Printcrete: Upgrading shotcrete

Abstract Printable concrete (hereafter printcrete) is a promising additive construction technology and a novel alternative to conventional shotcrete for tunnel engineering, offering advantages such as eliminating rebound and enhancing flexibility. Despite its potential, challenges remain in upscaling, performance, and applicable equipment. This paper consolidates the prior research on printcrete carried out by the authors, while also offering insights into the advancement of printcrete technology from both sustainable and intelligent perspectives. It begins by addressing the mixture design at both the concrete and paste levels to reduce the carbon footprint of printcrete. The advantages of incorporating coarse aggregates in reducing binder content, along with the associated challenges in processing, are discussed. Additionally, various reaction mechanisms based on low-carbon, fast-setting binders, such as aluminate-based cement and other supplementary cementitious materials, have been studied for printcrete, enabling the decoupling of productive strength from service strength to improve its sustainability. Based on these reaction mechanisms, a twin-pipe pumping technology has been developed to balance the conflicting requirements of pumpability and buildability. This highlights the need for novel indices and standardized testing methods to characterize the early-age hydration and rheological evolution, addressing the accurate time-dependent demands of printcrete. Lastly, a detailed discussion on smart construction is presented, emphasizing its importance in extreme environments, where automated equipment integrated with artificial intelligence is essential for real-time monitoring and adaptive decision-making.