Sample preparation — the key to SEM studies of failed concrete

Abstract

The proper selections of a representative specimen and the sample preparation technique to be used for a scanning electron microscope (SEM) study require a knowledge of the investigated material and the skill of an experienced scientist. Based on comparative SEM studies of concrete samples prepared as either traditional or ‘modem’ fluorescent epoxy-impregnated thin sections, as-polished or epoxy-impregnated surfaces, or as simply sawn unpolished and fractured surfaces, the sawn unpolished and the fractured surfaces proved to be the best for many SEM investigations. The sawn surfaces can disclose those cracking patterns and fine crystal formations that are usually destroyed by polishing and that cannot be seen on thin sections. Further, concrete components soluble in the preparation media can be removed by the preparation procedures, and impregnation materials can introduce elements that are not original components of the studied material, possibly leading to false diagnosis of the damage mechanism.