The rheological performance of wet-process sprayed mortars

This paper, which reports on part of a three-year research project into wet process sprayed concrete for repair, examines the influence of rheology on the pumping and spraying of mortars. The performance of seven commercially available prepackaged repair mortars and six laboratory-designed fine mortars was examined using the Tattersall two-point and Viskomat rotational viscometers, the pressure bleed test, the slump test, a build test and a vane shear strength test. These tests were used to form a rheological audit of each mortars. The two-point apparatus was successful with low-workability mortars, and their flow resistance and torque viscosities were determine. These parameters were also obtained with the Viskomat, although problems were encountered owing to the low workability of the mortars. The pressure bleed test measured both the rate and the total volume of liquid emitted from the mixes, while the vane shear strength test provided an instantaneous reading of the shear strength of the mortars and is compared with their slump. The mortars were pumped and sprayed through a worm pump to assess their suitability and to measure their adhesion to a substrate by build thickness. This value is a measure of sprayability and is converted into values of maximum shear and bending stress, which are then compared with the workability parameters in order to determine their interrelationship.