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- 2003 (10) (entfernen)
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- Concrete (5)
- Radar (5)
- Impulse thermography (3)
- Non-destructive testing (3)
- Non-destructive testing in civil engineering (3)
- Beton (2)
- Data fusion (2)
- Hohlstellen (2)
- Impuls-Thermografie (2)
- Masonry (2)
New thermography systems enable the application of active investigation techniques, i.e. the observation of the cooling down process after heating the surface of a structure under investigation. Defects like voids in concrete having a different thermal diffusivity in comparison to the bulk material are visualised by different surface temperatures. The differences between temperature transient curves above sound regions and above inhomogeneities are expected to include information about the defect parameters.
Experimental investigations with impulse thermography and radar on a concrete test specimen containing voids were analysed. Radar was used to determine the depth of the voids. The influence of size and depth of the voids on the temperature transient curves was studied for different heating times. The transient curves were also fitted with a simple semi-empirical model.
Non-destructive testing (NDT) of concrete structures is performed using pulse-echo methods. According to the type of the applied waves it can be classified as acoustic (Impact-Echo, Ultrasonics) and electromagnetic methods (Radar). The results are visualised through different imaging processes. This work is performed in the frame of a research project promoted by Deutsche Forschungsgemeinschaft (FOR384).The objective of data fusion is to use the complementary information of the different methods. Radar can detect metallic reflectors in concrete (metallic ducts and concrete reinforcement) very well. This method is not able to locate defects behind these reflectors (injecting defects, defects behind close concrete reinforcement), because the electromagnetic waves are completely reflected at metals. The acoustic methods are able to compensate this deficit i.e. acoustic waves can penetrate through metal. But acoustic waves in the ultrasonic range are completely reflected by air layers. Air layers have smaller influence on radar propagation, so that both methods complement each other.In order to be able to combine the NDT-data from several methods records at the same volume, the different data setsmodes of signals must be adapted. The ultrasonic and radar data have to be reconstructed with programs based on the Synthetic Aperture Focusing Technique (SAFT) before data fusion. Subsequently, a conversion of the data into a uniform format has to be carried out. This is a prerequisite in order to keep the data exchange between the project partners as simple as possible. After the data sets are imported and transferred into a common reference system, they can be processed with operations according to the purpose of the investigation. Results, which have been achieved in concrete test specimen with radar and ultrasonics, will be presented and will show the feasibility of the data fusion method.
Active infrared thermography in civil engineering - quantitative analysis by numerical simulation
(2003)
The cooling-down process of building structures after heating-up with an external radiation source was analysed to detect voids inside and below the surface. Quantitative results of concrete test specimen containing voids with different sizes at various depths will be presented here. The experimental results were compared to numerical simulations performed with a Finite Difference program developed at BAM.
The structural safety, durability and performance of the infrastructure is of primary interest in every country. An efficient system for early and regular structural assessment as well as for quality assurance during and after the construction of new structures and of reconstruction processes is urgently required. At BAM, NDT methods to be applied in civil engineering are developed and their application improved. From the experience of on-site assessments, quality assurance systems and methodologies for regular inspections are elaborated. This work is mainly performed in the frame of externally funded research projects.