Section: New Results

Material characterization

Quantitative non destructive testing in civil engineering

Participants : Jordan Brouns, Antoine Crinière, Jean Dumoulin, Alexandre Nassiopoulos.

By the aging of civil engineering structures a crucial need of reparation or reinforcement appeared through years. This can be done using bonded CFRP plate to assure the mechanical behavior of the structure. This type of reparation need diagnosis to insure the reliability of the reparation procedure. This part focus on the development of 1D to 3D method to asses the quantitative non destructive testing of a repaired structure thanks to active thermography (see [16] and [54] ).

Thermo-physical characterization for civil engineering application

Participant : Jean Dumoulin.

This papers presents the development of a new device for the determination of thermal conductivity and diffusivity of anisotropic composite plates. The excitation signal is provided through a thermoelectric cooler and does not require any optical source like a laser source for instance. Infrared thermography is used to follow apparent surface temperature evolution with time. Experiments were carried out two composite sample systems (with two different fiber orientations). Result analysis is presented and discussed [42] .

Emissivity characterization for civil engineering applications

Participant : Jean Dumoulin.

The knowledge of the infrared emissivity of materials used in buildings and civil engineering structures is useful for two specific approaches. First, quantitative diagnosis of buildings or civil engineering infrastructures by infrared thermography requires emissivity values in the spectral bandwidth of the camera used for measurements, in order to obtain accurate surface temperatures; for instance, emissivity in the band III domain is required when using cameras with uncooled detectors (such as micro-bolometer arrays). Second, setting up accurate thermal balances by numerical modeling requires the total emissivity value for a large wavelength domain; this is, for instance, the case for computing the road surface temperature to predict ice occurrence. Furthermore, periodical surveys of emissivity variations due to aging or soiling of surfaces could be useful in many situations such as thermal mapping of roads or building insulation diagnosis. The use of portable emissivity measurement devices is required for that purpose. A device using an indirect measurement method was previously developed in our lab; the method uses measurement of the reflectivity from a modulated IR source and requires calibration with a highly reflective surface. However, that device uses a low-frequency, thermal modulation well adapted to laboratory measurements but unfit for fast and in situ measurements. Therefore, a new, portable system which retains the principle of an indirect measurement but uses a faster-frequency, mechanical modulation more appropriate to outdoor measurements was developed. Both devices allow measurements in the broad (1$\mu$m to 40$\mu$m) and narrow (8$\mu$m to 40$\mu$m) bands. Experiments were performed on a large number of materials commonly used in buildings and civil engineering structures.The final objective of this work is to build a database of emissivity of these materials. A comparison of laboratory and on-site measurements of emissivity values obtained in both spectral bands will be presented along with an estimation and an analysis of measurement uncertainties [25] .