Filtern
Erscheinungsjahr
Dokumenttyp
- Beitrag zu einem Tagungsband (83) (entfernen)
Referierte Publikation
- nein (83) (entfernen)
Schlagworte
- Rheology (23)
- Cement (21)
- Concrete (14)
- Superplasticizer (7)
- Admixtures (6)
- Africa (6)
- Polycarboxylate ether (6)
- Rheologie (6)
- Self-compacting concrete (6)
- Sustainability (6)
- Cement hydration (5)
- Fließmittel (5)
- Polycarboxylatether (4)
- Polysaccharides (4)
- Superplasticizers (4)
- Diutan gum (3)
- Hydration (3)
- Polysaccharide (3)
- Robustness (3)
- Starch (3)
- Structural build-up (3)
- Adsorption (2)
- Analytics (2)
- Carbon emissions (2)
- Cassava (2)
- Chloride migration (2)
- Civil Engineering (2)
- Climatic conditions (2)
- Corrosion potential (2)
- Dye (2)
- Early hydration (2)
- Electrical resistivity (2)
- Erstarren (2)
- Freeze-thaw (2)
- Materials (2)
- Metakaolin (2)
- Mixture composition (2)
- Polycarboxylate ether (PCE) (2)
- SHCC (2)
- Schallemission (2)
- Selbstverdichtender Beton (2)
- Setting (2)
- Stabilisierer (2)
- Standards (2)
- Sub-Saharan Africa (2)
- Thixotropy (2)
- Urban heat island effect (2)
- Viscosity modifying agent (2)
- Water absorption (2)
- Welan gum (2)
- 1H NMR relaxometry (1)
- 3D concrete printing (1)
- Additions (1)
- Admixture (1)
- Akaziengummi (1)
- Alkali-activated binders (1)
- Ambient conditions (1)
- Analysis of variance (1)
- Atmospheric humidity (1)
- Autogenous deformation (1)
- Bauchemie (1)
- Baustoffe (1)
- Beton (1)
- Betonstahl (1)
- Bias (1)
- Biomass (1)
- Box-Behnken (1)
- C3A (1)
- C3A hydration (1)
- CFD (1)
- Calorimetry (1)
- Capillary suction (1)
- Carbon dioxide (1)
- Carbon emission (1)
- Casting environment (1)
- Cement production (1)
- Cement, hydration (1)
- Clean and safe cement production (1)
- Clinker reduction (1)
- Compressive strength (1)
- Concrete multilayer pavers (1)
- Concrete multilayers pavers (1)
- Construction (1)
- Control Chart (1)
- Creep (1)
- Cusum (1)
- Delayed addition (1)
- Depassivation (1)
- Durability (1)
- Dyes (1)
- EN 196 (1)
- Earth-moist concrete (1)
- Education (1)
- Energy sustainability (1)
- Faserverstärkter Beton (1)
- Fib model code (1)
- Fibre concrete (1)
- Fibres (1)
- Flowable concrete (1)
- Fluorescence (1)
- Fresh concrete (1)
- Frischbeton (1)
- Global engineering (1)
- Grouting (1)
- Guar Gum (1)
- Guar gum (1)
- Heat evolution (1)
- Heat flow calorimetry (1)
- Heat of hydration (1)
- High strength concrete (1)
- Hochduktiler Beton (1)
- Hydratationswärme (1)
- Influence of temperature (1)
- Lignosulfonate (1)
- Limestone filler (1)
- Lochkorrosion (1)
- Material characterization (1)
- Mix design (1)
- Model calibration (1)
- Mortar (1)
- Mukuru (1)
- NMR imaging (1)
- Nano engineered materials (1)
- Nano scale (1)
- Numerical modelling (1)
- One-part geopolymers (1)
- Optical Spectroscopy (1)
- Optical spectroscopie (1)
- PVA-Fasern (1)
- Packing density (1)
- Peat (1)
- Penetration test (1)
- Permeability (1)
- Polycarboxylate (1)
- Polycarboxylate superplasticizer (1)
- Polymer adsorption (1)
- Polyphosphate (1)
- Pore solutions (1)
- Porous medium (1)
- Potato starch (1)
- Pre-hydration (1)
- Proficiency Testing (1)
- Proficiency testing (1)
- Quality Infrastructure (1)
- Reinforcement (1)
- Relaxation time distribution (1)
- Repair (1)
- Research (1)
- Rheological (1)
- Rice husk ash (1)
- SCC (1)
- SHCC corrosion crack (1)
- Schwinden (1)
- Science (1)
- Sciences (1)
- Scientific network (1)
- Self-cooling pavement (1)
- Shrinkage (1)
- Simulation (1)
- Slump flow (1)
- South Africa (1)
- Stabilising agent (1)
- Stabilising agents (1)
- Starches (1)
- Storage (1)
- Superplasticiser (1)
- Superplaticizer (1)
- Supplementary cementitious materials (1)
- Temperatureffekte (1)
- Texture analyzer (1)
- Triumfetta Pendrata A. Rich (1)
- Upscaling (1)
- Urban planning (1)
- Urbanisation (1)
- Verarbeitungseigenschaften (1)
- Volume fraction (1)
- Waste paper sludge (1)
- Water storage (1)
- Workability (1)
- Zementleim (1)
- Zugversuch (1)
- Zusatzmittel (1)
- control chart (1)
- cusum (1)
- quality control (1)
- robustness (1)
Organisationseinheit der BAM
- 7 Bauwerkssicherheit (20)
- 7.4 Baustofftechnologie (17)
- 6 Materialchemie (5)
- 6.6 Physik und chemische Analytik der Polymere (5)
- 7.0 Abteilungsleitung und andere (3)
- 1 Analytische Chemie; Referenzmaterialien (2)
- 1.2 Biophotonik (2)
- 8 Zerstörungsfreie Prüfung (2)
- 8.0 Abteilungsleitung und andere (2)
- 7.2 Ingenieurbau (1)
- 7.7 Modellierung und Simulation (1)
- KM Kommunikation, Marketing (1)
- P Präsident (1)
Die Rheologie von fließfähigen zementären Systemen mit Fließmitteln wird durch eine Vielzahl parallel stattfindender Effekte beeinflusst. Zu diesen Effekten zählen Wechselwirkungen zwischen den Polymeren und Ionen in der Porenlösung, frühe Phasenbildung, zeitabhängige und kompetitive Adsorption zwischen anionischen Polymeren und Sulfationen, Bildung von Phasen in der Porenlösung sowie Morphologieänderungen an Partikeloberflächen. Die frühe Hydratation von Zement, die durch Lösungs- und Fällungsprozesse angetrieben wird, beeinflusst diese Effekte erheblich. Das permanente Ungleichgewicht der Porenlösung führt zu Veränderungen der Partikeloberflächen, welches widerum zur Folge hat, dass rheometrische Messungen dieser Zementleime anfällig für Streuungen sind. Um die Einflüsse aus der Zementhydratation zu minimieren, wurden die rheometrischen Untersuchungen mit Zement in Porenlösung durchgeführt. Die Experimente wurden mit verschiedenen Feststoffvolumenfraktionen durchgeführt und mit den Ergebnissen identischer Systeme mit Wasser anstelle von Porenlösung verglichen. Zusätzlich wurden die gleichen Systeme mit Zugabe von Polycarboxylatethern untersucht.
Die Ergebnisse zeigen, dass die Leime mit Wasser niedrigere Werte für Fließgrenze und plastische Viskosität aufweisen, als die Systeme mit Porenlösung. Während die Polymere eine Verminderung der Fließgrenze zur Folge hatte, war die Wirkung von Polymeren auf die plastische Viskosität vernachlässigbar. Zusätzlich wurde die frühe Hydratation unter Verwendung von Wärmeflusskalorimetrie, Rasterelektronenmikroskopie und Nadeleindringtiefe beobachtet.
This paper describes the fibre-reinforced strain hardening cement-based composite (SHCC) performance under various exposure conditions. Cracked and uncracked SHCC beam specimens were subjected to cyclic wetting and drying under chloride exposure to observe the time of depassivation and corrosion potential of the imbedded reinforcement. Two reference mortars, one of the same strength class as the SHCC (Mortar 1) and the other of high strength class (Mortar 2) were used under the same conditions. Finally, tests for determining the rapid chloride migration coefficient, electrical resistivity, capillary water absorption and freezethaw were also performed to observe the corrosion probability and diffusion rate in uncracked SHCC and mortars.
Influence of the hydroxypropylation of starch on its performance as viscosity modifying agent
(2022)
Synopsis: Starch is a commonly used viscosity modifying agent (VMA). The performance of starch as VMA depends on its origin (e.g. potato, corn, cassava, etc.) and corresponding molecular properties, such as molecular weight, ratio between amylose and amylopectin etc. Depending upon the application, the efficiency of starch can be enhanced by hydroxypropylation. The maximum degree of substitution (DoS) cannot be greater than 3.0, which is the number of hydroxy groups per glucose monomer in the polymer. In the current research three potato starches exhibiting the DoS of 0.4, 0.6 and 0.8 were utilised. The influence of the modified starch on the rheological properties and hydration of cement paste, as well as the viscosity of the pore solution were investigated. Our findings show that the starch with the highest DoS increases the dynamic yield stress the most, while the plastic viscosity is less dependent on the DoS. Additionally, starch with the highest DoS retards hydration to lower degree than other starches.
The African cement, concrete and construction business is growing at rapid pace. The cement sales are expected to grow rapidly until 2050. The number of newly built cement plants increases dramatically and in addition more cements are being imported from outside the continent, e.g. from Turkey, Pakistan, Indonesia, and China, driven by overcapacities in the countries of origin. This causes a high number of potentials and challenges at the same time. Newly built cement plants can operate directly at best technological state of the art and thus incorporate more sustainable technologies as well as produce new and more sustainable products such as cements blended with sustainable supplementary cementitious materials such as calcined clays, and industrial or agricultural by products. At the same time the new variety of binding agent as well as the international imports, which are driven by price considerations, make the cement market prone to quality scatter. This puts pressure on the quality control regulations and institutions to ensure safety of construction, healthy application, and environmental safety for the population. The paper presents possible solutions to build up the rapidly increasing African cement production more sustainably than in the rest of the world as well as the related challenges and obstacles that need to be overcome. Based on experiences with a series of pan-African cement testing laboratory proficiency schemes conclusions are made on technical, regulative and political level.
With ongoing innovation in process technology, the challenges of concrete technology are more and more focused on the rheological optimisation for these processes, since improper mixture stability or poor compaction ability negatively affect the concrete homogeneity and quality. However, along with the increasing complexity of today’s concrete mixture compositions, concrete becomes more prone to failure regarding the casting process. Variable properties of the raw materials typically cause changing workability. The reasons can be found among others in scattering water contents, physical or chemical properties of the cement or varying environmental temperatures. Robustness in the delicately adjusted rheology, however, is of utmost importance for modern and future process technology, from sprayed concrete over pumpable concrete towards 3D-printing, with regard to the long-term strength, the function and the durability. Typically, material induced changes cannot be identified easily due to the complex interactions of concrete constituents. Therefore, a precise and prompt counteraction is impossible. However, it is known that the yield stress can be controlled by addition of supplementary superplasticizer or stabilising agent. In combination with computerized process observation tools that can rapidly interpret and react on changes in the rheology, it is therefore thinkable, that only these two admixture types can adjust the rheology steadily and permanently, regardless of the actual root cause for observed macroscopic rheology change. The presentation will firstly give a comprehensive overview of effects at the interface between pore solution, particles and hydrates, which affect the rheology of fresh concrete. Secondly, ways are recommended how the rheology can be actively manipulated before eventually computerized methods are demonstrated that help to actively and rapidly assess and counteract performance scatter during steady casting processes.
Synopsis: Lately, there has been rising attention to superplasticizers (SP) based on polyphosphate esters. However, the influence of the molecular structure of the polyphosphate polymers on time-dependent properties such as structural build-up has not been examined yet intensively. To investigate this effect, three comb polyphosphate superplasticizers with different charge densities were synthesised by free radical polymerisation. Our findings indicate that SP with the lowest and medium charge densities extend the induction period more strongly than the SP with the highest charge density. The reduction of the structural build-up rate is linearly dependent on the dosage and concentration of the functional group of polyphosphate SP in the cementitious system. This study proposes a mathematical equation expressing the relationship between the structural build-up rate during the induction period and the molecular structure of the polyphosphate SP.
Hochduktiler Beton eröffnet neue Möglichkeiten bei der Instandsetzung von Bauwerken, der Herstellung dünnwandiger Bauelemente oder dem Einsatz von Dämpfungselementen in stoßartig beanspruchten Bauwerken (z.B. in Erdbebengebieten).
Die Steigerung der Duktilität kann durch die Zugabe von Kurzfasern erreicht werden. Im Falle einer Rissbildung in der Zementsteinmatrix überbrücken die Fasern den Riss, nehmen die Spannung vollständig auf und stoppen lokal das Risswachstum. Bei weiterer Steigerung der Last reißt die Matrix an anderer Stelle. Auf diese Weise wird die Rissbildung fein verteilt und es werden große Dehnungen erreicht, bevor das Bauteil versagt. Zur Optimierung der Festbetoneigenschaften müssen die Matrixfestigkeit und die Faserart sowie deren Gehalt aufeinander abgestimmt werden. Dabei sind auch die Verarbeitungseigenschaften des Frischbetons zu berücksichtigen.
Anhand der Schallemissionen kann die Rissbildung in der Matrix und die Interaktion mit den Fasern analysiert werden. So konnte in ersten Zugversuchen gezeigt werden, dass sich Schallereignisse dem Versagen der Zementsteinmatrix bzw. dem Auszug der Fasern aus der Matrix zuordnen lassen. Damit steht zur Beurteilung des mechanischen Verhaltens von hochduktilem Beton neben der Spannungs-Dehnungs-Linie ein weiteres Verfahren zur Verfügung.
Chemical admixtures like superplasticisers or stabilising agents are of ever increasing importance for modern concrete technology. They liberate the workability of concrete from its dependency on water content, and thus, open the gate towards innovative and future oriented concrete technologies such as self-compacting concrete.
Today, admixture addition has become common practice in concrete technology, but the understanding of their highly complex mode of operation is extremely difficult and demands for understanding of processes within the range between nanometres and centimetres.
Due to its complex time-dependent, multi-phase and multi-scale behaviour, flowable concrete systems are highly complicated and cannot be described comprehensively by simple models. It is therefore extremely challenging to identify the relevant parameters that predominantly control flow phenomena on different size scales, since these may occur on any scale between the nano scale (e.g. superplasticizer adsorption) and macro scale (e.g. grading of the aggregates). The present study discusses fundamental mechanisms at the interface between particle or hydrate surfaces and the fluid phase at a very early stage of concrete formation, and links these effects to macroscopic flow phenomena. Methods are discussed that appear promising interdisciplinary tools for enhancement of the understanding of the relevant interactions that are responsible for the macroscopic flow of flowable concrete.
The use of starch and its derivatives in concrete as an admixture to modify relevant properties of concrete is on the increase in recent times. It is known to modify the rheology, to affect the hydration kinetics of cement, and influence on initial and final setting time of cement. This paper examines the effect of cassava starch on concrete. shrinkage properties of concrete, with and without starch addition, were studied. Various percentages (0, 0.5, 1.0, 1.5 and 2 %) of starches by weight of cement were added to concrete mixes prepared in the laboratory. Shrinkage tests were conducted for duration of up to one year. The result show that concretes with starch additions exhibit lower shrinkage, which is an indication the addition of starch as admixture in concrete improves the ability of the concrete reduce shrinkage problems.