Investigation of the effect of mix composition on the rheological properties, mechanical performance, durability, and structural behaviour of 3D printing concrete

Abstract

This study investigates concrete composition to optimize mix design for effective extrusion (extrudability) and early strength (buildability) necessary for 3D concrete printing (3DCP). Using factorial design of experiments, the effects of various constituents on material properties were systematically assessed, contrasting with traditional trial-and-error methods. The findings highlight the inadequacy of existing codes for 3DCP, emphasizing the need for scientific guidelines based on predictive models. The optimized mix design incorporates basalt fibre, fly ash, superplasticizer, and Portland cement to enhance extrudability, printability, and strength. The optimized mix added with different concentrations of nanoclay then focuses on plastic failure in printed concrete layers due to insufficient yield strength, which increases the risk of collapse as more layers are added. A simple field-friendly method is proposed for determining the yield strength of cementitious materials and construction rates in 3DCP. Microstructural analyses reveal that early strength gains are linked to increased hydration and enhanced by higher nanoclay dosages, which provide nucleation sites for C₃S consumption. The combination of nanoclay and basalt fibre helps reduce shrinkage. This research addresses the anisotropic properties of printed concrete and the impact of viscosity-modifying agents on compressive and flexural strengths and interlayer bond strength. Findings show that nanoclay significantly influences interlayer cohesion and mechanical performance, while basalt fibres improve flexural strength. SEM and EDX analyses illustrate influence of nanoclay on C-S-H phase development at interlayer regions. This work investigates the effects of nanoclay dosage and basalt fibre on the freeze-thaw performance of 3D printed elements. The surface deterioration mechanism under repeated freeze-thaw cycles is attributed to changes in pore size and distribution, along with increased capillary porosity at layer interfaces due to varying nanoclay dosages.

Date of Award	Dec 2024
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	The Ministry of Education, India
Supervisor	Mohammed Sonebi (Supervisor) & Giuseppina Amato (Supervisor)