Birgit Meng

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.

Effects of Superplasticizer and Viscosity-Modifying Agent on Fresh Concrete Performance of SCC at Varied Ambient Temperatures

Varying ambient temperatures in plants or on construction sites during casting of SCC can cause serious problems affecting the fresh concrete performances, such as rheological properties and setting time, with consequences for the hardened properties in the structure. By sensible choices of the components, the robustness of SCC mixtures against temperature variations can be improved. However, this aspect has not been the focus of intensive research yet. In this study the effects of varied ambient temperatures on the early performance of differently composed SCC mixtures are investigated, with emphasis on changes in rheology, early deformations, heat evolution and setting. Focus is placed on the study of the influence of the polycarboxylate ether molecule type as well as different viscositymodifying agents on the temperature robustness. Effects on the relevance for practical concrete applications are evaluated, which will provide a reliable framework of possible actions on the appropriate use of admixtures for SCC.

Polypropylene Fibres and Micro Cracking in Fire Exposed Concrete

Though, concrete in general is a non-combustible building material, modern High Performance Concrete (HPC) is very susceptible to violent explosive spalling during a fire attack. This requires protective measures for fire safety design of concrete structures. The current most worthwhile method to prevent explosive spalling is the addition of monofilament Polypropylene fibres (PP-fibres). However, since it has become common knowledge that PP-fibres are suitable for fire safety design, a variety of theories concerning the mode of action of PP-fibres have been suggested. The present article summarizes the most important hypothesis and presents an innovative method for the analysis of micro structural processes in heated specimens. The results show that due to the thermal decomposition of PP-fibres capillary channels are created. Simultaneously, a netlike micro crack formation occurs, which connects these capillary channels. This enables the relief of internal stresses (mechanical effect) and the formation of a permeable transport system for the escaping water vapour (permeation effect).

Detection of early-age cracking due to restrained autogenous shrinkage

The influence of the mix composition on the early-age autogenous shrinkage of high-strength cement paste with and without silica fume and the resulting crack formation were investigated. The mechanisms of autogenous shrinkage were studied systematically by linking the measured deformations to hydration kinetics and to pore structure data. The time t0 which assigns the transition from the plastic state to a solid structure was determined by analysis of the measured strain rate. It was demonstrated that the autogenous shrinkage correlates reasonably well with the self-desiccation and the thereby expected capillary stresses. The crack formation was detected using acoustic emission (AE) analysis. AE measurements were performed simultaneously on hardening silica fume cement pastes with and without external restraint of deformation. The results showed that the intense autogenous shrinkage during the acceleration period of cement hydration was associated with the begin of micro cracking shortly after t0, irrespective of the existence of external restraint. The cracking was more pronounced in the case of restraint.

Concept for a holistic sustainability assessment of the end-of-life phase of masonry

Abstract In Germany, a quantity of more than 10 million metric tons of masonry rubble is generated per year. With regard to a sustainable closed substance cycle waste management, these rest masses have to be recovered if possible. The end-of-life (EOL) phase of masonry includes the planning steps of demolition, processing and application. The choice of the most sustainable solution raises questions regarding material technology, plant engineering, economic efficiency and ecological issues. For this purpose, a methodological concept for a holistic assessment of the EOL phase of masonry is developed within the scope of a doctoral thesis. For the assessment the Cost-Effectiveness Analysis (CEA) is adapted. The assessment concept enables a holistic comparison of different EOL scenarios for masonry while integrating all planning steps. It combines Material Flow Analysis (MFA), Life Cycle Analysis (LCA), Life Cycle Working Environment (LCWE), economic evaluation methods and material testing. In future, various scenarios can be evaluated with regard to the goals of the European and German waste management industry.

Influence of Polypropylene Fibres on the Thermal Strain of High Strength Concrete at High Temperatures

This paper presents the results of an experimental study on the influence of polypropylene (PP) fibres on the thermal strain of high strength concrete (HSC) at temperatures up to 750°C. Concerning this topic only few results can be found in the literature and systematic investigations are missing. However, basic knowledge is necessary to understand the internal damage processes as well as for structural design.To explain the differences in the thermal strain of HSC with and without addition of PP fibres the internal damage processes were investigated with acoustic emission (AE) analysis and ultrasound (US). Furthermore the weight loss was measured continuously during heating to monitor the drying of the specimen. This novel approach by combining these different methods with strain measurements at high temperatures allows the integral description of the internal damage processes. The results reveal significant differences in the thermal strain of HSC when PP fibres are added. Between 200°C and 250°C the th...

Computational Modeling of SCC Flow through Reinforced Sections

Computational modeling of fresh SCC flow is a comprehensive and time consuming task. The computational time is additionally increased when simulating casting of reinforced sections, where each single reinforcement bar has to be modeled. In order to deal with this issue and to decrease the computational time, an innovative approach of treating a reinforcement network as a porous medium is applied. This contribution presents the model for concrete flow through reinforced sections, based on Computational Fluid Dynamics (CFD), coupling a single-phase flow model for SCC and a continuum macroscopic model for porous medium. In the last part of this paper, numerical simulations are compared with experimental results obtained on model fluids.

Prompt Phase Analyses of Ultrahigh-Performance Concrete

AbstractPowder X-ray diffraction is a time-consuming and challenging task, especially for preparation of sensitive phases like ettringite and calcium-silicate-hydrate (C-S-H) phases. Fine-grained u...

Zwangsinduzierte Rissbildung in Hochleistungsbeton durch autogenes Schwinden

In diesem Beitrag werden Untersuchungsergebnisse vorgestellt, die den Einfluss von Mikrosilica auf die Selbstaustrocknung und das damit verbundene autogene Schwinden der Bindemittelmatrix von Hochleistungsbetonen beschreiben. Die dadurch hervorgerufenen Schadigungsprozesse wurden mit Hilfe von zerstorungsfreien Prufmethoden verfolgt. Dabei zeigte sich, dass eine durch auseren Zwang bedingte Mikrorissbildung durch Schallemissionsanalyse detektiert werden kann.

Components in concrete and their impact on quality: an overview

Abstract: This chapter provides a general background of the material aspects to be considered in typical testing problems. It gives an introduction and motivation for the essential issues to be discussed in more detail later in the book and in volume II, and some recommendations on how to proceed in practice. This includes a short outline of the different concrete constituents and their relation to microstructure, pointing out their relevance for the overall concrete properties.