Design of mechanically enhanced concrete using hemp shiv

Abstract

Hemp shiv ultra lightweight concretes are more and more used in European countries for their coupled insulation, mechanical and transfer properties. One of the scientific limitations of this material is related to the weakness of the interface zone between woody particles and mineral binder. A new way of approach to address the problem is the use of cellulose ether (CE) as an additive in order to explore to the potential of the improvement of the interface zone of between hemp shiv and binder. Two mixes were tested without CE and with 1%CE. An experimental work was carried out to investigate the binder’s properties like the paste water retention or interstitial water surface tension and viscosity. The influence of CE addition on the interface between hemp shiv and hardened binder was investigated using a Secondary scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDX) were also conducted on selected surfaces. Two hemp shiv concrete mixes with a dry density of 490 (kg/m3) are tested. Bidirectional compression and thermal conductivity tests were carried out at 60 days. The effect of particles’ orientation during manual casting was also studied. The results of SEM observations and EDX analysis showed that the transition zone contained the calcium ions (Ca2+) and had a porous thickness around hemp shiv of 200 µm. This transition zone is not visible when CE is added to the binder. As a result, the young modulus of hemp shiv concrete is increased by 2.5 to 5 times and compressive stress (ε=5%) by approximately 2.5 times, no matter the direction of compression loading. The thermal conductivity values in both directions of the aggregates were different. The results also underlined the interest of the angle parallelepiped aggregates during the compression loading direction, which affected to enhance hemp concrete rigidity.