If building loads cannot be transferred into the soil, ground improvements are often used, which require the addition of cement with considerable emissions of CO2. Thermo-mechanically processed crushed concrete fines can partially replace the required cement. This article deals with comprehensive laboratory tests to improve the soil mechanical properties of a typical sand as a building ground and demonstrates the applicability of thermo-mechanically processed concrete fines for the substitution of 25 wt.-% to 50 wt.-% of cement for practical construction purposes. Processing temperatures of 400 degrees C and 600 degrees C proved to be particularly effective, with greater reductions in strength and stiffness occurring outside this temperature range.