The Effect of Accelerator Dosage on Fresh Concrete Properties and on Interlayer Strength in Shotcrete 3D Printing

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.

Penetration of Cement Pastes into Particle-Beds: A Comparison of Penetration Models

“…A drawback of the depositing process is the lack of freedom of form, since strong overhangs can only be realized with the help of supporting structures [ 24 , 25 , 26 ]. An exception is shotcrete 3D printing technology, which enables also strong overhanging structures [ 27 ]. However, these techniques could require the use of a combination of additives and admixtures which increase the cost and the complexity of the mix-design of the material.…”

Effect of Structural Build-Up on Interlayer Bond Strength of 3D Printed Cement Mortars

“…In 3DPC, it is difficult eliminate the weak connections or defects between two adjacent layers, due to the special way of casting (printing layer by layer), which significantly affects the interlayer bond strength of 3D printed samples [ 15 ]. This is an important consideration and a significant limitation on the viability of concrete 3D printing for structural applications [ 8 , 16 ]. Recently, there are a number of variables have been proved to affect interlayer bond strength of 3DPC: namely, printing parameters [ 17 , 18 ], time gap between printed layers [ 5 ], surface moisture [ 19 , 20 ], effective contact area [ 21 , 22 ] and topological interlocking [ 23 ].…”

Use of 3D printing to create multifunctional cementitious composites: review, challenges and opportunities

“…Most approaches involve an extrusion-like process, whereby concrete is prepared and mixed as usual, and a concrete pump is guided to produce the desired structure [8][9][10]. Other, somewhat less developed approaches include shotcrete 3D printing [11] and powder bed concrete 3D printing [12]. Most studies of concrete 3D printing focus on development of large printing systems capable of producing entire houses and buildings.…”