What is the logic behind pouring a concrete slab around metal scaffolding legs?

This usually boils down to a massive scheduling cluster. When the concrete trucks are stacked up at the curb and the crew is on site, they aren't going to wait three hours for a scaffolding company to show up and tear down a setup. If the GC says to pour, the finishers are going to pour. I’ve seen this happen when a sub-contractor refuses to move thier gear and the site supervisor just gets fed up. It’s often cheaper to sacrifice a few metal frames than it is to pay the standby time for a line of mixers and a pump truck. As for the finish, it’s going to be a headache for the flooring guys. Most of the time, they’ll come back with a **reciprocating saw** or a grinder and cut those pipes just below the surface once the concrete has enough strength. Then they’ll try to patch the holes with a high-strength grout or a floor patch compound. But you’ll almost always see those circular outlines unless they’re putting down a thick topping or an opaque epoxy floor. If the plan was polished concrete, those spots will look like an eyesore forever. Rust is a legitimate concern if that slab is on grade. Moisture will eventually wick up trough the metal pipe if it isn't capped or sealed perfectly. Over time, that metal expands as it oxidizes, wich can cause the surrounding patch to crack or pop out. It’s a total hack move from a quality standpoint, but in the world of high-pressure commercial or fast-track residential builds, sometimes the "get it done" approach wins out over doing it the right way. I've been on sites where a different trade left their gear in the way after multiple warnings. After the final warning, you just pour around it and let them figure out how to get their equipment back. It's spiteful, sure, but the **concrete schedule** is the one thing on a job site that usually doesn't have any flex once the batch plant starts loading those drums.

That sounds like a nightmare for whoever has to come in next. If they cut the pipes and patch the holes, does it mess with the structural strength of the slab? I'm just thinking about a heavy kitchen island or a safe sitting right on top of one of those patches and causing a crack. Also, is that scaffolding basially ruined once they saw the feet off? It seems like a huge waste of gear just becuase someone didn't want to move out of the way. I'd be fuming if I was the owner of that equipment.

Beyond the ruined gear, you're looking at a major breach of the vapor barrier. Those pipes create a direct line from the dirt to the living space. Since concrete shrinks during the cure and steel doesn't, you'll end up with a microscopic gap that's an express lane for radon or termites.

A little floor patch doesn't fix a hole in the moisture membrane. I’ve seen cases where the homeowner dealt with a "musty" smell for years before realizing it was coming from those exact spots. It’s a total failure of building science just to save a few hours on a pour.