous (Lower Mississippian) Huaco Intrusive Complex, NW Argentina. Similar values of ϵNdt and δ18O, of −3.2 ± 0.7 and +11.2‰ ± 0.3‰ (V-SMOW), respectively, for both units indicate that they shared the same source, as a result of mixing and later homogenization of a crustal component at the Late Devonian (378 to 366 Ma), with metasomatized mantle-derived melts. Slightly higher contents of TiO2, FeO, MgO, CaO and rare earth elements for the Sanagasta unit in comparison with the Huaco unit suggest an increase in the degree of partial melting, which may have been caused by a higher temperature at the lower crust. In addition, the previous structural model of the Huaco Intrusive Complex points to an increase in thermal maturation in the upper crust, which drives a change in the emplacement style from tabular subhorizontal (Huaco) to vertically elongated (Sanagasta) bodies. Therefore, the evolution of the intrusive complex may reflect a generalized thermal maturation of the complete magmatic column, at both upper and lower crustal levels.

Influence of water to binder ratio on the rheology and structural Build-up of Alkali-Activated Slag/Fly ash mixtures

In this study, the effects of water to binder (w/b) ratio on the rheological and fresh state properties of alkali-activated cement (AAC) pastes have been investigated. A mixture of 50% type F fly ash (FA) and 50% ground granulated blast furnace slag (GGBFS) was activated by a mixture of sodium hydroxide and sodium silicate, in three different w/b ratios of 0.32, 0.37 and 0.42. Setting time, ultrasonic pulse velocity (UPV), heat evolution by isothermal calorimetry, flow spread by mini-slump test, rheological properties by means of flow curve and viscoelastic properties such as storage modulus (G') and loss factor (G'') were determined on the paste mixtures. The results showed that the higher w/b ratio led to structural build-up with higher rate compared to lower w/b ratios. GGBFS provided the main contribution to the increase of storage modulus in the early stage of hybrid mixture of GGBFS and FA. The dynamic yield stress, plastic viscosity and thixotropic index values decrease with an increase in w/b ratio of AAC mixture. The setting times of AAC mixtures were found to be less dependent on the w/b ratio as compared to ordinary Portland cement mixtures.

Mud-clast armoring and its implications for turbidite systems

ABSTRACT Seafloor sediment density flows are the primary mechanism for transporting sediment to the deep sea. These flows are important because they pose a hazard to seafloor infrastructure and deposit the largest sediment accumulations on Earth. The cohesive sediment content of a flow (i.e., clay) is an important control on its rheological state (e.g., turbulent or laminar); however, how clay becomes incorporated into a flow is poorly understood. One mechanism is by the abrasion of (clay-rich) mud clasts. Such clasts are common in deep-water deposits, often thought to have traveled over large (more than tens of kilometers) distances. These long travel distances are at odds with previous experimental work that suggests that mud clasts should disintegrate rapidly through abrasion. To address this apparent contradiction, we conduct laboratory experiments using a counter rotating annular flume to simulate clast transport in sediment density flows. We find that as clay clasts roll along a sandy floor, surficial armoring develops and reduces clast abrasion and thus enhances travel distance. For the first time we show armoring to be a process of renewal and replenishment, rather than forming a permanent layer. As armoring reduces the rate of clast abrasion, it delays the release of clay into the parent flow, which can therefore delay flow transformation from turbidity current to debris flow. We conclude that armored mud clasts can form only within a sandy turbidity current; hence where armored clasts are found in debrite deposits, the parent flow must have undergone flow transformation farther up slope.

Elasticity and plasticity of highly concentrated noncolloidal suspensions under shear

The rheological properties (viscosity, plasticity, viscoelasticity, and elasticity) of noncolloidal suspensions with varying concentrations of a solid phase (Al powder) in oligomeric polyethylene glycol have been studied in the shear mode of deformation. All typical types of rheological behavior have been observed. In the concentration range up to approximately 30%, suspensions are Newtonian liquids, while at a certain concentration, non-Newtonian and viscoelastic effects appear. With further increases in concentration, the flow curves become a power-law type, though the yield stress can be found only for suspensions with a high solid phase content. The elasticity of the suspensions can be detected at concentrations in the order of 55%. In a narrow range of concentrations, the rheological state of the suspensions can be treated as viscoplastic, wherein they preserve fluidity and become elastic. This concentration threshold, determined by the change in various rheological characteristics including the loss tangent, corresponds to the gelation or “colloid” glass transition. The most detailed experiments were devoted to the concentration range of 60–70 vol. %, which are treated as highly concentrated suspensions (HCSs). A concentration of 70% is the upper limit, because mixtures with higher concentrations do not keep their continuity and crumble. The rheological state of HCSs corresponds to the elastoplastic type of behavior. The separation of the total deformation into plastic and elastic components showed that plastic deformations (but not the flow) in the shearing of HCSs are small. Repeated shearing in the loading-unloading mode has been performed. In this case, a decrease in the elastic deformation and a remarkable growth of the shear elastic modulus was observed. This effect is presumably explained by the orientation of the particles and shear-induced anisotropy. A stress-concentration diagram of the physical states of suspensions has been proposed. The concentration range somewhat below that of the HCS state is of special interest for the powder injection molding technology, which is limited by the domain of plasticity.

Structure Evolution of Epoxidized Natural Rubber (ENR) in the Melt State by Time-Resolved Mechanical Spectroscopy.

In this work, time-resolved mechanical spectroscopy (TRMS) was used to accurately characterize the rheological behavior of an epoxidized natural rubber (ENR) containing 25 mol% of epoxy groups. Conventional rheological tests are not suitable to characterize with accuracy the frequency-dependent linear viscoelastic behavior of materials, such as ENR, in a transient configurational state. For this reason, TRMS was used to determine the true rheological behavior of ENR, as well as to gain some insights into the changes of its macromolecular architecture under the dynamic conditions experienced during the measurements. The constructed master curves for the moduli revealed a gradual transition of the ENR rheological state from liquid-like to solid-like through the formation of an “elastic gel” throughout the bulk of the polymer. Furthermore, the evolution of the stress relaxation modulus revealed a slow relaxation mechanism, resulting from thermally activated reactions in the molten state attributed to the formation of crosslinks. Finally, the crosslink density evolution was estimated from the TRMS data and compared with results derived from equilibrium solvent-swelling measurements. These demonstrated the accuracy of the TRMS data in the prediction of the structural changes that can take place in polymers during processing.

Базові моделі кінетики деформування-руйнування деревних композиційних матеріалів

Існуючі наразі моделі кінетики деформування і руйнування пов'язані здебільшого з описом переходу з незруйнованого стану матеріалу в зруйнований в одну стадію. Це належить як до класичних теорій міцності, зокрема і кінетичної теорії міцності, так і до теорій і моделей розсіяного накопичення пошкоджень (Continuum Damage Mechanics, CDM). Метою цього дослідження було створення базових моделей кінетики деформування-руйнування (ДР), які описують цей процес у вигляді декількох послідовних переходів окремих структурних елементів (СЕ), у матеріалі, що деформується в часі з одного реологічного стану в інший. Для опису цього процесу залучено апарат формальної кінетики, який дає змогу, знаючи швидкість переходу СЕ з одного реологічного стану в інший, спрогнозувати час досягнення критичної концентрації зруйнованих СЕ. Встановлено, що процес ДР можна розглядати як процес поступового переходу СЕ спочатку пружного стану у в'язкопружний і потім зруйнований. Причому цей перехід може відбуватися як послідовно, так і паралельно. Таким чином, у процесі руйнування постійно змінюється число, а отже, і концентрація СЕ, які перебувають у різних реологічних станах. Зміну концентрації того чи іншого СЕ можна визначити експериментально способом вимірювання величин, що корелюють з параметрами ДР того чи іншого виду деформації тіла. При цьому загальне число елементів структури, що перебувають у різних станах, згідно із законом збереження мас у кожен момент часу ДР має залишатися постійним. Вперше запропоновано двостадійну нелінійну кінетичну модель втрати ресурсу за повзучості композиційних матеріалів на підставі деревини. Застосування методів формальної кінетики під час моделювання фізико-хімічних процесів, які відбуваються під час ДР, дає змогу будувати багатостадійні кінетичні моделі. Застосування методу базових діаграм деформування у поєднанні з двостадійним описом процесу накопичення пошкоджень дає змогу збільшити точність прогнозу допустимого часу за різних схем навантаження під час повзучості.

Hydrothermal circulation cools continental crust under exhumation

The formation of continental crust in magmatic arcs involves cooling of hot magmas to a relatively colder crust enhanced by exhumation and hydrothermal circulation in the upper crust. To quantify the influence of these processes on the thermal and rheological states of the crust, we developed a one-dimensional thermal evolution model, which invokes conductive cooling, advection of crust by erosion-driven exhumation, and cooling by hydrothermal circulation. We parameterized hydrothermal cooling by adopting depth-dependent effective thermal conductivity, which is determined by the crustal permeability structure and the prescribed Nusselt number at the surface. Different combinations of erosion rate and Nusselt number were tested to study the evolution of crustal geotherms, surface heat flux, and cooling rate. Simulations and scaling analyses quantify how erosion and hydrothermal circulation promote cooling via increasing total surface heat flux compared to pure conductive cooling. Hydrothermal circulation imposes intense short-term and persistent long-term cooling effects. Thinner, warmer, fast exhuming crust, with higher permeability and more vigorous hydrothermal circulation, leads to higher steady-state total surface heat flux. Hydrothermal cooling at steady state is more effective when the Péclet number is small. Hydrothermal cooling also changes crustal rheological state and thickens the brittle crust. This in turn promotes the initiation of brittle deformation in the upper crust in magmatic arcs or in regions undergoing exhumation. Interpretation of low-temperature thermochronological data could overestimate average cooling rates if hydrothermal cooling is not considered.

Selection and substantiation of cultivator adjustment parameters for differential soil treatment on potato based on the rheology state of soil horizons

The article presents results of theoretical studies on the determination rational parameters of placement tines on the frame interrow cultivator for differential tillage of potato field. Differential tillage means depth adjustments of tines according soil condition and their placement on the cultivator frame. The main goals of differential tillage by inter row cultivators are the elimination of soil compaction between ridges, formed by potato planters, as well as loosening of the zone of location of the potato tubers. Deep loosening after planting provides good conditions for the complete assimilation of water by soil after rain or irrigation, protects the top soil layer from erosion and also eliminates the over moistening in the autumn. Loosening the soil in the zone of the tuber placement ensures the obtaining of a fine-grained soil structure, which helps to create best conditions for the growth of plants and development their root system, as well as to ensure favorable conditions for soil separation during harvesting. The substantiation of rational parameters for tine placement on the frame of row cultivator was carried out on the base of the regularities of soil rheology, the heterogeneity of soil composition in different layers of arable and subsoil horizons, as well as the variability of their physic-mechanical properties. These regularities influence the development of deformation and cracked zones during the interaction ripper tines with the soil. As a result of the theoretical studies was developed a method for calculating the rational placement of ripper tines on the frame of the row cultivator for fulfil differential tillage on the potato based on the rheological state and heterogeneous structure of the soil horizons. Using of this method allow ensure high quality structure of tilled soil.

Magnetic resonance elastography in nonlinear viscoelastic materials under load

Characterisation of soft tissue mechanical properties is a topic of increasing interest in translational and clinical research. Magnetic resonance elastography (MRE) has been used in this context to assess the mechanical properties of tissues in vivo noninvasively. Typically, these analyses rely on linear viscoelastic wave equations to assess material properties from measured wave dynamics. However, deformations that occur in some tissues (e.g. liver during respiration, heart during the cardiac cycle, or external compression during a breast exam) can yield loading bias, complicating the interpretation of tissue stiffness from MRE measurements. In this paper, it is shown how combined knowledge of a material’s rheology and loading state can be used to eliminate loading bias and enable interpretation of intrinsic (unloaded) stiffness properties. Equations are derived utilising perturbation theory and Cauchy’s equations of motion to demonstrate the impact of loading state on periodic steady-state wave behaviour in nonlinear viscoelastic materials. These equations demonstrate how loading bias yields apparent material stiffening, softening and anisotropy. MRE sensitivity to deformation is demonstrated in an experimental phantom, showing a loading bias of up to twofold. From an unbiased stiffness of 4910.4 pm 635.8 Pa in unloaded state, the biased stiffness increases to 9767.5 pm ,1949.9 Pa under a load of approx 34% uniaxial compression. Integrating knowledge of phantom loading and rheology into a novel MRE reconstruction, it is shown that it is possible to characterise intrinsic material characteristics, eliminating the loading bias from MRE data. The framework introduced and demonstrated in phantoms illustrates a pathway that can be translated and applied to MRE in complex deforming tissues. This would contribute to a better assessment of material properties in soft tissues employing elastography.

Noninvasive in vivo characterization of erythrocyte motion in human retinal capillaries using high-speed adaptive optics near-confocal imaging.

The flow of erythrocytes in parafoveal capillaries was imaged in the living human eye with an adaptive optics near-confocal ophthalmoscope at a frame rate of 800 Hz with a low coherence near-infrared (NIR) light source. Spatiotemporal traces of the erythrocyte movement were extracted from consecutive images. Erythrocyte velocity was measured using custom software based on the Radon transform. The impact of imaging speed on velocity measurement was estimated using images of frame rates of 200, 400, and 800 Hz. The NIR light allowed for long imaging periods without visually stimulating the retina and disturbing the natural rheological state. High speed near-confocal imaging enabled direct and accurate measurement of erythrocyte velocity, and revealed a distinctively cardiac-dependent pulsatile velocity waveform of the erythrocyte flow in retinal capillaries, disclosed the impact of the leukocytes on erythrocyte motion, and provided new metrics for precise assessment of erythrocyte movement. The approach may facilitate new investigations on the pathophysiology of retinal microcirculation with applications for ocular and systemic diseases.

CO2-induced destabilization of pyrite-structured FeO2Hx in the lower mantle

Abstract Volatiles, such as carbon and water, modulate the Earth's mantle rheology, partial melting and redox state, thereby playing a crucial role in the Earth's internal dynamics. We experimentally show the transformation of goethite FeOOH in the presence of CO2 into a tetrahedral carbonate phase, Fe4C3O12, at conditions above 107 GPa—2300 K. At temperatures below 2300 K, no interactions are evidenced between goethite and CO2, and instead a pyrite-structured FeO2Hx is formed as recently reported by Hu et al. (2016; 2017) and Nishi et al. (2017). The interpretation is that, above a critical temperature, FeO2Hx reacts with CO2 and H2, yielding Fe4C3O12 and H2O. Our findings provide strong support for the stability of carbon-oxygen-bearing phases at lower-mantle conditions. In both subducting slabs and lower-mantle lithologies, the tetrahedral carbonate Fe4C3O12 would replace the pyrite-structured FeO2Hx through carbonation of these phases. This reaction provides a new mechanism for hydrogen release as H2O within the deep lower mantle. Our study shows that the deep carbon and hydrogen cycles may be more complex than previously thought, as they strongly depend on the control exerted by local mineralogical and chemical environments on the CO2 and H2 thermodynamic activities.

The impact of crustal rheology on natural seismicity: Campi Flegrei caldera case study

We analyze the crustal rheology beneath the active resurgent Campi Flegrei caldera (CFc) in Southern Italy by modelling the 3D brittle-ductile (B/D) transition, based on available thermal, geological and geophysical data. Firstly, the thermal field in the conductive physical regime is modeled using a finite element method; based on an optimization tool, this method is applied to evaluate the location and dimensions of the deep thermal source beneath the caldera. A horizontally-extended thermal anomaly located at about 5000 m depth below sea level is identified beneath Pozzuoli Bay, a part of the CFc. The same isotherm is located at a depth of 20,000 m beyond the caldera. This indicates a higher horizontal temperature gradient in the caldera with respect to the surrounding area. Next, we utilize this thermal model to image the 3D rheological stratification of the shallow crust below the caldera with two different values of strain rates. Within the caldera, the B/D transitions with ɛ equal to 10−12 s−1 and 10−8 s−1 are located at 3000 m and 5000 m depths, respectively. Outside the caldera, the transition is very deep (15,000–20,000 m), seemingly uninfluenced by the thermal state of the CFc volcanism. Finally, we compare these results with the spatial distribution of earthquake hypocenters, Benioff strain release and b-value distribution to investigate the relationship between crustal rheology and seismicity characteristics. Our analysis reveals that the image of the B/D transition is in agreement with the distribution of earthquake hypocenters, constraining the potential seismogenic volume of the region. Our study demonstrates that knowledge of the rheological state of a volcanic system is an important element to interpret its dynamic, forecast future activity and improve evaluation of the associated seismic hazard.

Interpolation Environment of Tensor Mathematics at the Corpuscular Stage of Computational Experiments in Hydromechanics

Stages of direct computational experiments in hydromechanics based on tensor mathematics tools are represented by conditionally independent mathematical models for calculations separation in accordance with physical processes. Continual stage of numerical modeling is constructed on a small time interval in a stationary grid space. Here coordination of continuity conditions and energy conservation is carried out. Then, at the subsequent corpuscular stage of the computational experiment, kinematic parameters of mass centers and surface stresses at the boundaries of the grid cells are used in modeling of free unsteady motions of volume cells that are considered as independent particles. These particles can be subject to vortex and discontinuous interactions, when restructuring of free boundaries and internal rheological states has place. Transition from one stage to another is provided by interpolation operations of tensor mathematics. Such interpolation environment formalizes the use of physical laws for mechanics of continuous media modeling, provides control of rheological state and conditions for existence of discontinuous solutions: rigid and free boundaries, vortex layers, their turbulent or empirical generalizations.

Intrinsic modification of repair mortars made with EVA and CaO, impacts at the earlier ages

Many studies have been realised on polymer-modified mortars (PMMs). Among the polymers used, ethylene vinyl acetate (EVA) has revealed evident interaction between calcium ions and its acetate groups. Most of the studies have shown a positive impact of EVA on mortar performance, which is enhanced by the combination of the EVA with calcium oxide CaO. However, there is still a lack of understanding of the nature of these interactions and no clear link has been established between these interactions and the properties of the cementitious materials at early ages. This article aims to tackle this topic by focusing on the evolution of EVA particles in a pore solution and the properties of a cement modified with EVA and CaO, especially the rheological behaviour. As results, it is observed that the zeta potential of the pore solution decreases when EVA is added. Furthermore, the hydrodynamic radius of this polymer tends to increase over time in the pore solution. On the other hand, the EVA tends to delay the setting time while the CaO accelerates it. For the rheological state, EVA tends to govern the plastic viscosity of the cement paste while CaO governs the yield stress and these parameters are not affected by the mixing time during the first 100 min. Their combination enhances these rheological parameters.

Rheological State Diagrams for Rough Colloids in Shear Flow

To assess the role of particle roughness in the rheological phenomena of concentrated colloidal suspensions, we develop model colloids with varying surface roughness length scales up to 10% of the particle radius. Increasing surface roughness shifts the onset of both shear thickening and dilatancy towards lower volume fractions and critical stresses. Experimental data are supported by computer simulations of spherical colloids with adjustable friction coefficients, demonstrating that a reduction in the onset stress of thickening and a sign change in the first normal stresses occur when friction competes with lubrication. In the quasi-Newtonian flow regime, roughness increases the effective packing fraction of colloids. As the shear stress increases and suspensions of rough colloids approach jamming, the first normal stresses switch signs and the critical force required to generate contacts is drastically reduced. This is likely a signature of the lubrication films giving way to roughness-induced tangential interactions that bring about load-bearing contacts in the compression axis of flow.

The role of lateral strength contrasts in orogenesis: A 2D numerical study

In this paper we present a series of thermo-mechanical experiments on continent-continent collision zones to investigate the role of lateral strength contrasts in terms of collision dynamics and orogen geometries. Our results show that differences in crustal rheology, may lead to a variety of different patterns of deformation and crustal geometries. Upper plate indentation forms a sequence of foreland propagating thrust units made of brittle upper crust on the lower plate. The strong deformation of the lower plate stands in stark contrast to the undeformed upper plate. In contrast, subduction of strong lithosphere beneath a weak upper plate forms a complex pattern of deformation. Deformation initiates on the lower plate and forms an antiformal stack made of brittle upper crust, before it indents the upper plate. Hence, deformation is present on both, the lower and upper plate, despite differences in initial strength. The outcome of this study has direct implications to natural collision zones, where differences in strength between the upper and lower plate exist. For example, along strike variability of upper vs. lower plate shortening in the Alps are likely to be controlled by contrasts in crustal strength. Furthermore, we suggest that the antiformal stack in the axial zone of the Pyrenees might indicate a strong lower plate at the onset of collision. Our results may therefore provide important constraints for the rheological state of continents during collision.