Utilising a water-based spraying method to improve 3D printed concrete

Three-dimensional concrete printing (3DCP) is a transformative technology poised to modernise the construction industry, yet its structural application is fundamentally limited by the anisotropic nature of the printed material. The weak interlayer bond strength between successively deposited filaments, primarily caused by surface moisture loss during the printing pass time, creates preferential failure planes and compromises the integrity of 3D printed concrete (3DPC). This issue is severely exacerbated by extended pass times, which are a practical inevitability in on-site construction. This dissertation introduces and validates a novel, water-based spraying method as a practical solution to enhance interlayer adhesion. A comprehensive experimental program was conducted to systematically investigate the effects of spraying a fine film of water, various chemical admixtures (retarders, accelerators, bonding agents), and cementitious suspensions (metakaolin and silica fume) at the interlayer. The performance of these treatments was evaluated under both normal and extended pass times through a suite of mechanical, durability, and microstructural characterisation techniques. Furthermore, the fresh-state deformation behavior was tracked in real-time using Digital Image Correlation (DIC), providing crucial data for the development and validation of a novel displacement model. The findings demonstrate that the strategic application of interlayer spraying can effectively mitigate the detrimental effects of construction delays. The timing of the application was found to be critical; spraying water at the end of an extended pass time restored significant bond strength, whereas spraying at the start was counterproductive. The application of pozzolanic suspensions, particularly metakaolin, and specific admixtures such as set retarders and bonding agents, led to improvements in flexural strength and durability by creating a denser, more robust interlayer. The study also underscores the paramount importance of sealed curing to retain moisture, which facilitates more complete hydration and prevents the formation of microcracks. The analytical model, which uses the material's dynamic yield stress, proved to be a robust tool for predicting the buildability and failure mode of 3D printed structures, aligning well with experimental results. This research validates a practical and simple method for improving the performance of 3DPC, contributes to the fundamental understanding of interlayer mechanics, and provides a valuable predictive tool to advance 3DCP from a novel technology into an engineered construction method.

Grantor dc:publisher

Stellenbosch : Stellenbosch University

Year dc:date.issued

2026

Author dc:creator

• Kanyenze, Simba Simon

Advisor dc:contributor.advisor

• Combrinck, Riaan

Language dc:language.iso

en

Repository record dc:identifier.uri

https://scholar.sun.ac.za/handle/10019.1/136150

OAI identifier oai:identifier

oai:scholar.sun.ac.za:10019.1/136150