ABSTRACT
The relationship between the hardness and the strength for cementitious materials has long been discussed, however, there is as yet no a physical model for hardness. In this paper, a physical model is proposed based on the confined force chain buckling, due to the nanogranular nature of calcium silica hydration (C-S-H). By means of energy criterion for equilibrium applying to the averaged total potential energy density, the critical load including tangential component and supporting component is derived. The main finding of this paper is that the hardness for cement paste is actually the compressive strength with the additional constrain effect. Consequently, an expression of constraint factor with a clear physical meaning is obtained. The case study involves nano and micro indentation, as well as the PDF of constraint factor on the two scales.
