Investigation of Cement Mortar and Steel Used in Reinforced Concrete in Nigeria
CHAPTER ONE
OBJECTIVES OF STUDY
The aim of this work is as follows:
- To analyze chemical composition & microstructure of locally produced cement and steel
- To relate the microstructure to mechanical properties of steel reinforced concrete
- To investigate cement-strength
- To improve on locally produced materials for the construction industry
CHAPTER TWO
LITERATURE REVIEW
INTRODUCTION
The onset of the nineteenth century witnessed the transformation of structural materials with better mechanical behavior. This is of no exception to the construction industry. The construction industry uses concrete to enhance the strength and thereby improve the durability of the structure. Concrete is a composite which constitutes steel, cement and aggregate. Thus, contemporary concrete is reinforced with steel to enhance appropriate mechanical properties.
The appearance and strength of concrete can directly affect the final structure. The two major constituents of concrete are cement and steel bars in modern structures such as buildings, bridges, tunnels and etc. These structural materials must be produced with some level of sanctity for applications in the construction industry.
On the contrary, with the use of these new materials, the fact still exists that structures mentioned still suffer from various failures. In some parts of the World such as Europe, the Americas and Asia suffer structural losses as a result of natural disasters such as earthquakes, storm (e.g. typhoons, hurricane), flood etc. unlike Africa where most of such disasters are uncommon and rare. Yet, in the past two decades, there has been an alarming report of structural failures especially in one of Africa’s most populated country of Nigeria[ 1] .
According to a source , The World’s second largest continent-Africa with 53 nations, about 750 million people, with the highest population growth and with diversified natural resources looks forward at the beginning of the twentieth century for real development in all fronts. Africa needs to apply technology wisely, needs to comprehend the lessons of its predecessors examples in Europe, America and more recently in Asia. As per an estimate by 2050 more than 75% of the African population will live in urban areas. To meet and serve these frequent and far reaching changes, large quantities of materials are required for the construction of shelters and infrastructures. Concrete due to obvious reasons lends itself as the only feasible material capable of meeting these needs [2].
The amount of materials needed for decent living is unimaginable. Concrete being the most important material for construction Worldwide plays a predominant role in any society. In fact, concrete consumption is a real indicator of social progress and development in any country. There is a clear need for materials of better quality to address this concern [p3]. Therefore some of these materials include cement and steel which should be of good quality to address these requirements.
STEEL
An addition of carbon in small quantities generates steel. The influence of carbon on mechanical properties of iron is much larger than other alloying elements. Varying the amount of alloying elements and the form of their presence in the steel (solute elements, precipitated phase) controls qualities such as the hardness, ductility, and tensile strength of the resulting steel. Steel with increased carbon content can be made harder and stronger than iron, but such steel is also less ductile than iron.
CHAPTER THREE
MATERIALS AND METHODOLOGY
INTRODUCTION
Two samples of locally produced steel bars were analyzed along with two samples of locally manufactured cement.
STEEL
Samples of construction steel bars produced and used in Nigeria were 12mm and 16mm diameter reinforced steel bars. These samples were obtained from the local market in Dei-dei, Abuja FCT. The bars were products of one of Nigeria’s biggest steel producing industry- Prism Steel Rolling Mill (PSM).Two specimens each of 335mm length were collected on each of the diameter for tensile test, and 15 mm of each length was used for chemical analysis. The chemical analysis was conducted using a Solaris CCD Plus spectrometer at the Scc Laboratory, Abuja FCT. Mechanical properties which include yield strength, ultimate tensile strength, percentage elongation , hardness and one unidirectional bending tests were investigated at the same Mechanical laboratory of Scc. . Figgures 3.1 show prepared samples and tensile equipment. It also show the polished steel samples and the equipment used to determine the chemical composition of the steel. The Vickers hardness test was used to study the hardness of the steel samples.
Additionally, the microstructure of the steels was characterized using an Optical microscopy at Akure, Ilesia. The grain sizes of the phases were determined using the Gwyddion Software and the volume fraction of the phases was determined using the Lever rule.
CHAPTER FOUR
RESULTS AND DISCUSSION
Two samples of each component (steel and cement) were studied and analyzed.
STEEL
Tables 4.1a and 4.1b show the results of the chemical compositions of the 12mm and 16mm iron rods investigated. Iron (Fe) with the composition of 98.127 and 98.254 percent for the 12mm and 16mm respectively is the element with the highest composition. According to sources [1], the higher the carbon content in steel, the greater the hardenability, the strength, hardness and wear resistance of the steel. But high carbon content in steel decreases weldability, ductility and toughness.
However, the steel samples studied have a maximum carbon contents compare to the standards [2].
As seen on Table 4.1a, the carbon content is 0.209 and 0.262 for the 12mm and 16 mm respectively. Table 4.1c shows the standard composition of structural steels.
CHAPTER FIVE
CONCLUSION AND FUTURE WORK
CONCLUSION
Based on the investigation and experimental results, the following conclusions are made: That the steel manufacture by PRISM Company nowadays is much better as compare to the past years. It appears that improved processing methods have been put into practice. Thus, the steel mechanical properties indicate its fitness for the construction industry. However, when it is wrongly applied in structures, it may lead to structural failure.
Likewise, the cement samples showed early compressive strength up to standards which could be attributed to the tricalcium Silicate (3CaO.SiO2) contents. This indicates that consumers can remove forms in early days after casting.
However, the supaset cement exceeds standard strength of 28 days specifications and needs further investigations. Such a high strength might cause catastrophic failure with age without prior warnings. The flexural strength of the mortar shows its weakness, hence needs fiber reinforcement for optimum strength in flexure.
Finally, the steel produce by PRISM Company and the Dangote 3x cement investigated might not cause adverse effect on structures based on their properties.
SUGGESTIONS FOR FUTURE WORK
The following recommendations are necessary for further improvements on the quality of the locally produced construction materials:
There is need to investigate the alkali and corrosion effects of locally produced cement on steel- reinforced concrete.
A comprehensive study of locally produced steels and cements to include, microstructure and processing techniques.
The high strength of Supaset cement requires further investigations because of its excessive strength shown beyond standards.
And local materials (cement and steel) should be designed for durability rather than for strength alone.
REFERENCES
- Kutz M. (2002). Role of Alloying Elements in Steel, Hand Book of Materials Sellection, Kutz Myer Associates, John Wiley and Sons Inc., 45 – 65. ref.
- British Standards, BS (1997). Reinforcement Bar, Jentayu Venture, www.jentayu venture.com.
- ASTM Standards, A706. (1990). Metals, Test Methods and Analytical Procedures, Metals – Mechanical Testing; Elevated and Low – Temperature Tests; Metallography; Section 03: volume
- EN 197-1 2000, Cement – Part 1: Composition, specifications and Conformity criteria for common cements, 1-20. September 2000.
- S. Ramachandran, V.M.Malhotra, C, Jolicoeur and N. Spiratos (Superplasticizers: properties and applications in concrete( March 1998: 13) ].
- BS 12-1996, Specification for Portland cement, 1-16. May 1996.
- SLS 107-2 2008, Ordinary Portland Cement – Part 2: Test methods, 1-24. September 2008.
- H. Obla, “Variation in Concrete Strength due to Cement,” Part III of concrete quality series, Technical services, NRMCA, pp. 1-5.