Volume 19, Issue 5

Adhesive properties of fresh mortar joints containing different dosage rates of a water-soluble polymer (cellulose ether based) are investigated using the probe tack test. This test consists of measuring the evolution of the normal force required to separate at a given velocity two plates between which a thin layer of the sample is sandwiched. Three different adhesive components are inferred from the measured stretching force: cohesion, adhesion and adherence. The influence of the polymer dosage rate and the pulling velocity on the evolution of these adhesive properties is investigated. The adhesive components are then related the rheological properties of the mortars which are shown to behave as Herschel-Bulkley shear-thinning fluids.

Rheological characterisation of mortar is complicated by phenomena of slip, the formation of shear bands and depletion. At relatively low solid fractions a typical Couette geometry and a medium-size mixer-type rheometer were used to determine flow curves. At higher solid fractions a large-size coaxial cylinder rheometer with multiple blade vane geometry was used up to the point where slippage occurred. The viscosity as a function of concentration responds to the Krieger-Dougherty law, when a mortar is considered as a suspension of sand in a matrix of binder slurry. The limits of this description corresponds to a critical solid fraction above which air is entrapped during the mixing procedure: air content measurements demonstrate this phenomenon. A clear relationship between mortar and slurries was established, based on the measured properties of both binder and sand particles, and on the Farris model for polydisperse suspensions. Intrinsic viscosity can be used as a tool to evaluate shape characteristics of the binder particles. A procedure for mixture optimisation of mortars using this model is demonstrated for the case of a trimodal mortar.

The stability of the flow induced by the extrusion forming process of a cement based material is largely influenced by the relative migration between the lubricating liquid phase and the granular skeleton. In the present work, we propose linking rheological concepts and soil mechanics (consolidation theory, Darcy’s law) to reach a simple criterion which predicts the extrusion ability of a mortar. Extrusion tests on studied mortar are performed at different ram velocities for criterion validation.

“Single-point” equations used for intrinsic viscosity determination are greatly used when working with synthetic polymer solution systems. In this work we have applied them to a biological macromolecule in a bovine serum albumin (BSA)/water system. Almost all single-point equations are available and errors can be lowered. However, we have detected a systematic bias in the estimations provided by “single-point” methods. To overcome it we propose a “double-point” method which gives lower estimation errors for this system. This novel method is not system specific and could be applied to other polymeric solution.