Abstract
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.
Highlights
The extrusion‐based 3D printing technique is a new technology under development for construction of buildings and complex geometries without the use of expensive formwork
Depending on the printing procedure used, the inter‐layer bonding strength will 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
The before mentioned two layered specimens were used to investigate the mechanical properties of the printed samples, while surface roughness measurements and moisture content measurements were conducted on an individual single base layer
Summary
The extrusion‐based 3D printing technique is a new technology under development for construction of buildings and complex geometries without the use of expensive formwork. Previous research [2,3,4], focussing on the bonding between fresh and hardened concrete interfaces, namely repair mortars applied on pre‐treated hardened concrete surfaces, showed that mainly because of stress concentrations at the interface and the creation of voids between two subsequent layers, the chance of failure at the interfaces is higher. These interfaces are able to form a weak link in the overall construction and can affect the structural stability in a negative way. These results will be correlated with the mechanical performance of the cementitious material
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