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- 2006 (12) (entfernen)
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- Englisch (12)
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- Concrete (12) (entfernen)
An advanced quantitative approach of pulse-phase-thermography for nondestructive
testing in civil engineering is described in this contribution. The
characteristic frequency of the maximum phase-contrast between defects and sound
areas is used as a means for the characterization of its depth.
The new approach is tested in the laboratory on concrete structures with defects of
polystyrene. The surfaces of the structures were heated with IR-radiators for varying
time periods.
The presented investigations were funded by the Deutsche Forschungsgemeinschaft
(DFG) and were carried out in co-operation with the Technical University of Berlin
(TUB).
The active approach for non-destructive-testing in Civil Engineering (NDT-CE) with infraredthermography (IR), developed at the Federal Institute for Materials Research and Testing (BAM), is described in part one of this contribution. The active IR-approach is based on the principles of impulse- (IT) and pulse-phase-thermography (PPT). The concept is a direct result of a research project at the BAM in cooperation with the Technical University of Berlin (TUB) and was funded by the Deutsche Forschungsgemeinschaft (DFG). In the second part results of the new thermography-scanning system (thermo-scanner) of BAM on debonding of multi-layered structures, especially carbon fibre reinforced plates (CFRP) on concrete are presented. Both, the thermo-scanner developed at BAM, and the investigations carried out, are part of the
EU-Project Sustainable Bridges. In the third part of the paper the characteristic frequency of the optimum phase-contrast as a means for the characterization of defects depth in CE by means of PPT is introduced. A new quantitative approach is tested and discussed on concrete structures with defects of polystyrene and gas concrete.
The interaction of municipal solid waste incinerator bottom ash (MSWI bottom ash), when utilized as an aggregate in concrete, with the cement matrix was investigated. The most prominent reaction observed in lab and field concrete was the formation of aluminium hydroxide and the release of hydrogen gas from aluminium grains reacting in the alkaline environment. The expansive aluminium reaction was identified as a main cause of extensive spalling on the concrete surface. Due to the higher content of bottle glass as part of the ash, in all samples, reaction products of an alkali-silica reaction (ASR) could be observed as well. However, damage due to ASR were less severe than those caused by the aluminium reaction. The expansion rates were low and only a few of the lab samples showed cracking. Microstructural analysis of the samples indicated clearly that a large quantity of the alkali-silica gel which was formed was accommodated in the pores and voids without exerting any strain on the material.
Ultrasonic Reflection Properties at Interfaces Between Concrete Steel and Air: Imaging and Modelling
(2006)
Laser-induced breakdown spectroscopy has been used for quantitative measurement of trace elements, e.g. sulfur and chlorine, in concrete. Chloride and sulfate ions have a large effect on the durability of concrete structures, and quantitative measurement is important for condition assessment and quality assurance. Concrete is a highly heterogeneous material in composition and grain-size distribution, i.e. the spatial distribution of elements. Calibration plots were determined by use of laboratory-made reference samples consisting of pressings of cement powder, hydrated cement, cement mortar, and concrete, in which the heterogeneity of the material is increasing because of the aggregates. Coarse aggregate and cement paste are distinguishable by the intensity of the Ca spectral lines. More advanced evaluation is necessary to account for the effect of the fine aggregate. The three series of reference samples enable systematic study of the effects of heterogeneity on spectral intensity, signal fluctuation, uncertainty, and limits of detection. Spatially resolved measurements and many spectra enable statistical evaluation of the data. The heterogeneity has an effect on measurement of the sulfur and chlorine content, because both occur mainly in the cement matrix. Critical chloride concentrations are approximately 0.04% (m/m). The chlorine spectral line at 837.6 nm is evaluated. The natural sulfur content of concrete is approximately 0.1% (m/m). The spectral line at 921.3 nm is evaluated. One future application may be simultaneous determination of the amount of damaging trace elements and the cement content of the concrete.