Knife Cut Test of Concrete: The Introduction of a New Test Method for Measurement of the Structural Build-Up of 3D Concrete Printing Materials

This study introduces a new and simple test method to measure the structural build-up of printing concrete. The proposed test draws inspiration from the food industry and uses a knife to cut the concrete and measures its resistance to the cutting as an indicator of its strength. This method evaluates the structural build-up of printing concrete by assessing the resistance to cutting with the increasing age of the concrete. For the proof of concept, a device was customized to conduct the knife cut test upon printing concrete. An accelerated printable concrete mixture was tested with the developed device. For the measurement of the structural build-up, prismatic specimens of printing concrete were cut in slices at the speed of 2.5 mm/sec with the increasing age of concrete. The cutting force versus cut depth profiles were used for measuring the peak cut strength and firmness of concrete over time. Rapid penetration tests were also conducted alongside. Analysis of the results showed the high capacity of the developed tool to measure the structural build-up of printing concrete. This simple test can be conducted by attaching a cutting blade with the compression testing machines at a concrete or soil mechanics laboratory and utilizes minimum concrete material. The developed testing system can be applied to the multiple aspects of 3DCP such as material design, printing process design and also as a daily quality control test method.