Radar‐Magnet‐Betontest: Eine neue Methode zur Bestimmung der Feuchte und des Chloridgehalts von Brückenfahrbahnplatten aus Beton

Radar‐Magnetic Concrete Testing – A Novel Technique for Determination of Moisture and Salinity of Concrete Bridge Decks For the assessment of the condition of concrete bridge decks it is important to know the moisture and the salinity of the concrete. In this paper, a novel technique for nondestructive determination of moisture and salinity of concrete through the pavement is presented. Using Ground Penetrating Radar, the transient time of the electromagnetic wave to the upper layer reinforcement bars (rebars) is measured. It depends on the dielectric properties of the intermediate materials. The depth of the rebars is determined by a measurement of the static magnetic field of the premagnetized rebars. This magnetic depth determination technique is independent of the dielectric properties of the materials covering the rebars. Comparison of the Radar delay and the magnetically extracted depth yields the averaged real part of the dielectric permittivity of the intermediate material. The imaginary part is estimated from the reflected Radar amplitude. Then, moisture and salt content of the concrete are derived from calibration curves. The method was verified in the lab using concrete test blocks with and without asphalt cover. A Radar‐magnetic measurement vehicle was developed and tested on two highway bridge decks. The dielectric permittivity of the concrete close to the surface was mapped on a large area. The technique is well suited for quick and nondestructive scans over large areas in order to identify potentially damaged regions. These conspicuous locations should be analyzed in more detail afterwards.     

Eine Methode zur Bewertung von Restspalten in Schweißnähten an T‐ und Kreuzstoßverbindungen

A method to assess root gaps in welded seams of T‐ and Cross joints. Design and welding codes require full penetration in case of complete butt splices. This often ends up to time‐ and cost‐intensive repair work for the executing steel work company. Quite recently, classification methods and along with these, a method of tolerating such partial penetrations (here: root gaps) to be considered right from the weld design or planning stage were actually missing, so that additional manufacturing work was preassigned from the outset. Within an AiF‐DASt‐research project [1] an assessment method has been developed basing on an accurate detection of root gaps by non‐destructive testing methods. That method guarantees the demanded structural reliability of a steel structure despite of leaving a weld that actually is to be rejected due to insufficient penetration according to the conventional codes.     

Konzeptionelles hydrogeologisches Modell zur Analyse und Bewertung von Verweilzeiten in Hessen

A regional scale conceptual hydrogeological model has been developed for evaluating residence times of groundwater in the upper aquifers and unsaturated zone within the Federal State of Hessen (Germany). The model is based on digitally available data bases and was applied with a spatial resolution of 60?m×60?m. Typical residence times for areas of unconsolidated deposits ranged between 10 and 25 years, whereas residence times of less than 5?years were found in areas of consolidated rock. Within the EU-Water Framework Directive, these results may help in assessing temporal and regional impacts of measures to reduce mass loading from the surface to groundwater. This will lead to better decisions, for instance whether additional measures to reach the environmental objectives should be applied.     

Bewertung und Optimierung von dynamischen Dämmsystemen unter Berücksichtigung des Wiener Klimas

In den letzten Jahren fanden immer wieder Anstrengungen statt um den CO₂‐Haushalt der Erdatmosphäre zu senken. Begriffe wie “sparsamer”, “effizienter” oder “effektiver” werden häufig in diesem Zusammenhang verwendet. Auch das Fachgebiet Bauphysik kann einen wesentlichen Beitrag zur Energieeffizienz leisten. Das ist eine berechtigte Forderung, da Gebäudeheizung und Gebäudekühlung einen bedeutenden Anteil am Ausstoß schädlicher Treibhausgase besitzen. Grenzwerte für die U‐Werte werden immer niedriger angesetzt, was dickere und teurere Dämmsysteme zur Folge hat. Neben diesen trivialen Lösungen werden auch komplexere Systeme entwickelt und erprobt. In dieser Untersuchung werden zwei davon genauer betrachtet und bezugnehmend auf den Heiz wärmebedarf sowie den Kühlbedarf gegenüberstellt. Dabei handelt es sich um sogenannte schaltbare Dämmungen, und um ein neues System mit der Bezeichnung “Thermocollect”. Ein Vergleich beider Systeme ist mit Software‐Standardlösungen nicht möglich, da diese mit nichtvariablen Wärmeleitwerten arbeiten, weshalb ein eigenes Simulationsmodell entwickelt werden musste. Zunächst werden im Rahmen einer Einführung beide Systeme vorgestellt. Ein Abschnitt beinhaltet eine Ausführung zum Simulationsmodell und Erläuterungen zu seinen Eigenheiten. Abschließend folgen Ergebnisse von Parameterstudien, eine Interpretation der Ergebnisse sowie Schlussfolgerungen und die Optimierung der neuartigen Dämmsysteme. Evaluation and optimization of switchable insulation using the climatic conditions of Vienna. There have been numerous efforts to reduce CO₂ emissions in recent years. Terms such as ”more economical”, ”more efficient”, and ”more effective” are often used in discussion of this theme. The field of building physics can make a significant contribution to energy efficiency since building heating and cooling produces a significant portion of overall hazardous greenhouse gases. In response, heat transfer coefficient limits are being set lower and lower resulting in thicker and more expensive insulation systems. Very creative systems are being developed and tested parallel to conventional solutions. This study examines and contrasts two of the systems focusing upon the heating and cooling requirements: the so called ”switchable insulation” and a new system called ”Thermocollect”. The systems cannot be compared using standard software programs as the calculations are based on steady‐state thermal conductivities. Therefore, an in‐house simulation model was developed. Both systems are described in the introduction. A presentation of the basic thermodynamic concepts applied in the simulation fol lows. One section contains an explanation of the simulation model and its distinctive properties. The study is concluded by the results of the parametric studies, an interpretation of the results and implications, and engineering optimizations for the new insulation systems.     

Tragverhalten von geschichteten Deckenelementen aus Normal‐ und Porenleichtbeton

Load bearing behaviour of layered ceiling elements made of regular and porous lightweight concrete Lightweight and efficiently bearing steel reinforced elements may be achieved through the application of regular and porous concrete in a three‐layer cross‐section. While exterior layers of higher strength carry bending moments, a lightweight core layer material holds up to shear stresses. In order to quantify the potential of this construction method, the bearing behaviour of 18 layered ceiling elements with six different geometries was investigated. The goals were both to identify different failure modes, as well as evaluate the suitability of commonly used calculation procedures. The following paper shows that an optimal usage of cross‐sections of ceiling elements can already achieved by using concrete with strengths between 5 MN/m² and 20 MN/m². The efficiently bearing elements are characterized by the fact, that both the concrete, the reinforcing steel and the layer's interface are highly stressed both under pressure and tension. The tested specimens showed both a tensile bending and interface failure with a partly very high utilization of the flexural compressive zone.