Mostly the extensive subgrade work, as I understand. Similar to a road, there’s a bed of sand and aggregate under the concrete surface.

The concrete they use is very precisely mixed to a specification and then it’s tested for adherence to the spec.

A runway is also going to be 3-4x thicker than a 4-6” thick driveway slab. Probably they also use fiberglass or PVC coated rebar instead of plain steel rebar.

Definitely not an expert here but I can read a civil site plan and hire civil site work subcontractors frequently.

Here’s some information on concrete testing: https://www.concrete.org/frequentlyaskedquestions.aspx?faqid...

Also, Grady is one of the best creators on YouTube, I can’t help but watch his full videos whenever they pop up. I always learn something, even if I’m familiar with the subject.

Edit: Granite is not one of the listed materials in Part 4 - Base Courses of the FAA runway construction guide, here’s the entire thing for reference - https://www.faa.gov/airports/engineering/construction_standa...