Rheological model for self consolidating concrete
However, due to pumping, changes in fresh concrete properties and the air-void system have been noticed.This paper describes the consequences of pumping on the fresh properties of SCC by means of two experimental pumping campaigns.In this paper, the results of two series of full-scale pumping tests carried out on SCC mixtures with different compositions and rheological properties are described.The changes in rheological properties, workability and pumping pressure observed with increased pumping time or flow rate are described and analyzed.The first horizontal straight section was constructed with 100 mm diameter pipes.After making a 180° turn and enlarging the diameter, a second straight horizontal section in 125 mm pipes was installed, followed by a vertical part enabling the concrete to flow back inside the reservoir of the pump (Fig. Starting at the lowest flow rate step of the pump (1), flow rate was maintained until pressure achieved equilibrium, followed by taking a sample and a quick stepwise decrease in flow rate, not exceeding the maximum flow rate already applied (except for step 1, where there is no descending The lowest flow rate was first examined (around 4 l/s), and logically, there was no decreasing curve.As a result, the flow rate estimated by determining the time was equal to the real flow rate during which pressure was registered [The pump used at the Université de Sherbrooke was a Schwing BPL 900 truck-mounted piston pump.The maximum pressure that the pump can deliver is 60 bar, while the maximum flow rate is 25 l/s. Behind the pump, a 30 m long loop circuit was installed.
A calibration procedure has revealed, in this case, that the correction needed for the incomplete filling of the cylinders was compensated for by the correction imposed by the dead time of the pumping stroke.
Typically in concrete, increasing the air content would lead to a decrease in plastic viscosity .
However, due to a limited number of data points in some of the experiments, or a negligible presence of shear-thickening in other cases, shear-thickening is not taken into account in this paper.
As shearing can significantly affect concrete rheology, SCC properties should be largely affected by pumping.
A second effect that influences the rheology of concrete during pumping is the change in air content and air-void system.The changes in yield stress or slump flow are anticipated to be influenced by the same phenomenon, but the final outcome is assumed to depend on the availability of residual superplasticizer in the mixing water.Pumping can cause a stable SCC to become segregating if both the yield stress and plastic viscosity decrease, or it can provoke a significant loss in filling ability, passing ability and self-consolidation of the concrete if the yield stress increases dramatically.In many cases, the concrete undergoes a large shear rate in the pipe, thus (re-)dispersing cement particles.