Direct shear test for the assessment of rheological parameters of concrete for 3D printing applications

Abstract

Rheology of concrete plays a major role in concrete 3D printing applications, where the concrete is pumped at high pressure and extruded through a nozzle at low speed to build the structural component. The 3D printable concrete should be stiff and is different to normal or self-compacting concrete. Hence, the common testing methods used to estimate the rheological parameters are not suitable for 3D printable concrete. In this study, the direct shear test is trialled as a potential method to measure the rheological parameters of different mixes of concrete. The effects of water–cement ratio and shear rates on rheological parameters were examined. The tests were carried out with varying shear rates, ranging from 0.5 to 15 min−1, and normal stresses, ranging from 2 to 15 kPa, for mixes with water–cement ratios of 0.3, 0.4 and 0.6. Further testing was carried out on mixes with varying aggregate to cement and fine to total aggregates ratios to study the effect of binder and aggregate proportions on the rheology of mortar. It was found that the shear rates, 0.5 to 15 min−1, have little effect on the cohesion values and friction angles. Further, the behaviour of the mixes was found to be following the Mohr–Coulomb model.