Thermo-physical Properties of the Clay of Balkuy Combined with Millet Pods for the Thermal Insulation of Building Envelopes

The empirical and traditional use of millet waste mixed with clay to make bricks is widespread in the Sahel region, particularly in Burkina Faso. The aim of this study is to characterize the thermal properties of these composite bricks according to the content of millet pod. Adding an insulator to a building material is one of the simplest and oldest methods to improve its thermal properties. In this work, we report on the thermal properties of clay taken from the site of BALKUY, geographical coordinates (Latitude: 12.30 North; Longitude: -1.47 West) south of OUAGADOUGOU, which we mixed with millet pod at rates ranging from 0 to 4%, in steps of 1. The respective addition for rates ranging from 1% to 4% reduces thermal conductivity respectively by 31.57%; 41.03%; 43.49%; and 54.54%. The rate of millet also has an effect on the thermal diffusivity of the sample. Indeed, the respective addition between 1% and 4% per step of 1 reduces the thermal diffusivity by 81.51%; 93.26%; 93.46% and 94.44%. When 1% of millet pod is added to the clay, the mechanical strength increases 6.55 times. It reaches 6.95 times when 2% of millet pod is added to the clay. Then, it rises from 7.35 to 7.40 when 3% and 4% of millet pods are added to the clay. The addition of the millet pod therefore improves the compressive strength. The optimum value for the millet pod content is 3%.