I know I'm a little late here but the article is about making a training bar for people who can't use a 45 lb barbell. This wasn't meant to hold 100's of pounds.

Yes

I was thinking similar. The only way I could think to do it would be to fill the bar with something of substantial density, such as maybe sand, steel shot, etc. You'd need to have a way to plug the ends so whatever you fill with doesn't leave the side and also create a tight enough seal that whatever you plug with won't shoot out when the internal pressure gets high from dropping or excessive bending of the bar. Completely spitballing here, but maybe 12 inches of wooden dowel of just barely smaller diameter than that of the inside of the steel pipe, with adhesive in multiple circles along the length of the wooden dowel. Do that to each side and I think it would seal well enough against shooting out/losing the filler and still give you enough volume inside the pipe to add at least SOME weight.

I know I'm a little late here but the article is about making a training bar for people who can't use a 45 lb barbell. This wasn't meant to hold 100's of pounds and if you made the bar weigh 45 lbs it would defeat the purpose of it in the first place.

What's a cooler tub and pond curing? Do you mean by submersing the plates in water? Or do you mean by just putting some water on top of the concrete before it gets removed from the cooler tub?

I like the trash can one so far because it gives the 45 lb plates handles.