Urs Mueller

Deciphering the Sulfate Attack of Cementitious Materials by High-Resolution Micro-X-ray Diffraction

The durability of cementitious materials depends, among others, on their resistance against chemical attack during the service life of a building. Here, we present an approach to analyze changes in the phase composition due to chemical attack in the form of sulfate ingress within the microstructure. Micro-X-ray (μX-ray) diffraction using synchrotron radiation in Debye-Scherrer (transmission) geometry allowed a spatial resolution of 10 μm. Phase transformations in the wake of damaging processes were observed in a detailed high-resolution imaging study. In comparison, samples containing supplementary cementitious materials were investigated and used to reconstruct the influence of different degeneration processes in detail. Additionally, reaction fronts within the bulk were localized by micro-X-ray fluorescence analysis. The experimental setup provided the possibility for analyzing the phase assemblage of a given sample without destroying the microstructure. The specimens for phase analysis are thick sections of the primary material and can be used for further microscopic analysis of the microstructure and microchemistry, e.g., scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX) or Raman spectroscopy.

Performance of a New Anti-Graffiti Agent Used for Immovable Cultural Heritage Objects

Cultural Heritage objects are in many cases invaluable and irrecoverable, therefore their protection is a major goal. One threat arises by intentionally defacing such objects with graffiti. One possibility to face the imminent threat is the application of a surface protection in form of anti-graffiti systems (AGS). However, the knowledge about the performance and durability of AGS on substrates used for historical buildings is still fragmented. The goal of the present study was to investigate the performance of a newly developed anti-graffiti agent in comparison to a selection of commercial anti-graffiti agents on different substrates that were used for historical buildings. Four commercial anti-graffiti agents with different chemical formulations were selected and tested with the new agent on different stone and brick substrates. The results showed clearly that AGS based on dense, water-vapor impermeable coatings are not suitable to porous substrates such as sandstone, brick, or porous limestone due to their impairment of the hygric properties and the visual appearance of a substrate. The new agent could not completely reach the cleaning efficacy of the dense coatings but exhibited a much lower impact on the properties of the substrate and was therefore better compatible to historical surfaces.

Relevance of Hydrophobic and Oleophobic Properties of Antigraffiti Systems on Their Cleaning Efficiency on Concrete and Stone Surfaces

The problem of graffiti is not entirely restricted to urban areas, but also appears frequently in rural communities and along traffic infrastructure. Besides its aesthetic and societal effects, graffiti cause considerable removal costs and subsequent costs for repairing damages caused by improper graffiti removal. Over the last two decades, strategies have been developed to combat graffiti in the built environment, including the development of protective measures in the form of antigraffiti systems (AGSs). Antigraffiti systems promise to be affordable and easily applicable for a wide range of substrates, and many products have already been on the market for many years. In practice, however, successful application of AGS and removal of graffiti depend on many factors in which the type of coating and condition of the substrate play critical roles. The optimal environmental goal is to use AGS without any cleaning chemicals except for pure water. Available studies on the behavior of the same AGS on various substrates can show completely different results concerning the cleaning efficacy and the durability of the AGS under different climatic conditions. The question of which properties of an AGS are most essential for its efficiency has still not been fully investigated. The goal of this study was to investigate cleaning efficacy in conjunction with hydrophobic and oleophobic properties of the AGS on different substrates. The results showed that hydrophobicity and oleophobicity are important for dense substrates but have a low influence on porous substrates. In this case, cleaning efficiency is majorly determined by the physical properties of the substrates.

Structural performance of GFRP connectors in composite sandwich facade elements

To take structural aspects into consideration in the SESBE research project, focusing on the development of “smart” facade elements a systematic testing and modelling program has been developed for the verification of the structural performance of the facade sandwich elements. The present paper mainly focuses on the verification of the mechanical performance of the glass fibre reinforced polymer (GFRP) connectors of the novel type of facade element composed of reactive powder concrete (RPC) panels with foam concrete insulation between them. Because of the reduced thickness of the large facade elements, the performance of the connectors is critical for the entire structural concept. The first series of the testing programme concerning connector performance are presented here. The results suggest that sufficient strength and ductility of the connectors can be ensured using GFRP in the proposed thin light-weight facade elements.

Synthesis and Characterization of Reactive Powder Concrete for its Application on Thermal Insulation Panels

This paper describes the synthesis and characterization of a set of textile reinforced reactive powder concrete (RPC) mixes that have been prepared in the framework of the SESBE project which aims ...