Green Intelligent Building
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- 7 Bauwerkssicherheit (193)
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Paper des Monats
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The behavior of concrete under high strain rates is often described by plasticity models with softening, which is modeled by a reduction of the yield surface as a function of the local equivalent plastic strain. Among these are the RHT model, the K\&C model and the Johnson-Holmquist concrete model. These models are however local and therefore produce mesh-dependent results.
In this contribution, the gradient-enhancement of such models is investigated. First, the mesh-dependency of these local formulations based on the analysis with a modified JH2 model as a representative for these constitutive formulations is demonstrated using a one-dimensional benchmark example. The central difference method is used as solver with a diagonal mass matrix obtained from a Gauß-Lobatto integration.
In the benchmark, the width of the damaged zone decreases upon mesh-refinement and the dissipated plastic energy tends to zero. It is further shown that a significantly small safety factor for the critical time step is needed in order to achieve accurate results for the benchmark example.
Next, two gradient-enhancement approaches are investigated. The enhancement is based on the inclusion of inertia and damping to the additional Helmholtz equation which enables the use of the central difference method as an explicit solver. In the first formulation, the yield surface and therefore the softening is formulated in terms of a nonlocal equivalent plastic strain. In the second approach, a hardening term which depends on the local equivalent plastic strain is introduced to the modified JH2 model in addition to the nonlocal softening. This approach is inspired by results from gradient plasticity in quasi-static loading scenarios. It is shown that the approach without hardening can still lead to mesh-dependent results while the model that includes hardening successfully inhibits strain localization and leads to a converging dissipated plastic energy. This is further confirmed in a two-dimensional wedge-splitting experiment where the damage pattern produced by the local model is mesh-dependent as well and the dissipated plastic energy tends to zero with mesh-refinement. The proposed nonlocal model with hardening results in a consistent damage pattern and the dissipated plastic energy converges. Furthermore, the nonlocal model with hardening is less sensitive to time step refinement, such that computational efficiency can be improved compared to the local model.
The numerical experiments are implemented using the free and open-source tool FEniCSx.
The presentation summarizes the 1H NMR relaxation pinciple for the nondestructive material characterization of building materials. We explain the basic principle of NMR and showcase 3 application cases: 1) Moisture transport and 2) In-situ pore size characteriztaion of buildiing materials and 3) Hydration characteristics of new, more climate friendly cementitious binders and mortars.
Implementation, data, and results for the generation of the study "Characterization of temperature influence on the structural built-up of 3D concrete".
In this study, the influence of temperature on structural build-up is investigated. A significant temperature influence is demonstrated for three experimental setups (small amplitude oscillatory shear, constant shear rate, and small amplitude oscillatory extensional tests) using different materials.
A common modeling framework capturing the time- and temperature evolution is derived based on the maturity approach. Two alternative formulations for the time evolution were proposed. Both models were calibrated using a probabilistic approach, allowing for uncertainty quantification. The calibrated models successfully predict the structural build-up under different ambient temperature conditions.
As part of the EU Reincarnate project, BAM has developed an AI-based tool that signifi-cantly accelerates the development of materials in an iterative process of laboratory work, experimental validation, and data-driven optimization. This approach has already been suc-cessfully tested and validated. In Reincarnate SLAMD is currently being applied in demon-stration projects together with two industrial partners – a recycling company specializing in construction and demolition waste and a leading supplier of cement-based building materi-als. The recycling company aims to process recycled concrete fines and glass waste into composite cements with improved performance characteristics. The building materials' manufacturer, on the other hand, aims to reuse processed concrete waste primarily as aggre-gate and to develop suitable materials for five different exposure classes. The integration of SLAMD is envisioned to enable the rapid identification of optimal material compositions that consider the performance and ecological and economic aspects.
In addition, we currently further develop in the Circular B-I/O project, a joint effort with African partners to develop alternative, more biobased building materials. The goal is to integrate agricultural residues – such as corn cobs, rice hulls, and sugarcane bagasse – into large-scale, robust supply chains for the construction industry. AI-driven decision-making will be used to create a sustainable framework to transform these seasonally variable raw materials into reliable, high-performance concrete components. Building stable ecosystems and supply chains is crucial to ensure the continuous availability of sustainable materials for a resilient and circular construction industry.
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.
Traditionell wurde Regenwasser aus Siedlungsgebieten schnell über Kanalnetze abgeleitet. Dies führte zu einer geringeren Verdunstung und Bodenspeicherung sowie zu einem verstärkten Abfluss von versiegelten Flächen. Dadurch werden der Wasserkreislauf, das Kleinklima und die Grundwasserneubildung beeinträchtigt, während Klär- und Regenwasseranlagen belastet werden. Starkregenereignisse können die Anlagen überlasten und lokale Überschwemmungen verursachen. Gleichzeitig gelangen Schwermetalle wie Kupfer, Zink und Blei in das Wassersystem und verursachen Umweltprobleme.
Um den Wasserkreislauf ökologisch wiederherzustellen, Überschwemmungen zu verhindern und Schadstoffeinträge zu reduzieren, rücken Versickerung und Rückhaltung von Regenwasser im Sinne des Schwammstadtkonzeptes in den Fokus. Gründächer, Versickerungsmulden oder Retentionsbodenfilter verzögern den Abfluss und entlasten so die Kanalisation. Dabei spielen Filter- und Speichermaterialien eine zentrale Rolle, um das Regenwasser zusätzlich zu reinigen und nutzbar zu machen.
Durch die Nutzung recycelter Bau- und Abbruchstoffe als Filtermaterialien können Primärrohstoffe eingespart und natürliche Ressourcen geschont werden. Im Rahmen des Forschungsprojekts „RC-Filtersubstrate“ werden Granulate aus recyceltem Kalksandsteinbruch und Porenbetonbruch sowie einer daraus speziell hydrothermal hergestellten Körnung als Retentionsfilter für verunreinigtes Niederschlagswasser untersucht.
Aufgrund ihres mesoporösen Gefüges und ihrer Calciumsilicathydrat-Phasen (C-S-H) zeigen diese Materialien großes Potenzial zur Abtrennung von Kupfer, Zink und Blei. Dieser Ansatz des rohstofflich-chemischen Recyclings von Bau- und Abbruchabfällen überführt die Reststoffe in neue maßgeschneiderte Produkte. Durch die gezielte Steuerung der Porosität und der Mikrostruktur der Hydrothermalgranulate lässt sich die Reinigungsleistung optimieren.
Zusätzlich können die RC-Filtersubstrate mit Bakterien besiedelt werden, um die Filterleistung weiter zu steigern.
Es soll nachgewiesen werden, dass RC-Filtermaterialien als effektive Niederschlagswasserfilter geeignet sind. Zudem soll die Filterleistung in Abhängigkeit von den Eigenschaften der Filtersubstrate untersucht werden.
Im Vortrag werden die Erfahrungen zur Herstellung der Hydrothermalgranulate aus Kalksandsteinbruch- und Porenbetonbruchmehlen vorgestellt.
Lightweight aggregates can be manufactured from masonry rubble by a thermal expanding process pursuing the idea of feedstock recycling. Throughout a series of research projects, the manufacturing process has been developed, optimized and scaled up. Various test results prove that the engineering properties of the new expanded masonry rubble aggregates are similar to those of traditional expanded clays. The aggregates show a heterogeneous and macroporous pore structure. The grains consist of cracks, cavities, large bulky pores and a solid skeleton containing small capillary pores as well as partly melted areas. But which differences and similarities exist to expanded clay aggregates, which are made from a relatively homogeneous clayey raw material? To answer this question, comparative studies on the chemical, physical, mineralogical and microstructural characteristics of expanded masonry rubble aggregates and commercial expanded clay aggregates have been conducted. In our contribution, results of particle shape and porosity measurements, mercury intrusion porosimetry and electron microscopy are presented. The microstructural characteristics are correlated with engineering properties, such as water absorption and particle strength.
A silica-based protective system modified with rock powder for the preservation of tuff stone
(2025)
Tuffs are lightweight and porous pyroclastic rocks composed of a volcanic ash matrix containing pumice and rock fragments, quartz, sanidine and other individual crystals, zeolites, and clay minerals. Due to their low density and high porosity, tuff stones are easy to work with and transport. They have been used as construction material in many historical buildings in Germany. However, most tuff stones exhibit poor resistance to weathering due to their morphology and porosity. If the physico-chemical degradation of the stones is already well advanced, ensuring the safety of the buildings often requires extensive stone replacement. However, this contradicts the fundamental principle of conservation, which prioritises the preservation of the original material. In a recently completed research project, a silica-based protective system modified with rock powder was developed for the preservation of tuff stone. Suitable colloidal silica dispersions and modified rock powders customised produced from tuff waste were used. The protective system was optimised to reduce the capillary water absorption of tuff while maintaining its water vapour diffusion properties, to build a durable protective system-tuff bond, and to achieve a visual and tactile resemblance to tuff. The protective system was developed at laboratory scale. It was subsequently applied to a test area at a restoration site in Berlin-Zehlendorf, Germany, to assess its performance under outdoor conditions. By applying the new protective system, the historic building structure is better preserved, tuff stone resources are saved, and tuff waste is effectively recycled.
Methodology for Assessing Phosphorus Adsorption Kinetics in Novel Constructed Wetland Materials
(2025)
Although various special materials have been studied for their potential for phosphorus removal in constructed wetlands, varying methodologies make direct comparisons of adsorption capacities observed in laboratory experiments difficult. This paper aims to establish a methodology for determining the optimal ratio of phosphate to material mass for different materials and for achieving the necessary contact time for adsorption isotherms. To minimise the number of experiments required, pretests over 24 h should be repeated to determine the phosphate-specific ratios until they show around 60% of the initial concentration. The tested materials included lava sand and expanded sand (ExS), which showed saturating kinetics curves after 24 to 48 h. However, aggregates containing calcium silicate hydrate (CSH) phases (autoclaved aerated concrete AAC, sand–lime brick SLB, and hydrothermal granules HTG) did not show saturating curves, complicating contact time determination. Consequently, adsorption velocity is proposed to identify the phase with the lowest adsorption rate, which is then used as the contact time in adsorption isotherm experiments. Using this method, adsorption times of 48 h were observed for HTG and SLB, while that for AAC was 24 h. This methodology is intended as an initial approach to establish a common basis for researchers investigating novel materials and make the results comparable.