EVALUATION OF MATERIAL TESTING AND CONSTRUCTION CODES

EVALUATION OF MATERIAL TESTING AND CONSTRUCTION CODES

Abstract 

 

The study explores the evaluation of material testing and construction codes used in reinforced concrete. The compositions and mechanical properties of the locally produced steel were analyzed to ascertain their potential for applications for construction.  

Two   samples of construction steels produced and used in Nigeria were studied along. The chemical compositions of these steels were determined using Solaris CCD techniques. The microstructure of the steels was characterized using an Optical microscopy.

Similarly, two of the cement samples that are produced and commonly used in the Nigerian market were studied. The chemical compositions of the cements were determined using Xray Fluorescence and X-ray Diffraction techniques. The  cements were mixed with standard river sand to produce mortar with well controlled mixed proportions .The setting time and soundness of the mortar were determined  along with their  compressive and flexural strengths. The implications of the results were discussed for the development of manufacturing of steel and cement and construction codes that could significantly improve the safety and reliability of African buildings.

 

 

CHAPTER ONE: BACKGROUND AND INTRODUCTION

1.1 INTRODUCTION

Engineering failure of buildings has been a general concern to civil, structural and materials engineers. Studies have shown that some of these causes are as the results of bad designs, Faulty construction, Foundation Failure, Over Loads, Fatigue, and Thermal environmental effects on concrete. However, most of the failures are frequently are also attributed to the misuse of materials.  The major constituents of materials used in reinforced concrete are cement, steel and aggregates. These materials are essential components of enhancing better mechanical properties and the durability of said reinforced concrete.

In virtually every construction project the safety and durability of the finished structure are critical to its success. Essential to achieving this, is the implementation of effective quality control procedures of  construction materials such as steel and cement. Steel and cement are the two very essential construction materials  of this century. The construction industry is largely dependent on these materials for durable and quality structures.

Ever since steel began to be used in the construction of structures, it has  made possible some of the grandest structures both in the past and also in the present  day .

For instance, Considerable progress has been achieved through the use of steel-fiber  reinforced concrete (SFR) to enhance structures.

The fundamental properties of SFRC using these new materials have been investigated and compare with those of standard/  imported .

The tensile strength is important for concrete structures as a basic mechanical property and factor of good durability. Since concrete is generally weak and brittle in tension compared to its  capacity in compression, steel –fiber reinforcing is a practical means developed for a better control of the tensile performance of concrete.

According to  studies, Steel- fiber reinforced concrete (SFRC) has various excellent properties as a  composite material;  for instance, flexural strength, tensile strength, shear strength, toughness, impact resistance etc are improved by the used of steel fiber.

In order for this properties to be achieved, the production of the steel serving as a fiber must highly be considered [1] .

1.2 STEEL

The chemical composition of steel is not the only mechanistic means to control the properties of structural steel. The chemical composition is linked to processing and microstructure for the overall quality of the steel. Most properties depend on the microstructure for a specific steel composition. For example, Yield strength and hardness of the steel are microstructure dependent. Such properties are described as microstructure-sensitive.

In order to achieve the desire microstructure, the steel is processed.  Through processing of   steel, the means of developing and controlling the microstructure is obtained, hence mechanical properties. For example, hot rolling, quenching, normalizing and so forth. It cannot be over-emphasized that the microstructure plays a primary role in providing the properties desired for application. It is therefore glaring that the properties of a material can be tailored by its chemical structure and microstructural manipulations [2] .

Several studies have been done to investigate the quality of locally produced construction steel bars used for concrete reinforcement. Most of these studies have focused on chemical composition of the bars and relate the composition to the mechanical properties.

According to a report, high carbon concentration of locally produced steels from scraps is noticed in Nigerian products. The source reported that this could be one aspect of structural failure as these bars contained high carbon content [3] .

Furthermore, cement is another component of the concrete. It is a paste that holds concrete ingredients (steel, sand and aggregates) together. Without cement, none of these ingredients of concrete can successfully combine  to achieve desired structural support.

1.3 CEMENT

Cement is defined as an adhesive material that is good at holding fragments of  solid matter together  and make it rigid over time [4] .

When cement is mixed with water, cement  functions  by performing plastic paste with  water which grows very rigid(sets)  and gradually  grows in compressive strength through  reactions that occur chemically. This is said to be the hydration reaction of cement. The material is categorized hydraulic when it is  store in water such as hardened cement and  increases in strength [5] . Portland cement is pre-eminent based on its balanced of composition and excellent performance. As it has been said, processing plays a major role in the manufacturing of any material.

The properties of the final products of Portland cements are reliant  on the chemical and morphological composition of gypsum, clinker and other additives introduced during the process of grinding. However, changes in cement properties could occur during subsequent storage in different environments.  The quality of cement can be extremely reliant on the quality of clinker which means that any consideration of this characteristic requires basic knowledge of the factors the control the quality of processing clinker [6] .

According to Ashby, concrete as a particulate composite  held together by an adhesive-the cement paste. Cement  contains flaws and cracks when it is made, with a low fracture toughness: K_IC is about 0.3MPa m^1/2 [7] .

However, Plain unreinforced cementitious materials(mortars) are likewise characterized by low tensile strength, and low tensile strain capacities, that is, they are brittle materials. They thus require reinforcement before they can be used extensively as construction materials. The livelihoods of  the structure is  promoted when reinforced with   quality steel, as the reinforcement remains the main portion that bears the loads.

 

Therefore, to ensure sustainable and reliable structures, construction materials such as steel and cement should be designed  with the concept  of quality and durability rather than strength alone.

1.4  UNRESOLVED  PROBLEMS

While structural collapse remains challenging in our environment today, studies have been conducted to ensure that these failures are minimize. These studies have shown that, faulty construction, poor designs, substandard materials, inadequate application of materials and poor construction methods etc, are amongst impediments of such failures.

 

However, construction materials such as steel bars may appear as “fit” for application even when subjected to so-called quality checks. External quality does not account for the internal and durability of structures. Equality, chemical compositions, strength, hardness  are amongst properties that contribute to the properties of a material. But these properties are empirical to the overall properties of the structural materials. Generally, the chemical structure and the microstructure of a material control its properties.  An important difference between the two is that while the chemical structure is relatively fixed, the microstructure depends strongly on how the material is made and can thus be controlled.  Hence, the microstructure gives information why the properties of a material change.  Thus the microstructure provides a link between processing (how a material is made) and properties (how a material behaves).These relationships significantly influence the quality of the material. The below paradigm of materials science depicts this relationship:

 

PROCESSING

MICROSRUCTURE

PROPERTIES

 

The microstructure of a material depends on the way that it is processed, and the properties depend on the microstructure.  If these relationships are understood, the material properties can be controlled, predicted, and improved.

The solutions to these problems such  as maintaining the Quality of locally construction materials-steel and cement,  and  the microstructure of steel as it relates to its mechanical properties  are the reasons of this paper. It aims at the   development of manufacturing and construction codes that could significantly improve the safety and reliability of African buildings and steel structures?

1.5 OBJECTIVES

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
  • SCOPE OF WORK

This paper investigates the chemical composition, microstructure and mechanical properties of locally produced steel and cement .The paper then relates the implications of the results to reinforced concrete for the construction industry.

 

• REFERENCES

• Fiber reinforced cement and concrete. Edited by R.N. Swamy 1992 p 51
• R. Davis, Editor, 1998 [“Metals Handbook Desk” Edition, Second Edition pp.153 & 155]
• Alabi, A G F Onyeji, L I, 2010

“Analysis and Comparative Assessment of Locally Produced Reinforcing Steel Bars”  Journal of Research in Cicil Engineering,  volume 7, pp49-60

• Ghosh, S.N. (Ed.). 1983. Advances in Cement Technology: critical reviews and case studies on manufacturing, quality control, optimization and use. Pergamon Press, Oxford, UK.
• Lea, F.M. 1970. The chemistry of cement and concrete. 3rd ed. Edward Arnold, London, UK.
• Bye, G.C. 1983. Portland cement: composition, products and properties. Pergamon Press, Elmsford, NY, USA.
• [Michael F. Ashby and David R. H. Jones 1998, 2^nd pp.207-215)

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