Mechanical Properties and Microstructure Evaluation of Cement Mortar with Different Cement Strength Classes by Image Analysis

It is well demonstrated that the macro- and micro-characteristics of cement mortar (CM) depend on cement strength, which in turn depends on the cement strength class (CSC). Image analysis, as an objective tool, was used to examine the effects of CSC based on CM experimental characteristics including macro- and microstructure. The investigations were carried out using porosity, flexural and the compressive tests, SEM, XRD, and 3D morphology surface analysis. Analysis of the experimental results demonstrated that finer cement (CSC 52.5 MPa) substantially decreased porosity (about 22-55%) and significantly increased strength properties of the CM (6-91%). This findings was confirmed by changes in hydration phases, pore structure, interfacial transition zone (ITZ) thickness, and crack propagation. Image analysis showed that different CSC caused different changes in contribution of hydration products, in ITZ and also pores structure. The porosity of CMs was obtained using image analysis, and then the results were compared with the laboratory porosities. Image analysis tool was also employed for determining the crack dimensions. It was found that different distributions of pore sizes in the specimens with various CSC caused a variety of cracks development with different widths.