Deterioration of Coating Materials Applied on Roofing Iron Sheets Under Marine Environments in Kenya
Abstract
Roofing iron sheets are prone to rapid corrosion when exposed to harsh environmental conditions leading to loss of mechanical strength and collapse of structures that results into huge economic loses. The aim of this study was to investigate the effect of marine environmental conditions on deterioration of the coating materials applied to protect roofing iron sheets in Kenya. We studied fading and gloss retention of green and blue coatings applied to roofing iron sheets for a period of 450 days under an outdoor setting at Diani Beach and Mariakani sites representing severe marine and industrial marine environmental conditions respectively. Prepainted roofing sheets obtained from manufacturers MR, MB and CH were cut into130 mm x 190 mm sizes, placed on racks and exposed to the atmosphere. Exposed sheets were removed at predetermined time intervals, cleaned and assessed for glossiness and fading using a Spectro guide BYK Gardner GMGH. Fourier Transform Infrared Spectroscopy was used to determine variations in functional group composition of the coatings. Meteorological data including rainfall, temperature, Ultraviolet radiation and relative humidity were collected during experimental period. Fade variations for green coating followed 0.77-5.00 and 1.33-19.60 for Diani and Mariakani respectively, while blue coating recorded 0.86-5.60 and 1.94-6.86 Hunter units per year for Diani and Mariakani respectively. Percent gloss retention for green coating varied from 30-63% and 18-63% at Diani and Mariakani respectively, while the blue coating varied from 2-77% and 10-82% at Diani and Mariakani respectively. MR coating recorded the highest percentage gloss retention between 75-77 % and the lowest fading at 0.32 - 0.86 Hunter units per year for both green and blue coatings. Mariakani site recorded higher rates of fading compared to Diani attributed to severe marine environmental conditions experienced at the site, characterized by higher levels of chloride, relative humidity- 81%, ultraviolet radiation-12 mW/cm2 and temperature -27 oC. High ultraviolet radiation increases photo-oxidative reactions and significant degradation of the binding material in the pigments. Fourier Transform Infrared Radiation results revealed dominance of esters, polybasic acid, and phthalate O-CH2 groups and pigments, and the disappearance of some of functional groups due to photodegradation. Based on the data obtained, high chloride levels from the ocean coupled with high ultraviolet radiation and relative humidity are likely to accelerate fading and loss of gloss in marine environments which may lead to poor performance of roofing sheets under such environments. The findings of this study are of significance in improving the quality of coating materials for roofing sheets applied in marine environments.
