Screening Plant-Derived Residues for Bio-Based Construction Materials: A Comparative Physicochemical Characterisation

Plant-derived residues are promising renewable feedstocks for bio-based building materials, but their suitability depends on structural, thermophysical, fire-related, and mineral characteristics. This study characterises ten plant residues—corn stalk (CS), hemp stalk (HS), luffa (Lu), olive branches (OB), olive pit (OP), Posidonia oceanica (PO), rice husk (RH), rice straw (RS), sunflower stalk (SS), and wheat straw (WS)—to establish a first-stage screening framework for lightweight construction applications. The raw materials were assessed through morphological, density-related, microstructural, thermophysical, thermogravimetric, and microscale combustion analyses, while their calcined fractions were examined by ash-yield determination, X-ray fluorescence, and X-ray diffraction. Apparent bulk density varied by approximately a factor of 30, from 0.0275 g cm−3 for RS to 0.8279 g cm−3 for OP, while thermal conductivity ranged from 0.0436 to 0.1204 W/(m·K). Most residues remained within the range associated with lightweight insulation, whereas OP showed the highest conductivity. Peak heat release rate (PHRR) ranged from 45.7 W g−1 for PO to 145.5 W g−1 for Lu, with SS also showing low heat-release parameters. Ash yield varied from 1.66% to 26.23%, accompanied by silica-rich, calcic, alkali-rich, amorphous, and crystalline mineral profiles. The results provide preliminary criteria for categorising and prioritising residues for lightweight insulation-oriented applications or mineral-related valorisation, as a basis for future composite development and application-level validation.