Microstructure and mechanical performance of modified hemp fibre and shiv mortars: Discovering the optimal formulation

• Hemp–mortar workability is less affected by shives compared to fibres.
• Porosity < 5% is determined using X-ray μ-tomography of modified mortars.
• Hemp content 2% and length 20 mm optimal for workability and mechanical strength
• Mortar compressive strength of 66 MPa obtained with 15% of milled fly ashes.
• Hemp and fly ashes as cement substitutes result in the highest mechanical performance.

In this work, we investigate the effect of hemp fibre and shive addition on modified mortars microstructure and mechanical performance. The mortar formulation is adjusted with different percentages and lengths of either hemp fibres or shives. Workability of fresh modified mortars is carried out using two main techniques including maniabilimeter and flow table experiments. Microstructural effects are revealed using X-ray μ-tomography where the pore content and 3D spatial arrangement and content of hemp are all investigated. Mechanical performance is derived from bending and compression testing at different curing times. Results show the potential of using natural fibres as substitutes leading, in this study, to improvement of mechanical strength but deterioration of stiffness. Superior mechanical performance with compression full strengths as large as 66 MPa is achieved using high-energy ball milling process of fly ashes that are added to unmodified mortar. Results show also that optimal formulations need to involve both hemp fillers and milled fly ashes. These formulations reveal superior mechanical performance compared to all tested conditions after only 7 curing days.

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