Yield stress during setting of cement pastes from penetration tests

Measurements of highly visco-elastic media such as cementitious materials during hardening and setting are difficult with standard rheometers. That is why the transition between liquid and solid state of cement based materials is currently measured with standardized penetration tools such as Vicat needles, ball indentation, penetrometers and Hilti nail guns. The obtained results however depend on the measuring device and only give information in arbitrary units. Moreover, no existing theory correlates these tests together although empirical correlations between the Vicat, the Proctor or the Hilti nail gun measurements and more classical rheology can be found in literature. In the present paper, an overview of this type of test is presented. By examining in detail experimental results, elasto-plastic finite elements simulations and visco-plastic fluid dynamic simulations in the specific case of penetrometer test, it is demonstrated that there exists a systematic correlation between these test results and the yield stress of the tested material. Finally more general analytical relations for several penetration tests between yield stress of the tested material and experimental data are proposed.