Rheology and pumpability of mortar

The rheological and material parameters determining the pumpability of fresh self-compacting mortar have been studied. A full-scale set up was used with 50 mm rubber hoses fed by a screw pump delivering a constant concrete flow rate and pressure for a given pumping frequency, hose diameter and - length. The concrete pressure gradient over the pipe length (dp/dx) and flow rate were measured to quantify pumpability. The rheological properties of the pumped mortars were measured with a BML viscometer. Finally, the rheological properties of the paste were studied with a parallel plate rheometer. Measured values of plastic viscosity and yield stress were altered simultaneously from mix to mix, sometimes in opposite directions. It was thus challenging to interpret the data. Increased plastic viscosity of mortar and paste was found to correlate with decreased mortar pumpability. No clear trends could be found for mortar yield stress. Increased paste yield stress was, however surprisingly, related to increased pumpability. Increased hysteresis area calculated from the paste measurements correlated, moreover, very well with reduced pump flow indicating a relation to the rheology of the slip layer. Keywords: Rheology, pumpability, mortar, slip layer