Post‐Storage Characterization of Recycled High‐Density Polyethylene–Sand Composites for Cement‐Free Paving Applications

ABSTRACT Recycled high‐density polyethylene (HDPE)–sand composites were characterized after multi‐year indoor storage for cement‐free paving applications. Eight formulations containing 30–100 wt% HDPE were evaluated using n = 3 within‐batch specimens per formulation from a single composite batch, without independent production‐batch replication. The same specimens were sequentially tested for bulk density, water absorption, and compressive strength after 24 h water immersion. Shore D hardness and morphological, spectroscopic, and thermal analyses were interpreted descriptively. Bulk density decreased from 1.52 ± 0.13 to 0.77 ± 0.01 g cm −3 with increasing HDPE content. The highest mean compressive strengths occurred at 40% and 50% HDPE (14.01 ± 0.60 and 12.87 ± 0.71 MPa), with low water absorption (0.53% ± 0.12% and 0.43% ± 0.06%). The 30% formulation showed low, highly variable strength, whereas 90%–100% HDPE showed lower mean strength. Shore D hardness ranged from 55.75 to 62.54. Spectroscopic and thermal profiles were characteristic of HDPE‐containing composites, while microscopy identified local polymer‐rich and mineral‐rich regions. The 40–50 wt% range showed the most favorable numerical property balance. Because equivalent baseline measurements and continuous storage records were unavailable, the findings describe within‐batch post‐storage performance rather than aging kinetics or field durability.