Investigation of continuous and discontinuous carbon fibers in Joule-heated cement composites

This study examines the Joule heating performance of carbon fiber-reinforced cement pastes to advance multifunctional building materials with self-heating and de-icing capabilities. Discontinuous (5, 10, and 15 mm) and continuous (150 mm) carbon fibers were compared under identical mixing and testing conditions. Specimens were prepared with fiber volume fractions of 0.21%, 0.28%, and 0.35%, and water-to-cement ratios of 0.30, 0.40, and 0.50. Alternating current voltages of 30, 45, and 60 V were applied for 45 min, and surface temperatures were monitored via infrared thermography. Discontinuous fibers demonstrated superior heating efficiency compared to continuous fibers. The maximum temperature of 64 °C was achieved with 0.35% 10 mm fibers at 0.30 w/c and 60 V, while continuous fiber specimens reached only 28 °C under the same conditions. Fiber length also influenced heating: at 0.40 w/c and 0.35% fiber content, 15 mm fibers reached 57.0 °C versus 49.4 °C (10 mm) and 41.1 °C (5 mm). Increasing w/c ratios consistently reduced performance. The results reveal that randomly oriented, discontinuous fibers yield significantly greater resistive heating than continuous fibers, particularly under higher voltage and lower porosity. These findings offer practical insights for optimizing fiber geometry and matrix design in conductive cement composites intended for thermal functionality.