Putting steel in prestige building
01 October 2002
A leading European maker of stainless steel long products is currently providing its reinforcement solution to a prestigious new building in Oman.
Acciaierie Valbruna Spa says it is supplying OSCO with Reval bar and wire rods for substructure 2 of the new guest complex at Qsar Al-Alam in Muscat. The steel grade used is 1.4462 (duplex stainless steel), from 8 to 12 mm diameter in wire rod and from 16 to 32 mm in straight bar 11,900 mm long.
Highlighting the importance of stainless steel reinforcement bar and wire rod in providing greater longevity for buildings, the company explains the principles involved:
"Reinforced concrete structures are not as long-lasting as was generally assumed up until the 1970s. Instead, their service life is limited, essentially because of corrosion of the reinforcement. "Actually, concrete provides the ideal environment for protecting embedded steel because of the high pH of its pore solution (around 13).
"If the design of a structure, choice of materials, mix design, casting compaction and curing are carried out in compliance, for instance, with current European standards, then under most environmental conditions, concrete is capable of providing protection for more than 50 years.
"In fact, cases of corrosion that have been identified in a great many structures within much shorter periods can almost always be traced to a failure to comply to current standards.
"However, under environmental conditions of high aggressiveness (generally related to the presence of chlorides), even concrete which has been properly prepared and placed may lose its protective properties and cause corrosion of the reinforcement, long before 50 years have elapsed, sometimes resulting in very serious consequences.
"Therefore, under conditions of high environmental aggressiveness, or when the service life has to be very long because of the extreme importance of the structure, it is necessary to provide additional protection to reinforced concrete.
"Since the seventies, several preventative techniques aimed at increasing the service life of reinforced concrete structures have been developed, along with remedial techniques for already damaged structures.
"Among the preventive techniques, the complete or partial substitution of carbon steel rebars with stainless steel rebars has proved to be effective in preventing corrosion even under very aggressive environmental exposure.
"Although stainless steel rebars can provide remarkable corrosion resistance, their use may have a significant impact on the cost of a structure. Now the combined use of stainless steel andcarbon steel bars is encouraged to reduce costs. The use of stainless steel bars can rightly be considered an 'expensive' choice when the exposure conditions of a structure are such that the required service life can simply be guaranteed by a proper design of the concrete mix and the cover thickness, or selecting more economical preventative techniques. On the contrary, the high corrosion resistance of stainless steel can account for very high long term saving in costs of maintenance and repair for reinforced concrete structures exposed to aggressive environments."
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