Case Sample

Concrete and Construction Materials Example

In this case, our client, a major developer, observed the sidewalks in his new housing development falling apart six months after construction.  Cored specimen of a failed sidewalk was sectioned into a thin, semi transparent slices. The slices were viewed in a special microscope and the air void counts were taken (petrographic analysis).

 

The various aggregates (stones) were identified by our technician as quartz, granite, limestone, argillite and cement. He also made a careful count of the air voids. The voids are important because in a freeze-thaw situation, they prevent the concrete from cracking.

Petrographic analysis shows the cement, sand, aggregate rock and air voids, all of which are found in concrete.  The blue areas are filled with epoxy that is impregnated into the thin section to help keep it from falling apart.

It was found that air was unevenly dispersed in the concrete. The “tops” lacked air. This meant that the contractor had not cured the concrete properly and caused the sidewalk crack failures after a few winter freeze-thaw periods.