Evaluating the effective thermal conductivity of cement mortar through x-ray scanning

Abstract

The effective thermal conductivity of cement mortar as a porous material depends on its solid phase and void phase conductivity. Therefore, a sample's pore distribution can highly impact the value of effective thermal conductivity. For this reason, an x-ray CT scanner was applied to detect air-void content in mortars with different mix proportions. After 28 days of curing, the thermal conductivity of samples (40 × 40 × 80 mm3) was measured by the transient plane source (TPS) apparatus, TPS2500. Then, the samples were scanned by a Zeiss Metrotom 1500 CT scanner to detect the macro pore content. Finally, the VGStudio Max 3.0 software was applied to observe the voids and simulate the effective thermal conductivity. The results showed that the total macro void contents (in this study, voids bigger than 52 μm) were increased up to 15% and 33% for samples with the cement the sand ratio of 1:3 and 1:4 compared to the sample with the c:s ratio of 1:2. However, the results indicated that the void fraction is not uniform. Therefore, effective thermal conductivity can vary in different sample locations. The finding shows that x-ray scanning and image analysis is the proper method to precisely determine the effective thermal conductivity of cement-based materials.