Material Properties and Full-Scale Rain Exposure of Lime-Hemp Concrete Walls : Measurements and Simulations

University dissertation from Sveriges Lantbruksuniversitet

Abstract: Lime-hemp concrete (LHC) is a building material consisting of a lime-based binder combined with hemp shiv that is suitable for various building applications. This thesis aimed to elucidate the possibilities for using LHC for exterior walls in a cold, wet climate through investigating mechanical, thermal and moisture-related properties of the material. The mechanical properties of LHC containing both shiv and fibres of the hemp stalk in combination with different binders were tested in order to find a mixture with increased mechanical strength so that a supporting timber load-bearing structure could be omitted. A larger amount of cement in the binder mix improved compressive strength. However, even when using unseparated hemp (both shiv and fibres) in combination with a high-cement binder, mechanical strength was not sufficient for the material to be load-bearing without additional support.The moisture properties of LHC were studied in order to determine its robustness and durability in cold, wet conditions. Sorption isotherms and moisture diffusivity were determined over the complete moisture range for two LHC mixes with different lime:hemp ratios. Compared with other building materials (e.g. timber, cellular concrete and lime-based render), LHC showed a high moisture diffusion coefficient in the 35-95% relative humidity (RH) range. The sorption isotherm of LHC appeared quite planar up to 95% RH, but steep between 95 and 100% RH. The thermal properties of specimens with different relative humidities were found to be influenced by RH. At higher RH values thermal conductivity was higher, whereas differences in thermal diffusivity and specific heat capacity as a consequence of differences in RH were less apparent. Four full-scale wall sections combining different renders and LHC mixes were exposed to a rain scenario in order to fully understand the hygric performance. Moisture properties were used in computer simulations of these full-scale wall sections and the simulation results compared with measured data. It was found that even after prolonged rain exposure, some wall sections had low moisture levels inside the wall. A lime-cement render allowed rain to penetrate the wall more easily than a cement render and also dried more slowly after exposure to rain. LHC with a larger proportion of hemp absorbed moisture more slowly and dried more quickly after construction than a mix with a larger proportion of lime. This indicates that LHC with more hemp in the mix in combination with a cement render would be more suitable for use in a cold, wet climate.