Enhancing bio-based concrete mechanical properties: a novel approach with composite sandwiches and confined cylinders

This paper addresses the growing use of bio-based materials in Europe, thanks to their low embodied energy and carbon sequestration. Despite favorable hygrothermal and acoustic properties, the inherent challenge lies in the low mechanical properties of biobased concrete. This study presents an innovative approach to strengthen hemp concrete through natural FRCM (Fabric Reinforced Cementitious Matrix), using two distinct reinforcement techniques. Firstly, a bending reinforcement consists of applying natural FRCM as the outer skins of a composite sandwich, with hemp concrete as the core. The effect of textile layers and pre-impregnation on the FRCM mechanical properties within the composite sandwich is evaluated. Secondly, compressive reinforcement entails confining hemp concrete specimens with FRCM. The results show a significant improvement in the mechanical properties of hemp concrete, with bending and compressive reinforcement leading to increases in the mechanical strength up to 17,530% and 258%, respectively. Configurations involving mineral-impregnated fabric (PM FRCM) demonstrate superior mechanical reinforcement since it allows a better interphase bond between fabric and cementitious matrix. Different failure modes are observed between reference (non-reinforced) specimens and reinforced specimens, with bending reinforced specimens exhibiting shear failure and debonding at the interface of the composite sandwich, while reference specimens fail in bending. Moreover, compressive reinforced specimens undergo crushing of hemp concrete after tensioning rupture of the fabric, while reference specimens present angular shear path in the middle of the specimens. The results underscore the promise of FRCM in mechanically reinforcing bio-based concrete, opening new opportunities for their expanded use in the construction industry.