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Structural and Durability Performance of 3D Concrete Printing

Ghoneim, Abdalla
A Master of Science thesis in Civil Engineering by Abdalla Ghoneim entitled, “Structural and Durability Performance of 3D Concrete Printing”, submitted in July 2023. Thesis advisor is Dr. Adil Tamimi. Soft copy is available (Thesis, Completion Certificate, Approval Signatures, and AUS Archives Consent Form).
3D concrete printing, 3DCP, is considered the latest digital technology in the construction industry, it has proven its potential in a wide range of disciplines. Recently, there has been growing interest in exploring 3D concrete printing as a novel construction method. This technique offers several advantages, including reduced waste, decreased labor-force requirements, and the ability to create complex geometries. However, utilizing concrete for 3D printing presents its own set of challenges. The material needs to maintain a flowable consistency to facilitate extrusion, while ensuring that the printed layers maintain their shape and quickly develop sufficient strength to support their own weight and subsequent layers. Unfortunately, there is a lack of guidance available for designing concrete mixes specifically tailored for 3D printing. Furthermore, there is limited understanding of how 3D printed concrete performs under varying environmental conditions. This study will assess the durability of 3DCP through water permeability, water absorption, ISAT and RCPT by testing a total of 48 specimens. The findings of the durability study revealed that the inclusion of fibers in the mix improved the stability of the printed shapes. Printed samples were less durable than cast ones due to their high porosity ratio and lack of compacting. However, samples with fibers showed higher permeability and absorption ratios compared to non-fiber reinforced samples, due to the inconsistency of the fiber distribution. Furthermore, the experimental program addressed fresh and hard state properties through flow table, vicat needle, compressive and flexural strengths using 45 different samples. The results of the flow percentage of the mix without fibers was 86%, however, the percentage of the mix containing fibers was less by 10%. The results of the Vicat needle test of the mix with fibers showed higher shape stability parameters. The compressive strength of the mix was almost similar for samples without fibers compared to cubes with fibers, with strengths of 49 and 50 MPa respectively. The failure state in flexure of the samples with no fibers was instant, whereas in comparison, the samples with fibers showed a gradual increase in strength as the beam deflects, which shows an elastic behavior.
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