Today, the extrusion-based 3D printing of concrete is a potential breakthrough technology for the construction industry. It is expected that 3D printing will reduce the cost of construction of civil engineering structures (removal of formwork) and lead to a significant reduction in time and improve working environment conditions. Following the use of this additive manufacturing layer-wise process, it is required to change the way concrete structures are designed and reinforced, especially for the parts of the structure under tension loads. Indeed, the extrusion-based concrete 3D printing process does not allow for the production of conventional reinforced concrete, and there is a need to develop other ways of compensating for the low mechanical performances of concrete, particularly in tension. In this study, the reinforcement of printed structures by using steel nails through the deposited layers of fresh concrete was investigated. Additionally, three-layer and 10-layer samples were reinforced with nails with varying inclination and spacing. The results show that inclined nails can be used to provide a flexural strengthening of the printing material in different directions.
Of the digital concrete-additive-manufacturing techniques, extrusion-based systems are probably the most widespread and studied. Despite the significant potential offered by 3D printing, several challenges must still be overcome. For instance, although several solutions have already been explored, the automated reinforcement of the layer-wise printed structures represents a challenge. The inline quality control of the fresh-state properties of 3D-printed materials is also an open question that needs to be addressed to find an efficient shared practice. This study proposes a new device designed to simultaneously reinforce 3D-printed structures along and through the layers and to be used as an inline quality-control device. This device consists in a sewing system, which is composed of a rotating system, and a hollow needle, which drives a reinforcing cable or yarn and can be used to inject cement grout to fill holes and improve bonding with reinforcement. The rotation is induced by a stepper motor, which measures the torque that is required to make the needle penetrate. This measurement can be used as a quality-control index to ensure material homogeneity. This paper aims to present an original reinforcement system that can be fully automated and simultaneously create reinforcement patterns in different directions of the printed structure while controlling the material’s fresh properties.
This paper presents testing methods based on the deformation and fracture of fresh cementitious materials only subjected to their own weight. These new methods are dedicated to the study of cementitious materials designed for 3D printing of concrete in order to verify rheological requirements related to the process. The first testing methods consists in measuring the tip deflection of a fresh cementitious materials, horizontally extruded, and allows for the determination of apparent elastic modulus of the material, while the second test consists in measuring the tensile strength of material filament leaving the nozzle of a vertical downward extruder. Both methods are based on the video capture of the deformation of the materials loaded by gravity, and provide results that are in agreement with tests performed with conventional testing machines (tensile and unconfined compression tests). This work shows the potential of the video capture of the gravity induced deformation of cementitious materials to describe behavior of cementitious materials at fresh state or for the in-line control of the 3D concrete printing process.
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