Electromagnetic Methods for the Assessment of Structures; Development and Validation

For investigating the inner condition as well as for determining the moisture distribution in building structures non-destructive testing methods (NDT methods) are developed and optimised based on the transmission and reflection of electromagnetic waves. These testing methods can be applied directly on-site to assess concrete as well as masonry structures. The measurement tasks are not only related to the localisation and causation identification but also includes the structural analysis like geometry. For example, the following problems might be solved:

• Determination of thickness of building structures which are only accessible from one side (e. g. of pavements, base slabs etc.)
• Localisation and determination of concrete cover of reinforcement bars and tendon ducts in concrete
• Localisation of voids and metallic and non-metallic inclusions in concrete and brickwork (e. g. honeycombing in concrete, metallic anchors in masonry etc.)
• Determination of moisture content and distribution in concrete and masonry
• Localisation of delaminations in multiple layer systems (e. g. plaster on masonry, carbon fibre reinforced laminates on concrete, tiles in a mortar bed on concrete surfaces etc.)

For analysing these problems, the following NDT methods are applied and further developed

• Radar for structural assessment as well as for the determination of lateral moisture distribution in concrete and brickwork
• Microwave borehole method for the determination of depth resolved moisture distribution in thin boreholes
• Time domain reflectometry (TDR) for long time moisture measurements

The development of these methods is mainly funded by third parties. These are among others the German Research Council (DFG), the European Commission and the Deutsche Bahn (DB AG).

In particular, BAM was co-ordinator of the European research project ONSITEFORMASONRY. The main aim of ONSITEFORMASONRY was the development of non-destructive and minor-destructive testing methods for the structural assessment of historic masonry. These methods are ultrasonic echo, impact echo, microseismic, radar, microwave borehole method, impulse thermography, videoscopy and flat-jack. These techniques enhance the accuracy and enable the performance of cheaper, faster and more effective investigations of historic masonry structure. Strategies for the combination of different techniques have been worked out. The research project was funded in the 5th Framework Programme Energy, Environment and Sustainable Development (EESD) and was related to the key action "The City of Tomorrow and Cultural Heritages".

The European research project CHEF (Cultural Heritage Protection Against Flooding), also coordinated by BAM, is settled in the European Framework Programme FP6 and provides scientific support to policies (e.g. new European Flood Directive) that help protecting Cultural Heritage from environmental damage particularly in relation to flooding.
The main objective is the identification of typical flood hazards threatening Cultural Heritage objects or buildings. Strategies for risk assessment of Cultural Heritage based on quantified hazards, exposure maps and GIS will be developed. These strategies will help to classify Cultural Heritage according to its vulnerability. Damage may range from moisture penetration and pollution of valuable heritage objects to complete destruction of structures and loss of objects and buildings through the tremendous force of floodwaters. Various Cultural Heritage objects and buildings and their interaction with moisture, salt, pollution and other phenomena related to flooding will be investigated. The application of non-destructive and minor-destructive methods for damage detection and quantification, as well as a classification of damage and definition of damage threshold will be subject of several case studies, which are going to be carried out at selected historic sites in flood-affected regions.

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