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    Influence of nano-silica and r-MgO on rheological properties, 3D printability, and mechanical properties of one-part sodium carbonate-activated slag-based mixes
    (Elsevier, 2025) Akturk, Buesra; Ertugrul, Onur; Ozen, Omer Can; Oktay, Didem; Yazar, Tugrul
    Interest in 3D concrete printing is growing quickly in academia and industry. Alkali-activated materials (AAMs) are a greener alternative to cement but traditional AAMs face challenges with high-viscosity alkaline solutions and energy demands. One-part AAMs, using solid activators and aluminosilicate precursors, present a promising solution. This research investigated the potential producibility of one-part sodium carbonate-activated, slag-based 3D printable mixes. The disadvantages of sodium carbonate activation were mitigated by using reactive MgO (r-MgO), obtained through low-temperature calcination, as a partial substitute for the primary precursor, slag. Additionally, nano-silica was incorporated into the mixes to improve rheological and mechanical properties as well as printability. Several mixes were developed using varying amounts of r-MgO, up to 15 %, and a small amount of nano-silica, 1 % by weight. Rheological properties, including static and dynamic yield stress and viscosity recovery, were evaluated. The printability and buildability of the mixes were experimentally assessed to determine their feasibility for 3D printing. The test results indicated that printable, buildable mixes with proper setting times and sufficient compressive strength can be obtained by substituting slag with r-MgO in specific amounts, namely 10 % and 15 % by weight. While yield stress, compressive strength, printability, and buildability improved with r-MgO substitution, setting time decreased. Furthermore, the inclusion of nano-silica significantly enhanced rheological properties, while mechanical properties showed a slight improvement in 3D-printed samples, which also enabled printable mixes with low r-MgO content (5 %). Moreover, the environmental impact of the produced mixes was found to be much lower than that of Portland-cement-based mixes. In conclusion, one-part sodium carbonate-activated, slag-based mixes present a viable and environmentally friendly alternative for 3D-printable mortar, in case of the inclusion of r-MgO.
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    Material Characterization and Damage Assessment of Byzantine Rock-Cut Monastery: A Case Study of Kiyikoy Hagia Nicholas
    (Istanbul Univ, Research Inst Turkology, Dept Art History, 2024) Ozata, Serife; Akturk, Buesra; Akturk, Engin
    Rock -cut historical structures have been constructed worldwide for various functions throughout history, including during the Byzantine Empire. The Kiyikoy Hagia Nicholas Monastery is an exceptional one of the surviving rock -hewn buildings in the Thrace Region. It has a basilical plan and was constructed in the Early Byzantine Period. The study goals are to provide original material characterization, suggestions for damage prevention and conservation measures for rock -cut structures of Byzantine architecture through this monastery case. Therefore, firstly the distinct architectural style of the building was revealed through a comprehensive analysis and by comparing it with similar structures. Then, a damage reconnaissance was performed and material samples were subjected to mechanical, physical, and chemical analyses and acid treatment experiments. Investigations focused on identifying the original materials and understanding the reasons for various decay and damage types observed in the monastery. Proposals for materials compatible with the original material, considering physical, mechanical, and chemical properties, were developed. The effectiveness of the characterization methods was explained. To prevent the effect of cracks, which is the main structural damage, constructing strengthening structural elements by using suitable materials was recommended. For non-structural damages, the removal of moisture in the main rock was recommended, and possible actions for surface cleaning, conservation and consolidation were described. It is concluded that the documentation, diagnostic and restoration steps developed for this monastery can be applied to similar Byzantine rock -cut structures.