Assessing workability of mortars by means of rheological parameters and desorptivity

Assessing the workability of mortars for restoration and more general purposes has been the subject of many standards and scientific publications over the last decades. A series of mortars made with different binders was brought to optimum water content for workability by an international group of masons. Two methods are proposed to assess the static yield stress and water retention of these fresh mortars, two key parameters of workability as defined by practitioners. Yield stress is measured with a vane test, originally designed for clayey soil, and found to be related to specific surface area of the binder. The increase of yield stress with resting time is quantified and the differences due to the effect of air entraining agent are demonstrated. Water retention is characterised by the desorptivity of the mortars and measured in a vacuum suction experiment. The setup is a modified version of an existing ASTM design. Both methods are complementary to assess the defined workability parameters for different mortars and eventually can be an aid to design suitable mortars for specific purposes.status: publishe