Building blocks
Tarp Fence Corner Red
While not as sturdy as solid concrete, iron constructions have high structural integrity, requiring fewer support pillars.
Harvest drops
Iron× 10
Taken apart with a harvesting tool (axe, pickaxe, shovel), before perks and tool bonuses.
When it collapses
Falling, it leaves 
Scrap Metal Pile (60% of the time) where it lands.
Where to find (8 POIs)
Doominium Tower (tier 4), NDC Checkpoint One (tier 4), Treats Terrace (tier 2), Jerry's Fill (tier 1), Mushroom Mining Company (tier 1), Oskar's Dumpster (tier 1), The Smokehouse (tier 1), Industrial Demolition Site.
Points of interest built with this block (any of its variants), the highest tiers first, from the game's prefab files.