Shotcrete 3DCP Projection Angle and Speed Optimization: Experimental Approaches and Theoretical Modelling

Abstract

Shotcrete has been lately used for additive manufacturing because of the high versatility of this method and possibility to integrate reinforcement. However, it is known that shotcrete generates waste due to rebound. To minimize the waste, the spraying process needs to be optimized. This work shows the optimization of wet-mix shotcrete from both experimental and theoretical sides for the use in shotcrete 3D concrete printing (S-3DCP). A better control must be reached to reduce the waste from rebounds and for improving the concrete mechanical properties.

A strategy to reduce the waste coming from rebounds is to narrow the concrete jet angle, accelerate all particles at the same speed and ensure a homogeneous sprayed material across the jet. Several types of nozzles have been developed and assessed to ensure high mechanical properties, minimal waste and homogeneous spraying. The classic value of the cone angle is about 15°. The nozzle developed and assessed in experiments managed to reduce it to 8° by optimizing the air inlet and the internal shape of the nozzle, and it was reduced to 2.5° by using an additional air intake.

A model of S-3DCP using aerodynamics (drag force), considering both paste and aggregate phases and the rheological properties of concrete has been developed to evaluate the influence of different parameters. The best configuration between the nozzle shape, air settings (pressure and flowrate) and concrete settings (aggregate distribution, paste composition and mass flowrate) allowed to find an optimum for the concrete jet speed. The speed of the spray has a major influence on the cohesion between the concrete layers. Using optimized nozzle geometry and particle velocity, the improvement in strength performance has been measured from 20–25%. The model has been verified by reproducing experimental conditions and comparing speed results.