Thermal mass in building structures, such as concrete floor slabs, offers an opportunity to passively cool the building interior when coupled with natural ventilation, thereby reducing the reliance on mechanical cooling, and associated operational carbon emissions. However, most studies related to thermal mass focus on adding material thickness and volume to the floor slabs, which increase embodied carbon associated with additional material use. Using 3D concrete printing, the geometry of the floor slabs can be customized and shaped to optimize the surface area exposure and thickness under a material volume constraint. We present an experimental assessment of full-scale, robotically 3D-printed modules of a structurally optimized shaped concrete floor slab and its flat volumetric equivalent. The two concrete slab modules are tested in a climate-controlled chamber. The shaped floor slab has an expanded surface area 2.6 times to that of the flat slab. Multi-day experiments are conducted to assess air temperatures, internal and surface temperatures of the floor modules under a 15°C diurnal temperature difference. Results show that the shaped module improves air temperature damping by 14.2% and extends time lag by 28.1% on average compared to the flat module of the same material volume, due to its overall geometry, feature thickness and expanded surface exposure. This work provides important experimental data on geometric modulation of building thermal mass as a sustainable technique for operational energy reduction and indoor thermal comfort improvement without an added carbon footprint related to material use.
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