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The Faculty of Engineering at Stellenbosch University is one of South Africa's major producers of top quality engineers. Established in 1944, it currently has five Engineering Departments.

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Browsing Faculty of Engineering by Subject "3D printing -- Concrete"

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    3D Printing of rapid setting ordinary concrete mixtures
    (Stellenbosch : Stellenbosch University, 2021-12) Gunzel, Friedhelm Stefan; Combrinck, Riaan; Kruger, Pienaar Jacques; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
    ENGLISH ABSTRACT: In recent years, significant research and development has gone into 3D printed concrete. This construction technique requires no formwork as in ordinary construction projects. The addition of admixtures increases the complexity of 3D printable mixtures in comparison to ordinary concrete mixtures in which cement, water and aggregate are the main constituents. In this study, more ordinary concrete mixtures are used for 3D printing in order to minimise the complexity of 3D printable mixtures. The combination of a more ordinary concrete mixture with the efficiency of 3D printing as a construction technique, combines the benefits of both construction techniques. The aim was to 3D print ordinary concrete mixtures that have improved buildability characteristics due to a rapid setting behaviour. Three types of rapid setting behaviours were tested in this study: false setting, ordinary Portland cement (OPC) cement replacement with belitic calcium sulfoaluminate (BCSA) cement and flash setting. The study was conducted in two phases. The first phase was used to characterise the three rapid setting mixtures. Compressive strength, hydration temperature development, setting time and early age compressive strength were tested for the characterisation. In the second phase, the three rapid setting mechanisms were printed in a 3D printer to determine the buildability of the three rapid setting mechanisms. In addition to buildability, the economic feasibility of the rapid setting mixtures was analysed. It was found that false setting does not significantly influence the mechanical characteristics of concrete. The early age strength gain is not as rapid as for flash setting or with the addition of BCSA cement. Flash setting improves the early ages strength gain of concrete but reduces the long-term compressive strength development. Replacing OPC cement with BCSA cement improves the early age strength gain and does not impact the mechanical properties significantly. Higher cement replacement rates increased the intensity of the rapid setting mechanisms, shorter setting times and higher early age strength was improved. From the buildability study it was found that flash setting has the largest positive impact on the buildability characteristics of 3D printed concrete. The buildability could be increased by 321% with flash setting. OPC cement replacement with BCSA cement resulted in a buildability increase of 214%. False setting was found to be the least effective rapid setting mechanism with a 35% increase in buildability. Flash setting and BCSA replacement are cost effective methods to improve the buildability of 3D printed concrete. False setting is found too expensive to induce and the compressive strength gain at early ages is little compared to the other two rapid setting mechanisms. The aim of this study was achieved by 3D printing rapid setting ordinary concrete mixtures. Significant buildability improvements could be made, and the rapid setting ordinary concrete mixtures are beneficial for the rapid construction of 3D printed components or structures.