Power floating plastic-state concrete for additive manufacturing applications

Additive manufacturing (AM) for delivering construction is rapidly developing worldwide, with significant effort on the control and measurement of the quality materials, and less di-rected towards enhancing the surface quality of printed parts. The presence of the staircase effect, a well-known feature of 3DCP (3D Concrete Printing), imposes limitations on achiev-ing desired aesthetics and manufacturing tolerances. Secondary processes like floating have been demonstrated to show benefits for sprayed concrete surfaces, however, studies of the parameters for application using mix designs for additive manufacturing based on extrusion of cement-based mortars have not been explored.

This thesis addresses this gap by proposing and evaluating a micro-power floating technique to enhance surface quality in 3DCP before the material hardens. Traditional surface finishing methods like sandblasting, trowelling, and grinding require the concrete to be set; how-ever, applying power floating in an intermediary stage offers a more efficient solution that reduces energy use and minimizes waste. Power floating, conventionally employed to achieve smooth finishes in concrete slabs, is adapted here for automation using smaller-scale floating devices on a robotic arm. This approach enables finishing of complex, smaller elements such as panels and slabs within AM workflows.

The novelty of this research lies in experimentally determining optimal power-floating pa-rameters—specifically tool pressure, rotational speed, dwell time, traverse speed, and tool-path patterns—to achieve enhanced surface metrics. Trials with 123 mm and 215 mm diame-ter floating devices yielded quantifiable improvements in flatness and smoothness, measured by high-resolution optical instruments (Talysurf CLI 2000, Alicona G4 InfiniteFocus) and Basler L acA4096-30 imaging.

Results indicated that an applied tool force between 20-40 N, rotational speeds of 150-300 RPM, and a traverse speed of 200 mm/s provided the best surface quality outcomes. Surface roughness, represented by Ra values, ranged from 1.92 to 13.81 μm, aligning with the Honed Smooth to Heavy Texture grades of ST115 standards. These measurements corresponded well with subjective quality assessments, validating the process effectiveness. This work thus establishes a practical framework for enhancing surface quality in 3DCP, bridging the current gap in finishing techniques applicable to AM for construction.