Microstructure-Driven Feasibility of Crushed Bamboo Coarse Aggregate for Structural–Insulating Wall Composites

This study evaluates crushed bamboo as a coarse aggregate for structural–thermal wall composites, comparing its performance against mixes with wood sawdust and rice husk. Crushed bamboo was used in both smooth and surface-roughened conditions, where particle morphology and surface features were characterized by SEM and AFM methods. The roughened bamboo aggregate exhibited greater surface roughness, thereby improving interfacial adhesion with cement. Surface roughening increased 28-day compressive strength by ~39–44% relative to smooth particles. Incorporating fine plant-based fillers into cement–bamboo composites increased their compressive strength by ~33–75% and reduced thermal conductivity by ~12–18%, compared with the analogues without fine particles. Water-absorption tests on bamboo aggregate showed rapid uptake in the first 24 h (43–45%) and saturation after 7 days of ~65–70%, values lower than typical wood by-products, thereby helping to limit mix water demand. Findings indicate that crushed, surface-roughened bamboo, especially with fine bio-fillers, can produce sustainable wall materials with a strong balance between strength and insulation.