Suchergebnisse

Abstract
Carbon nanotube (CNT) as a reinforcement enhances durability and performance of concrete composites. Exposure to some forms of CNT is known to cause adverse pathological outcomes. To understand potential toxicity arising from use of CNT-enabled concrete composites as it goes through various occupational life cycle stages, we evaluated 1) the physicochemical characteristics and toxicity of the as-produced CNT and 2) how particulate release during concrete manipulation (e.g., cutting) is altered by CNT incorporation. Physical dimensional profiling indicated a geometric mean length of 0.72 µm and 32 nm in diameter. The toxicity of the as-produced CNT was similar to an agglomerated CNT studied in our previous research, lacking the more severe toxicity associated with longer length and diameter CNT. Four concrete test samples, three different formulations with CNT and one without, were cut in a specialized chamber to simulate an occupational scenario. The mass median aerodynamic diameters from varying CNT incorporated composites did not change and was 5.23 µm in diameter. No free CNT was captured in the aerosols or was visible on the surface of the concrete. The toxicity of the released particulate is currently being investigate using in vitro screening tests designed to investigate mechanisms of potential toxicity. There were minimal changes in the particulate size distribution profiles after cutting, suggesting adding CNT to concrete may have subtle effects on the toxicity of the generated particulate.

Abstract
Engineered nanomaterials are revolutionizing many industries, but little is known about potential exposures during the life cycle of nano-enabled composites. This study was conducted to characterize aerosolized particles using direct-reading instruments and integrated air samplers during cutting multi-walled carbon nanotubes (MWCNT)-embedded concrete cylinder blocks. Three types of blocks, 0% (reference), low%, and high% MWCNT, were tested in a specially designed enclosure housing an apparatus for the cutting of a block with an automated computer-controlled process. The highest particle number concentration (163,821 particles/cm3) was measured for the reference cylinder, while others showed similar concentrations (131,689 particles/cm3 and 140,954 particles/cm3 for the low% and high% blocks, respectively). Regardless of the cylinder type, the size-selected particle number concentrations revealed one main mode with a peak at 0.72 µm indicating no shift in the size distribution from addition(s) of MWCNT. Respirable mass concentrations were 342 mg/m3, 405 mg/m3, and 432 mg/m3 for the reference, low%, and high% blocks, respectively. The mass median aerodynamic diameters were similar, 5.23 µm for the reference and 5.05 µm for both low% and high% blocks, indicating a predominant respirable fraction. Respirable particles (quartz, feldspar, paste, etc.) often appeared to be agglomerated materials that included both paste and aggregate minerals. No free MWCNT were observed by electron microscopy from low% and high% samples. These initial studies found no evidence of free MWCNT by cutting concrete test blocks and only minor differences in the particulate aerosol generated, which included a general increase in respirable mass with increasing % CNT.