Sample preparation, image acquisition and image analysis on interfacial transition zone of steel fiber-reinforced mortar

A good sample preparation for steel fiber-reinforced mortar is very important mainly for the quantification of porosity and microstructure in the interfacial transition zone (ITZ) using backscattered electrons imaging analysis (BSE-IA). Due to the ductile behaviour of steel fiber, artifact such as smearing or imperfect cut at the edge of steel fiber could happen, and this could affect the microstructure examination in the ITZ between steel fiber and matrix. Through trial, an improved grinding and polishing procedure with short duration for obtaining steel fiber-reinforced mortar specimen (water/cement (w/c) ratio of 0.3 and 0.5) with minimum artifact is found. Scanning electron microscopy (SEM) settings for backscattered electrons image acquisition and an image analysis technique for porosity and microstructure quantification are proposed. Countermeasures that minimize artifacts during sample preparation are also discussed. It is found that the neighbouring aggregates, depending on their geometries and arrangements, can disturb the trend of the porosity in the ITZ. Profiles of porosity and unhydrated cement in the ITZ of steel fiber are presented.