Effects of layer-interface properties on mechanical performance of concrete elements produced by extrusion-based 3D-printing

Nerella, Venkatesh Naidu; Hempel, Simone

doi:10.1016/j.conbuildmat.2019.01.235

Cited by 386 publications

(116 citation statements)

References 36 publications

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“…Depending on the printing procedure used, the inter-layer bonding strength will also be affected by factors related to the print process parameters, surface roughness and quality, moisture content of the fresh deposited layers, inter-layer time gap and the concrete composition. Consequently, compared to previous research on repair mortars, the occurrence of chemical bonding as well as the effect of restrained shrinkage (caused by different curing conditions) and a changing stiffness over time are phenomena that cannot be neglected in case of 3D printing [5][6][7].…”

Section: Introductionmentioning

confidence: 95%

Surface modification as a technique to improve inter-layer bonding strength in 3D printed cementitious materials

2019

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The structural capacity of 3D printed components mainly depends on the inter-layer bonding strength between the different layers. This bond strength is affected by many parameters (e.g. moisture content of the substrate, time gap, surface roughness,..) and any mismatch in properties of the cementitious material may lead to early failure. A common technique to improve inter-layer bonding strength between a substrate and a newly added layer is modifying the substrate surface. For the purpose of this research, a custom-made 3D printing apparatus is used to simulate the printing process and layered specimens with a different delay time (0 and 30 minutes) are manufactured with different surface modification techniques (wire brushing, addition of sand or cement and moisturizing substrate layer). The surface roughness was measured and the effect of the modification technique on the inter-layer-bonding strength was investigated. Results showed that the most effective way to increase the inter-layer bonding is increasing the surface roughness by a comb. This creates a kind of interlock system that will provide a higher inter-layer strength. The compressive strength is most influenced by the addition of cement, where the changing W/C-ratio will create a higher degree of hydration and consequently a higher strength.

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Section: Introductionmentioning

confidence: 95%

Surface modification as a technique to improve inter-layer bonding strength in 3D printed cementitious materials

2019

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“…It is commonly known that the bond between two layers in 3D-printing is a prerequisite to avoid weak spots and anisotropy (e.g., [21,22,[30][31][32]). There are two main factors influencing the interface bond between two concrete layers [33]:…”

Section: Effects On Interlayer Strengthmentioning

confidence: 99%

“…(a) mechanical effect: mechanical bonding relies solely on the physical attributes of the layers, e.g., micro roughness of substrate, cohesion and friction coefficients of the layers and age of the bottom strand as well as rheological properties of the single layers [31,32]. The inability of the layers to interlock lead to a reduced contact area and herewith to a reduced interlayer adhesion.…”

Section: Effects On Interlayer Strengthmentioning

confidence: 99%

“…The inability of the layers to interlock lead to a reduced contact area and herewith to a reduced interlayer adhesion. (b) chemical effect: chemical bonding occurs if the hydration and chemical bonding of particles occurs in between two layers [31].…”

Section: Effects On Interlayer Strengthmentioning

confidence: 99%

“…A reduction of flexural strength with interlayer time in between the manufacturing of two layers was explained with a higher amount of pores/voids [41], microcracks at the interface as well as drying and plastic shrinkage [31,39]. In the latter, a reduction in flexural strength has been reported for specimen with a water-binder-ratio of 0.42 when the interlayer time in between the layers increased from one minute to ten minutes (up to 45% strength loss) or even one day (up to 85% strength loss), whereas, in [41], an interlayer strength reduction of 89% for a 10 minutes-interlayer time and 97% for 60 minutes-interlayer time was reported for a mortar with a water-cement-ratio of 0.36 for a printing speed of 3 cm/s.…”

Section: Effects On Interlayer Strengthmentioning

confidence: 99%

See 2 more Smart Citations

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

2020

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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.

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Ressourceneffizientes Bauen mit Betonfertigteilen Material – Struktur – Herstellung

Kromoser¹

2021

Beton Kalender 2021

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Effects of layer-interface properties on mechanical performance of concrete elements produced by extrusion-based 3D-printing

Cited by 386 publications

References 36 publications

Surface modification as a technique to improve inter-layer bonding strength in 3D printed cementitious materials

Surface modification as a technique to improve inter-layer bonding strength in 3D printed cementitious materials

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

Ressourceneffizientes Bauen mit Betonfertigteilen Material – Struktur – Herstellung

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