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While a high content of reclaimed asphalt in road construction is targeted, recycled bitumen has often undergone chemical and physical damages characterized as ageing. This can be counteracted with additives denoted as rejuvenators and by controlling the heating process during mix production. This study investigated the surface and base layers of three asphalt variants with different levels of reclaimed asphalt and rejuvenator. Asphalt samples were heated either through conventional heat conduction or through dielectrical heating using radio waves. Bitumen analyses included Ring-and-Ball, Needle Penetration, Dynamic Shear Rheometry and Fourier-Transform Infrared Spectroscopy while asphalt performance was assessed by Cyclic Indirect Tensile Test. Ageing indicators were derived and correlated quantitatively, revealing high correlation among bitumen analysis results and lower correlation of asphalt analysis results. Some of the test methods explicitly supported the hypothesis that radio wave heating may induce a lower ageing than conventional heating combined with rejuvenation.

Die Feintrocknung spielt eine Schlüsselrolle für den Einsatz und insbesondere die Einspeisung von Wasserstoff in die Erdgasinfrastruktur. Zur thermischen Regenerierung des Trockenmittels können Radiowellen für eine direkte dielektrische Erwärmung des Schüttbettes eingesetzt werden. In Abhängigkeit von den verwendeten Zeolithen, NaX oder NaY, sind dabei sowohl eine homogene Erwärmung als auch eine selektive Erwärmung der wasserbeladenen Trockenmittelschüttungen möglich. Nach entsprechenden Tests steht nunmehr ein einsatzfähiger druckfester Prototyp für die Wasserstofftrocknung zur Verfügung.

Selective measurement of hydrogen in the natural gas grid as large transport and storage infrastructure is a crucial requirement for establishing a hydrogen economy. Cost-effective sensors must face mainly two critical conditions: (i) absence of oxygen contents capable for ensuring the sensor function and (ii) presence of a large surplus of another reducing gas, methane. The developed Pt/TiO2 sensor is based on the combination of the catalytic spillover effect and an impedance measurement. It allows hydrogen detection in a wide concentration range and it is specific for hydrogen while other gases such as methane or carbon dioxide behave like inert gases. The sensor curve with decreasing relative sensitivity for higher hydrogen concentrations and the temperature dependence of the sensor effect are in agreement with the spillover-based sensor principle, where hydrogen is activated on Pt and then spills over onto the TiO2 where it acts as electron donor.

Reductive catalytic conversion of DDT (p,p′-dichlorodiphenyltrichloroethane) was studied under ambient conditions in a hydrogen atmosphere using platinum and palladium deposited on several supports, in particular on porous alumina and silica. Almost complete hydrodechlorination and hydrogenation of DDT and its dehydrochlorination byproduct DDE (p,p′-dichlorodiphenyldichloroethene), leading to the formation of diphenylethane (with Pd) and dicyclohexylethane (with Pt), were observed at ambient temperature within minutes or hours. Rapid hydrodechlorination also takes place after depositing DDT and the metal component on separate particles and mixing them mechanically. This long-range reactivity can be explained either by a fast surface diffusion of DDT or DDE, or by hydrogen spillover. Irrespective of the mechanism, the reactivity thus bridges the barrier across solid particle interfaces. Most findings indicate the fast diffusion of target compounds as dominant mechanism for the observed long-range reactivity.

Mit Erwärmung durch Radiowellen Holzschädlinge bekämpfen: Im Rahmen eines von der Deutschen Bundesstiftung Umwelt im Netzwerk RWTec geförderten Forschungsprojekts [1] entwickelten das Helmholtz-Zentrum für Umweltforschung (UFZ) und die Hochschule für Technik, Wirtschaft und Kultur (HTWK) Leipzig in Zusammenarbeit mit Praxispartnern ein Verfahren, mit dem durch eine kontrollierte Erwärmung Holzschädlinge abgetötet werden können. In der Regel sind dabei Temperaturen von 55 °C bis 60 °C ausreichend. Der Einsatz wurde an unterschiedlichen Objekten erfolgreich demonstriert, wobei das Einsatzpotenzial von der Sanierung von Dachstühlen bis zur Behandlung von wertvollen Kunstgegenständen reicht.

[EN] For drying building structures, dielectric heating using RF energy (13.56 MHz) is an efficient and fast alternative to conventional heating methods relying solely on heat transfer from the surface to the interior of the masonry. Another innovative application of volumetric RF heating is chemical-free pest control in wood-based materials. For such applications where the RF systems often cannot be completely shielded, the propagation or coupling of the electromagnetic waves into wires that are placed inside the field cannot be neglected which represents a certain risk. Depending on the different electromagnetic coupling mechanisms, several interference signals can be generated. In order to protect electrical equipment in the surrounding, these interferences have to be significantly reduced by electrical filters. For this purpose, a cost-effective and robust measuring concept was developed. With the help of this system, the common mode (iCM) interference could be identified as the dominant part and the differential mode (iDM) interference as a minor disturbance. Based on the experimental evaluation, a cost-effective filter for the respective disturbance was constructed and successfully tested.

The non‐thermal plasma (NTP) technique was shown to be a method to improve indoor air quality. In particular in kitchens, odorous emissions can be removed by NTP. A combined concept of adsorption of volatile organic compounds (VOC) and plasma regeneration of the adsorber was tested in adsorption‐regeneration‐adsorption cycles. As reference VOC, 2‐methylthiophene, 2‐methylpyrazine, 2‐acetylthiazole, nonanal and trans‐2‐nonenal were used in humid air streams. These odorous compounds are emitted during cooking and frying processes. The adsorption‐regeneration concept was also tested during a simulated frying process with garlic in rape oil. A hydrophobic zeolite was chosen as adsorber material and placed directly into the discharge zone of a plasma reactor.

Decontamination of air or other gas streams loaded with low VOC concentrations is a prevalent task for adsorption using zeolites. Emphasizing the importance of adsorber selection, several zeolites varying in type, Si/Al ratio and provider were tested for toluene as representative organic target compound and water as adsorbate both in single and competing adsorption studies. In some cases, the toluene breakthrough is mainly caused by water-driven desorption. It was shown that for adsorption capacity, kinetics and competition behavior not only type and Si/Al ratio of the zeolite are important but also producer-specific parameters such as crystallinity, binder type and content which are usually not explicitly documented. This study offers a basis for the selection of adsorber materials for treatment of gas streams with significant water contents.

Non-thermal plasma technique can be a method to improve indoor air quality. In particular in cuisines, odorous emissions can be removed by non-thermal plasmas. In this study 2-methylthiophene, 2-methylpyrazine, 2-acetylthiazole, nonanal and trans-2-nonenal were used as target compounds in concentrations in the low ppmv range. These odorous compounds are emitted during cooking and frying processes. The oxidation of these target compounds as multi-component mixture in a non-thermal gas-phase plasma was studied in dry mixtures of argon and oxygen and in humid air. Complete oxidation of the odorous compounds to COX was achieved in both atmospheres. The energy efficiency was higher in the dry mixture of argon and oxygen, whereas the selectivity of the oxidation towards carbon dioxide was significantly higher in humid air. The main products of plasma treatment were identified as CO, CO2 and polymeric deposits. Some minor organic intermediates in the pptv range were also identified. Although odor carriers could be completely degraded and the concentrations of potentially harmful organic byproducts were several orders of magnitude below critical values, high ozone and CO emissions during plasma operation are critical for indoor application of non-thermal plasma as stand-alone technique. The combination with a catalytic step, either as in-plasma or post-plasma catalysis, might be a promising approach to tackle this problem.

Thermal pest control with hot air is widely accepted as an alternative to chemical methods. However, it requires relatively long treatment times due to the low thermal conductivity of wood. Direct dielectric heating applying radio waves or microwaves has the advantage of a more homogeneous heating. However, sound experimental data on this technique are rare at present. Therefore, thermal treatment of wood-destroying insects with radio waves and microwaves was studied with two model pests, Anobium punctatum and Hylotrupes bajulus, and with Tenebrio molitor as reference. It was shown that a secure elimination of pests can be achieved by temperatures above 55°C; the corresponding treatment time was in the range of a few minutes. Temperature profiles were more homogeneous when applying radio waves.

Dielectric heating with radio waves (RW) and microwaves (MW) are alternatives to treatments with hazardous chemicals or hot air for pest control. In particular, RW can be used to heat up bulky materials with larger size (in the meter range) homogeneously and smoothly in order to eliminate embedded pest organisms. Dielectric heating, in principle, enables selective overheating of certain materials in a heterogeneous mixture. This unique feature of electromagnetic heating methods, in contrast to techniques being based on thermal conduction, is caused by significant differences in the dielectric properties of pest organisms and matrix materials. The present study proves unambiguously that selective heating of cylindrical pest organisms in wood matrices occurs under defined conditions. The selective heating effect strongly depends on the orientation of the pest organisms in the electric field. For a parallel alignment, maximum overheating factors (ratio of adiabatic local heating rates) of 2 to 3 were determined experimentally. In case of a perpendicular alignment, no overheating was detected. A simulation of electric field and power loss density distributions in pest organisms and in their vicinity in the wood matrix, using a finite element method, can qualitatively explain the experimental results. According to the simulation, the overheating occurs not directly within the pest organism but in the wood matrix in the vicinity on both ends of the cylinder-shaped pest organism

The application of radio waves with a frequency of 13.56 MHz on electrolyte solutions in a capillary reactor led to the formation of reactive hydrogen and oxygen species and finally to molecular oxygen and hydrogen. This process of water splitting can be principally used for the elimination of hazardous chemicals in water. Two compounds, namely perfluorooctanoic acid (PFOA) and tetrahydrofuran, were converted using this process. Their main decomposition products were highly volatile and therefore transferred to a gas phase, where they could be identified by GC-MS analyses. It is remarkable that the chemical reactions could benefit from both the oxidizing and reducing species formed in the plasma process, which takes place in gas bubbles saturated with water vapor. The breaking of C–C and C–F bonds was proven in the case of PFOA, probably initiated by electron impacts and radical reactions.

For mitigation of the impact on flood-damaged cultural heritage buildings and sites, solely conservation-compatible and noninvasive strategies can be applied. All procedures have to take into account not only the specific situation after flooding but also the material properties and the characteristics of the artwork related to the building. After a heavy flooding event damaging the monastery Marienthal in Germany demonstration studies were proceeded to evaluate heritage-adequate treatment strategies for the drying of a decorated chapel. To respect and preserve the original gypsum stucco interior drying in certain temperature limits had to be respected. Particularly, direct volumetric heating methods were employed working with electromagnetic waves in the frequency ranges of either microwaves or radio waves. The studies comprised heating tests on site and experiments on a heritage-representative masonry specimen. It could be shown that the removal of water could be significantly enhanced by both techniques. Radio wave heating was demonstrated to allow a more homogeneous and better controlled treatment in comparison to microwave application, which is especially relevant in case of sensitive materials such as gypsum. With respecting that limits the techniques can be applied in combination with efficient removal of moisture from the ambient air by ventilation in order to reduce the drying time thus limiting subsequent damage of the heritage building.

By means of radio-wave technology it is possible to allow the uniform, rapid and accurate, temperature-controlled heating of fresh concrete. This results in the significantly accelerated release of hydration heat. The heat release from this second source can be easily compensated by the temperature-controlled reduction of RF energy input. The consequences are accelerated hydration and higher early-age compressive strength. Early-age concrete, heat-treated by radio waves, have a denser microstructure with a higher gel-pore content and more C-S-H phases than untreated concrete. When cured at the maximum temperature of 80 °C, secondary ettringite can be formed in concrete, whereas this is not the case for the treatment temperatures of 40 °C and 60 °C. At the age of 28 d, heat-treated concretes exhibit a looser microstructure than does untreated concrete. Larger portlandite crystals and secondary ettringite are its characteristic features as a consequence of the much faster reaction rates in the early-age concrete. This results in lower values of the compressive strength of the heat-treated concrete.