Abstract
The technology of 3D printing concrete has undergone rapid development in the last few years due to its lower environmental impact than that of conventional concrete. To investigate the fresh and hardened behaviour as well as the microstructure of 3D printing cementitious materials (3DPC) containing nano-CaCO3 (NC), four replacement ratios of NC to binder from 1% to 4% are investigated. 3DPC without NC is as a control specimen. The workability, such as fluidity, extrudability, printability limit, and deformation under self-weight, flexural and compressive strength of 3DPC, are tested. The strength development of 3DPC is compared with that of the cast specimens. The hydration products and microstructure of specimens were also investigated by derivative thermogravimetry (DTG), thermogravimetry analysis (TGA), scanning electron microscope (SEM) and backscattered electron imaging (BSE). Results indicate that the fluidity, extrudability, printability limit, and deformation under self-weight demonstrate a decreasing tendency to increase NC’s content. This is attributed to the large specific surface area of NC, which increases the mixtures’ consistency. Adding 2% of NC exhibited about 7.2%, 39.1%, and 22.5% higher compressive strength than that of the control mixture at 7, 28, and 90 days. The enhancement of strength of 3DPC with NC can be ascribed to the filler effects and seeding effects of NC. Furthermore, NC refines the pore structure and improves the microstructure of 3DPC due to its filler effects and accelerating effects.
Highlights
Three-dimensional concrete printing is defined as an automated process based on 3D model data to realize objects from bottom to top layer by layer
Type I 42.5 Portland cement (PC), NC, and fly ash (FA) were used as binders
The main conclusions could be drawn as follows: (1) Due to the highly specific surface areas of NC, greater addition of NC caused the lower fluidity of fresh 3D printing cementitious materials (3DPC)
Summary
Three-dimensional concrete printing is defined as an automated process based on 3D model data to realize objects from bottom to top layer by layer. This technology decreases the building procedure to a one-step process (Ma G.W.et al, 2018), and concrete is only deposited whereby it is necessary. It may contribute to a sustainable environment (De Schutter et al, 2018) Besides that, it would be one of the emerging technology in the construction industry due to its advantages such as rapid construction speed, a higher degree of customization, low-cost production, material savings, and energy conservation (Kazemian et al, 2017; Long et al, 2019). Contour crafting, invented by Dr Behrokh Khoshnevis of the University of Southern California, is commonly recognized as the first building-scale 3D concrete printing process (Feng et al, 2015), and it would be a feasible way for constructing
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