Structural, Thermal and Reaction-to-Fire Performance of a Load-Bearing Sandwich Panel Reinforced with Corrugated Date-Palm Leaf Midrib Mats

This study develops and experimentally characterizes a prototype sandwich panel intended for load-bearing applications, incorporating continuous corrugated date-palm leaf midrib (DPLM) mats within a polyurethane (PU) foam core between plywood facings. Retaining the midribs’ natural cross-sections preserves their peripheral fiber structure while reducing material processing. Independent DPLM properties were estimated using rectangular and triangular section idealizations. The corresponding mean nominal estimates were 8054.04–24,162.11 MPa for bending modulus, 63.62–254.47 MPa for bending stress, 2568.54–5137.08 MPa for compression modulus and 32.17–64.34 MPa for compression failure stress. The triangular bending stress refers to the apex. The sandwich panels achieved a mean ultimate facing bending strength of 10.21 MPa and an apparent flexural stiffness of 7.90 kN·m2, with a mean gross-section edgewise failure stress of 2.87 MPa and an apparent compression modulus of 308 MPa. Failure involved tensile rupture of the bottom plywood facing under bending and global buckling accompanied by localized core crushing under compression, without visible skin–core delamination. Finite-element models were compared with experimental results, with a bending displacement difference of 13.3% at the maximum sustained load comparison point. Preliminary full-scale analyses identified 4.8 m as the largest analyzed roof-slab span satisfying the adopted numerical checks for load-bearing wall applications (without full-scale buckling verification). For roof or floor applications, increasing the panel thickness from 114 to 220 mm reduced the modeled maximum deflection from 17.5 to 6.4 mm under self-weight plus live load. The 220 mm panel’s live-load deflection was 5.7 mm, below the adopted span/360 limit of 6.78 mm. Guarded-hot-plate measurements on a 135.57 mm thick specimen yielded an effective thermal conductivity of 0.08154 W/(m·K), thermal resistance of 1.6626 m2·K/W and specimen-level thermal transmittance of 0.6015 W/(m2·K). For the nominal 114 mm panel, the estimated specimen-level thermal transmittance was 0.7153 W/(m2·K), exceeding the SBC 601 nonresidential Zone 1 wall comparison value. Following surface treatment, the tested 60 mm thick plywood-faced specimens achieved Euroclass E in single-flame ignitability testing, with no ignition, flame spread or flaming droplets observed. The findings support the potential of minimally processed corrugated DPLM mats in multifunctional sandwich panels. Further full-scale structural validation, manufacturing optimization, creep, vibration and durability assessment, thermal improvement and assembly level fire assessment are required before broader building application.