New eco-bio-based insulating material from raw diss fiber and terracotta waste: hygrothermal performance and microstructural evolution

In the context of sustainable construction, optimizing building envelopes to reduce environmental and energy impacts has become essential. This study investigates the combined valorization of two local wastes, terracotta waste powder (TWP), used as a partial substitute for hydrated lime, and raw diss fibers (Ampelodesmos mauritanicus), to develop a new eco-bio-based insulating composite for enhancing the hygrothermal performance of walls. Conducted within a circular economy framework, this research enhances the understanding of composites that integrate biobased resources with recycled mineral waste. The influence of TWP, fiber content and size was investigated through multiphysical characterization measuring density, porosity, capillary absorption, hygrothermal properties and mechanical strength, complemented by X-ray diffraction, micro-thermogravimetric analysis, scanning electron microscopy and optical microscopy. Increasing diss fiber content from 0 to 35 % of the binder mass resulted in a lighter, more porous composite while improving thermal insulation, with thermal conductivity decreasing from 0.357 to 0.166 W m−1 K−1. The moisture-buffering value also increased from 1.05 to 1.89 g m−2·%RH−1. Although mechanical strengths decreased, they remained suitable for the intended non-structural applications. Long fibers accentuated porosity and thermal improvements while enhancing flexural resistance, whereas short fibers favored moisture regulation and compressive strength. In addition, TWP contributed to maintaining and then moderately increasing the long-term compressive strength by improving the matrix microstructure, while also providing additional gains in thermal insulation and moisture regulation without significantly altering porosity, density or liquid water uptake. Overall, the material demonstrates promising potential for thermal insulation and moisture control in building envelopes while valorizing low-carbon local resources.