10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Inflammatory Effects of Fine Aerosols Generated from Rapid Concrete Failure
LUPITA MONTOYA, Harish Gadde, Wyatt Champion, Ning Li, Mija Hubler, University of Colorado Boulder
Abstract Number: 264 Working Group: Health Related Aerosols
Abstract Engineered materials in the built environment can deteriorate and fracture into particle shapes and sizes that may cause negative health effects in the wake of natural and man-made disasters, like the attack on the World Trade Center (WTC). Two and a half years after the attack, responders still experienced respiratory symptoms and pulmonary function effects. Similarly, ten years after the attack, excesses in total and specific cancers were reported in both responders and civilians exposed to WTC aerosols. Elemental analysis of these aerosols indicated that the main components were construction materials such as cement, concrete aggregate, ceiling tiles, and wallboard. Aerosol generated during concrete demolition have long been classified as an occupational health hazard for construction workers, reflected in OSHA’s Crystalline Silica Rule: Construction. The primary risk comes from the inhalation of particles by workers; however, these particles can spread widely and pose an exposure risk to the public and the environment.
Results from our team showed that the aerosol size distributions generated by rapid fragmentation of concrete follow a bi-modal distribution tied to microstructural features of the concrete mix. This behavior is well described by introducing additional length scales in Gilvarry’s derivation of the Rosin-Rammler-Sperlin-Bennet (RRSB) distribution. On this basis, we proposed that no new fragmentation theory is needed to describe aerosol particles if concrete fragmentation is regarded a composite material explicitly considering microstructural features, which create stress concentration at the microscale. By identifying a direct link between microstructural features and aerosol distributions, we proposed that it is possible to design concrete microstructures to limit aerosol exposure during dynamic failures such as structural collapse.
Reinforcing concrete with steel fibers has gained popularity in the construction industry as a composite material because it improves ductility of the concrete and distributes cracking. Recent work determined that multiple failure mechanisms act in composite materials to create macro-scale particle sizes and sub-micron aerosols by controlling the type of inclusion added to the concrete.
In this experimental study, cylindrical specimens of concrete mixtures containing steel fibers of different sizes were prepared and tested in a closed environment. Six types of concrete mixes were used to create 8 in x4 in test cylinders; 35 cylinders of each mix (total of 210) were made. Three fiber lengths (1, 1.5, and 2 in) as well as two inclusion percentages (0.6% and 0.8%) were chosen for this study. Dynamic compression tests were conducted on the cylinders at a constant displacement rate to simulate an extreme loading event. The generated fine aerosols (i.e., particulate matter ≤ 2.5 um in diameter, PM2.5) were collected during and after the failure. Aqueous extracts from these samples were then evaluated for pro-inflammatory effects (tumor necrosis factor alpha, TNF-alpha) using a RAW 264.7 murine cell line. Preliminary results of this study show that introducing fibers of any length or mass fraction increased the TNF-alpha response, compared to the control.