Improving the Dimensional Accuracy in Selective Cement Activation by w/c-Ratio Gradation

Selective Cement Activation (SCA) is a powder bed 3D printing technique that offers the possibility to precisely manufacture free-form building elements with a high degree of complexity and surface quality. Expanding upon initial findings, we aim to further improve the dimensional accuracy. This fundamental research will explore the effect of vertically adjusting the water content over height to account for the often observed uneven dimensional deviations across the height of a component printed with SCA. Therefore, we investigated three types of w/c-ratio gradation: (a) core-shell gradation, (b) core-shell gradation with shell thickness adaption and (c) core-shell gradation with core water content adaption. The samples produced in this way are compared with samples printed with a uniform w/c-ratio in terms of dimensional accuracy, compressive strength and homogeneity. The results show that grading the w/c-ratio, in general, can increase the dimensional accuracy compared to specimens printed with a high uniform w/c-ratio while simultaneously not significantly decreasing the compressive strength. The adapted gradation concept with core water content adaptation further increased the dimensional accuracy, resulting in just slightly less accuracy than the reference specimens printed with a low uniform w/c-ratio of 0.3. However, these specimens achieved 51% higher compressive strength compared with the specimens printed with a constant w/c-ratio of 0.3 while simultaneously having the highest homogeneity in density over their cross-section.