PM2.5 generated during rapid failure of fiber-reinforced concrete induces TNF-alpha response in macrophages

Failure of large, concrete structures can lead to the generation of very small fragments, including aerosols in the fine fraction, which have aerodynamic diameters of ≤2.5 μm (PM_2.5). These aerosols can persist in the environment, pose exposure risks, and potentially cause negative health effects. New trends in construction favor the use of concrete reinforced with steel fibers, but little is known about the nature of the fragments generated during its failure. This study investigated the fragmentation of several steel-fiber reinforced concrete formulations using dynamic compression testing. The release of tumor necrosis factor alpha (TNF-α), an inflammatory marker widely used in both human and animal studies, was then analyzed to determine the effects of the fragments in the aerosol fine fraction on mouse macrophages (RAW 264.7). All concrete formulations studied showed statistically increased TNF-α release, which was inversely correlated with fiber length and fiber content (% weight). In addition, results from a select set of concrete formulations also showed a clear dose-response relationship. This paper postulates the fracture mechanisms by which concrete parameters (i.e., fiber length and content) lead to the generation of PM_2.5, producing the observed TNF-α release.