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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.
Algal biofilm façades are an alternative to traditional green façades which can help to improve biodiversity and air quality within cities. They present a low maintenance approach in which subaerial algae are grown directly on concrete substrates. The intrinsic bioreceptivity of the substrate is a critical factor in successful facade colonisation. Existing research has identified several environmental and material properties which influence concrete bioreceptivity, however a consensus has yet to be made on which properties are most influential and how the interaction between properties may promote algal biofilm growth under specific conditions.
Building envelopes & natural rock surfaces represent the frontier between solid material surfaces, biosphere and the atmospheric environment – and are subject to permanent change in structure and chemistry. These surfaces are a natural habitat of subaerial rock biofilms (SAB) that are an important stage of primary succession. As their metabolic processes have a great impact on the composition of the near-surface layers of the earth biofilms on natural and manmade hard substrates are a research focus of geomicrobiology. In technical systems immobilized algae biofilms are already used successfully for wastewater cleaning. Algae can eliminate bacteria from the water and at the same time increase the oxygen concentration and the pH value in the water through photosynthesis, which again allows phosphate elimination to take place. Nitrificants contained in the algae biofilm convert ammonium to nitrite and nitrate.
Mineral claddings for building facades could be engineered to sustain either natural or previously established carefully selected algae-dominated biofilms and this way help to clean the air.
For a targeted engineering of the mineral substrates and the biofilms attached to them basic knowledge is however missing. By systematic research in an interdisciplinary team of microbiologists and building material scientists the following questions shall be clarified
• How can a curated biofilm be stabilized on the surface and designed to be durable without compromising the substrate
• What exactly do the biofilms need in terms of moisture in their respective growth stages? Or how long water must be available in what form and quantity to enable growth.
• What is the influence of the substrate on the availability and quality of the (rain) water (water quality, leaching of substances (alkalis) from the building materials, leaching of aerosol components, surface tension, suction tension, thickness of the water molecule layers adsorbed in the pore spaces....)
There are several research groups working on bioreceptive building materials which emphasizes the general interest in the topic. The idea of speeding-up the process by the targeted establishment of biofilms on building façade panels is a unique approach that has so far only been researched at BAM. Architects are very interested in biofilm facades as a new co-designing method of humans and nature reflecting the changing awareness for the loss of biodiversity in cities. If the biofilms need irrigation the evaporative cooling would reduce the urban heat island effect.
The bond between polymer fibers and the surrounding cementitious matrix is essential for the development of concrete reinforcement. The single fiber pull-out test (SFPT) is the standard characterization technique for testing the bond strength. However, the different phases of debonding cannot be distinguished by the SFPT. This study investigates the debonding of different polymer fibers from the surrounding cementitious matrix with a modified SFPT and proposes methods to change the SFPT setup to generate more valuable information on the debonding mechanism. The SFPT was equipped with linear variable differential transformers (LVDT), digital image correlation (DIC) and acoustic emission (AE) analysis. The results demonstrate that the modified SFPT allows a better understanding of the different phases of debonding during fiber pull-out. Furthermore, bond strength values calculated by different methods reveal that the chemical bond of the investigated polymers is not different as reported by previous studies. Deformation measurements performed using LVDTs and DIC are suitable measuring techniques to characterize the debonding mechanism in SFPT. A correlation between recorded AE and debonding phases was not found.
The accelerating climate crisis results in a rising demand for ecologically driven concepts. Regarding construction, this does not only include environmentally friendly materials but also the establishment of greenery in urban regions.
This contribution presents the progress of two projects in which textured concrete slabs were designed to grow a stable biofilm of photosynthetic eukaryotic organisms. The greened panels represent an alternative to classic fa9ade greening with plants. Current literature suggests that the development of bioreceptive surface materials in the construction sector is difficult because there are no standardized methodological approaches for measuring said bioreceptivity. Therefore, the long-term. ahn is proposing a suitable measurement concept combining material Science and biology. Among other things, the intrinsic Substrate property pH value is expected to have a significant influence on biological colonization. In the current contribution the focus lies on the theoretical approach and design of experiment regarding this parameter.
Available experimental data will be presented.
Materials that support natural biodiversity on their surfaces can compensate for human activities that have a negative impact on nature and thus contribute to a carbon-neutral and nature-positive world. Specifically designing bioreceptive materials which favor the growth of biofilms on their surface is an approach complementing conventional, macroscopic green façades. But what exactly characterizes a bioreceptive substrate and how do biofilm and substrate interact? How and why does a spontaneous colonization and the formation of biofilms take place? What are biofilms and how can they be established in a laboratory setting? How can this existing knowledge be transferred to the artificial stone concrete so that this material can be tuned to increase (or decrease) its bioreceptivity?
This review paper aims at summarizing the existing state of knowledge on bioreceptive concrete and pointing out inconsistencies and contradictions which can only be removed by more interdisciplinary research in the field.
Understanding the fundamentals of bioreceptivity enables the developement of functionalized materials. Concrete as the most used building material worldwide is of special interest as microbially greened panels may represent an alternative to classic façade greening with plants. This project includes extensive outdoor experiments, in which eight differently structured concrete panels are weathered under different conditions, aiming to grow a stable biofilm of photosynthetic eukaryotic organisms. Documentation and data analysis of this experiment will be demonstrated using an example of one of the surfaces.
NMR is becoming increasingly popular for the investigation of building materials as it is a non-invasive technology that does not require any sample preparation nor causes damage to the material. Depending on the specific application it can offer insights into properties like porosity and spatial saturation degree as well as pore structure. Moreover it enables the determination of moisture transport properties and the (re-)distribution of internal moisture into different reservoirs or chemical phases upon damage and curing. However, as yet most investigations were carried out using devices originally either designed for geophysical applications or the analysis of rather homogeneous small scale (< 10 mL) samples. This paper describes the capabilities of an NMR tomograph, which has been specifically optimized for the investigation of larger, heterogeneous building material samples (diameters of up to 72 mm, length of up to 700 mm) with a high flexibility due to interchangeable coils allowing for a high SNR and short echo times (50 - 80 m s).
Alkali-silica reaction (ASR) is a chemical reaction within concrete which can lead over time to cracking and spalling. Due to the complexity of the problem, it still causes damage to concrete constructions worldwide.
The publication aims to illustrate the interdisciplinary research of the German Federal Institute for Materials Research and Testing (BAM) within the last 20 years, considering all aspects of ASR topics from the macro to the micro level. First, methods for characterization and assessment of ASR risks and reaction products used at BAM are explained and classified in the international context. Subsequently the added value of the research approach by combining different, preferably nondestructive, methods across all scales is explained using specific examples from a variety of research projects. Aspects covered range from the development of new test-setups to assess aggregate reactivity, to analysis of microstructure and reaction products using microscopical, spectroscopical and X-ray methods, to the development of a testing methodology for existing concrete pavements including in-depth analysis of the visual damage indicator and the de-icing salt input using innovative testing techniques. Finally, research regarding a novel avoidance strategy that makes use of internal hydrophobization of the concrete mix is presented.