| dc.description.abstract | Atmospheric corrosion of metallic materials is of concern due to structural failures and massive losses in infrastructure associated with corrosion. A study was conducted to assess the accelerated and outdoor corrosion rate of metallic coated and pre-painted roofing sheets. The metallic coated and pre-painted steel roofing sheets were obtained from the Mabati Rolling Mills (Manufacturer 1) and other selected manufacturers. The atmospheric corrosion study sites were based at Mariakani (industrial marine environment) and Mlolongo (industrial urban environment). The accelerated tests which were performed in the laboratory showed that metallic coated sheets of Aluminium-Zinc (AZ) from manufacturer 1 had the lowest corrosion rate (0.345
0.004 mmpy) while Galvanized Iron (GI) sheets from manufacturer 5 had the highest corrosion rate (2.065
0.006 mmpy) at lower salt spray concentrations. The accelerated tests for the sheets pre-painted red and blue from manufacturer 2 gave the highest fade (4.98
0.02 and 4.41
0.03 Hunters units) respectively while gloss was-9.8
0.4 and–14.4
0.3 % respectively at lower concentrations. When the concentrations were increased to a mixture of 1.000% NaCl and 4.000% (NH4)2SO4, the corrosion rate for AZ coated sheet from manufacturer 1 was still the lowest with a value of 0.408
0.003 mmpy while GI sheets from manufacturer 4 had the highest corrosion rate of 2.318
0.004 mmpy. The red, green and blue sheets from manufacturer 1 showed the lowest fade of 2.42
0.02, 2.14
0.01 and 0.95
0.01 Hunter units respectively while gloss was -4.7
0.1, -4.4
0.2 and -1.9
0.1 % respectively. The highest fade was given by pre-painted sheets from manufacturer 2 for red and blue and manufacturer 3 for green with values of 5.60
0.02, 6.24
0.02 and 5.31
0.01 Hunter units respectively while gloss was -22.0
0.4, -15.0
0.4 and -8.4
0.2 % respectively. The outdoor exposure tests at Mariakani for the metallic coated sheets showed that the AZ samples from manufacturer 1 had the lowest corrosion rate of, 0.019
0.001 mmpy while GI sheets from manufacturer 4 had the highest corrosion rate of 0.128
0.001 mmpy. For the prepainted sheets red, green and blue from manufacturer 1 showed the lowest fade of 0.92
0.02, 0.45
0.01 and 0.89
0.02 Hunter units while gloss was -0.8
0.1,-2.3
0.2 and-2.1
0.2 % respectively. The pre-painted sheets from manufacturer 4 showed highest fade values in Hunter units of: red (2.75
0.02) and blue (1.53
0.02) while fade for green sheets from manufacturer 2 was 11.21
0.03 and gloss values
iv
were -15.6
0.1, -5.0
0.1 and 1.8
0.1 % respectively. The outdoor exposure tests at Mlolongo showed that AZ sheets from manufacturer 1, had the lowest corrosion rate of, 0.029
0.001 mmpy while GI sheets from manufacturer 4 had the highest corrosion rate of, 0.178
0.001 mmpy. The pre-painted sheets from manufacturer 1 showed that red, green and blue had the lowest fade in Hunter units of 1.03
0.02 for red, 0.79
0.02 for green and 0.51
0.02 for blue while gloss values in % were; -0.8
0.2, -3.5
0.2 and -3.5
0.2 respectively. The red and blue sheets from manufacturer 2 and green from manufacturer 3 showed the highest fade values of 2.94
0.02, 2.44
0.03 and 3.91
0.02. The corresponding gloss values were:-7.3
0.2, -9.2
0.3 and -4.7
0.2 % respectively. The study showed that aluminium-zinc metallic coated and pre-painted roofing sheets from Manufacturer 1 had lower corrosion rates in both accelerated and outdoor tests indicating that the roofing sheets from manufacture 1 were of good quality. The findings of this study are of significance in improving the quality of the roofing sheets. | en_US |
