Assessment of Thixotropy of Fresh Mortars by Triaxial and Unconfined Compression Testing

Triaxial and unconfined compression tests are widely used in geotechnical applications to analyze soil's shear strength properties, including its cohesion (C) and angle of internal friction (phi). A research program was undertaken to evaluate the suitability (advantages and limitations) of such tests for assessing the thixotropy of freshly mixed mortars. Validation of the results was achieved via the establishment of correlations between thixotropy and various static stability indexes, including water bleeding, surface settlement, and coarse aggregate segregation. The test results show that variations in structural build-ups (or thixotropy) can be detected well using triaxial and unconfined compression tests. Testing is realized under quasi-static conditions, with which the discrepancies related to rotational speed and resting periods prior to shearing in mortar rheometers can be eliminated. Tests conducted under drained conditions yielded higher C values than those realized under undrained conditions, indicating that water drainage increases the rate of restructuring (or thixotropy) of cementitious-based materials. A cohesion threshold of around 4 kPa was detected on tested mortars, below which the use of such tests becomes inappropriate.