สำนักราชบัณฑิตยสภา

85 ธั ชวี ร์ ลี ละวั ฒน์ วารสารราชบัณฑิตยสถาน ปีที่ ๓๗ ฉบับที่ ๔ ต.ค.-ธ.ค. ๒๕๕๕ thickness of the sheets. However, all types of tiles being investigated could be classified as category C of ISO 9933 (7) . This is due to the fact that the minimum thickness results for each individual tile were more than 4.5 mm. In addition, the nominal height of corrugations for all types of the tiles was found to be between 54 and 55 mm which could also be classified as category C of ISO 9933 (7) . Bending Strength The typical relationships between flexural load and deflection for all types of tiles are shown in Figure 5. It was found that the blue and brown tiles exhibited the flexural loads and deflections significantly more than the red and green tiles. Figure 6 shows the mean breaking loads per metre width for all types of tiles, comparing with the class specified within the ISO 9933 (7) . The results of mean breaking load per metre width for blue and brown tiles were significantly higher than those red and green tiles. This was also confirmed by the statistical analysis which the blue and brown tiles only exhibited similar results of breaking load per metre width. However, the mean breaking load per metre width of red and green tiles could still meet with the lowest class (Class 4) for the category C (see Figure 6). Impermeability Traces of moisture appearing on the underface of the sheet for all types of tiles are given in Table 1. The moisture could be observed on the underface of the sheet for blue, red and green tiles. However, many defects of coating could be investigated for the blue tiles having severely damped underface of the sheets (see Figure 7). Therefore, the failure of coating for the blue tiles could not constitute the failure of the product as specified in ISO 9933 (7) . However, no formation of water drops was observed on the underface of the sheet for brown, red and green tiles. It could be concluded that these tiles could meet with the standard requirement (7) . Warm water Warm water test was used for investigating the possible degradation of the tiles studied. The results of mean bending moment at rupture for each type of tiles are given inTable 2. It was found that the warm water minimized the mean bending moment at rupture of blue, red, and green tiles. However, no degradation due to warm water was observed for brown tiles. When the results