Set-on-demand 3D Concrete Printing (3DCP) construction and potential outcome of shotcrete accelerators on its hardened properties

Set-on-demand 3D Concrete Printing (3DCP) construction is a new method of handling printable concrete mixes to reduce the pumping and transport issues of 3DCP. In this method, rapid stiffening of a flowable mix is achieved near the nozzle by the chemical intervention of the accelerators. The literature on the set-on-demand 3DCP and the effect of the accelerators on the hardened properties of printed concrete is limited. Keeping in view the literature gap, the first part of this study presents a brief overview of the material handling issues when stiff mixes are used for printing and discusses the opportunities offered by set-on-demand 3DCP to mitigate these issues. Then this study selects a shotcrete set accelerator as a case study to tune the rheology of a self-compacting mortar for a set-on-demand 3DCP process and investigates the effects on the hardened properties. The experimental results showed that the set accelerator improved the compressive and flexural properties by 290% and 233% on the first day of concrete age and then slightly reduced these properties at the later ages (3, 7, and 28 days). Shotcrete accelerator remarkably changed the hydration kinetics by modifying hydration phases and produced new profile peaks in the calorimetry test. The change of hydration was reflected in the ultrasonic pulse velocity and X-ray diffraction test results.