Designing and transforming yield-stress fluids

We review progress in designing and transforming multi-functional yield-stress fluids and give a perspective on the current state of knowledge that supports each step in the design process. We focus mainly on the rheological properties that make yield-stress fluids so useful and the trade-offs which need to be considered when working with these materials. Thinking in terms of “design with” and “design of” yield-stress fluids motivates how we can organize our scientific understanding of this field. “Design with” involves identification of rheological property requirements independent of the chemical formulation, e.g. for 3D direct-write printing which needs to accommodate a wide range of chemistry and material structures. “Design of” includes microstructural considerations: conceptual models relating formulation to properties, quantitative models of formulation-structure-property relations, and chemical transformation strategies for converting effective yield-stress fluids to be more useful solid engineering materials. Future research directions are suggested at the intersection of chemistry, soft-matter physics, and material science in the context of our desire to design useful rheologically-complex functional materials.     

Evaluation of the consistency of fiber reinforced cementitious composites

The rheological properties of fresh concrete, mortar or cement paste are among the most important parameters when cementitious building materials are placed. New material designs, like high or ultrahigh performance concretes, include the addition of a high volume of fibers to the fresh mix influencing its workability properties. However, the analysis of the rheological properties of fiber reinforced cementitious composites is difficult. Conventional methods mostly do not apply, especially when a high fiber content and relatively stiff mixtures are used. For this reason, a new method was developed to evaluate the workability of fiber reinforced composites. This method was applied to carbon and PVA fiber reinforced high performance composites and was used to optimize the rheological properties of these composites for an application in a centrifugation casting process.     

Experimental study of the flow behaviour of superplasticized cement paste

The properties of high performance concrete, mainly in the fresh state are governed by the flow behaviour of the paste phase, which is controlled by the dispersion of cement particles by the superplasticizer. In this paper, experimental procedures for evaluating the flow behaviour of cement paste with different types and dosages of superplasticizers are studied. The rheological nature of the paste is represented through the Bingham and Herschel-Bulkley models. It is observed that the Marsh cone flow time, mini-slump spread and the rheological parameters show the same trend with change in dosage of superplasticizer. Also, the rheological parameters increase with time and rate of increase is more significant at dosages less than the saturation dosage, as determined from the Marsh cone test. It is confirmed that the Marsh cone flow time can be predicted using an appropriate model.     

Constitutive rheological control to develop a self-consolidating engineered cementitious composite reinforced with hydrophilic poly(vinyl alcohol) fibers

A self-consolidating engineered cementitious composite (ECC), which exhibits tensile strain-hardening behavior in the hardened state, while maintaining self-consolidating properties in the fresh state, has been developed by employing hydrophilic poly(vinyl alcohol) (PVA) fibers. The constitutive rheological design approach is adopted to separately control the aggregation between cement particles and sedimentation behavior with a combination of a strong polyelectrolyte and non-ionic polymer. This study suggests an effective formulation approach of fresh cementitious mix to maximize its fluidity without segregation, regardless of solids concentration employed. The resulting self-consolidating PVA-ECC exhibits tensile strain up to 5%. Besides, the methodology of constitutive rheological control can be extended to formulating other self-consolidating cementitious materials with various types of polymeric admixtures.     

Plastic viscosity of fresh concrete – A critical review of predictions methods

Rheological properties of fresh concrete, namely plastic viscosity and yield stress, are critical for the concrete industry because they affect placement and workability. Moreover, these rheological properties influence the productivity and quality of concrete, including mechanical properties and durability. Therefore proper characterization of these properties is needed to control the quality of fresh concrete and ensure sustainability of concrete structures.Fundamental and phenomenological rheological models have been proposed in the literature for characterizing the behaviour of fresh concrete. Establishing a model for predicting the plastic viscosity of concrete based on its composition will be extremely valuable for the concrete industry. This paper provides a critical review of the most prevailing models in concrete technology as well as models proposed in the literature for predicting the plastic viscosity of dense suspensions to a total of eight models. Review has revealed that Mahmoodzadeh and Chidiac models based on the cell method provides a higher degree of correlation to the experimental data as well as a more consistent and reliable predictions in comparison to the models currently proposed in the literature for concrete and/or dense suspensions.     

Particle Size Distribution of Limestone Fillers: Granulometry and Specific Surface Area Investigations

Mineral fillers can be defined as “inert materials included in a mix design for some useful purpose” (NF P18-508 Janvier 2012). They can be added to compounds in order to complete a large variety of final properties without increasing costs or to improve specific characteristics like hardness, brittleness, impact strength, compressive strength, softening point, fire resistance, surface texture, electrical conductivity, and so on. In Belgium, locally available limestone fillers are specifically very well adapted for the optimization of particle packing and flow behavior of cementitious pastes in concrete mixes. Limestone fillers may be easily characterized in terms of chemical and mineralogical properties. These properties are fundamental for the study of the behavior of concrete mixes in fresh state and for understanding interactions existing at the level of the interfacial transition zone between aggregates and cement paste. These properties are however insufficiently discriminant and particle size, as well as shape distribution, seem to have a potential influence on physical phenomena which happen during the setting process. The aim of this article is to compare five major techniques used to quantify the size and the shape of limestone fillers particles: laser diffraction scattering, wet sieving, and image analysis for particle size measurement; and BET adsorption and Blaine permeability methods for specific surface area.     

Simulation of fresh concrete flow using Discrete Element Method (DEM): theory and applications

This article provides an overview of the development and the contemporary state of research in the field of simulating fresh concrete flow using the Discrete Element Method (DEM). First, this work originating from TC 222-SCF simulation of fresh concrete flow, covers the mathematical methodology, the identification of the model parameters and the link between the rheological properties of fresh concrete and the parameters of DEM-based models. Various examples of the estimation of model parameters and calibration of the model were demonstrated, followed by verifications by comparing the numerical results and the corresponding predictions by analytical formula and laboratory experiments. Furthermore, software used in concrete engineering and existing industrial applications of the developed particle models were described, showing the potential of DEM.     

Simulation of coupling filtration and flow in a dual scale fibrous media

In this article, numerical simulation of suspension (particles filled-resin) flow through a fibrous media taking into account dual scale porosity in LCM (Liquid Composite Molding) processes is presented. During the flow, a strong interaction between the particle motion and the fluid flow takes place at the porous media wall (the fiber bundle surface). In this study, the Stokes–Darcy coupling is used to describe the resin flow at mesoscopic scale to treat the particles in suspension. A “fluid” model to describe the suspension flow, a “filtration” model to describe the particle capture and a “solid” model dedicated to the modeling of mass particles dynamics was used. The “solid” model is also operated to identify the particles retention.For validation, the numerical results of proposed model were compared with the experimental results from the literature and found in good agreement. Then, other numerical results studying the suspension’s rheological behavior are presented.     

自密实混凝土稳定性机理及其影响因素研究新进展

自密实混凝土浇筑成型后发生离析会对力学性能和耐久性能产生不同程度的危害,这一问题决定了自密实混凝土在满足施工性能的同时必须具有足够的稳定性。而自密实混凝土高流动性、高填充性及高间隙通过性等优异的工作性能特征,又决定了其拌合物的稳定性高度敏感。从静态稳定性和动态稳定性两方面分别阐述了自密实混凝土的稳定性机理,探讨了自密实混凝土静态稳定性和动态稳定性的表征方法,从配合比参数、拌合物流变性能、施工工艺等方面讨论了影响自密实混凝土稳定性的因素,提出了自密实混凝土稳定性的研究前景。     

Flow behaviour of high strength high-performance concrete

The workability of flowable High-Performance Concrete (HPC) is nowadays mainly measured using conventional test methods such as the slump test or the slump-flow test. These single-point tests do not seem sensitive enough to characterize the high-workability of HPC. Due to the fluid consistency and uniformity of fresh HPC, it is possible to describe its flow properties by using a rheological test method. To evaluate the flowability based on rheology, fresh HPC is regarded as a two-phase material composed of a matrix phase and a particle phase. In the study, the effects of materials and proportioning on the rheological properties were investigated experimentally. A new rheometer was established by conducting a two-point test to investigate the flow behaviour of high strength HPC. Test results show that the high strength HPC with good uniformity and without tendency of segregation can possess the properties of rheology according to Bingham’s equation. An increase of the fraction of mortar in HPC can lead to a more distinct the rheological behaviour. Moreover, it is found that the application of a rheological method can provide more stable results than any other test method in describing the flowability of high strength HPC.     

Mix design and fresh properties for high-performance printing concrete

This paper presents the experimental results concerning the mix design and fresh properties of a high-performance fibre-reinforced fine-aggregate concrete for printing concrete. This concrete has been designed to be extruded through a nozzle to build layer-by-layer structural components. The printing process is a novel digitally controlled additive manufacturing method which can build architectural and structural components without formwork, unlike conventional concrete construction methods. The most critical fresh properties are shown to be extrudability and buildability, which have mutual relationships with workability and open time. These properties are significantly influenced by the mix proportions and the presence of superplasticiser, retarder, accelerator and polypropylene fibres. An optimum mix is identified and validated by the full-scale manufacture of a bench component.     

From virgin to recycled bitumen: A microstructural view

In the present work, soft and hard bitumens recovered from unaged, aged and recycled asphalt concrete (AC) mixtures, which in laboratory tests performed mechanically as well as an AC mixture produced with virgin materials, were investigated regarding rheological, thermal and surface microstructural aspects. For comparison purposes, bitumen containing 50 wt% of virgin bitumen and 50 wt% of bitumen recovered from reclaimed asphalt pavement (RAP) was studied. Some properties of the bitumens remained unchanged throughout the preparation of the AC mixture, aging and recycling: Soft and hard bitumens retained their general rheological properties significantly, and their thermal and surface microstructural properties partially. Soft bitumens presented larger “bee” structures and, therefore, higher surface roughness, while hard bitumens presented smaller “bee” structures and, thus, lower surface roughness. Furthermore, soft bitumens seemed to contain higher crystalline-like content than hard bitumens. For the soft cases, the unaged recovered bitumen did not show the same characteristics (rheological and surface microstructure) as the virgin bitumen. Similarly the recovered recycled bitumen did not show the same characteristics (surface microstructure) as the bitumen prepared from the mixture of virgin bitumen and RAP bitumen. Aging of the AC mixture changed the rheological properties of the soft bitumen by increasing the complex modulus and decreasing the phase angle. Similarly, recycling changed the rheological properties by increasing the complex modulus and decreasing the phase angle. Compositional changes occurred during AC mixture preparation (possibly also aging and recycling) for both soft and hard bitumens. Consequently, more “phases” were observed on the surface microstructure for the recovered bitumens as compared with the virgin bitumens. However, no significant trend was found for the surface microstructure characteristics between the unaged, aged and recycled recovered bitumens. Moreover, the nature of the virgin bitumen influenced the properties of the recycled recovered bitumen, e.g. the glass transition temperature.     

Rheology of semi-solid fresh cement pastes and mortars in orifice extrusion

Short fiber-reinforced semi-solid fresh cement pastes and mortars, tailored for extrusion, have much lower water-to-binder ratio and higher viscosity than normal cement pastes or mortars. The rheology of these pastes or mortars cannot be characterized by traditional rheology test methods suitable for normal fresh cement pastes or mortars with much greater water-to-binder ratio and lower viscosity. In this paper, orifice extrusion is employed to calibrate rheology of the semi-solid fresh cement mortar. An analytical model is developed for orifice extrusion of semi-solid pastes and mortars obeying a rigid-viscoplastic constitutive relationship, von-Mises yield criterion and the associated flow rule. Orifice extrusion results are interpreted using the analytical model and the established experiment data interpretation method, and the associated rheological parameters are derived for the semi-solid fresh cement mortar. This study provides a simple analytical model, together with experiment and data interpretation methods, for characterizing the complex intrinsic rheological behavior of semi-solid fresh cement pastes or mortars.     

Rheology, fiber dispersion, and robust properties of Engineered Cementitious Composites

The capability of processing robust Engineered Cementitious Composites (ECC) materials with consistent mechanical properties is crucial for gaining acceptance of this new construction material in various structural applications. ECC’s tensile strain-hardening behavior and magnitude of tensile strain capacity are closely associated with fiber dispersion uniformity, which determines the fiber bridging strength, complementary energy, critical flaw size and degree of multiple-crack saturation. This study investigates the correlation between the rheological parameters of ECC mortar before adding PVA fibers, dispersion of PVA fibers, and ECC composite tensile properties. The correlation between Marsh cone flow rate and plastic viscosity was established for ECC mortar, justifying the use of the Marsh cone as a simple rheology measurement and control method before fibers are added. An optimal range of Marsh cone flow rate was found that led to improved fiber dispersion uniformity and more consistent tensile strain capacity in the composite. When coupled with the micromechanics based ingredient-tailoring methodology, this rheological control approach serves as an effective ECC fresh property design guide for achieving robust ECC composite hardening properties.     

Applicability of approximate models in calculating the boundary region in dust-laden flows

The limits of application of “single-particle” and “quasihomogeneous liquid” models are established on the basis of analysis of Couette flow for a dustladen gas.     

Utility of statistical models in proportioning self-consolidating concrete

In addition to sound material selection, the mix design of self-consolidating concrete requires careful tailoring of mixture constituents to secure a proper balance between contradictory properties necessary for the successful production of such a complex material. Mixture optimization of self-consolidating concrete often requires several trial batches to secure the required characteristics. This paper reviews statistical models developed using a factorial design approach to understand the effect of mixture parameters on key responses, including slump flow, rheological parameters, filling capacity, V-funnel flow time, surface settlement, and compressive strength. The models are valid for mixtures with 0.37 to 0.50 W/CM, 360 to 600 kg/m³ of binder, 240 to 400 l/m³ of coarse aggregate, 0.05 to 0.20% of viscosity-enhancing agent, by mass of water, and 0.3 to 1.1% of high-range water reducer, by mass of binder. Although the predicted response changes with the deviation from material characteristics used in establishing the models, the models remain quite useful in determing the significance of mixture parameters and their interactions on self-consolidating concrete properties. This paper demonstrates the usefulness of the models in establishing trade-offs among mixture parameters necessary for mixture optimization and compares the effect of changes in such parameters on key self consolidating concrete responses. The utility of the models to establish correlation between different workability characteristics useful for quality control is also highlighted.     

Effect of internal curing by using superabsorbent polymers (SAP) on autogenous shrinkage and other properties of a high-performance fine-grained concrete: results of a RILEM round-robin test

The article presents the results of a round-robin test performed by 13 international research groups (representing fifteen institutions) in the framework of the activities of the RILEM Technical Committee 225-SAP “Applications of Superabsorbent Polymers in Concrete Construction”. Two commercially available SAP materials were used for internal curing of a high-performance, fine-grained concrete in combination with the addition of extra water. The concrete had the same mix composition in all laboratories involved but was composed of local materials. All found a considerable decrease in autogenous shrinkage attributable to internal curing. Also, with regard to the shrinkage-mitigating effect of both particular SAP materials, the results were consistent. This demonstrates that internal curing using SAP is a robust approach, working independently of some variations in the concretes’ raw materials, production process, or measuring technique. Furthermore, the effects of internal curing on other properties of concrete in its fresh and hardened states were investigated. These are consistent as well and expand considerably the existing data basis on properties of concrete materials containing SAP.     

Modeling law of a meandering channel

Abstract

The sedimentary processes in river curves are difficult to reproduce in a model because of the distinctly 3‐D nature of the flow pattern. It is virtually impossible to build a model that can satisfy all criteria associated with the scaling of a 3‐D flow. Most sediment‐transport related models in use today are “1‐D model”, for which established scaling techniques are available. These models are built to provide similarity of the cross‐sectional average velocity and resistance coefficient; and they are “straight‐channel model”. This study shows how a set of 1‐D scaling criteria which can be expanded to allow for modeling of secondary currents and lateral variations in depth in river curves. This expansion is based upon theories which relate the strength of the centrifugally induced secondary velocity component to flow depth, channel planform curvature, and depth averaged mean velocity.