Compressive and shearing behavior of lime and hemp concrete

Abstract

In the literature, most of blocks of Lime Hemp Concrete (LHC, hemp shiv and mineral binder mix) that have been studied show a brittle behavior and a very low mechanical strength. The formulations are generally rich in binder and slightly compacted. Up to now, this material is then not considered as a load bearing material and is mainly used as filler insulation, combined with structure components made of wood, concrete or masonry. Some other formulations have been tested, with higher contents of aggregates thanks to a compaction process, in order to improve both the rigidity and the strength of the hardened mixtures. The higher amount of shiv, lighter and more porous than lime, avoids significant increase in thermal conductivity. The present work is an experimental study of the compressive and shearing behavior of hemp concrete, in order to study the load-bearing capacity and bracing of this bio based material, while maintaining good qualities of thermal insulation. For this study, a special device has been developed. The samples tested with this device are cubic specimens of hemp concrete with 7 cm length. Two compacted formulations were tested, as well as samples obtained from LHC trade-blocks. Two series of tests are performed. The first one is a uniaxial compression test in each direction for characterizing the mechanical anisotropy of the material. This anisotropy is induced by the compacting process. The second one permits to characterize the shearing behavior of the different mix-designs. This is an original device, specifically designed for this kind of material, which allows shearing under controlled normal stress. The first results show a high ductility of this material in shear, which confirms the results of the literature on wall structures. These preliminary results are very promising especially for seismic applications.