Impact of Hemp Fiber Content and Length on the Hygrothermal, Mechanical, and CO2 Emission Performance of Hemp-Lime Composites

As the construction industry advances toward more sustainable material alternatives, hemp-lime composites have emerged as promising candidates due to their potential for carbon sequestration, low environmental footprint, and excellent hygrothermal performance. Traditionally, these composites utilize only the woody core (shivs) of the hemp plant. However, incorporating a portion of hemp fibers alongside shivs could improve material performance while simplifying processing by eliminating the need for full decortication. This study provides the first controlled investigation of the effects of varying hemp fiber content (10%, 20%, and 40%) and fiber lengths (1.15, 6, 12, and 25 mm) on key properties of hemp-lime composites, including thermal conductivity, specific heat capacity, moisture buffering capacity, and compressive strength. Results indicate that increasing fiber content enhances both thermal insulation and moisture regulation. Thermal conductivity decreased from 0.068 to 0.053 W/(m·K), and moisture buffering capacity increased from 2.12 to 2.73 g/m 2 ·%RH as fiber content rose from 0% to 40%. Additionally, longer fibers (up to 25 mm) further improved insulation, particularly in composites with higher fiber content, reducing thermal conductivity by up to 4% compared to short fibers. However, variations remained within the experimental coefficient of variation. Beyond performance gains, the combined use of hemp shivs and fibers also offers a significant environmental benefit, with the potential to reduce CO 2 emissions by 40.74%. These findings provide novel insights into optimizing hemp-lime composites through partial fiber integration, offering a practical and scalable approach to enhancing both hygrothermal and mechanical performance for sustainable construction applications. • Thermal conductivity decreases by up to 20% with the addition of 40% hemp fiber. • Fiber length has a negligible impact on thermal conductivity performance. • Hemp fiber enhances moisture buffering by up to 24% in low-density mixes. • Fiber addition lowers strength but remains comparable to insulation boards. • Using lower-purity shiv reduces CO 2 emissions by up to 40%.