Abstract
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.
Highlights
The development of 3D concrete printing (3DCP) is changing the way the rheology of cementitious materials in the fresh state is studied [1,2,3,4,5]
This study mainly aims to highlight the ability of viscosity modifying agent (VMA) to increase the material visco‐ elastic domain, with further consideration given to its influence on the tensile behavior [25]: a deeper analysis of the impact of VMAs could be performed in further studies
Inspired from the combination of the slump flow, which is a gravity driven flow, and using video capture in order to obtain a shear flow rheometer, two new tests were proposed to measure material parameters that are required in the design, monitoring, and optimization of 3DCP processes
Summary
The development of 3D concrete printing (3DCP) is changing the way the rheology of cementitious materials in the fresh state is studied [1,2,3,4,5]. It is important to note that both methods can be performed before a 3DCP process by just changing the orientation of the printhead Results of these gravity driven tests are satisfactorily compared with results obtained with tensile and compressive tests carried out on a loading machine. Based on squeeze flow tests performed on different samples as proposed in the work of Panda et al [19], the water to cement mass ratio of mortars displaying the same apparent elastic modulus can be determined In agreement with these preliminary compressive tests, the amount of water for mix designs containing VMA is increased to reach an adjusted effective water to cement mass ratio increased by 3% (e.g. W/C=0.37 becomes 0.40 and W/C=0.39 becomes 0.42)
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