Comment by metadat
11 days ago
Do you know how they keep the concrete from cracking? All the pads in general are in way better shape than my driveway, and the driveway has decent support underneath and is subjected much, much less load.
Maybe they use plentiful jagged interlocking sharp granite as the base l? (like railroad track foundation)
Next time you're at SFO, SJC, or any other major hub sitting in the plane before it backs out of the gate take a second to gaze upon and admire how pristine all the concrete pads are, it's really impressive.
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...
Most concrete cracking you will see in residential construction and private driveways are either because the ground wasn't compacted well enough before the pour, or more often they didn't put a thick enough layer of stone to prevent the ground from moving. Cutting out depth from the base of crushed stone is often the easiest way to cut costs because it means less material brought in and less material to dig out.
Granted private driveways don't need to be absolutely perfect, but if you want it to last for a really long time you need deeper base layers.
Same with any roadway. The base is everything. I visited some European contries and noticed that the roads seemed to have fewer cracks and potholes than many roads in the US. I had assumed it was better maintenance, but the reason I was told is that they spend a lot more on preparing the base than is typical in the US.
Most of Europe sees far fewer freeze-thaw cycles than most of the US does, which are a huge killer of roads.
The color scales aren't equivalent here but you can see the difference:
Europe - pretty much only unpopulated northern Scandinavia + up in the Alps/Pyrenees getting over 64 days, most of the most densely populated areas with lots of infrastructure below 32 days: https://www.atlas.impact2c.eu/en/climate/freeze-thaw-days/?p...
US - https://www.semanticscholar.org/paper/Climatology-of-Freeze-... (Fig 4.2) - Probably more than 50% is over 75 cycles, and large chunks breaking 100 cycles a year (almost all of New England and some other scattered patches, the Rockies/interior West/Western Plains).
If I had to guess, all things equal, its probably much thicker than your average driveway.
Yes, for example taxiways and aprons designed to take the weight of large aircraft like A380s can be ~470mm (almost half a metre) thick, and that's only half of the structure with the subgrade and sub-base together being about as thick! Whereas the standard for driveways where I live is 125mm thick.
Not sure if that's a serious question, but your driveway might lack a proper foundation, so the surface is moving and cracks. Also, it's likely not concrete, but tarmac (which is much softer).
A significant number of American driveways are concrete. I'm not going to look up numbers, but I would have to believe that more are concrete than asphalt/tarmac. Unpaved driveways could outnumber both, who knows, but most people with paved driveways have concrete.
I think that depends on the region and weather differences. In the northeast at least, asphalt seems to be a lot more common than concrete.
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I’ve never understood why people so frequently choose poured concrete over cheap interlocking pavers. Where I live, it’s extremely common to see someone pour a concrete driveway then promptly cut it up because they forgot something.
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