(317d) Using 3D Printing Process Parameters to Assess the Robustness of Cement-Based Printing Material

Concrete is the most widely used material on earth, second only to water. Due to its high consumption, over 10 billion metric tonnes of concrete is produced annually to provide roadways, housing, foundations, dams, hospitals, schools, power plants and other critical infrastructure. Concrete is made up of water, aggregates and cement. Since portland cement is the strength bearing component of concrete, its annual global production is likewise very high. This high production of cement leads to the generation of huge amounts of CO₂ and potential danger to the environment. In addition, current construction practices generate large volumes of concrete waste. Embracing 3D printing in construction promises reduced construction waste, thus reducing the demand for portland cement and benefiting the earth and its inhabitants. Researchers around the world are currently pushing to demonstrate the printability of large-scale structural components. To ensure sustained gains from 3D printing in construction, issues regarding printability and structural integrity of printed infrastructure materials must be addressed. The printability of cement-based pastes depends strongly on the paste rheology. Several factors including the water-to-cement ratio, type and dosage of additives and the mixing protocol, among others, affect the paste rheological properties. Cement-based printing pastes have been developed using hydrogel forming polymers as printing aids. The performance and robustness of two different pastes formulated at 0.25 and 0.27 gel-to-cement ratio respectively were explored by varying print-process operating variables including extrusion speed, layer thickness and scale of select benchmark object geometries. Printed shapes including cones, vases and cylinders, were used to correlate print quality and the paste viscoelastic properties.