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Papers by Patrick Fontana

Proceedings of 9th International Conference on Structural Analysis of Historical Constructions, SAHC 2014, Oct 2014

Connections improvement plays a key role in seismic upgrade of historical buildings. Their global... more Connections improvement plays a key role in seismic upgrade of historical buildings. Their global response is related to the behavior of the single structural elements as well as to their mutual connections. Up to now only few data are available about the performance of grouted anchor pins in earthen materials where the critical point is the bond between the grout and the earthen substrate.
In this paper, results of the experimental testing performed on earth block masonry, rammed earth and cob are presented. Pull-out tests were carried out to investigate the bond strength and failure modes of stainless steel rods with a lime based hydraulic grout and their compatibility with earthen materials. Rods with nuts were investigated to improve the pull-out capacity of the anchors. They showed higher pull-out capacity than rods without nuts. The performances of rods with nuts in cob were influenced by the rough surface at/of the earthen substrate. It is assumed that the non homogeneous surface caused an interlocking mechanism, which allowed to reach a pull-out capacity of about 54% higher than in earth block masonry.

Mauerwerk‐Kalender 2013, 2013

Schätzungen zufolge leben und arbeiten zurzeit 30 bis 40 % der Weltbevölkerung in Gebäuden aus Le... more Schätzungen zufolge leben und arbeiten zurzeit 30 bis 40 % der Weltbevölkerung in Gebäuden aus Lehm. Darunter befindet sich auch eine nicht unerhebliche Anzahl an Baudenkmälern, davon viele in einem gefährdeten Zustand. Bauwerke aus Lehm erfordern einen hohen Unterhaltungsaufwand, da sie anfällig sind für Erosion bei Regen sowie Abplatzungen und Querschnittsschwächung, wenn Salze kapillar transportiert werden und auskristallisieren. Außerdem sind sie empfindlich gegenüber mechanischen Beanspruchungen. So führen bereits relativ niedrige Zug- oder Druckspannungen zu Schädigungen durch Rissbildung. Einige Lehmbauweisen werden heute nicht mehr ausgeführt und das Wissen über sie ist zumindest teilweise verloren gegangen. Die verschiedenen Lehmbauweisen unterscheiden sich deutlich in Bezug auf die Zusammensetzung des Materials und die Bautechniken. Obwohl einige Regelwerke für das Bauen mit Lehm zur Verfügung stehen, z. B. ASTM E2392 / E2393 M [1], NTE E.080 Adobe [2] und IS13827 [3] fehlen häufig Bemessungsregeln für den Tragwerksplaner. Darüber hinaus wird bei den angegebenen Kennwerten nicht die große Variabilität der Lehmbaustoffe hinsichtlich ihrer mechanischen Eigenschaften berücksichtigt, die von einer ganzen Reihe verschiedener Parameter abhängen, wie z. B. Partikelgrößenverteilung, Feuchtegehalt, Art der Tonminerale, Fasergehalt oder Verdichtung. Weiterhin ist festzustellen, dass das Wissen über die Materialeigenschaften und die Versagensmechanismen bei Lehmbaustoffen begrenzt ist [5]. Deshalb wurden im Rahmen des EU-Projekts NIKER die mechanischen Eigenschaften von Bauteilen aus Lehm bestimmt. Ziel war es, grundlegende Daten zum Festigkeits- und Verformungsverhalten von Lehmbauteilen zu erhalten. Hierfür wurden unter anderem Druck- und Schubversuche an Prüfkörpern aus Lehmmauerwerk durchgeführt.

In this paper a modelling approach is presented to reproduce the mechanical behaviour of sandwich... more In this paper a modelling approach is presented to reproduce the mechanical behaviour of sandwich panels via finite element analysis. Two types of panels were investigated in this scope of work. The first sandwich element was a textile reinforced concrete (TRC) panel with cellular lightweight concrete insulation and the second configuration was an ultra-high performances concrete (UHPC) panel with aerated autoclaved concrete insulation. The goal was to obtain a reliable numerical strategy that represents a reasonable compromise in terms of sufficient accuracy of the element characteristics and the computational costs. The results show the possibility of describing the composite action in a full sandwich panel. The achieved modelling approach will later be used for the optimization of TRC and UHPC panels in terms of minimizing the thickness, identifying the number and location of connectors, as well as evaluating varying anchorage systems.

The current paper focuses on the determination of reliable numerical models of earth block masonr... more The current paper focuses on the determination of reliable numerical models of earth block masonry wallettes under different loading conditions. Uniaxial compression and diagonal compression tests were performed. Experimental behaviour was modelled with a non-linear model able to describe the cracking behaviour. The simplified approach based on macro-modelling shows a satisfactory accuracy and low computational costs. The results reproducing the uniaxial compression are in good correspondence with the post-elastic behaviour observed in the experimental campaign. The micro-modelling approach adopted to reproduce the shear behaviour, even with high computational cost, represents a suitable tool to predict the masonry collapse mechanism.

Journal of Facade Design and Engineering, vol. 3, no. 1, May 2015

The awareness of the environmental impact of the building sector is increasing. Steel reinforced ... more The awareness of the environmental impact of the building sector is increasing. Steel reinforced concrete is the most commonly used construction material though with a high embodied energy and carbon footprint. Large environmental gains may arise if an alternative to steel reinforced concrete is developed. In this context, ultra-high performance concrete (UHPC) materials are shown to be promising alternatives with advantages such as lower embodied energy and reduced environmental impact. Predictions suggest that UHPC composite elements for building envelopes could have other benefits such as an increased service life, optimised use of building area due to thinner elements and minimised maintenance due to the absence of reinforcement or use of non-corrosive reinforcing materials such as carbon fibres. In the framework of the H-HOUSE project funded by the European Commission, composite elements are developed. The aim is to create façade panels combining an autoclaved aerated concrete or cellular lightweight concrete insulation layer with an external UHPC supporting layer. To enhance occupant comfort and health, hygroscopic materials that are capable to buffer indoor air humidity shall be applied to the inside of such elements. Indoor air humidity levels are expected to be more stable which shall subsequently improve the indoor climate and minimise potential decay to the construction.

Proceedings of 9th International Masonry Conference, 9IMC 2014, Jul 2014

Connections improvement plays a key role in seismic upgrade of historical buildings. Their global... more Connections improvement plays a key role in seismic upgrade of historical buildings. Their global response is related to the behaviour of the single structural elements as well as by their mutual connections. Up to now limited data is available on the performance of grouted anchor pins in earthen materials where the critical point is the bond between the grout and the earthen substrate.
In this paper results of the experimental testing performed on earth block masonry are presented. Pull-out tests were carried out to investigate the bond strength and failure modes of stainless steel as well as glass fiber reinforced polymer (GFRP) rods with a lime based hydraulic grout and their compatibility with earth block masonry. GFRP rods were investigated as an alternative bonded-in anchorage material to the commonly used steel. In comparison with steel, they have a reduced weight and a reduced coefficient of thermal expansion. Their lower modulus of elasticity seems to be more compatible with the modulus of elasticity of earthen materials, although they exhibit a brittle fracture with lack of plastic phase.

Beton- und Stahlbetonbau, 2005

In this paper results of the experimental testing performed on brick masonry and earth block maso... more In this paper results of the experimental testing performed on brick masonry and earth block masonry are presented. The paper outlines the development of the testing procedures for two different types of anchors. For this purpose, two experimental campaigns of pull-out tests on masonry corner connections strengthened by metallic rod grouted were carried out. Experimental results proved that the implemented testing procedures are suitable to determine the most recurring failure modes of the anchor pins. Moreover, a procedure is proposed to estimate the capacity of grouted anchor pins based on experimental studies.Mit diesem Beitrag soll die experimentelle Beurteilung von Verpressankern für Mauerwerk vorgestellt werden. Es wurden zwei Versuchsserien mit Ankerauszugsversuchen an Mauerwerksecken aus Ziegel- und Lehmsteinmauerwerk durchgeführt. Die Versuchsergebnisse haben gezeigt, dass die gewählten Versuchsabläufe geeignet sind, die am häufigsten wiederkehrenden Versagensarten der Verpressanker zu bestimmen. Darüber hinaus wird eine Vorgehensweise vorgeschlagen, die es ermöglicht, die Traglast von Verpressankern auf Basis experimenteller Untersuchungen abzuschätzen.

International RILEM Conference on Volume Changes of Hardening Concrete: Testing and Mitigation, 2006

The influence of the mix composition on the early-age deformations of the cement paste matrix of ... more The influence of the mix composition on the early-age deformations of the cement paste matrix of high-strength and self-compacting concretes has been investigated. Linear deformation measurements were started prior to setting. Setting (distinction between plastic and stress inducing shrinkage) was determined by analysis of deformation velocity. The measured deformations were linked to the hydration of the binders and to the structural properties of the hardening pastes. The effect of mineral and organic additives on the cement hydration was systematically assessed with isothermal calorimetry and thermogravimetric analysis. Based on hydration data the capillary tension (as the presumed main driving force of autogenous shrinkage) was estimated using pore structure data determined by mercury intrusion porosimetry. From the results conclusions were drawn on the deformation behaviour of the cement pastes.

Ultra High Performance Concrete (UHPC) is defined as a concrete yielding compressive strength abo... more Ultra High Performance Concrete (UHPC) is defined as a concrete yielding compressive strength above 150 MPa. Heat treatment up to 90° C is already in use for curing UHPC. With our study we wanted to go one step further by autoclaving UHPC. The main interest of our study was focused in how the nano structure and phase equilibrium was changed and any major advantages to normal heat curing under atmospheric pressure. First results of fly ash containing autoclaved UHPC at 200° C/15 bars showed that hydration evolved to a much larger extend than the series cured under ambient conditions, leading to a higher density of the cement paste. From high-resolution SEM-BSE images it became evident that micro pores and flaws are filled with short fibred Ca-silicate hydrate crystals what agrees well with the increased compressive and flexural strength. In addition the reaction of quartz grains with pore fluid led to the crystallization of a C-S-H phase, rich in silica around the quartz grain boundaries. Significant was the appearance of a sulfur rich calcium silicate hydrate replacing former portlandite precipitations. Micro chemical analysis revealed a general increase of the cement paste's atom ratios of Si/Ca with a ratio of 0.75 at 150 °C/5 bars and the appearance of crystals of afwillite, foshagite and xonotlite. At 200 °C/15 bar Si/Ca atom ratios ranged from 0.75 to 1.1 and crystals of tobermorite, xonotlite and gyrolite were observed. In all autoclaved specimens portlandite was not anymore detected. The results showed that by autoclaving UHPC at 200 °C and 15 bar the micro/nano structural as well as its mechanical properties can be increased significantly. Future work will be focused on using different types of secondary cementitious materials for the replacement of cement.

Autoclaving of UHPC has a significant influence on its micro structure and its mechanical propert... more Autoclaving of UHPC has a significant influence on its micro structure and its mechanical properties. It generally leads to enhanced cement hydration and accelerated pozzolanic reactions forming crystalline CSH. Quartz fillers are added usually to UHPC in order to optimise the particle size distribution and may improve the mechanical properties of UHPC by partial reaction and thus enhanced cohesion to the cement paste when autoclaving is applied. In the first part of our study we added secondary cementitious materials to the UHPC in order to reduce the very high amounts of cement and silica fume commonly used in UHPC. Due to the autoclaving these materials were activated to a large extent and contributed to the hydration process by significant reactivity. In the second part of our study we replaced the quartz filler by recycled industrial waste materials in order to compare their reactivity and their contribution to structural changes during autoclaving. The results showed that the ...

Betonwerk und Fertigteil-Technik/Concrete Precasting Plant and Technology

Das Gefüge von UHPC ist durch eine dicht gepackte und fehlstellenarme Matrix gekennzeichnet. Eine... more Das Gefüge von UHPC ist durch eine dicht gepackte und fehlstellenarme Matrix gekennzeichnet. Eine zusätzliche Optimierung ist durch eine Wärmebehandlung bzw. hydrothermale Nachbehandlung (Autoklavierung) unter einem Wasserdampfsättigungsdruck möglich. Die Wärmebehandlung von Beton ist ein in der Betonfertigteilindustrie geläufiges Verfahren, um die Erstarrungszeit zu verkürzen und höhere Frühfestigkeiten zu erreichen. Bei der Autoklavierung wird der Beton zusätzlich mit Wasserdampf druckbehandelt, wodurch sich die Hydratationsbedingungen deutlich verbessern. Dieses Verfahren ist aus der Porenbetonindustrie bekannt, wo die Herstellung großformatiger Bauteile gängige Praxis ist. Die umfangreichen Untersuchungen der BAM hatten den Einfluss von Wärmebehandlung und Autoklavierung auf die Eigenschaften von UHPC ohne und mit Stahlfaserbewehrung zum Inhalt. Dabei sollte geklärt werden, auf welche Weise und in welchem Umfang mikrostrukturelle Veränderungen erfolgen und wie sich diese auf die...

Industrial byproducts and natural pozzolanas are increasingly being used as supplementary cementi... more Industrial byproducts and natural pozzolanas are increasingly being used as supplementary cementitious materials. In the group of natural pozzolanas volcanic ashes are the most prominent. Despite the fact that volcanic pozzolanas were used since Roman times, not much is known about their role in influencing the long term durability of concrete. The paper presents results of the volcanic pozzolana ‘Rhenish trass’, which is quarried in western Germany and its role during an alkali silica reaction (ASR). Field data and laboratory experiments indicate that trass releases alkalis into the pore solution but also changes cement paste chemistry and alkali binding behavior. There seems to be a sensitive balance between alkali release and increase of alkali binding capacity, both mechanisms crucial for the course of an ASR in concrete.

Brittle Matrix Composites 9, 2009

Cement and Concrete Composites, 2015

ABSTRACT Water-repellent mortars were prepared using different hydrophobic compounds as admixture... more ABSTRACT Water-repellent mortars were prepared using different hydrophobic compounds as admixtures. Calcium and zinc stearates, silane/siloxane products (as liquid solution and powder) were mixed into limestone cement mortars for obtaining in-bulk water-repellent mortars suitable for building protection and resistant to the degrading action of water. The influences of the admixtures on the hydration and structure of the designed mortars were investigated by SEM, TG-DSC, FT-IR, XRD, and isothermal calorimetry. The effectiveness of these agents against water action was evaluated by using techniques and methods such as mercury intrusion porosimetry, water absorption tests and contact angle measurements. Siloxane products conveyed good water-repellent effectiveness, without strongly influencing the setting and hydration of the binder, while the zinc stearates slowed down the hydration reactions.

Proceedings of 9th International Conference on Structural Analysis of Historical Constructions, SAHC 2014, Oct 2014

Connections improvement plays a key role in seismic upgrade of historical buildings. Their global... more Connections improvement plays a key role in seismic upgrade of historical buildings. Their global response is related to the behavior of the single structural elements as well as to their mutual connections. Up to now only few data are available about the performance of grouted anchor pins in earthen materials where the critical point is the bond between the grout and the earthen substrate.
In this paper, results of the experimental testing performed on earth block masonry, rammed earth and cob are presented. Pull-out tests were carried out to investigate the bond strength and failure modes of stainless steel rods with a lime based hydraulic grout and their compatibility with earthen materials. Rods with nuts were investigated to improve the pull-out capacity of the anchors. They showed higher pull-out capacity than rods without nuts. The performances of rods with nuts in cob were influenced by the rough surface at/of the earthen substrate. It is assumed that the non homogeneous surface caused an interlocking mechanism, which allowed to reach a pull-out capacity of about 54% higher than in earth block masonry.

Mauerwerk‐Kalender 2013, 2013

Schätzungen zufolge leben und arbeiten zurzeit 30 bis 40 % der Weltbevölkerung in Gebäuden aus Le... more Schätzungen zufolge leben und arbeiten zurzeit 30 bis 40 % der Weltbevölkerung in Gebäuden aus Lehm. Darunter befindet sich auch eine nicht unerhebliche Anzahl an Baudenkmälern, davon viele in einem gefährdeten Zustand. Bauwerke aus Lehm erfordern einen hohen Unterhaltungsaufwand, da sie anfällig sind für Erosion bei Regen sowie Abplatzungen und Querschnittsschwächung, wenn Salze kapillar transportiert werden und auskristallisieren. Außerdem sind sie empfindlich gegenüber mechanischen Beanspruchungen. So führen bereits relativ niedrige Zug- oder Druckspannungen zu Schädigungen durch Rissbildung. Einige Lehmbauweisen werden heute nicht mehr ausgeführt und das Wissen über sie ist zumindest teilweise verloren gegangen. Die verschiedenen Lehmbauweisen unterscheiden sich deutlich in Bezug auf die Zusammensetzung des Materials und die Bautechniken. Obwohl einige Regelwerke für das Bauen mit Lehm zur Verfügung stehen, z. B. ASTM E2392 / E2393 M [1], NTE E.080 Adobe [2] und IS13827 [3] fehlen häufig Bemessungsregeln für den Tragwerksplaner. Darüber hinaus wird bei den angegebenen Kennwerten nicht die große Variabilität der Lehmbaustoffe hinsichtlich ihrer mechanischen Eigenschaften berücksichtigt, die von einer ganzen Reihe verschiedener Parameter abhängen, wie z. B. Partikelgrößenverteilung, Feuchtegehalt, Art der Tonminerale, Fasergehalt oder Verdichtung. Weiterhin ist festzustellen, dass das Wissen über die Materialeigenschaften und die Versagensmechanismen bei Lehmbaustoffen begrenzt ist [5]. Deshalb wurden im Rahmen des EU-Projekts NIKER die mechanischen Eigenschaften von Bauteilen aus Lehm bestimmt. Ziel war es, grundlegende Daten zum Festigkeits- und Verformungsverhalten von Lehmbauteilen zu erhalten. Hierfür wurden unter anderem Druck- und Schubversuche an Prüfkörpern aus Lehmmauerwerk durchgeführt.

In this paper a modelling approach is presented to reproduce the mechanical behaviour of sandwich... more In this paper a modelling approach is presented to reproduce the mechanical behaviour of sandwich panels via finite element analysis. Two types of panels were investigated in this scope of work. The first sandwich element was a textile reinforced concrete (TRC) panel with cellular lightweight concrete insulation and the second configuration was an ultra-high performances concrete (UHPC) panel with aerated autoclaved concrete insulation. The goal was to obtain a reliable numerical strategy that represents a reasonable compromise in terms of sufficient accuracy of the element characteristics and the computational costs. The results show the possibility of describing the composite action in a full sandwich panel. The achieved modelling approach will later be used for the optimization of TRC and UHPC panels in terms of minimizing the thickness, identifying the number and location of connectors, as well as evaluating varying anchorage systems.

The current paper focuses on the determination of reliable numerical models of earth block masonr... more The current paper focuses on the determination of reliable numerical models of earth block masonry wallettes under different loading conditions. Uniaxial compression and diagonal compression tests were performed. Experimental behaviour was modelled with a non-linear model able to describe the cracking behaviour. The simplified approach based on macro-modelling shows a satisfactory accuracy and low computational costs. The results reproducing the uniaxial compression are in good correspondence with the post-elastic behaviour observed in the experimental campaign. The micro-modelling approach adopted to reproduce the shear behaviour, even with high computational cost, represents a suitable tool to predict the masonry collapse mechanism.

Journal of Facade Design and Engineering, vol. 3, no. 1, May 2015

The awareness of the environmental impact of the building sector is increasing. Steel reinforced ... more The awareness of the environmental impact of the building sector is increasing. Steel reinforced concrete is the most commonly used construction material though with a high embodied energy and carbon footprint. Large environmental gains may arise if an alternative to steel reinforced concrete is developed. In this context, ultra-high performance concrete (UHPC) materials are shown to be promising alternatives with advantages such as lower embodied energy and reduced environmental impact. Predictions suggest that UHPC composite elements for building envelopes could have other benefits such as an increased service life, optimised use of building area due to thinner elements and minimised maintenance due to the absence of reinforcement or use of non-corrosive reinforcing materials such as carbon fibres. In the framework of the H-HOUSE project funded by the European Commission, composite elements are developed. The aim is to create façade panels combining an autoclaved aerated concrete or cellular lightweight concrete insulation layer with an external UHPC supporting layer. To enhance occupant comfort and health, hygroscopic materials that are capable to buffer indoor air humidity shall be applied to the inside of such elements. Indoor air humidity levels are expected to be more stable which shall subsequently improve the indoor climate and minimise potential decay to the construction.

Proceedings of 9th International Masonry Conference, 9IMC 2014, Jul 2014

Connections improvement plays a key role in seismic upgrade of historical buildings. Their global... more Connections improvement plays a key role in seismic upgrade of historical buildings. Their global response is related to the behaviour of the single structural elements as well as by their mutual connections. Up to now limited data is available on the performance of grouted anchor pins in earthen materials where the critical point is the bond between the grout and the earthen substrate.
In this paper results of the experimental testing performed on earth block masonry are presented. Pull-out tests were carried out to investigate the bond strength and failure modes of stainless steel as well as glass fiber reinforced polymer (GFRP) rods with a lime based hydraulic grout and their compatibility with earth block masonry. GFRP rods were investigated as an alternative bonded-in anchorage material to the commonly used steel. In comparison with steel, they have a reduced weight and a reduced coefficient of thermal expansion. Their lower modulus of elasticity seems to be more compatible with the modulus of elasticity of earthen materials, although they exhibit a brittle fracture with lack of plastic phase.

Beton- und Stahlbetonbau, 2005

In this paper results of the experimental testing performed on brick masonry and earth block maso... more In this paper results of the experimental testing performed on brick masonry and earth block masonry are presented. The paper outlines the development of the testing procedures for two different types of anchors. For this purpose, two experimental campaigns of pull-out tests on masonry corner connections strengthened by metallic rod grouted were carried out. Experimental results proved that the implemented testing procedures are suitable to determine the most recurring failure modes of the anchor pins. Moreover, a procedure is proposed to estimate the capacity of grouted anchor pins based on experimental studies.Mit diesem Beitrag soll die experimentelle Beurteilung von Verpressankern für Mauerwerk vorgestellt werden. Es wurden zwei Versuchsserien mit Ankerauszugsversuchen an Mauerwerksecken aus Ziegel- und Lehmsteinmauerwerk durchgeführt. Die Versuchsergebnisse haben gezeigt, dass die gewählten Versuchsabläufe geeignet sind, die am häufigsten wiederkehrenden Versagensarten der Verpressanker zu bestimmen. Darüber hinaus wird eine Vorgehensweise vorgeschlagen, die es ermöglicht, die Traglast von Verpressankern auf Basis experimenteller Untersuchungen abzuschätzen.

International RILEM Conference on Volume Changes of Hardening Concrete: Testing and Mitigation, 2006

The influence of the mix composition on the early-age deformations of the cement paste matrix of ... more The influence of the mix composition on the early-age deformations of the cement paste matrix of high-strength and self-compacting concretes has been investigated. Linear deformation measurements were started prior to setting. Setting (distinction between plastic and stress inducing shrinkage) was determined by analysis of deformation velocity. The measured deformations were linked to the hydration of the binders and to the structural properties of the hardening pastes. The effect of mineral and organic additives on the cement hydration was systematically assessed with isothermal calorimetry and thermogravimetric analysis. Based on hydration data the capillary tension (as the presumed main driving force of autogenous shrinkage) was estimated using pore structure data determined by mercury intrusion porosimetry. From the results conclusions were drawn on the deformation behaviour of the cement pastes.

Ultra High Performance Concrete (UHPC) is defined as a concrete yielding compressive strength abo... more Ultra High Performance Concrete (UHPC) is defined as a concrete yielding compressive strength above 150 MPa. Heat treatment up to 90° C is already in use for curing UHPC. With our study we wanted to go one step further by autoclaving UHPC. The main interest of our study was focused in how the nano structure and phase equilibrium was changed and any major advantages to normal heat curing under atmospheric pressure. First results of fly ash containing autoclaved UHPC at 200° C/15 bars showed that hydration evolved to a much larger extend than the series cured under ambient conditions, leading to a higher density of the cement paste. From high-resolution SEM-BSE images it became evident that micro pores and flaws are filled with short fibred Ca-silicate hydrate crystals what agrees well with the increased compressive and flexural strength. In addition the reaction of quartz grains with pore fluid led to the crystallization of a C-S-H phase, rich in silica around the quartz grain boundaries. Significant was the appearance of a sulfur rich calcium silicate hydrate replacing former portlandite precipitations. Micro chemical analysis revealed a general increase of the cement paste's atom ratios of Si/Ca with a ratio of 0.75 at 150 °C/5 bars and the appearance of crystals of afwillite, foshagite and xonotlite. At 200 °C/15 bar Si/Ca atom ratios ranged from 0.75 to 1.1 and crystals of tobermorite, xonotlite and gyrolite were observed. In all autoclaved specimens portlandite was not anymore detected. The results showed that by autoclaving UHPC at 200 °C and 15 bar the micro/nano structural as well as its mechanical properties can be increased significantly. Future work will be focused on using different types of secondary cementitious materials for the replacement of cement.

Autoclaving of UHPC has a significant influence on its micro structure and its mechanical propert... more Autoclaving of UHPC has a significant influence on its micro structure and its mechanical properties. It generally leads to enhanced cement hydration and accelerated pozzolanic reactions forming crystalline CSH. Quartz fillers are added usually to UHPC in order to optimise the particle size distribution and may improve the mechanical properties of UHPC by partial reaction and thus enhanced cohesion to the cement paste when autoclaving is applied. In the first part of our study we added secondary cementitious materials to the UHPC in order to reduce the very high amounts of cement and silica fume commonly used in UHPC. Due to the autoclaving these materials were activated to a large extent and contributed to the hydration process by significant reactivity. In the second part of our study we replaced the quartz filler by recycled industrial waste materials in order to compare their reactivity and their contribution to structural changes during autoclaving. The results showed that the ...

Betonwerk und Fertigteil-Technik/Concrete Precasting Plant and Technology

Das Gefüge von UHPC ist durch eine dicht gepackte und fehlstellenarme Matrix gekennzeichnet. Eine... more Das Gefüge von UHPC ist durch eine dicht gepackte und fehlstellenarme Matrix gekennzeichnet. Eine zusätzliche Optimierung ist durch eine Wärmebehandlung bzw. hydrothermale Nachbehandlung (Autoklavierung) unter einem Wasserdampfsättigungsdruck möglich. Die Wärmebehandlung von Beton ist ein in der Betonfertigteilindustrie geläufiges Verfahren, um die Erstarrungszeit zu verkürzen und höhere Frühfestigkeiten zu erreichen. Bei der Autoklavierung wird der Beton zusätzlich mit Wasserdampf druckbehandelt, wodurch sich die Hydratationsbedingungen deutlich verbessern. Dieses Verfahren ist aus der Porenbetonindustrie bekannt, wo die Herstellung großformatiger Bauteile gängige Praxis ist. Die umfangreichen Untersuchungen der BAM hatten den Einfluss von Wärmebehandlung und Autoklavierung auf die Eigenschaften von UHPC ohne und mit Stahlfaserbewehrung zum Inhalt. Dabei sollte geklärt werden, auf welche Weise und in welchem Umfang mikrostrukturelle Veränderungen erfolgen und wie sich diese auf die...

Industrial byproducts and natural pozzolanas are increasingly being used as supplementary cementi... more Industrial byproducts and natural pozzolanas are increasingly being used as supplementary cementitious materials. In the group of natural pozzolanas volcanic ashes are the most prominent. Despite the fact that volcanic pozzolanas were used since Roman times, not much is known about their role in influencing the long term durability of concrete. The paper presents results of the volcanic pozzolana ‘Rhenish trass’, which is quarried in western Germany and its role during an alkali silica reaction (ASR). Field data and laboratory experiments indicate that trass releases alkalis into the pore solution but also changes cement paste chemistry and alkali binding behavior. There seems to be a sensitive balance between alkali release and increase of alkali binding capacity, both mechanisms crucial for the course of an ASR in concrete.

Brittle Matrix Composites 9, 2009

Cement and Concrete Composites, 2015

ABSTRACT Water-repellent mortars were prepared using different hydrophobic compounds as admixture... more ABSTRACT Water-repellent mortars were prepared using different hydrophobic compounds as admixtures. Calcium and zinc stearates, silane/siloxane products (as liquid solution and powder) were mixed into limestone cement mortars for obtaining in-bulk water-repellent mortars suitable for building protection and resistant to the degrading action of water. The influences of the admixtures on the hydration and structure of the designed mortars were investigated by SEM, TG-DSC, FT-IR, XRD, and isothermal calorimetry. The effectiveness of these agents against water action was evaluated by using techniques and methods such as mercury intrusion porosimetry, water absorption tests and contact angle measurements. Siloxane products conveyed good water-repellent effectiveness, without strongly influencing the setting and hydration of the binder, while the zinc stearates slowed down the hydration reactions.