Virtual Sliding Pipe Rheometer for estimating pumpability of concrete

Predicting the pumping pressure needed to ensure a consistent flow rate of concrete is crucial to the success of current construction processes and newly introduced, but fast-growing 3D-concrete printing techniques. The Sliding Pipe Rheometer (Sliper) has recently proved to be a reliable experimental tool in predicting pumping pressure. Building on the experimental results of an earlier investigation by means of Sliper, a single-fluid numerical model for simulating Sliper tests (virtual Sliper) was developed using Computational Fluid Dynamics (CFD). Various observations as well as numerical limitations of the model and their physical origins were analysed. It was demonstrated that lubricating layer has vital influence on concrete pumping and that single phase numerical models, not considering the lubricating layer are only applicable to some specific concrete compositions. Hence, the initial single-phase model was improved by implementing a separate lubricating layer; its properties were calculated using Chateau-Ovarlez-Trung and Krieger-Dougherty models. Experimental and numerical comparative analyses confirm the validity of the above-mentioned approach in calculating lubricating layer properties. Parameter sensitivity analysis showed that the plastic viscosity and thickness of the lubricating exert the dominant influences on pumping pressure. The virtual pumpability testing tool as developed should enable a more purposeful material design of pumpable concrete and pre-estimation of pumping processes.