P.F.G. Banfill Heriot-Watt University, Edinburgh.

Rheology can be applied to the workability of fresh mortars. The Viskomat is a commercial instrument which is capable of measuring their rheological properties to a high degree of discrimination and sensitivity. Mortars conform to the Bingham model and require the measurement of both yield stress and plastic viscosity to define their properties unambiguously. An experimental investigation of the effect of sand grading on four building mortars showed that yield stress and plastic viscosity were both reduced by increasing water content, but to a much lesser extent with the coarser sand. Sand grading and mix proportions interacted in a complex way and acted differently on yield stress and plastic viscosity, but this complexity presents possibilities for the control of mortar production.