0079 Characteristics of particle size distribution in concrete finishing work

It is known that workers at construction sites are exposed to the risk of dust containing crystalline silica while crushing concrete, grinding concrete surfaces, cutting bricks, cutting rocks, and ballasting structures. This study was conducted to identify size-distribution of crystalline silica among concrete finishers in the construction industry to establish systemized management for the construction sites. In order to measure the size of dust, a Personal Cascade Impactor (Model 298, Anderson Sampler Inc., USA) composed of an 8-stage impact board was used. Dust was weighed three times using an electronic balance with 10–7 g readability(XP2U, Mettler toledo,Switzerland) to acquire the mean value. Crystalline silica was analysed using Fourier-transform infrared spectroscopy (FT-IR) in accordance with the NIOSH Manual of Analytical Methods of NIOSH #7602. To calculate the mass fraction of dust for each size of dust particle, ACGIH’s Particle size-Selective Sampling Criteria for Airborne Particulate Matter was used. The results of weighing dust collected from each stage and a cumulative graph was illustrated from the stage with the smallest particle size (stage, 0.52 μm or smaller) to draw the trend line and find the median diameter of mass using the effective diameter limit corresponding to 50% cumulative probability. Then, it was 10.958 μm~12.206 μm for concrete chipping and 10.462μm~11.476 μm for concrete grinding. Considering the proportion of crystalline silica in the dust from each stage, crystalline silica content was higher for smaller particle sizes. The content was particularly high in stage 6 (1.55~3.5 μm) and stage 8 (0.52~0.93 μm).