Characterization of Reinforcing Steel Bars in the Nigerian Construction Industry
Chapter One
AIM AND OBJECTIVES OF THE STUDY
AIM OF THE STUDY
The research aimed to determine the properties of reinforcing steel bars in the Nigerian Construction Industry.
OBJECTIVES OF THE STUDY
The objective of the study is to examine the properties and quality of reinforcing steel bars in the Nigerian Construction Industry. This involves determination of the strength and deformation characteristics of the reinforcing steel bars with respect to properties known to have adverse effect on fitness for use in design and construction. The specific objectives of this study are to determine:
The tensile characteristics of the reinforcing steel bars used in the Nigerian Construction Industry.
The bending behaviour of the steel bars used in the Nigerian Construction Industry.
The chemical composition of the reinforcing steel bars used in the Nigerian Construction Industry.
The effect of the elemental composition on the strength of the reinforcing steel bars used in the Nigerian Construction Industry.
CHAPTER TWO
LITERATURE REVIEW
PREAMBLE
The literature review comprises an overview of some selected scholarly related works on tensile tests, bend tests and chemical composition of reinforcing steel bars that have been undertaken by researchers from recognised institutions. The chapter also discusses provisions made by some British Standards (BS4449: 1966 & 1997), American Standards for Testing and Measurement (ASTM A38/A38M).It also discussed the steel industry in some selected countries across the world – Inuwa (2011) and the standard manufacturing processes for reinforcing steel – Omoweh (2005).
Steel is an alloy consisting mostly of Iron, with carbon content ranging from 0.05% to 2.1% by weight, depending on grade (Steel Wikipedia). Carbon is the most cost effective alloying mineral for iron. However, alloying elements such as manganese, chromium, vanadium, tungsten and many others are either found or included. Alloys with higher carbon content are known as cast iron because of their lower melting point and castability. Steel is also distinguished from wrought iron as the latter can contain smaller amount of carbon in the form of slag inclusions. Two distinguishing factors of steel are increased rust resistance and better weldability.
Reinforcing steel possesses many properties. However, the ones whose specifications were given by codes such as BS, ASTMs, Euro codes and many others are the tensile properties, bend test and chemical composition.
REQUIREMENTS FOR REINFORCING STEEL
The UK Certification Authority for Reinforcing Steels (UK CARES Part 1) has prescribed that a satisfactory reinforcing steel must be able to:-
Be bent into shape with precision to fit complicated structures. Possess a minimum strength to discharge its load bearing function.
Possess ductility to satisfy formability requirements to be bent into the designed shape and also sufficient ductility to provide progressive failure under certain conditions.
Possess good weldability in part, for site fabrications and in part to minimize damage. For many structures of particular design, possess good fatigue properties.
Possess good bond properties.
The authority (UK CARES Part 1) went further to highlight some conflicts that often arise such as between strength and ductility or between strength and weldability which must be sorted through metallurgical controls during manufacturing processes. .
CHAPTER THREE
MATERIALS AND METHOD
Steel mills in the country can be generally classified into three as follows: Ajaokuta Steel Company.
Delta Steel Company with the Inland rolling mills at Katsina, Jos and Osogbo.
Mini Mills groups together.
While Ajaokuta is yet to be completed, Delta’s concept is to process and pass billets as raw materials for Katsina, Jos and Oshogbo rolling mills. The mini mills which are mainly foreign dominated are privately owned. Many of them have been in operation even before the establishment of the ones stated above.
As mentioned earlier, Ajaokuta is yet to be completed. Jos and Oshogbo have been sold out while Katsina seems to be importing billets for its milling operations.
STEEL PRODUCTION IN NIGERIA
The idea that led to the development of Iron and steel industry in Nigeria was born in 1958 by the Federal Government. To a very large extent the different establishments that make up the steel industry in Nigeria are interdependent to the level that under performance of one adversely affects the other. A proper understanding of this interrelationship and interdependence will not only direct policy construct but will go a long way to stabilize and advance the steel sub-sector in the country. The readiness on the part of the government to revamp the steel sector and achieve the goal of industrialization for the country has led to the establishment of the various bodies and industry with the dissolution of the National Steel Development Agency in (1979).
CHAPTER FOUR
ANALYSES OF RESULTS
GENERAL INTRODUCTION:
The analysis of the results obtained from the experiment in chapter three is hereby presented in chapter four for analyses and discussions.
CHAPTER FIVE
CONCLUSION AND RECOMMENDATIONS
CONCLUSION
Based on the results of the tests conducted, the following conclusions were made.
- Most of the bars could not comply with the rolling deviations over and under nominal mass as provided by BS4449:1969, 1995 and 1997
- The characteristic strength values for 92% of the locally produced bar samples are low compared to the BS4449:1969, 1995& 1997 standards for high tensile steel which is 460N/mm2 minimum
- The characteristic strength values in respect of the local bars suggest similarities with that of mild steel as determined by the tensile test and chemical composition results. This implies the products are actually mild steel rolled and openly sold as high tensile steel after
- 95 % of the reinforcement bar samples complied with the minimum ultimate to yield strength ratio as specified by BS 4449: 1969 and 1997 code
- The percentage elongation values for 92 % of the locally produced bar samples are within acceptable code
- The percentage elongation values for 67 % of the foreign bar samples are below the minimum standard
- 95% of all the samples tested have passed the bend However, one sample out of the three samples from company C, i.e. (C16 B) failed the bend test.
- The chemical concentration test results showed 12 elemental constituents only, while the percentage composition showed 27
- BS4449(1997) gave specifications in respect of only 10 of the elements. However, Russian standards and ASTM were used to make other
- All the bar samples tested could not fully comply with the chemical percentage composition requirements as prescribed by the
- Some of the elements showed presence only in traces and this may be due to their unavailability in the locations where the steel raw materials were obtained.
- There is a strong indication of the presence of impurities as evidenced by the percentage compositions of silicon, phosphorus, sulphur or their combination in most of the samples
- Elements that add to strength and carbon equivalent value like Molybdenum, Vanadium, Nickel, Copper, etc. were conspicously not present in all the samples.
- Iron being the principal component of reinforcement steel varies from 74.5% to 98.4% in the samples.
- All the samples tested complied with BS4449(1997) value on carbon equivalent
RECOMMENDATIONS
On the basis of the findings of this study, the following recommendations are hereby made.
- There is a need to develop a local standard which will give clear guidelines based on characteristics strength, bend tests, elongation and percentage elemental compositions as determined in the laboratory for applications in structural
- There should be technical information on all steel reinforcement sold in the open markets so as to guide the designers on their strength and deformation
- Regulatory authorities such as the Standards Organisation of Nigeria, Council for the Regulation of Engineering in Nigeria and tertiary institutions should strengthen their collaborations on ensuring quality standards through materials
- Steel rolling mills in the country should be compelled to carry along or make their quality testing facilities available to regulatory and other quality enforcement agencies for periodic inspection and
- All imported reinforcing steel must be checked for quality compliance prior to accepting such consignment into the country and such must be accompanied with an accredited
REFERENCES
- Akanya, N. J. (2003) –“Activities of Standard Organisation in Nigeria- A paper presented at the World Congress on Metrology in the 3rdMillenium June 22 to 27. Dubrovnic, Republic of Croatia. pp. 1-18.
- American Society for Testing of Materials (2003): AASHTO No. M 31 “Standard Specifications for Deformed & Plain Billet Steel Bars for Concrete Reinforcement”:A615/A615M- 03a
- American Society for Testing of Materials: (2007) “Standard Test Methods and Definitions for Mechanical Testing of Steel Products”: ASTM A37-07a
- American Society for Testing of Materials: (1988) “Standard Specifications for Structural Steel”, ASTM – A38/A38M, 25th edition, pp.105
- American Society for Testing of Materials: (1988) “Standard Specifications for Structural Steel”, ASTM – A38/A38M, 25th edition, pp.562
- Amstead, B.H. (1987) – Manufacturing process. John Wiley & Sons Inc. Toronto, Ontario, Canada.
- Arum, C. (2008) : “Verification of Properties of Concrete Reinforcement Bars:- Nigerian Case Study” – Published by : http:ibe.sagepub.com PP.370-376
- Ashby, M.F. (1992): Materials Selection in Mechanical Design. Butterworth-Heinemann
- Bhupinder S. and Kaushik S.K. (2002): “Influence of Steel making Process on the Properties of Reinforcement” Indian Concrete Journal: pp. 407-412
- British Standards Institutions. BS 4449(1997) -“Carbon Steel Bars for the Reinforcement of concrete” London. pp.1-17
