Microhardness testing of cementitious materials

The present paper discusses the underlying principles of microhardness testing, addressing the theoretical background and the testing procedures. The advantage and limitations of this technique are highlighted and on that basis guidelines for its proper use in the research of cementitious systems are presented. For proper micro-structural characterization of restricted zones such as the interfacial transition zone (ITZ), there is a special need for adequate preparation of the surface and choice of the right load. For measurements at the ITZ, this load should be in the range of 0.02 to 0.05 N (2 to 5 gmf). The various microhardness profiles obtained next to inclusion surface can be classified and discussed in terms of the influence of a rigid inclusion that should be superimposed on the influence due to a weak ITZ. In the study of the properties of bulk pastes, linear relations were reported between the microhardness value and the compressive strength. The load sensitivity of the microhardness test might be used to generate additional parameters (n, lnKL) to quantify microstructural characteristics. However, because the interpretation of such parameters is based on empirical relations, they should not be used their own, but in combination with other test methods.