bluuebunny/crossref_metadata_2025_split huggingface dataset:
α‐calcium sulfate hemihydrate formation using natural anhydrite as raw material
Authors: Eicheler Christina , Heisig Anne , Hilbig Harald , Machner Alisa 
Published: December 2023

AbstractThis study investigates the potential of α‐HH formation from gypsum originating from activated and hydrated natural anhydrite. For this, gypsum was prepared from natural anhydrite and treated in an autoclave process under hydrothermal conditions (150 mbar and 130 °C). For comparison, fgd‐gypsum was treated accordingly. Succinic acid, maleic acid and additional α‐HH seeds were used as crystallization aids. QXRD results show the transformation of gypsum into hemihydrate after a residence time of 8 h and 4 h. SEM images distinguish the α‐HH and β‐HH modifications. For fgd‐gypsum pellets, the β‐HH modification predominates. Gypsum from natural anhydrite shows α‐HH crystals with succinic acid and without crystallization aid. When maleic acid is present, crystals appear as intermediates between α‐HH and β‐HH. To isolate the effect of the crystallization aids, α‐HH and succinic acid were used separately and simultaneously. SEM images indicate the formation of α‐HH from β‐HH. The shapes of the original β‐HH conglomerates are still visible, yet acicular crystals with smooth surfaces (α‐HH) are visible at a high magnification. Longest crystals appear when α‐HH and succinic acid are used simultaneously indicating a synergetic effect of both crystallization aids.
Autogenous Self‐healing of CTRC Repair Layers Exposed to Tensile Threshold Loading
Authors: Cruz Cynthia Morales 
Published: December 2023

AbstractThe experimental investigations presented in this paper contribute to fill the knowledge gaps on the subject of autogenous self‐healing of DURTEX layers for the surface repair of cracked or cyclic crack opening of concrete and reinforced concrete structures. Composite specimens, so‐called crack distribution specimens, were subjected to at least 1000 and up to 6900 cycles. Investigations show that neither the crack characteristics (e. g. crack width, crack geometry) change nor the mechanical properties (e. g. adhesive tensile strength or tensile load‐bearing behavior) are reduced compared to the reference specimens as a result of cyclic loading with both pore and crack water pressure. Also, the self‐healing potential of a selected material combination is demonstrated despite cyclic loading. It was observed that cracked DURTEX layers with wmax = 0.116 mm, under cyclic loading (Δwop = 0.6 mm) at a constant test speed set to 0.05 mm/min (piston controlled) with a 5 m pore and crack water pressure can self‐heal themselves leading to water tightness after 14 days. Chemical‐mineralogical analysis using X‐ray diffraction (XRD) on material taken from the cracked surface of the specimen evidenced the formation of CaCO3 as calcite.
Faserbewehrter UHPC auf Basis von alkalisch aktivierten Bindemittel
Authors: Wetzel Alexander , Link Janna , Middendorf Bernhard 
Published: December 2023

KurzfassungDie mechanische Leistungsfähigkeit von faserverstärktem Ultrahochleistungsbeton auf der Grundlage alkalisch aktivierter Schlacke wurde untersucht, wobei der Schwerpunkt auf der Verwendung von Stahlfasern lag. Die Biegezugfestigkeit ist im Vergleich zu UHPC auf der Basis Portlandzement als Bindemittel erhöht. Die Korrelation der Biegezugfestigkeitsprüfung mit Faserauszugsversuchen ergab eine Verbesserung des Verbundverhaltens in der Grenzflächen‐Übergangszone des AAM‐UHPC im Vergleich zum OPC‐UHPC. Bei Vergleichen von Mehrfachfaserauszugsversuchen mit den Biegezugfestigkeiten zeigt sich eine Tendenz zu höheren Festigkeiten für Edelstahlfasern, während bei dem Faserauszug die messingbeschichteten Stahlfasern eine höhere Verbundstärke aufweisen. Zusätzliche Auszugsversuche unter Variation des Auszugswinkel zeigen jedoch eine Bestätigung der Biegezugfestigkeitsergebnisse. Bei schrägem Faserauszug weisen die Edelstahlfasern Vorteile auf. Mittels μ‐CT durchgeführte in‐situ Auszugsversuche weisen auf einen stärkeren Verbund von Edelstahlfasern im schrägen Auszug auf. Dies ist vermutlich auf einen stärkeren Reibungsverbund infolge einer stärkeren Topographie im Vergleich zu den messingbeschichteten Stahlfasern zurückzuführen. Im Vergleich zum geraden Auszug scheint die Topographie der Edelstahlfasern einen stärkeren Effekt zu bewirken.
Characterization of recycled sands and aggregates from selective separation
Authors: Vargas‐Serrano Encarnacion , Tian W. , Mikanovic N. , Skocek Jan 
Published: December 2023

AbstractThe use of recycling materials from demolished concrete as raw material for structural application represents an opportunity for decreasing the consumption of primary raw materials and waste generation, thus increasing global sustainability. However, this potential is nowadays not fully exploited due to standards limitations and concerns from the construction industry about the negative effect of the recycled sand in the fresh and hardened concrete performance. Thus, most of the recycled sand produced is only reused as roadbed or dumped in the landfill, whereas the recycled coarse aggregate is commonly downcycled when used for lower‐grade applications.This paper presents an overview of the quality properties of recycled materials obtained through advanced recycling technologies designed to separate high‐quality sand and coarse aggregates from hardened cement paste in demolished concrete. The study focuses on evaluating the selective separation technologies implemented in various industrial pilots and examining how the properties of recycled sands and aggregates compare to those of virgin materials of good quality, and their impact on performance.The test results indicate that there is a strong link between recycled sand quality and its effect on workability and strength development of cement‐based materials. This study also identifies critical aggregate parameters based on which one can come up with realistic replacement levels of natural with recycled sands and aggregate without compromising performance in fresh and hardened state. Our intention is to provide sufficient evidence to specifiers and designers that good quality recycled sands can be used in larger amounts in structural concrete.
Use of treated municipal waste incinerator ashes as concrete aggregate after fragmentation and sorting
Authors: Siebert Björn , Hirsch Marius , Leiss Norbert , Spektor Vitaliy , Vollpracht Anya , Winkler Rebecca , Wolf Christian 
Published: December 2023

AbstractAnnually about 5.7 million tons of waste incinerator ash accumulate in Germany through the incineration of municipal waste. The new method of electrodynamic fragmentation allows waste incinerator ashes with complex material compositions to be broken at material interfaces and then sorted into materially pure components. The aim of current ASHCON research project is to substitute natural aggregate of the grain fraction 2/8 mm in conventional formulations for ready‐mixed concrete and concrete blocks by these secondary raw materials in order to keep them within the material cycle and reduce the use of primary raw materials. Since the utilization of fragmented waste incinerator ashes in concrete must be below the limit values with regard to possible pollutant concentrations (e.g. heavy metal concentrations), the suitability of a so‐called non‐destructive neutronic analysis method on real samples is also being investigated within the ASHCON project. The first results of sample collection, preparation and analysis as well as material properties of the produced concretes with the implementation of mineral residues from waste incinerator ashes are presented in this paper.
Phase formation and hydration of alumina cements on the basis of cobalt‐molybdenum‐containing waste
Authors: Logvinkov Sergii , Korohodska Alla , Shabanova Halyna , Levadna Svitlana 
Published: December 2023

AbstractThe subject of the research is features of synthesis of alumina cements on the basis of compositions of system CaO – CoO – Al2O3 – MoO3 with use of cobalt‐molybdenum‐containing waste for reception of refractory materials with a complex of the set properties. The processes of phase formation in raw mixtures have been investigated. X‐ray phase studies of clinkers fired at different temperatures and holding times proved that as a result of the interaction of the raw materials of the mixture in the material synthesizes a mixture of hydraulically active calcium mono‐ and di‐aluminate and refractory cobalt spinel, which provides the resulting complex high strength, accelerated curing time, fire resistance. The absence of phases corresponding to molybdenum compounds is explained by the fact that they are part of hydraulically active aluminates as limited solid solutions, deforming the crystal lattice and increasing hydraulic activity. Thus, it was found that the high strength of cement is due to the presence of calcium hydroaluminates such as C2AH8, aluminum hydroxide, as well as unhydrated grains of calcium aluminates, which will contribute to further long‐term strength. It is this coexistence of phases in both the crystalline and colloidal states provide high strength cement stone.
Sulfate consumption during the hydration of Alite and its influence by SCMs
Authors: Maier Matthias , Scherb Sebastian , Thienel Karl‐Christian 
Published: December 2023

AbstractSCMs with a large specific surface area, such as calcined clays or fine limestone powder, can significantly accelerate the occurrence of the aluminate heat flow peak during the early hydration of blended cements. These systems therefore require a higher amount of sulfate. While this effect has been drawn back to the sulfate incorporation into C‐S‐H, which is formed more rapidly due to the filler effect, it has been recently shown that in systems with high amounts of metakaolin, the sulfate balance is influenced by further mechanisms. This study provides new results on the influence of aluminum‐rich and aluminum‐free SCMs on the early hydration of alite in presence of calcium sulfate. A synthesized alite was blended with 5 wt% of anhydrite and its hydration was investigated by isothermal calorimetry and in‐situ XRD at a w/b ratio of 0.5. It was shown that the formed C‐S‐H is able to take up the calcium and sulfate ions, indicated by a depletion of the solid anhydrite after approximately 20 hours. This process is significantly accelerated by incorporating 30 wt% of a fine limestone filler. The addition of metakaolin leads to an acceleration of the alite hydration compared to the reference as well, but to a significantly lower extend compared to the limestone. However, this system requires a lower degree of alite reaction to reach sulfate depletion. This indicates that in metakaolin‐rich systems, the sulfate demand is influenced by further effects. The results from in‐situ‐XRD reveal that significant ettringite formation is taking place in the metakaolin‐blended system already during the first hours of hydration. Correlations between the degree of alite hydration and the rate of sulfate depletion provide new insights into the mechanisms affecting the sulfate balance and early hydration of blended cements.
Challenges for Embedding RFID Sensors in Reinforced Concrete for Low‐effort Structural Health Monitoring
Authors: Walther Christian , Alkam Feras , Nguyen‐Tuan Long , Lieboldt Matthias , Lahmer Tom 
Published: December 2023

AbstractThe structural health of civil infrastructure can be monitored using non‐destructive testing methods and wireless sensor technology. Buildings are often made of reinforced concrete, in which the sensors can be embedded during construction. The implementation of sensor‐based monitoring therefore fundamentally requires robust electronics. The wireless sensors must meet the special requirements of different areas such as communication, durability in the concrete, and compatibility with future readers. Taking into account previous approaches from practice and research, an elicitation of basic requirements for a Radio Frequency Identification (RFID) sensor system that can be embedded in concrete was carried out. Specific problems related to embedding electronic sensors in concrete and their design are investigated. Simple RFID sensor systems have been developed that allow operation without cables or batteries. The main sensor requirements are listed accordingly. Challenges and issues that need to be considered when using RFID sensors in concrete are described. Finally, the “life cycle” of a sensor system embedded in reinforced concrete is briefly discussed.
Nachträgliche Beschleunigung einer verzögerten Zementhydratation mit Kristallisationskeimen
Authors: Unbehau Sophie , Sowoidnich Thomas , Müller Matthias , Goretzki Lothar , Ludwig Horst‐Michael 
Published: December 2023

KurzfassungVerzögerer oder verzögernd wirkende Fließmittel werden im Betonbau eingesetzt, um ausreichend lange Verarbeitungszeiten zu realisieren, insbesondere bei hohen Temperaturen. Das zielsichere Einhalten der gewünschten Verzögerungsspanne kann dabei problematisch sein. Starke Abweichungen können zu Störungen des Bauablaufs führen. Durch eine gezielte Aufhebung der Verzögerungswirkung kurz vor dem Einbau des Betons kann hier eine deutlich höhere Anwendungssicherheit erreicht werden. Die Machbarkeit dieses Ansatzes wurde in der vorliegenden Studie untersucht. Hierzu wurde die Hydratation eines Portlandzementes gezielt verzögert und zu verschiedenen, späteren Zeitpunkten durch Zugabe von Keimbildnern wieder angeregt. Die Auswirkungen auf die Kinetik der Zementhydratation, auf das Erstarrungsverhalten und die Festigkeitsentwicklung wurden charakterisiertDie Ergebnisse zeigen, dass die gezielte Verzögerung der Zementhydratation durch eine spätere Zugabe von Kristallisationskeimen kompensiert werden kann (Stichwort: setting on‐demand). Damit kann der Baupraxis ein zusätzliches Instrument zur Hand gegeben werden, um die Anwendungssicherheit von Verzögerern im Betonbau zu erhöhen. Zudem kann dieser Ansatz das Potential bieten, das Erstarrungsverhalten von Spritzbeton positiv zu beeinflussen.
Recycling of construction waste as an innovative direction of the program of post‐war reconstruction of destroyed cities
Authors: Shyshkin Eduard , Chernonosova Tetiana , Haiko Yurii , Ivasenko Viktoriia , Krasnokutska Iuliia 
Published: December 2023

AbstractThere are officially more than 5.5 thousand dumps in Ukraine, landfills with a total area of more than 9,000 hectares, and there are more than 2000 illegal dumps. The issue of waste disposal (garbage) has always been very acute, not only during the war, a significant part of this waste is construction waste. During the hostilities, many Ukrainian cities and settlements suffered various types of destruction, and some suffered almost the greatest destruction of various objects of urban infrastructure. All this contributed to the emergence of a large amount of demolition waste. The article analyzes the current state of management of demolition waste in Ukraine. The goals and objectives of recycling construction waste in the conditions of post‐war reconstruction of destroyed urban areas are formulated. The results of theoretical studies of methods of utilization of demolition waste by their reuse in construction are given. The preferred types of construction waste in case of destruction of buildings include clogged soil, asphalt, stone materials, brick, concrete and reinforced concrete, wood, ceramic tiles, etc. Each of these types of demolition waste needs a separate recycling. The article gives the classification and structure of demolition waste and defines, what operations to handle it are required. The requirements for the arrangement of temporary storage of construction waste are formulated. Prospects for the development of recycling of demolition waste in Ukraine are considered. The ways of reuse in construction of demolition waste components are proposed. Recommendations of measures of step‐by‐step management of construction waste in Ukraine were provided.
Entwicklung von Porenkeramik‐Sensorelementen für ein Monitoring des Trocknungsverlaufs von Calciumsulfat‐Estrichen
Authors: Helbig Stefan , Hildebrandt Stefanie , Bonitz Frank , Wagner Ralf , Haase Daniela , Adler Jörg , Lizarazu Jorge , Damaschke Anja , Schulz Tabea , Ulanov Alexander , Kersten Hans‐Jörg 
Published: December 2023

KurzfassungAusgehend von der Analyse der Porenstruktur typischer Calciumsulfat‐Estriche wurde eine Porenkeramik entwickelt. Ziel war dabei, ein keramisches Material mit ähnlicher Porenverteilung und folglich ähnlichen Feuchtespeichereigenschaften wie die von typischen Calciumsulfat‐Estrichen zu erhalten. Die Feuchtespeicherfunktionen der Calciumsulfat‐Estriche und der entwickelten Porenkeramiken wurden mit einem Taupunkt‐Potentiameter gemessen. Dadurch war eine detaillierte Charakterisierung der Feuchtespeichereigenschaften im überhygroskopischen Bereich möglich. Es wurden auch die dielektrischen und lichtoptischen Eigenschaften der Porenkeramik bestimmt. Aus der Porenkeramik wurden dielektrische und lichtoptische Sensoren sowie die zugehörige Technik für die kontinuierliche Messwerterfassung entwickelt. Die Sensoren wurden in Estrich‐Versuchsflächen während der Herstellung eingebettet und durch Monitoring während einer Trocknung der Estriche bis zur Belegreife getestet. Bei Estrichen, deren Feuchtespeicherfunktion hinreichend mit der Feuchtespeicherfunktion der Porenkeramik übereinstimmte, zeigte sich dabei eine gute Korrelation der Sensorsignale mit den durch Darr‐ und CM‐Verfahren bestimmten Feuchtegehalten.
Leistungsbezogene Bewertung der Dauerhaftigkeit von Betonbauwerken durch baustellentaugliche Abnahmeprüfungen
Authors: Ov David , Lozano‐Valcarcel Juan Mauricio , Breitenbücher Rolf , Kränkel Thomas , Gehlen Christoph 
Published: December 2023

KurzfassungFür die Dauerhaftigkeit eines Bauwerks ist die Qualität des eingebauten Betons entscheidend. Allerdings sind bislang für die dauerhaftigkeitsrelevanten Betoneigenschaften noch keine direkten Bewertungskriterien definiert worden. Die Qualität des eingebauten Betons wird in der Regel an separat hergestellten Proben nachgewiesen. Vergangene Forschungsarbeiten haben gezeigt, dass die am Bauwerk erzielten Betoneigenschaften von denen der separat hergestellten Proben erheblich abweichen können. In dem künftigen performance‐basierten Dauerhaftigkeitskonzept ist zudem die direkte Prüfung der relevanten Parameter (Karbonatisierungsrate, Chlorideindringung usw.) mit einem vergleichsweise hohen Aufwand verbunden. Es wird in der Praxis ohnehin nicht umsetzbar sein, die dauerhaftigkeitsrelevanten Eigenschaften im hinreichenden Umfang über die direkten Prüfverfahren zu überwachen. Vielmehr ist die Qualität des Betons auf der Baustelle durch indirekte Schnellprüfverfahren (z.B. Wenner‐Sonde) zu bewerten, die damit verbunden in engeren Zeitabständen durchführbar und somit auch baustellengerecht sind. Hierzu liegen jedoch noch keine ausreichenden Erfahrungen über die Anwendbarkeit und Reproduzierbarkeit auf den Baustellen vor.
Mechanical properties of fiber‐reinforced calcium sulfoaluminate cement mortars
Authors: Xu Linglin , Cai Qiang , Ouyang Jun , Liu Sijia , Yang Zhenghong , Wu Kai 
Published: December 2023

AbstractFiber contributes to the mechanical strength and toughness improvement of cementitious materials. In this study, effects of fibers types on the mechanical properties of sulphoaluminate (CSA) cement mortar were studied from aspects of mechanical strength and toughness. Polyvinyl alcohol fiber (PVAF) and steel fiber (SF) were chosen, with consecutive volumetric content from 0.4%, 0.8%, 1.2%, to 1.6%. Results show that the compressive strength of CSA cement mortar increases gradually with the increase of PVAF content within 1.2%. When the content exceeds 1.6%, the strength of PVAF reinforced CSA cement mortar decreases due to the agglomeration of fibers. The compressive strength of SF reinforced mortar increases with the increase of fiber content. Owing to the high bending stress and strength, SF shows better toughness in the bending test. PVAF exhibits better toughness in the tensile test, which is related to its better bonding with matrix.
Spatially resolved analysis of the progression of freeze‐thaw damage in concrete
Authors: Kind Vanessa Mercedes , Werneck Chiara , Müller Matthias , Unbehau Sophie , Ludwig Horst‐Michael , Dehn Frank 
Published: December 2023

AbstractTo assess the durability of concrete structures, it is necessary to understand not only how deterioration evolves over time but also how the damage progresses through the structure. To determine the evolution of the freeze‐thaw damage, different damage criteria were examined in a spatially resolved manner during the CIF test. By measuring the ultrasound pulse velocity (UPV) in different axes, depth‐dependent changes of the relative dynamic modulus of elasticity (RDME) were investigated. The RDME started to decrease in regions close to the surface, whereas the RDME in regions farther from the test surface decreased with higher speed. Changes in the water content during the CIF test were examined by nuclear magnetic resonance (NMR). The freeze‐thaw exposed specimens showed an increase in their water content that is assumed due to the micro‐ice‐lens pump as well as microstructural changes. These changes progressed from the surface into deeper layers of the specimens, following an increase of saturation also progressing into the concrete. To consider the frost damage evolution in service life design, the authors propose the use of depth‐dependent threshold values for freeze‐thaw exposed concrete structures.
Einflussfaktoren auf den Rapid Chloride Migration Test zur Bewertung des Chloridwiderstands von Beton
Authors: Fischer Christian , Drenkard Hannah 
Published: December 2023

AbstractDauerhafte Stahlbetonbauwerke sind besonders unter chloridexponierten Umgebungsbedingungen entscheidend von Art und Ausführung des Betons abhängig. Ein wesentlicher Parameter für die Bewertung ist in diesem Zusammenhang der Chloridwiderstand des Betons. Der häufig zur Bestimmung dieses Parameters eingesetzte Rapid Chloride Migration Test (RCM‐Test) ist für den deutschen und europäischen Bereich in der DIN EN 12390‐18, dem BAW Merkblatt MDCC und dem NT Build 492 geregelt. Die meisten Randbedingungen sind identisch, doch gibt es u.a. Unterschiede in der Zusammensetzung der Prüflösung (Katholyt). Der NaCl‐Gehalt und die Verwendung von KOH können, je nach Prüfvorschrift, in gewissen Grenzen gewählt werden. Die variierenden Chlorid‐ und Alkalikonzentrationen wurden an Mörtel‐ und Betonproben mit unterschiedlichen Bindemitteln untersucht. Es zeigt sich ein differenzierter Einfluss auf den Migrationskoeffizienten. Zusammenfassend kann festgehalten werden, dass der ermittelte Chloridmigrationskoeffizient mit zunehmendem Chloridgehalt und abnehmender Alkalikonzentration in der Prüflösung steigt. Vor dem Hintergrund des Konzepts der Expositions‐Widerstandsklassen können die Ergebnisse einen Beitrag zur besseren Interpretation der im RCM‐Test gewonnenen Daten leisten.