Effect of vibration on rheological properties of concrete and its application in concrete 3D printing
Advisor: Professor David Lange
In the last decade, 3D printing concrete has seen increasing popularity. It has the potential to increase construction efficiency and safety, as well as reduce costs. Typically, concrete that is 3D printed must achieve two targets: flow through the printer to exit the nozzle and hold its shape once printed. These two targets require the concrete to have contrasting rheological properties. This opposing requirement is typically addressed by extruding stiff cementitious material or by dosing the fluid cementitious material with chemical admixtures as it exits the nozzle to cause rapid hardening. The high extrusion pressure and/or thorough mixing at the nozzle limits the use of aggregates in printable concrete mixtures.
Increasing aggregate content has the potential to reduce material costs and decrease shrinkage compared to cementitious mixtures that are 3D printed currently. To address the hurdles of printing aggregates, especially coarse aggregates, this study proposes and investigates the use of vibration to facilitate the rheological properties required for 3D printing.
Vibration causes an immediate and reversible change in the rheological properties of granular suspensions such as concrete. This dissertation examines the role aggregates (granular material) play in the rheology of concrete, both without and during vibration. It was found that aggregates
substantially increase the rheological properties which can be reduced with vibration. The sensitivity of the rheological properties to changing the constituents of the mixture design was statistically modeled to help with mixture design for 3D printing. Additionally, the effect of changing vibration energy on concrete rheology was explored. It was found that the vibration energy input influences the extent of change in the rheology of concrete during vibration. The propagation and attenuation of different vibration amplitudes and frequencies in fresh concrete were investigated at different distances from the vibration source.
Based on these results, a prototype vibrating nozzle was built to control the rheology of concrete in a 3D printer. Rheological limits were established based on the performance of mixtures that could be successfully 3D printed. Other mixture designs that meet the target rheology were identified using regression equations.
The use of vibration to manipulate the rheology of concrete was found to be a feasible method to incorporate coarse aggregates into 3D printable mixtures. The developed statistical model can help guide mixture design for targeted rheological properties.