Thinking Outside the Petrographic Box: Application of Petrographic Techniques to Investigation of Failure between Composites of Cement-Based and Non-Cement-Based Materials

摘要

For more than a century, the construction industries have utilized petrographic techniques to evaluate the composition, characteristics, and quality of concrete, mortar, and other hydraulic cement-based construction materials. The analysis is performed under ASTM C856-18a, Standard Practice for Petrographic Examination of Hardened Concrete. This method provides a guideline for the examination and analysis of concrete (or mortar) to describe composition and characteristics of the mineral constituents and, in some circumstances, to investigate the causes of distress. Although the practice historically is based on visual and microscopical techniques, it allows the petrographer freedom to design the study to meet the needs of the investigation. The practice allows for the use of nonmicroscopical techniques to supplement the study. Such ancillary techniques may include X-ray spectrometry, computer-assisted imaging and analysis, and a variety of inorganic and organic chemical analyses. Such ancillary methods have been used successfully in conjunction with traditional petrographic examinations to investigate characteristics and properties of the concrete and to determine the use or omission of specified constituents or additives. Petrographic techniques, traditionally used for the study of cementitious materials, have been applied to the study of failures of bonded materials, such as coatings, adhesives, and other surface-applied materials that may or may not be cementitious in nature. In these investigations, it is not uncommon that microscopical techniques are supplemented by one or more ancillary techniques to properly determine the causes or contributing factors to failure. This paper includes three case studies in which we determined the explanations for failure between two or more separate materials only through the combination of microscopy and other ancillary techniques. The issues of whether such study of composite systems, not entirely composed of cementitious materials, can be said to have been performed in accordance with all or a portion of ASTM C856 are discussed.