Non-contact photopyroelectric approach for complete thermal characterization of porous building materials

Abstract The suitability of two photopyroelectric (PPE) methods for measuring the thermal diffusivity and effusivity of porous solids is described. The main characteristic of both methods, associated with the possibility of investigating porous solids, is the absence of coupling fluid between the pyroelectric sensor and sample. The first method (proposed initially by Salazar et al., Measurement 121, 96 (2018) [1]) relies on the front detection configuration with opaque pyroelectric sensor and thermally thick sample. Based on the phase frequency scan of the PPE signal, this method leads to the direct measurement of the sample’s thermal effusivity. The second method (proposed initially by Zammit et al., J. Appl. Phys. 117, 105104 (2015) [2]) is based on two successive measurements (frequency scans), one in back and one in front PPE configuration, followed by a self-normalization of the phase vs. modulation frequency dependence. This method uses transparent pyroelectric sensor and backing material, allowing the direct measurement of the sample thermal diffusivity. In the paper, both methods were adapted and improved for investigating some porous building materials of interest: old bricks with unknown values of thermal parameters. Additionally, classical methods (low-field 1H NMR and thermogravimetry) allowed the correlations between the thermal parameters and porosity or/and pore size distribution.