Decades of tiny, invisible hairline fractures in the concrete had allowed moisture to seep in. When water meets steel, it creates iron oxide—rust. As the rebar rusted, it did something terrifying: it expanded . Steel can expand up to four times its original size when it oxidizes, creating internal pressure that concrete simply cannot handle.
Concrete with excessive slump (high water-to-cement ratio) bleeds more and settles more dramatically, increasing the tensile strains above the rebar. toh rebar crack
When carbonation (CO2 penetration) or chlorides (road salt or seawater) reach the rebar, the steel begins to rust. Rust occupies up to of the original steel. This volumetric expansion acts like a hydraulic press, exerting over 5,000 psi of pressure against the surrounding concrete. Concrete, which has only 300-700 psi tensile strength, splits immediately. Decades of tiny, invisible hairline fractures in the