Special Issue "Rheology of Reactive, Multiscale, Multiphase Construction Materials"

A special issue of Materials (ISSN 1996-1944).

Deadline for manuscript submissions: 15 April 2020.

Special Issue Editors

Prof. Viktor Mechtcherine
Website
Guest Editor
TU Dresden
Interests: cement-based composites; concrete-3D-printing; rheology; fiber and textile reinforcement; fracture mechanics
Dr.-Ing. Egor Secrieru
Website
Guest Editor
TU Dresden
Interests: cement paste; concrete; hydration; rheology; processing; sustainability
Prof. Dr. Eddie Koenders
Website
Guest Editor
TU Darmstadt
Interests: multiscale modeling; modelling hydration and transport; sustainable binders; thermal energy storage; ultralight foams
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Special Issue Information

Dear colleagues,

The processing of cement-based building materials is the technological core in the construction and maintenance of structures. Although formability in the fresh state offers almost unlimited possibilities for shaping the structures and the development of new construction techniques, today, only a little fraction of this enormous potential is used. To master rheology-based processes and develop novel and highly innovative construction technologies, further significant progress is needed in the widening and deepening of the scientific framework for the rheology of fresh concrete and related materials. This Special Issue invites original articles dedicated to the following topics: • Interactions of reactive (hydrating) particles on the microscale, including the quantification of influences (morphology, chemistry, temperature, time, etc.) and the modeling of particle interactions; • Strategies and concepts for the description of deformation and flow processes of fresh concrete based on microscale processes and taking into account mesoscopic processes (segregation, deaeration, fiber distribution, etc.); • Analysis of the relevant processing operations of fresh concrete (transport, casting, compaction, finishing, etc.) using scientific tools and methods of rheology; • Measurement methods for the detection of the fresh concrete behavior at different levels of consideration and for various claim scenarios; • Constitutive material relationships for fresh concrete to simulate the phases and actions of processing.

Prof. Viktor Mechtcherine
Dr.-Ing. Egor Secrieru
Prof. Dr. Eddie Koenders
Guest Editors

Manuscript Submission Information

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Keywords

  • Fresh concrete
  • Processing
  • Rheology
  • Measurement methods
  • Interactions of reactive particles
  • Constitutive material relationships

Published Papers (8 papers)

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Research

Open AccessArticle
The Influence of Bleeding of Cement Suspensions on Their Rheological Properties
Materials 2020, 13(7), 1609; https://doi.org/10.3390/ma13071609 - 01 Apr 2020
Abstract
Flowable concretes tend to segregate. The risk of segregation is particularly high when the concrete is vibrated during the compaction process. A well-known segregation phenomenon is the so-called "bleeding". This is a rise of water to the surface of the freshly poured concrete [...] Read more.
Flowable concretes tend to segregate. The risk of segregation is particularly high when the concrete is vibrated during the compaction process. A well-known segregation phenomenon is the so-called "bleeding". This is a rise of water to the surface of the freshly poured concrete due to the difference in density between the mixing water and the concrete’s denser solid components (aggregates, cement and additives). This type of segregation occurs particularly within the paste. The focus of this paper is, therefore, on the sedimentation behavior at the microscale of concrete and especially on the influence of this process on rheological properties of the cement paste. In addition to common bleeding tests of cement suspensions using standing cylinders, rheometric measurements were performed on the suspensions during the bleeding process. A measuring procedure was developed for the rheometric measurements of the sedimenting cement suspensions. The rheological properties of the investigated cement suspensions were determined at four specific measuring times and at four specific measuring heights (i.e., positions) each. With this method it could be shown that the cement suspensions are not homogeneous over their height and that bleeding has a great influence on the rheological properties of cement suspension. Full article
(This article belongs to the Special Issue Rheology of Reactive, Multiscale, Multiphase Construction Materials)
Open AccessArticle
Effects of Volume Fraction and Surface Area of Aggregates on the Static Yield Stress and Structural Build-Up of Fresh Concrete
Materials 2020, 13(7), 1551; https://doi.org/10.3390/ma13071551 - 27 Mar 2020
Abstract
With increasing interest in the use of additive manufacturing techniques in the construction industry, static rheological properties of fresh concrete have necessarily come into focus. In particular, the knowledge and control of static yield stress (SYS) and its development over time are crucial [...] Read more.
With increasing interest in the use of additive manufacturing techniques in the construction industry, static rheological properties of fresh concrete have necessarily come into focus. In particular, the knowledge and control of static yield stress (SYS) and its development over time are crucial for mastering formwork-free construction, e.g., by means of layered extrusion. Furthermore, solid understanding of the influences of various concrete constituents on the initial SYS of the mixture and the structural build-up rate is required for purposeful material design. This contribution is concentrated on the effect of aggregates on these rheological parameters. The volume fraction of aggregates was varied in the range of 35% to 55% by volume under condition of constant total surface area of the particles. The total surface area per unit volume of cement paste was equal to 5.00, 7.25 and 10.00 m²/L, conditioned on the constant volume fraction of aggregates. Both variations were enabled by changing the particle size distributions of the aggregates while holding the cement paste composition constant for all concrete mixtures. To characterise the SYS and the structural build-up, constant shear rate tests with a vane-geometry rotational rheometer were performed. It was found that in the ranges under investigation the variation in volume fraction had a more pronounced effect on the static rheological properties of concrete than did the variation in surface area. An accurate mathematical description of the relationship between the initial SYS of concrete and the relative volume fraction of aggregate based on the Chateau–Ovarlez–Trung model was proposed. Challenges in deriving a similar relationship for the structural build-up rate of concrete were highlighted. Full article
(This article belongs to the Special Issue Rheology of Reactive, Multiscale, Multiphase Construction Materials)
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Open AccessArticle
Minimization of the Influence of Shear-Induced Particle Migration in Determining the Rheological Characteristics of Self-Compacting Mortars and Concretes
Materials 2020, 13(7), 1542; https://doi.org/10.3390/ma13071542 - 27 Mar 2020
Abstract
Determining the exact rheological properties of cementitious materials in fundamental units is a crucial step in concrete science. It is undisputed that before measuring rheological properties in concrete rheometers, it is necessary to pre-shear the fresh mortar or concrete. Due to the migration [...] Read more.
Determining the exact rheological properties of cementitious materials in fundamental units is a crucial step in concrete science. It is undisputed that before measuring rheological properties in concrete rheometers, it is necessary to pre-shear the fresh mortar or concrete. Due to the migration of the coarse particles into areas with lower shear stress, however, segregation takes place. An experimental set-up was developed to determine the effects on the measured values of the concrete rheometer ICAR. This allows the active homogenization (pre-shearing) of the material before each change of speed. In the tests higher raw values (macroscopic data) could be measured. This clearly influences the calculated rheological Bingham parameters and modified Bingham parameters for a self-compacting concrete (SCC) with a maximum grain size of 16 mm. Therefore, the homogeneity of the material, a main hypothesis of rheological measurements, does not seem to be fulfilled with the coaxial rheometer used. The process of the indispensable pre-shearing therefore requires more attention in the future so that measurement errors can be minimized. Especially in numerical simulation, suitable rheological models and the realistic determination of parameters are crucial. Since the shear-induced particle migration is largely dependent on the maximum grain size, an ultra-high performance concrete (UHPC) with a maximum particle size of only 0.5 mm was also investigated in the laboratory mixer KNIELE KKM-RT. The integrated rheometer enables also the active homogenization of the fresh concrete during pre-shearing but without the danger of over-mixing, as it is the case for the experimental ICAR setup. This article proves that relevant differences can also be identified for such a material. Full article
(This article belongs to the Special Issue Rheology of Reactive, Multiscale, Multiphase Construction Materials)
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Open AccessArticle
Interaction of Different Charged Polymers with Potassium Ions and Their Effect on the Yield Stress of Highly Concentrated Glass Bead Suspensions
Materials 2020, 13(7), 1490; https://doi.org/10.3390/ma13071490 - 25 Mar 2020
Abstract
The interaction of different charged polymers, namely anionic polycarboxylate superplasticizer (PCE) and neutral polyethylene glycol (PEG) with potassium ions, and their effect on the yield stress of highly concentrated glass bead suspension (GBS), were studied under different concentrations of potassium ions ([K+ [...] Read more.
The interaction of different charged polymers, namely anionic polycarboxylate superplasticizer (PCE) and neutral polyethylene glycol (PEG) with potassium ions, and their effect on the yield stress of highly concentrated glass bead suspension (GBS), were studied under different concentrations of potassium ions ([K+]). It was found that, compared to the neutral PEG, the negatively charged PCE can be adsorbed on glass beads (GB), and then decreases the yield stress of GBS. The increasing concentration of free polymer in the interstitial liquid phase with the increased polymer dosage leads to the higher yield stress of GBS, which may be caused by the higher depletion force. In addition, this effect is also related to the charge density of the polymer and the [K+] in the solution. Along with the increase in [K+], the yield stress of GBS increases significantly with the addition of PCE, but this cannot be observed with PEG, which indicates that potassium ions can interact with negatively charged PCE instead of the neutral PEG. At last, the interparticle forces between two single GB with adsorbed PCE in solutions containing [K+] and PCE were measured by colloidal probe atomic force microscopy to better understand the interaction of the charged polymer with counterions. Full article
(This article belongs to the Special Issue Rheology of Reactive, Multiscale, Multiphase Construction Materials)
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Open AccessArticle
Experimental Insights into Concrete Flow-Regimes Subject to Shear-Induced Particle Migration (SIPM) during Pumping
Materials 2020, 13(5), 1233; https://doi.org/10.3390/ma13051233 - 09 Mar 2020
Abstract
In this paper, the authors have focused on shear-induced particle migration (SIPM), its effect on concrete flow patterns, and lubricating layer formation during pumping. For this purpose, various volume-fractions ϕ of aggregates were selected. The particle migration was analyzed by applying two methods: [...] Read more.
In this paper, the authors have focused on shear-induced particle migration (SIPM), its effect on concrete flow patterns, and lubricating layer formation during pumping. For this purpose, various volume-fractions ϕ of aggregates were selected. The particle migration was analyzed by applying two methods: sampling hardened concrete exposed to pumping and performing X-ray microcomputed tomography (μCT) and image analysis to determine the thickness of the lubricating layer due to SIPM. The results indicate that the first approach is unsuitable due to the nearly equal molecular density of particles and matrix. The second approach indicated that the actual thickness of the lubricating layer depends on the discharge rate as well as on ϕ and viscosity of concrete bulk; hence, it cannot be defined as a constant parameter for all concrete mixtures. Additionally, the concrete pipe-flow pattern, i.e., plug versus shear flow, was captured and studied while considering pumping pressure and discharge rate. It was concluded that particle migration is essential in the cases of both flowable and very flowable concretes with a high volume-fraction of solids. The changes in rheological properties caused by SIPM are severe enough to influence the definition of the flow pattern as plug or shear and the discharge rate of pumped concrete as well. Full article
(This article belongs to the Special Issue Rheology of Reactive, Multiscale, Multiphase Construction Materials)
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Open AccessArticle
Experimental Investigation of the Pumping of a Model-Concrete through Pipes
Materials 2020, 13(5), 1161; https://doi.org/10.3390/ma13051161 - 05 Mar 2020
Abstract
Many practical aspects of processing fresh concrete depend on its rheology, such as the pumping of the material. It is known that a lubricating layer is formed in the process, which significantly reduces the pumping pressure. However, these phenomena can hardly be considered [...] Read more.
Many practical aspects of processing fresh concrete depend on its rheology, such as the pumping of the material. It is known that a lubricating layer is formed in the process, which significantly reduces the pumping pressure. However, these phenomena can hardly be considered in the usual rheological measurements. A main problem is the optical inaccessibility of the material, which prevents estimations about, e.g., the thickness of the plug flow or particle migration. In this paper, the pneumatic pumping of a transparent model concrete is performed by means of a test plant. The flow profile over the entire pipe cross-section is resolved in time and space via Particle Image Velocimetry (PIV) measurements. This allows the comparison with the analytical flow profile from rheological measurements of the material using the Buckingham–Reiner equation. A reduction of the pressure loss to around 60% induced through segregation of the material is found. These measurements reflect the rheology of the material under realistic pumping conditions including particle migration. This makes it possible for the first time to observe a transparent material with concrete-like rheology under pulsating pumping conditions and to compare the true and calculated time-resolved pressure loss. Full article
(This article belongs to the Special Issue Rheology of Reactive, Multiscale, Multiphase Construction Materials)
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Open AccessArticle
Investigation of the Incompatibilities of Cement and Superplasticizers and Their Influence on the Rheological Behavior
Materials 2020, 13(4), 977; https://doi.org/10.3390/ma13040977 - 21 Feb 2020
Abstract
The rheological behavior of cement paste and the improvement of its flowability takes center stage in many research projects. An improved flowability can be achieved by the addition of superplasticizers (SP), such as polycarboxylate ethers (PCE). In order to be able to use [...] Read more.
The rheological behavior of cement paste and the improvement of its flowability takes center stage in many research projects. An improved flowability can be achieved by the addition of superplasticizers (SP), such as polycarboxylate ethers (PCE). In order to be able to use these PCEs effectively and in a variety of ways and to make them resistant to changes in the environment, it is crucial to understand the influence of SPs on cement hydration. For that reason, the topic of this paper was the incompatibility of a specific SP and an ordinary Portland cement (OPC). The incompatible behavior was analyzed using rheological tests, such as the spread flow test and penetration test, and the behavior was compared by means of an ultrasound technique and explained by the phase content measured by in-situ X-ray diffraction (XRD) the heat evolution measured by calorimetry, and scanning electron microscope (SEM) images. We showed that the addition of the SP in a high dosage led to a prevention of the passivation of the most reactive and aluminum-containing clinker phases, aluminate and brownmillerite. This induced the aluminate reaction to take place in the initial period and led to an immediate stiffening of the cement paste and, therefore, to the complete loss of workability. The results showed that in addition to the ettringite, which began to form directly after water addition, hemicarbonate precipitated. The fast stiffening of the paste could be prevented by delayed addition of the SP or by additional gypsum. This fast stiffening was not desirable for SPs, but in other fields, for example, 3D printing, this undesirable interaction could be used to improve the properties of printable mortar. Full article
(This article belongs to the Special Issue Rheology of Reactive, Multiscale, Multiphase Construction Materials)
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Open AccessArticle
Absolute Rheological Measurements of Model Suspensions: Influence and Correction of Wall Slip Prevention Measures
Materials 2020, 13(2), 467; https://doi.org/10.3390/ma13020467 - 18 Jan 2020
Abstract
Since suspensions (e.g., in food, cement, or cosmetics industries) tend to show wall slip, the application of structured measuring surfaces in rheometers is widespread. Usually, for parallel-plate geometries, the tip-to-tip distance is used for calculation of absolute rheological values, which implies that there [...] Read more.
Since suspensions (e.g., in food, cement, or cosmetics industries) tend to show wall slip, the application of structured measuring surfaces in rheometers is widespread. Usually, for parallel-plate geometries, the tip-to-tip distance is used for calculation of absolute rheological values, which implies that there is no flow behind this distance. However, several studies show that this is not true. Therefore, the measuring gap needs to be corrected by adding the effective gap extension δ to the prescribed gap height H in order to obtain absolute rheological properties. In this paper, we determine the effective gap extension δ for different structures and fluids (Newtonian, shear thinning, and model suspensions that can be adjusted to the behavior of real fluids) and compare the corrected values to reference data. We observe that for Newtonian fluids a gap- and material-independent correction function can be derived for every measuring system, which is also applicable to suspensions, but not to shear thinning fluids. Since this relation appears to be mainly dependent on the characteristics of flow behaviour, we show that the calibration of structured measuring systems is possible with Newtonian fluids and then can be transferred to suspensions up to a certain particle content. Full article
(This article belongs to the Special Issue Rheology of Reactive, Multiscale, Multiphase Construction Materials)
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