Under the Microscope

June 1, 2001
Publication: Civil Engineering - ASCE v 71 n 6 p 66-71
Author(s): Paul Kelley Glenn Bell Michael Brainerd Mauro Scali

Abstract: Forensic engineering is typically more complex than engineering design because it requires the integration of specialized knowledge of materials science, structural analysis and design, and construction processes. In projects involving concrete and masonry, petrography is often used to impart valuable insight and direction to the forensic investigation. Petrography is the visual examination and evaluation of the composition and properties of rocks; concrete petrography applies the same techniques to the analysis of the paste, fine aggregate, and coarse aggregate constituents. Petrographic analysis begins with a visual examination followed by a more detailed examination drawing on conventional techniques, advanced techniques, or microscopic analysis. Typical petrographic microscopy involves a stereomicroscope (10x to 100x), a microscope that polarizes transmitted light (25x to 1,000x), and a microscope that reflects ultraviolet light (10x to 100x); scanning electron microscopy is also used on occasion, especially in conjunction with an elemental analysis using energy dispersion X-ray spectroscopy (EDXS). Four case studies presented in this feature reveal how petrographic studies can reveal the causes and timing of failures.