LECTURE #8 - CONCRETE PETROGRAPHY
Simpson, Gumpertz, and Heger
11 March 2009
Number of Students: 45
Number of Advisers: 1
Number of Faculty: 1
For this week’s lecture, Mauro Scali from Simpson, Gumpertz, and Heger spoke about the process and applications of concrete petrography. Concrete petrography is the study of hardened concrete micro-structure using microscopic techniques. This study can help with the understanding of concrete conditions that lead to the failure of structures. Mauro explained that the answers to questions on how and why a structure collapsed can be found by knowing exactly where to look. It is important to not only understand the problems in the concrete, but also how to repair the issues.
The process begins with an important visual examination of the concrete. Fractured aggregate and inadequate bonds in the concrete can be discovered just by looking at a photo of a structure. Photographs of existing conditions are vital because they can show factors in the surrounding environment affecting concrete. Next a cross cut section sample can also reveal more imperfections in the concrete. Finally, microscopic examinations of ground down samples will show important information such as the degree of cementation or the water/cement ratio. There are numerous causes for specific issues in concrete. Cracking caused by drying shrinkage, corrosion, and freeze/thaw cycles or an improper water/cement ratio will add to structural failures. One way to counteract cracking is with air entrainment. Very small air voids added to concrete act as buffers that relieve expansive stress due to freezing, etc. Concrete petrography is key in determining how a structure will fail.
Special thanks to Abe Finkelstein, our Secretary, for the write up.