Thermal-Conductivity Measurement of Thin Porous Composite Materials via Combined Transient Hot Wire and Comparative Approach

This study presents a concise two-step protocol that combines the transient fine-wire heating method with the fine-wire comparison method to obtain reproducible thermal-conductivity values for thin porous concrete. Using an axisymmetric analytical solution, a semi-log regression window was defined to satisfy the semi-infinite assumption; for the standard specimen, 30∼100 s of regression yielded 2.13 ± 0.02 W/m⋅K (n = 3). Layered tests on thinly sliced specimens identified a departure point of approximately 100 s for a total thickness of approximately 15 mm, thereby supporting a 30∼80 s analysis window for thin specimens. For concrete with a design strength of 100 MPa, the maximum difference from prior 30 ℃ data for similar mixes was 0.17 W/m⋅K, which is reasonable considering curing and moisture differences. Parametric comparisons showed that conditioning at 57% relative humidity increased conductivity relative to oven drying, whereas the polypropylene fiber dosage did not generate a clear room-temperature effect. This protocol uses simple equipment and short test times, improves reproducibility via an explicitly defined semi-log window and departure point, and is practical for thin concrete and similar porous materials in laboratory and field settings.