Strength and Fracture of Earth-Based and Natural Fiber-Reinforced Composites.
Abstract
This study examined the mechanical properties of earth-based materials that are relevant to the future development of affordable housing.
Earthcrete structures were produced by mixing various proportions of laterites, clay and cement, while natural fibre-reinforced composites were produced by mixing earth-based matrices with natural fibre (Straw).
Mechanical testing showed that optimum performance of the various samples was obtained at a fibre content of 20% by volume, with compressive strength values of about
2.91 MPa, flexural strength values of about 34.4 MPa and fracture toughness in the range of 1.40 – 1.50 MPa .
The results indicate that the mechanical performance of the composites being studied is in line with those in prior studies on natural fiber-reinforced cementious matrix composites.
Table Of Contents
DECLARATION……… ii
CERTIFICATION….. iii
ACKNOWLEDGEMENTS………. iv
LIST OF TABLES……….viii
LIST OF FIGURES……… ix
ABSTRACT…………xi
CHAPTER ONE: INTRODUCTION
- Background……………..1
- Problem statement……….. 2
- Scope of work………….2
CHAPTER TWO: LITERATURE SURVEY
- Earth-based materials………..4
- Laterite………….4
- Clay………………. 5
- Straw…………….. 6
- Composite concepts…………7
- Functions of fibres and matrix in composites……….. 9
- Rule of mixtures……………..10
- Strength of materials……………..11
- Fundamentals of fracture mechanics……….16
- Pre-existing cracks……………….17
- Fracture toughness……………..18
- Determination of strength intensity factor……….19
- Toughening mechanisms………………..20
- Indentation induced cracking…………..22
- Prior work on the reinforcement of earth-based materials……….25
CHAPTER THREE: MATERIALS AND METHODS
- Raw materials……………29
- Matrix preparation……..31
- Composite preparation…….32
- Mechanical testing……………33
- Characterization of Structure and Composition………..34
CHAPTER FOUR: RESULTS AND DISCUSSION
- Structure of Materials/Constituents…..36
- Scanning electron microscopy………….39
- Compressive strength…………………41
- Flexural strength………………43
- Fracture toughness…………….45
4.5 Implication of the current work for affordable housing…..48
CHAPTER FIVE: CONCLUSION AND RECOMMENDATION
- Conclusion………….49
- Suggestions for future work…….50
REFERENCES……… 51
Introduction
Background Of Study
In our society today, the choice of materials for building is greatly influenced by the cost, properties (mechanical and chemical) and availability.
Industrialized societies have developed various materials which are applied in all works of construction (including buildings).
Unfortunately, developing countries such as Nigeria where alternative materials exist have failed to explore such opportunities even when there is the possibility of producing such, locally.
There is therefore, a need to explore new ways of producing robust building materials from locally available materials.
Such needs have stimulated recent efforts to develop affordable building materials that are strengthened and toughened by locally available natural fibers (Savastano et al., 2003) and matrix materials that are available in developing countries.
However, in most cases, the matrix materials utilize cement, which is a relatively expensive synthetic material that emits ~ 14% of the CO2 emissions that are thought to contribute to global warming.
In contrast, earth-based materials are readily available materials that could be used as matrix material in building composites.
They can also be stabilized by the use of binders, such as dung or cement, to produce materials that are strong and tough enough for applications in buildings.
References
A.Schiesser et al., (1989): “Fine structure and Mechanical properties of Straw Filaments”. Biological Wastes 27, 87-
Agopyan V, John VM. Durability evaluation of vegetable fibre reinforced materials.Build Res Infor, 1992; 20(4):233-5.
Banthia N, Sheng J. Fracture toughness of micro-fibre reinforced cement composites.Cement & Concrete Composites 1996; 18(4):251-69.
Bear and Johnston (2006). Mechanics of materials (5th ed.). McGraw Hill.
B. Ponton and R. D. Rawlings (1989),”Dependence of the Vickers indentation fracture toughness on the surface crack length”, Br. Ceramics Trans.
Callister, W. D. (2007) Material Science and Engineering: An Introduction. 7th ed. John Wiley, New York.