Enhancing Buildability of 3D Printable Concrete by Spraying of Accelerating Admixture on Surface

The buildability of printable concrete signifies the ability of the printed structure to retain the extruded shape and to sustain the dead load of subsequent layers on first extruded layer without collapse. Higher buildability can help in construction of tall sections in minimum possible time. The buildability depends on structural build-up rate which is controlled by cement hydration (chemical) and interaction between particles developed by flocculation (physical). In several ongoing research studies related to 3D printing, a common method for dispensing the accelerator in concrete is by adding it at the nozzle. This study aims at developing a method to increase the buildability by spraying the accelerator at higher dosages (>8% by weight of cementitious material) post printing. In the print of a full-scale specimen, an empirical method of first printing up to n layers, followed by spraying the accelerator up to n-2 layers (where n > 2) from base was done. Based on the success of this empirical study, a controlled laboratory assessment was performed. The study is divided into three parts - a) the enhancement in buildability is assessed by printing a structure of 200 mm height with spraying of accelerator, b) the depth of penetration is determined by microstructure study using XRD, c) the build-up and flow value is determined for different dosages of accelerators. The study provides a way of application of accelerating admixture in digital printing to attain higher buildability in lesser time.