Micromechanical properties of cementitious composites

Micromechanical properties of cement matrices in cementitious composites we re investigated by means of the microindentation method. The research focus ed on the correlation between micromechanical properties such as modulus of elasticity and creep, and distance of the indentation from the aggregate-m atrix interface. Composites based on ordinary Portland cement (OPC) matrix were examined after exposure to two types of ageing procedures. The sub-mic ron accuracy of the positioning system of the microindentation apparatus pr ovided means for a meaningful investigation of cement matrix in close vicin ity to the aggregate-matrix interface. For the purpose of statistical analy ses, the data were divided into two groups with respect to the distance of the indent hom the aggregate-matrix interface. While the tests performed wi thin a 30 mu m distance from the interface were classified as indents withi n the interfacial transition zone (ITZ), indents outside this distance were considered to describe properties of the 'bulk matrix'. The results provid e quantitative comparison of the microstructural properties of the interfac ial transition zone (ITZ) with those of the bulk cement matrix assessed by well understood characteristics such as elastic modulus and creep. It was s hown that, for unaged specimens, the elastic modulus measured within the in terfacial transition zone was about 25% lower than that of the bulk matrix. Such results have significant consequences for improvement in modelling of cementitious composites.