Intro

Petrographic Testing (ASTM C856) is a method that uses microscopes to examine the mineralogical and chemical characteristics of concrete and minerals. Each of these characteristics gives the engineer a sense of what is going on with the concrete and its physical properties.

Fenagh primarily performs Petrographic Testing on concrete, but this method can also be applied to rocks and minerals to get a sense of how the sample was formed. However in Fenagh’s line of work, Petrographic Testing is primarily used on concrete for forensic purposes. If there is some type of failure with the concrete, the engineer can use this method to have a better understanding as to why the failure occurred.

Test Details

The test begins when the engineer takes a sample of the concrete, typically a core, and begins to trim the sample to a size small enough to be adhered to a microscope slide. The wafer of concrete, once fully adhered to the slide, is then trimmed further and placed into a specialized grinder that will polish the specimen down to 20 to 30 microns. This process produces a “thin section” of the concrete that allows light to travel through the specimen.

When the engineer examines this thin section under a specialized microscope, it allows him or her to see properties of the concrete such as mineral composition of aggregate, hydration of the cement, microfractures, air voids, and other traits that may be relevant depending on the type of Petrographic Test being performed.

Test Benefits

Petrographic Testing helps the engineer determine things like strength and air content of the concrete. Air content is important for durability and lifespan, which will vary based on the concrete’s purpose and use.

This method also shows engineers the degree to which the concrete is degrading, if it has been damaged by fire, and if there are any other durability issues. If there are durability issues, Petrographic Testing gives the engineer insight as to why these issues are occurring.

Example

Petrographic testing can be used for any type of project, but it is typically used when the client is having some type of issue with their concrete.

For example, Fenagh once had a case with a precast panel that required Petrographic Testing. A precast panel is a slab that is poured somewhere else then is moved onto the site and positioned in place. In this case, the panel had fallen once it was in place.

Just by looking at the concrete our engineers could see that 2 different types of concrete had been used within the same structural member. Once the Petrographic analysis was performed, our engineers saw that the properties of the two concrete mixtures found within the same panel had key differences that may have caused an issue with the overall stability of the panel that was being placed.

Conclusion

It is always important to understand the physical composition of concrete, especially when it is being poured for large construction projects.

While we all aim to avoid issues in construction, sometimes things happen.

If you need Fenagh to perform Petrographic Testing due to an unforeseen complication, just Give us a Call!
(617) 938-3774

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