PRECONDITIONING EFFECT ON SEM CONCRETE SAMPLES AND ITS IMPACT ON THE IMPLEMENTATION OF CONCRETE SURFACE ANALYSIS AT MICROSCOPIC SCALE

Abstract

To date, the literature on micro-scale concrete has been actively conducted. Scanning electron microscopy (SEM) is widely used not only for microscopic inspections but also on-the-fly elemental identification. However, prior to SEM, the precondition of concrete specimen is necessary. This included drying the samples in a vacuum heater which later on leaded to a significant alternation of microscale concrete surface. Consequently, the representative SEM images, therefore, might not reflect the actual condition. Also, coating by conductive materials such as gold, platinum or palladium may have limitations regarding the surface deteriorations. This research investigated the SEM preconditioning effect on concrete samples by using four surface conditions: 1. regular, 2. rough by natural bleeding, 3. emulated erosion by applying sandpaper, and 4. acidic attack. The before and after preconditioning effects were inspected using an optical light-inverted microscope, while the SEM images were captured by JXA-8200, an electron probed microanalyzer (SEM-EPMA). In addition, the metallic coating using platinum (Pt) and palladium (Pt) regarding the four surface cases were discussed. Findings postulated an inconsistency of the conductive coating (Pt-Pd) among the four surfaces. Also, the vacuum-heating process did alter the microstructure of cement hydrate on concrete surface. Furthermore, a significant increment of microcracks was detected across the specimen surface at ×100 magnification in all cases. Recently, the literature claimed that the concrete surface might have significant impacts on concrete properties and durability. This research might help in emphasizing the relationship between concrete surface and durability concerns such as weathering damage, and chloride attack.