CHEMICAL COMPOSITIONAL STUDY OF SOME REINFORCING STEEL REBARS FOR CONCRETE STRUCTURES PRODUCED BY SELECTED MINI MILLS IN NIGERIA

Abstract

Chemical Compositional Study of Some Reinforcing Steel Rebars for Concrete Structures Produced by Selected Mini Mills in Nigeria has been carried out. Reinforcement steel bars from seven different mini-mills across Nigeria have been investigated for chemical composition amidst the allegations that incidences of collapsed buildings in Nigeria can be linked to chemical compositional issues in reinforcement steel rebars produced in Nigeria from unprocessed steel scraps. This study was only targeted at mini-mills which produce their liquid steel from scraps and process it into reinforcement steel rebars. Seven samples of reinforcement steel rebars for concrete structure reinforcement were given chemical compositional and microstructural analysis using spectro-lab metal analyzer (Fe-01-F) and Energy Dispersive X-Ray Fluorescent, miniPal4 ED-XRF Model. Six of the bars were 12mm diameter and only one sample was 10mm; amazedly all of them had different chemical compositions. The carbon content percent of the samples varied as follows: sample A 0.256%; sample B 0.391%; sample C 0.361%; sample D 0.475%; sample E 0.206%; sample F 0.299%; and sample G 0.479%. The same thing applied to their carbon equivalent values which were all completely different indicating that they have different mechanical properties. Samples with carbon equivalent value outside the threshold value were sample D with 0.545 and sample G with 0.623. For different grades of steels the allowable chemical compositional deviation is normally ±0.05, however, most of the samples exceeded this allowable limits. The study therefore based on the above results drew this conclusion, that incidences of collapsed buildings in Nigeria cannot be unconnected with chemical compositional problems in the produced reinforcing steel rebars from Nigerian mini-mills given the astounding divergence in the standards of the bars; with every mill producing what they feel like producing. The work has recommended that if sanity is to be restored; Standard Organisation of Nigeria should enforce standard in the mini-mills. Mills should implement compositional adjustments, controlled rolling, and cooling to improve mechanical properties. Mills should substitute or complement scraps with direct reduced iron (DRI) to improve compositional control and quality of their produced reinforcement steel rebars.