Search

International audience; Lime and hemp concretes are used as infill materials manually tamped in timber stud walls or more recently in the form of precast blocks. In either case, the structural design practice of wood frame construction associated with hemp concrete does not assume any contribution of the plant-based concrete whereas it may contribute towards the racking strength of the wall. This work is intended to evaluate the shear behaviour of two different bio-based concretes by means of triaxial compression. Hemp shives and whole rice husks were mixed with a lime-based binder according to the same mix proportioning and mixes were vibro-compacted in cylindrical forms. Then, samples were cured at 23 degrees C - 65%RH before being tested under unconfined and triaxial compression. The triaxial shear test was performed after 60 days of curing on unsaturated specimens under drained conditions at air pressure and for increasing effective confining pressure (from 25 to 150 kPa). It was possible to estimate the shear strength parameters (peak friction angle and cohesion) of the two plant-based concretes. Comparing results, it appears a consistent value of cohesion but a different friction angle related to the binder and the aggregate contributions respectively. This leads to a first analysis of the relationship between the composition of the concrete (plant aggregates cemented with a binder) and its shear strength. Furthermore, the ductility of plant-based concretes is markedly enhanced as the mean effective pressure increases. Finally, the shear strength of plant-based concretes should be considered as part of the design practice of building envelopes.

The deinking paper sludge (DPS) generated by paper recycling incorporated in ceramic pastes has received significant attention to develop environmentally-friendly construction materials with a good thermal and sound insulation characteristic while maintaining a resistance mechanical acceptable by standards. The environmental risks associated with the incorporation of these sludge into clay bricks that rich in heavy metals such as Cr, Pb, Zn, Cu, Ni, etc. have been evaluated. The evaluation of these metals was carried out by performing the leaching test in order to be able to introduce this new material in the list of materials to be marketed in the field of civil engineering. Leaching tests were performed on clay, DPS and the finished product as fired bricks. Leaching results on clays show that they are non-hazardous products, while heavy metal leaching of DPS is above the limiting concentrations, which classifies DPS as a hazardous waste. In contrast, the leaching concentrations of the bricks incorporated by DPS, show that the heavy metals were immobilized in the ceramic structures of all the fired bricks. In this study, the percentages of DPS added in the composition of the bricks are 8%, 10% and 12%. Results of leaching test suggest that replacing up to 12% of clays with DPS can provide bricks to reduce the environmental impact of abundant waste and preserve non-renewable natural resources.