Filtern
Dokumenttyp
Sprache
- Englisch (8)
Schlagworte
- Concrete (4)
- Biofilm (2)
- Bioreceptivity (2)
- Blended cements (2)
- Dehydration (2)
- Fire concrete spalling (2)
- High temperatures (2)
- TGA (2)
- XRD (2)
- Bauwerkssicherheit (1)
Organisationseinheit der BAM
The recommendation is based on the co-authors’ work organized by the RILEM TC 256-SPF “Spalling of concrete due to fire: testing and modelling”. It aims to provide useful information, guidance and best practices in fire spalling assessment to laboratories that perform large-scale tests based on fire resistance test standards. It provides guidance on the spalling observation techniques during testing, as well as post-test spalling quantification/assessment methods. This document is intended to be used in conjunction with the fire resistance test standards, e.g. EN 1363-1 and ISO 834-1.
The recommendation is based on the coauthors’ work organized by the RILEM TC 256-SPF ‘‘Spalling of concrete due to fire: testing and modelling’’. The Committee has defined two types of screening tests for characterization of concrete propensity to fire spalling: Material screening tests and Product screening tests. Definitions of both types of tests are given in the paper. The following recommendations apply to Material screening tests. The material screening tests described in these recommendations are a set of minimum requirements to test concrete spalling propensity (for example, the minimal specimen size). This document covers the aspects of concrete characterization, specimen geometries, storage conditions, test methods and measured parameters.
Blended cements are gaining increasing popularity due to their lower CO2-footprint in comparison to ordinary Portland cement (OPC). However, this growing use raises the potential risk of buildings made with blended cement concrete being exposed to fire, which can lead to heavy damages caused by explosive concrete spalling. It has already been shown that the cement type strongly influences the fire-induced concrete spalling and the thermally induced moisture transport, however, to understand the mechanisms behind these findings the thermal decomposition behavior of the cementitious matrix must be investigated more systematically. Therefore, the phase content of three blended cement pastes (CEM II/A-LL, CEM III/A and CEM II/B-Q) was studied in comparison with a Portland cement paste (CEM I) after temperature exposure to 20 ◦C, 105 ◦C, 300 ◦C and 500 ◦C. Clear differences in the initial phase composition and their dehydration behavior between the individual cement types were recognized. In conclusion, blended cements showed lower amounts of AFt and AFm phases and additionally lower amounts of portlandite and C-(A)-S-H were found in CEM III/A and CEM II/B-Q pastes. The results suggest that higher AFt and AFm contents in CEM I, which are associated with greater water release at relatively low temperatures may ultimately reduce the spalling risk. Furthermore, C-(A)-S-H in CEM III/A and CEM II/B-Q showed increased thermal stability and large amounts of non-hydrated phases were found in every blended cement paste. Both of those aspects might contribute to thermomechanical spalling and the overall increased spalling susceptibility observed in blended cement concrete.
Blended cements are gaining increasing popularity due to their lower CO2-footprint in compar-ison to ordinary Portland cement (OPC). However, this growing use raises the potential risk of buildings made with blended cement concrete being exposed to fire,which can lead to heavy damages caused by explosive concrete spalling. It has already been shown that the cement type strongly influences the fire-induced concrete spalling and the thermally induced moisture transport, however, to understand the mechanisms behind these findingsthe thermal decompo-sition behavior of the cementitious matrix must be investigated more systematically. Therefore, the phase content of three blended cement pastes (CEM II/A-LL, CEM III/A and CEM II/B-Q) was studied in comparison with a Portland cement paste (CEM I) after temperature exposure to 20 ◦C, 105 ◦C, 300 ◦C and 500 ◦C. Clear differences in the initial phase composition and their dehy-dration behavior between the individual cement types were recognized. In conclusion, blended cements showed lower amounts of AFt and AFm phases and additionally lower amounts of portlandite and C-(A)-S-H were found in CEM III/A and CEM II/B-Q pastes. The results suggest that higher AFt and AFm contents in CEM I, which are associated with greater water release at relatively low temperatures may ultimately reduce the spalling risk. Furthermore, C-(A)-S-H in CEM III/A and CEM II/B-Q showed increased thermal stability and large amounts of non-hydrated phases were found in every blended cement paste. Both of those aspects might contribute to thermomechanical spalling and the overall increased spalling susceptibility observed in blended cement concrete.
The climate crisis is driving an increasing demand for ecologically oriented concepts. In the building sector, this demand includes not only the use of environmentally friendly materials but also the greening of urban areas. One promising approach is the development of bioreceptive concrete façades, which support the growth of green biofilms directly on their surfaces. These innovative façades are anticipated to deliver benefits comparable to those of macroscopically greened façades, such as enhanced biodiversity and improved air quality, while offering the advantages of being more self-sustaining and stable systems once fully established.
However, the development of bioreceptive concrete presents substantial challenges. Due to the interdisciplinarity and novelty of this field, standardized methods for material characterization and bioreceptivity assessment are currently lacking. This study proposes an approach for evaluating surface properties crucial for bioreceptivity, developed on differently structured samples of ultra-high-performance concrete (UHPC). Existing methods and standards from concrete technology are critically reviewed and, where necessary, modified to meet the unique requirements of measuring bioreceptive material properties. Special attention is given to the surface pH value and water retention characteristics, as these are essential for promoting microbial growth and ensuring the long-term stability of green biofilms. The observed surface characteristics vary according to the imprinted surface structures, offering a spectrum of material properties and enabling the evaluation of their impact on bioreceptivity. The findings presented form the foundation for subsequent laboratory weathering experiments, which will be discussed in a complementary publication.
Vertical greening systems are a promising solution to the increasing demand for urban green spaces, improving environmental quality and addressing biodiversity loss. This study facilitates the development microbially greened algal biofilm facades, which offer a low maintenance vertical green space. The study focuses on concrete as a widely used building material and explores how physical surface characteristics impact its bioreceptive properties. Concrete samples, produced from the same mix but differing in surface structure, were subjected to a laboratory weathering experiment to assess their bioreceptivity. A novel inoculation method was employed, involving a single initial inoculation with either alga ( Jaagichlorella sp.) alone, or a model biofilm consisting of a combination of the alga ( Jaagichlorella sp.) with a fungus ( Knufia petricola). The samples underwent four months of weathering in a dynamic laboratory setup irrigated with deionized water to observe subaerial biofilm attachment and growth. The formation of subaerial biofilms was monitored with high resolution surface imaging, colorimetric measurements and Imaging Pulse Amplitude Modulated Fluorometry (Imaging PAM-F), with Imaging PAM-F proving the most effective. Statistical analysis revealed that by impacting surface pH value and water retention capability, surface structures significantly influence microbial growth and that the concrete’s bioreceptivity can be influenced through thoughtful design of the materials surface. The inoculation of algae combined with a fungus facilitated the formation of a stable subaerial biofilm, enabling algae to colonize a surface structure that it could not colonize alone. This finding highlights the importance of modelling synergistic interactions present in natural biofilms.
The climate crisis is driving an increasing demand for ecologically oriented concepts. In the building sector, this demand includes not only the use of environmentally friendly materials but also the greening of urban areas. One promising approach is the development of bioreceptive concrete façades, which support the growth of green biofilms directly on their surfaces. These innovative façades are anticipated to deliver benefits comparable to those of macroscopically greened façades, such as enhanced biodiversity and improved air quality, while offering the advantages of being more self-sustaining and stable systems once fully established.
However, the development of bioreceptive concrete presents substantial challenges. Due to the interdisciplinarity and novelty of this field, standardized methods for material characterization and bioreceptivity assessment are currently lacking. This study proposes an approach for evaluating surface properties crucial for bioreceptivity, developed on differently structured samples of ultra-high-performance concrete (UHPC). Existing methods and standards from concrete technology are critically reviewed and, where necessary, modified to meet the unique requirements of measuring bioreceptive material properties. Special attention is given to the surface pH value and water retention characteristics, as these are essential for promoting microbial growth and ensuring the long-term stability of green biofilms. The observed surface characteristics vary according to the imprinted surface structures, offering a spectrum of material properties and enabling the evaluation of their impact on bioreceptivity. The findings presented form the foundation for subsequent laboratory weathering experiments, which will be discussed in a complementary publication.