Thermal conductivity of biochar-clay composites for the internal insulation of buildings

The application of biochar-clay composites as internal insulation of buildings is very promising since the employed materials are ecological and commonly available, corresponding to a forward-looking construction method. To bring this solution to its full potential however, additional data on the thermal performance of such composites are required. In this study new biochar-clay composites are investigated by varying composite’s parameters such as biochar and clay type, biochar weight fraction and addition of natural fibres. Measurements of the thermal conductivity are performed by the heat flow meter method at different temperatures and moisture contents. Based on the measured outcomes, an empirical model is developed and calibrated to predict the impact of the composite`s density, temperature and moisture content on the composite thermal conductivity. At an average temperature of 20°C and dry conditions, for composite densities ranging between 222 and 610 Kg/m 3 , thermal conductivities between 0.06 and 0.18 W/(m K) are obtained. Combined increases of temperature and moisture content of 10 K and 20 Kg/m 3 lead to an increase of the thermal conductivity of the composite between 10% and 26%, depending on the composite type. • The thermal conductivity of novel biochar-clay composites is measured • Effects of biochar-type and density on the thermal conductivity are investigated • Effects of composite´s temperature and moisture content are investigated • An empirical model of the thermal conductivity is calibrated against measured data • The application of biochar-clay composites as internal insulation is promising