Abstract
Recently, the progress in 3D concrete printing has developed enormously. However, for the techniques available, there is still a severe lack of knowledge of the functional interaction of processing technology, concrete rheology and admixture usage. For shotcrete 3D printing technology, we present the effect of accelerator dosages (0%, 2%, 4% and 6%) on fresh concrete properties and on interlayer strength. Therefore, early yield stress development up to 90 min is measured with penetration resistance measurements. Deformation of layers under loading is investigated with digital image correlation and a mechanical testing machine. One point in time (10 min after deposition) is examined to quantify vertical buildability of elements depending on the accelerator dosage. Four different interlayer times (0, 2, 5 and 30 min), which occur for the production of small and large elements as well as due to delay during production, are investigated mechanically as well as quantitatively with computed tomography regarding the formation of cold joints. With increased accelerator dosage, an instantaneous increase in early age yield stress and yield stress evolution was observed. An increase in interlayer time leads to a reduced strength. This is mainly attributed to the observed reduced mechanical interlocking effect of the strands. Finally, a model to describe interlayer quality is presented. In the end, advantages as well as limitations of the findings are discussed.
Highlights
3D printing seems to be ideally suited for construction where piece production and geometric complexity are common [2]
This paper presents for Shotcrete 3D Printing (SC3DP) technology the effectand of admixture
Both accelerator dosage and interlayer time are assumed to the time gap in between two strands of shotcrete on (a) vertical buildability and (b) interlayer strength, have an effect on the properties of the contact area in between the layers
Summary
3D printing seems to be ideally suited for construction where piece production and geometric complexity are common [2]. The major advantage of these techniques is the high contour crafting [11,12,13,14]) and (II) the deposition of broad strands of several decimetres’ width, which manufacturing for creating monolithic structures wellofas‘infinite the building size of the are used to buildspeed the whole width oflarge-sized the component in a single pass as aaskind brick’ The use of set Achieving the and minimum required yield stress is highly dependent on accelerators the mixturessignificantly composition changes and the the setting behaviour of the concrete and enables, derived from this, the manufacturing of large used admixtures. ThisHowever, reason, the usetoofthe high kinetic energy cansupporting lead to the formwork, theofSC3DP as well as the extrusion process based on awithout self-supporting of the printed minimization cold joints [28].
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