The Ganges, the Brahmaputra-Jamuna, the Surma-Meghna and the Padma and their numerous tributaries and distributaries are the arteries of the drainage system for the country. In such a geological formation, the construction and maintenance of an uninterrupted road-rail, telecommunication and power transmission network across the country poses to be the biggest challenge for the civil engineers. In this scenario, Steel bridges, e.g. Hardinge Bridge, Bhairab Bridge, Teesta Bridge, Keen Bridge are the examples of steel bridges, a few of those are serving us near about last 100 years. However, to maintain these bridges, the maintenance engineers need to combat with corrosion that is mostly resisted with painting and re-painting round the year.
Until the mid- to late-1970s around the world, virtually all steel bridges were protected from corrosion by multiple thin coats of lead- and chromate-containing alkyd paints applied directly over mill scale on the formed steel. The paint system commonly used for steel bridge members contains chromium and lead and can no longer be used because of the effects it has on humans and the environment. Furthermore, the telecommunication and power transmission backbone of Bangladesh depends largely on steel towers and monopoles that are mostly galvanized to resist corrosion. However, hot deep galvanization process restricts the maximum weight of steel members, therefore most of the galvanized bridges and towers are of small members connected through joints.
To remove the above difficulties, weathering steel, a new type of material that exploits the beneficial properties of corrosion has been developed in the past. This material has been proved successful in many countries around the world and now constitutes about 40% of total consumption of structural steel over the world. This type of high-performance and high strength weathering steel does not require painting/galvanization for corrosion protection. Introduction of this new range of steel has drastically increased the number of steel bridges being built through the world. Initial cost of weathering steel is almost similar to ordinary steel but the maintenance cost incurred for weathering steel is significantly less from that of ordinary steel. Life cycle cost ordinary steel is now estimated to be 4 times than that of weathering steel.
The absence of any first hand field data for Bangladesh on these aspects has certainly restricted the use of this new material. The proposed research is motivated to examine the feasibility of the use of weathering steel in Bangladesh, where the climatic conditions are hot, humid but presumed to be low in airborne salinity content.
Use of weathering steel reduces a significant amount of maintenance (in other turn, the life cycle cost) and increases lifetime of the structures. However, it has certain limits of applicability in regard to environmental conditions. Salinity is the major known limiting factor for its use and durability. Airborne salt affects inherent the mechanism of corrosion resistance of weathering steel and makes it ineffective. However, at present no information is available either on the airborne salt content or the weight loss of any type of steel due to corrosion in any location of Bangladesh. The aims of this research are as follows:
- - To collect first hand data for airborne salt at different geographical locations of the country.
- - To expose different grades of steel specimens including weathering steels to the actual environmental conditions and thereby to make direct comparisons between different grades of steel.
- - Attempts are being made to make a comparative assessment of life cycle costs for different grades of ordinary steel and weathering steels at different geographical and climatological locations of Bangladesh.
After successful completion of this study, the results and conclusions will be presented in seminar and published in local and international journal/proceedings to form a basis for forming the future design approach in the country with this promising material. The outcome of the study will also be valuable to rationalize the existing corrosion protection approaches in bridges and exposed structural members made of ordinary steel. The data gathered from the study will also be useful for developing corrosion models across the country for different climatic conditions and its expected change over the time.