Experimental Investigation on the Fracture Energy and Mechanical Behaviour of Hemp and Flax Fibre FRC Compared to Polypropylene FRC

Abstract

Natural fibre reinforced concrete is been studied for many years as a more sustainable option to current reinforced concrete used in industry. The most common fibre materials currently adopted are steel, glass and synthetic fibres. Apart from the high oxidation and cost, their environmental impact is a serious issue as they are petroleum-based materials. This study assesses the feasibility of replacing polypropylene fibre with hemp and flax fibres. According to the inventory of carbon and energy (ICE) the embodied energy of polypropylene (PP) is 95.4MJ/kg and the embodied carbon is 4.98kgCO2/kg during its lifetime. It represents approximately 3 times more than the estimated values for vegetable fibres. For this, Different concrete mixtures reinforced by 0.5% to 1.0% of hemp, flax and polypropylene fibres were tested, and their post-crack flexural tensile strength, elastic’s modulus, compressive strength and fracture energy were evaluated. The mixtures containing hemp fibres presented properties equivalent to those containing polypropylene under the same proportion. Although both compressive and tensile strength were reduced for the mixes containing flax fibres, the Young’s modulus was 49% smaller and could be an interesting approach for applications that require better elasticity from the concrete, such as industrial floors and structures that may be submitted to impact.