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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.
Attenuated Total Reflection Fourier Transform Infrared spectroscopy has become a popular spectroscopic technique in bituminous binder analysis. However, comparable results are not obtainable yet due to differences in devices, measurement routines, sample preparation procedures, and spectral evaluation. Thus, the Task Group 1 of the RILEM TC 295-FBB: “Fingerprinting bituminous binders using physicochemical analysis” focuses on bringing this method towards pre-standardization. This study evaluates the reproducibility and consistency from round robin test, where 21 participating laboratories performed six different preparation techniques on three different binders in an unaged, short-term, and long-term aged state. A total of 6461 spectra were recorded and evaluated for their mean, standard deviation and coefficient of variation (CV) in the spectral region between 1800 and 600 cm−1. The results show that the solid sample preparation methods provide excellent reproducibility, with a coefficient of variation below 2%. Only the solvent method showed a higher coefficient of variation at 7.18%. Outliers with a high CV were detected and categorized into two groups: one where only one of the four samples differed and the other where all 16 spectra showed slight scattering in the overall absorption. The consistency of the method is significantly influenced by the accuracy of sample preparation, which is crucial for minimizing differences in slope, baseline, and noise in the spectra. These findings show the excellent reproducibility of these sample preparation methods and will be further examined to establish universal indices for evaluating effects such as ageing, bringing the method closer towards standardization.
The cement industry is responsible for high CO2 emissions, which occur during the production of Portland cement clinker. To reduce These emissions, blended cements become more and more popular. Therefore, it is expected that these cements find frequent application in infrastructure and housing construction in the future. The increased use leads to a higher probability of concrete buildings with blended cements being exposed to extreme conditions such as fire. Concrete under fire can experience heavy damage in the form of explosive spalling which is caused by thermohydraulic and thermomechanical mechanisms leading to the lowering of the cross section. Furthermore, the reinforcement may be subjected directly to the fire, which can lead to a rapid decline in its load-bearing capacity.
The current state of the art showed that the cement type used can show great impact on the fire induced spalling behavior. However, large proportion of the reported spalling results took place under unsuitable testing conditions with insufficient evaluation. The smaller fraction of more profound spalling experiments showed inconsistences and contradictions, whereby no clear relation between cement type and spalling susceptibility could be drawn. Against this background in depth spalling experiments following the recommendations of RILEM TC 256-SPF of concrete with four different types of cement including Portland cement (CEM I), limestone cement (CEM II/A-LL), slag cement (CEM III/A) and Portland pozzolana cement (CEM II/B-Q) were carried out. Summarizing, CEM I concrete showed the lowest amount of spalling, followed by CEM II/A-LL and CEM III/A concrete and lastly CEM II/B-Q concrete. To understand the appearing differences in spalling susceptibility, the influence of the thermally induced moisture transport was studied by 1H-NMR relaxometry. From a thermohydraulic point of view, it was shown that initial differences of permeability and moisture content are responsible for the variations in spalling susceptibility.
Furthermore, the appearance of the moisture clog was confirmed in every sample. To further analyze the contribution of the thermohydraulic mechanism, the phase composition of the cement paste was analyzed before and after high temperature exposure regarding the dehydration behavior. Less C-S-H and portlandite were observed in CEM III/A and CEM II/B-Q pastes. However, the C-S-H seemingly showed increased thermal stability. In addition, lower amounts of AFt and AFm phases were found in blended cement pastes corresponding to lower amounts of degradation and water released at lower temperatures. In conclusion, the increased spalling proneness in blended concretes is caused by higher initial moisture contents paired with lower initial permeabilities and less amounts of early dehydrating phases. It was also shown that the addition of PP-fibers remains a successful avoidance strategy regardless of the cement type used, by increasing permeability and thus the release of water vapor.
Ab den 1950er Jahren setzte sich die Spannbetonbauweise für Brücken mit großen Spannweiten durch. Diese Technik ermöglicht den Bau sehr schlanker, eleganter Brücken. Die mangelnde Erfahrung aus der Anfangszeit der Bauweise stellt uns heute vor Probleme. So sind die bis in die 1970er Jahre verwendeten Spannstähle empfindlich gegenüber Spannungsrisskorrosion. Durch hohe Verkehrs- und Tempe-raturbelastungen können die durch Korrosion vorgeschädig-ten Spanndrähte reißen. Das kann zum Einsturz von Brü-cken führen, ohne dass sich dies durch äußerlich sichtbare Schäden ankündigt. Der Einsturz der Carolabrücke in Dres-den im November 2024 hat die Brisanz des Problems deut-lich gemacht.
Die derzeit einzige zuverlässige und ökonomisch vertretbare Technik zur Detektion von Spanndrahtbrüchen ist die Schal-lemissionsanalyse. Damit werden die durch einem Draht-bruch entstehenden und sich im Beton ausbreitenden Ultra-schallwellen erfasst.
Die im Mai 2024 erschienene Richtlinie SE 05 „Detektion von Spanndrahtbrüchen mit Schallemissionsanalyse“ beschreibt das Verfahren im Rahmen einer kontinuierlichen Bauwerks-überwachung. Sie ist heute eine wichtige Grundlage für die systematische Planung und Installation von Monitoringsys-temen und für die Bewertung der Monitoringergebnisse.
With the advancement of digitalization and related technological developments, Structural Health Monitoring (SHM) has become a useful and increasingly widespread tool to assist in the maintenance management of bridges and other engineering structures. The process of implementing monitoring requires expertise in many fields such as civil engineering, bridge operation and maintenance, monitoring technology, and data analysis. In recent years, monitoring has moved from method and technology development to standard practice. However, the implementation of monitoring as a standardized process can be an obstacle, especially for bridge operators, due to a lack of practical experience combined with the various expertise required. This can affect several areas, such as determining the cost-effectiveness of a monitoring measure, proper tendering and contracting, quality control, analysis and evaluation of measurement data, and last but not least, data management. In order to support the introduction of monitoring technologies into the practice of infrastructure operators, several guidelines have been developed in Germany in recent years by different interest groups, each with a different focus and essentially complementing each other. This paper aims to provide an overview of four different recently published guidelines and to highlight their strengths and advantages.
With the advancement of digitalization and related technological developments, Structural Health Monitoring (SHM) has become a useful and increasingly widespread tool to assist in the maintenance management of bridges and other engineering structures. The process of implementing monitoring requires expertise in many fields such as civil engineering, bridge operation and maintenance, monitoring technology, and data analysis. In recent years, monitoring has moved from method and technology development to standard practice. However, the implementation of monitoring as a standardized process can be an obstacle, especially for bridge operators, due to a lack of practical experience combined with the various expertise required. This can affect several areas, such as determining the cost-effectiveness of a monitoring measure, proper tendering and contracting, quality control, analysis and evaluation of measurement data, and last but not least, data management. In order to support the introduction of monitoring technologies into the practice of infrastructure operators, several guidelines have been developed in Germany in recent years by different interest groups, each with a different focus and essentially complementing each other. This paper aims to provide an overview of four different recently published guidelines and to highlight their strengths and advantages.
Cementitious materials are often exposed to aggressive environments, which have a significant impact on their durability. Proper prediction of concrete corrosion helps to apply the right measures and technologies, to extend the service life of structures. Carbonation and cyclic freezing are recognized among the most common corrosive factors for concrete. Their progress is linked to the penetration of CO2 and water into the concrete structure. Due to the random arrangement of aggregates and cement paste, concrete is an inhomogeneous material. Therefore, the progress of carbonation and frost-induced damage should be treated as random variables with appropriate probabilistic parameters. Experimental studies on concrete carbonation and freezing were conducted in accordance with the standards EN 12390–12 and EN 12390–9. As observed in the experiments, the progress of carbonation and frost damage of concrete could be described by zigzag, not necessarily monotonic functions. Stochastic differential equations (SDE) were employed to predict the behavior of concrete exposed to elevated CO2 concentrations and cyclic freezing. The stochastic model consisted of a drift term, which described the general trend of concrete durability exposed to carbonation and frost cycles, as well as a diffusion term, which accounted for the stochastic features of inhomogeneous concrete microstructure. The Euler–Maruyama approximation with Milstein improvement was applied to model the realization of the stochastic changes in concrete microstructure/durability. The proposed approach predicted experimental results with high accuracy. The application of the Monte Carlo (MC) method with 100,000 SDE realizations allowed to calculate the statistical parameters of the processes, such as concrete carbonation and freezing cycles. The probabilistic parameters, such as expected values and standard deviations, calculated using the SDE_MC approach, were in good agreement with experimental results for both problems, i.e. decelerating concrete carbonation and accelerating concrete scaling.
A strategy for enhancing the sustainable flame retardancy of polylactide (PLA) composites by partially replacing melamine polyphosphate (MPP), a commercial flame retardant proposed for PLA, with wastewater polyphosphate-enriched microalgae (P-Algae) has been explored. The incorporation of P-Algae at a 1:1 ratio with MPP leads to a notable synergistic effect, surpassing the expected additive behavior of the individual components. Comprehensive characterization encompassing thermogravimetric analysis coupled with FTIR, pyrolysis combustion flow calorimeter (PCFC), cone calorimeter, oxygen index (LOI), UL-94 tests, and rheological measurements—demonstrates that the presence of this biomaterial can significantly enhance flame retardant performance. Replacing 50% of MPP with P-Algae in PLA resulted in a 17% reduction in peak heat release rate (pHRR) and maintained a V-0 rating in UL-94 testing. The use of P-Algae does not compromise the flame retardancy of PLA but rather contributes positively, offering a promising path toward more sustainable flame-retardant systems. By leveraging naturally derived biomass, this approach aligns with the growing demand for novel eco-friendly technologies in polymer engineering. Insights into an innovative renewable additive as a functional and effective component in flame-retardant biocomposites have been achieved.
Hydrophobic agents are one of the most commonly used means of prolonging the lifespan of cement-based materials. However, when water-repellent is added to the batch water it can interfere with cement hydration leading to deteriorated mechanical properties of the hardened material. To eliminate this drawback, a novel methodology of indirectly applying hydrophobic agents to cement-based materials is introduced. The presented approach uses super absorbent polymers (SAPs) as a delivery medium. SAP containing water-repellent is added to the fresh cement mixture, which ensures a gradual release of the admixture. The release is driven either by drying which generates moisture gradient or by compression of polymer particles by hydrates arising in their vicinity. Such mechanisms lead to a delayed dosage of the hydrophobic agent, which is when the partially hardened cement matrix is less vulnerable to interference compared to the fresh mixture. The effectiveness of the proposed methodology was verified in the extensive experimental program. Cement mortars of two water-to-cement ratios (0.4, and 0.5) were tested in terms of compressive strength, capillary absorption, and contact angle among others. Based on the obtained results it is concluded that the proposed methodology limits the negative impact of the hydrophobic agent on cement hydration. The mechanical performance of the samples modified with the indirectly dosed admixture is improved compared to the conventionally hydrophobized material in each analysed case. The results of isothermal calorimetry support the thesis. Additionally, the effectiveness of imparting hydrophobic characteristics to the cement matrix was as good as in the case of the conventional dosing. The mercury intrusion porosimetry, as well as thermogravimetric tests, were run to provide a deeper insight into the microstructure and composition of the modified material. Scanning electron microscopy was used to give a better insight into samples’ morphology. The novel methodology presented can also potentially be used
to dose other types of admixtures that can interfere with cement hydration.