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Natural fiber reinforced cementitious composites.

Applications of natural fibers in composites used for building purpose have been performed for centuries. Examples, in the Egypt of Pharaohs, Israel or China show the reinforcement of clay bricks by natural straw. Fiber reinforced cement-based composites can use for many applications in civil engineering. For example, fiber reinforced cementitious tiles [Agopyan 2005], corrugated roofing sheets [Paramasivam 1984], simple slab panels [Ramakrishna, 2005], wallboard [Li 2007] [Asasutjarita 2007], and mortar [Toledo Filho 2005]. There have reported in the recent literature. Currently, the construction is the largest are of application of fiber composites (in volume).
Natural fibers have a low environmental impact comparing to synthetic or steel ones. As a result, they are suitable to design eco-friendly building materials. Fiber reinforced concrete can absorb seismic waves like a massive stone. Concrete made with flexible fiber reinforcements can withstand earthquakes [Shelly 2006].
Since ancient time, fibers are added to brittle materials to give them more tensile strength and more ductile properties. Since 1910, steel wire is attached to cement-based materials. Later studies using glass fibers in cement took place in the50‘s. In the 60‘s, the synthetic fiber was also examined as concrete reinforcement. Since 1970, the study of natural fibers, to replace relatively expensive synthetic fibers, began. Gradually since 1980, research has been conducted on the characteristics of coconut fiber from tropical countries such as India, Brazil, Malaysia, Thailand, Vietnam, Sri Lanka, Bangladesh, and Tanzania.
The applications of materials made of natural and local resources have increased worldwide. Their significant variation in properties and characteristics is the greatest challenge in working with natural fiber reinforced composites. Some variables, including the fiber type, environmental conditions where the plant fibers sourced, processing methods, and any modification of the fiber influence composite properties. Products processed with Portland cement blended with natural fibers such as coconut, sisal, bagasse, bamboo, hemp, wood and vegetable fibers. It has shown to be suitable to add to construction materials [Aziz 1981], [ Paramasivan 1984]. Although the results are encouraging, there are some drawbacks especially some durability issues. It seems that the interface between fiber and cement paste is affected by the fiber swelling in the presence of moisture. For that reason, some researchers are now investigating remedial measures for improving durability. Accordingly, natural fiber-reinforced cement composites are most suitable. It is for earthquake resistant construction, foundation floor for machinery in factories, fabrication of lightweight cement-based roofing and ceiling boards, wall plaster, and building materials for low-cost housing [Aziz 1981]. The use of natural fibers in the construction industry will help to achieve sustainable patterns of consumption of building materials.
Natural fibers used as reinforcement in concrete is a cost-effective replacement for expensive, high energy consumed and non-renewable fibers [Pacheco 2011]. Recently, the use of natural fibers to replace carbon/glass fibers as reinforcement in fiber-reinforced polymer composites has gained popularity due to increasing environmental concern. Natural fibers are low-cost fibers with low density. They are Biodegradable, non-abrasive, renewable, recyclable, required reduced energy consumption and present less health risk. Also, they are readily available, and their specific mechanical properties are comparable to those of glass fibers used as reinforcement [Malkapuram 2008]. Therefore, natural fibers represent a highly ―sustainable‖ material. The use of natural fibers in fiber reinforced concrete composites as building materials will promote the ―sustainable‖ development in the construction industry.
The natural fibers are used for a long time in many developing countries in cement composites because of their availability and low cost [Ghavami 1999] [Savastano 2000]. Also, for low-cost building construction in developing countries, natural fiber-reinforced cement composites are found attractive [Ramakrishna 2005]. Un-reinforced cement concrete has low tensile strength and low strain capacity at fracture. Then researchers began looking for other alternatives for concrete reinforcement. Along with an increase in the environmental awareness in the world, researchers have focused their work on the valorization of bio-based high-performance materials such as natural fibers. Natural fibers are locally available in many countries. So their uses as a construction material for increasing properties of composites at a very little cost (almost nothing when compared to the total cost of the composites) are very promising. Moreover, their use can lead to having sustainable development [Ramakrishna 2005].
The researchers have used plant fibers as an alternative to steel fibers in the manufacture of fiber composites such as cement paste, mortar, and concrete. For example, natural fibers blended cements include coir, sisal, jute, hemp bast, pineapple leaves, kenaf bast, leaf abaca, bamboo, banana, flax, cotton and sugarcane [Ramakrishna 2005] [ Agopyan 2005] [Li et al., 2007] [Asasutjarita 2007] [Toledo Filho 2005] [ Munawar 2007] [ Rao 2007] [Li 2006] [Fernandez 2002] [Reis 2006] [Corradini 2006].
A problem of workability arises when a high percentage of fibers is incorporated into a fresh mix, as in the case of steel fibers [Martinie 2010]. Volume fraction and fiber content are two terminologies used for expressing the quantities of fibers in a given composites [Ramakrishna 2005] [Agopyan 2005] [Paramasivam 1984] [Li 2007] [Asasutjarita 2007] [Toledo Filho 2005] [Li 2006] [Fernandez 2002] [Reis 2006] [Aggarwal 1992] [Corradini 2006] [Toledo Filho 1999]. The various researcher has already studied uses of coconut coir as reinforcement in cement. Among them, a study on the feasibility of cement board [Asasutjarita 2009] or the durability of coir cement composites [Toledo Filho 2000] is reported.
Natural fibers are a valuable renewable resource materials; the substitution of steel fibers by coconut vegetal fibers presents many advantages because the coir is an abundant, versatile, renewable, cheap, and biodegradable lignocellulosic material.

Rheological behavior

In the building industry, fresh concrete flowability is required to ensure a smooth casting and to keep the mix homogeneously. This property is defined as workability. The workability of concrete depends on their rheological properties. Concrete or more cement-based materials are mainly considered to behave as Bingham materials. The Bingham behavior is modeled using two parameters: the yield stress and the plastic viscosity.
Fibers have a very positive influence on the mechanical properties of cementations materials in the hardened state. This impact depends primarily on the fibers (shape, constitutive material, volume fraction) but also on the casting process. Indeed, contrary to traditional aggregates, flow, in the case of fiber-reinforced materials. It can induce a preferred orientation of the fibers, which actively modify both fresh and hardened material properties as presented by [Martinie 2010].
The yield stress, plastic viscosity, and thixotropy are important rheological parameters to analyzes fresh concrete. Newtonian liquids, such as water and oil, show a linear relationship between shear stress (τ) and shear rate ( ) as shown in Figure 2.8 as: τ = η …………… (2.1).
Where: η is the viscosity. There is considerable evidence that the cement-based materials behave as a Bingham material. The Bingham model can be modeled as follow: ………………….(2.2) If ………………….(2.3).
Where: τ is shear stress (Pa), Is the shear rate (1/s), τo is the yield stress (Pa), and μ is a plastic viscosity (Pa-s) respectively. If the shear stress is lower than the yield stress, the material behaves as an elastic solid but when the yield stress was exceeded, the material start to flow. Yield stress is the critical shear stress required to initiate flow deformation and is directly linked to entering particular forces. As shown in Figure 2.8, the plastic viscosity is the slope angle of the shear stress vs. shear rate relationship.

Physical properties

Sugar components of fiber such as hemicellulose and lignin may interfere with cement hydration. Savastano mentioned that acid compounds released from natural fibers increase the setting time of the cement matrix [Savastano 2003a]. According to Sedan, fiber inclusion can increase the delay of setting by 45 min. It relies on the fact that fibers pectin can fix calcium preventing the formation of CSH structures [Sedan 2007].

Mechanical properties

Fiber characteristics such as tensile strength, elastic modulus, diameter or length affect the mechanical properties of fiber-reinforced composites. Fibers dispersion and orientation within the matrix play also an important role. The bond strength of the fiber-matrix interface is essential to reach high mechanical properties. Also, factors like processing conditions/techniques have a significant influence on the mechanical properties of the fiber reinforced composites. The most important characteristic of the composites is their strength. Their high mechanical strength combines with they’re a relatively low weight for optimized use in engineered structures such as ships, cars or buildings. Composites tensile strength can be four to six times greater than that of steel or aluminum [Biswas 2002]. Structures made of composites are 30-40% lighter than similar ones made of aluminum.
Environmental interactions influence the strength of composites. A recent study shows that the tensile strength of composite resins presents lower values after storage and test in water as compared to the dry condition due to its water absorption [Tani 2002]. Tensile strength expressed as the breaking load per unit cross-sectional area of the test specimen is an important physical property of fibers. 34% can increase the fiber tensile strength, fiber toughness and fiber– concrete bond strength, 55%, and 184%, respectively when fibers are boiled and washed [Ali 2013]. The flexural strength can be slightly increased by using only coconut fiber. Natural fibers such as coconut are reported to improve the compressive and tensile strength of cement based composites [Asasutjarit 2007]. Likewise, fracture toughness and fracture energy of polymer concrete can be increased by using chopped coconut fiber and sugarcane bagasse fiber [Reis 2006].
The use of natural fibers in the cement matrix leads to lightweight materials with excellent tensile behavior. Previous researchers on fiber reinforced concrete have shown that short natural fibers can modify tensile and flexural strength, toughness, impact resistance and fracture energy of cementitious materials [Pacheco 2011].
Pacheco-Torgal and Jalali reviewed the mechanical impact of several vegetable fibers (i.e. sisal, hemp, coir, banana and sugar cane bagasse) as reinforcement in cementitious building materials. Among those natural fibers, coir fiber presents some advantages to being used as reinforcement. Its highest toughness among natural fibers, it’s extremely low cost, as well as its availability [Baruah 2007] makes coir fiber very interesting. Li et al. stated that flexural toughness and flexural toughness index of cementitious composites with coir fiber are increased by more than ten times due to coir fiber bridging effect [Li 2004].
Reis also reported that coir fiber increases concrete composite fracture toughness. Moreover, the use of coir fibers shows even better flexural properties than synthetic fibers (glass and carbon) [Reis 2006]. Therefore, the inclusion of coir fiber might be useful to increase the flexural performance of concrete composites, particularly in changing the brittle failure pattern of the concrete core.
Meanwhile, according to Filhoa et al. [Filho 2000], cementitious composites made with coconut fiber present a significant decrease in toughness after six months out of aging or submitted to cycles of wetting and drying.
Majid Ali et al, show that fibers have the maximum bond strength with concrete when (i) embedment length is 30 mm, (ii) fibers are thick, (iii) fibres are treated with boiling water, and (iv) concrete are mix designed with ratio of one mass of cement; 3 masses of sand; 3 masses of gravel [Majid Ali 2013].
Single fiber pull-out tests have been carried out to determine load–slippage curves with the help of an Instron tensile machine fitted with a load cell. Bond strength and energy required for fiber pullout are computed from experimental data [Majid Ali 2013]. The use of natural fibers in concrete is not only useful to improve the mechanical properties of concrete, but also promote the sustainable development of green concrete and thus conserve natural resources [Awwad 2012].

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Table of contents :

1.1. Research background
1.2. Research Question
1.3. Objective of research
1.4. Limitation of Research.
1.5. Contribution of Research
1.6. Overview of Dissertation
2.1. Introduction
2.2. Natural Fiber
2.2.1. Structure and chemical composition.
2.2.2. Physical and mechanical properties
2.2.3. Microstructure
2.3. Coir fibers
2.3.1. Production coir fibers
2.3.2. Extraction of coir fibers
2.3.3. Physical and chemical properties
2.3.4. Mechanical properties
2.3.5. Thermal properties
2.3.6. Microstructure
2.4. Natural fiber reinforced cementitious composites.
2.4.1. Rheological behavior
2.4.2. Physical properties
2.4.3. Mechanical properties
2.4.4. Thermal properties
2.4.5. The fiber–matrix interface
2.5. Extrusion of cementitious composites
2.5.1. Extrudability of cementitious materials.
2.5.2. Extrudability of fibers cementitious materials.
2.6. Environmental impact
2.6.1. Life cycle assessment methodology
2.6.2. CO2 emissions
2.7. Conclusions of chapter
3.1. Introduction
3.2. Flow chart of the experimental approach
3.3. Fibers
3.3.1. Preparation of fibers
3.3.2. Water absorption
3.3.3. Density tests
3.3.4. Optical microscopy
3.3.5. Mechanical testing
3.3.6. Scanning electron microscopy
3.3.7. Thermal gravimetric analysis
3.4. Fiber reinforced cement mortars, at fresh state.
3.4.1. Materials are tested.
3.4.2. Mix proportion
3.4.3. Mixing procedures
3.4.4. Rheometer tests
3.4.5. Screw Extrusion
3.4.6. Casting procedure
3.5. Fiber reinforced mortar composites at hardened state.
3.5.1. Specimens preparation
3.5.2. Water absorption.
3.5.3. Density tests.
3.5.4. Compressive tests.
3.5.5. Tensile tests
3.5.6. Digital image correlation
3.5.7. Microscopic observation.
4.1. Introduction
4.2. Physical properties
4.2.1. Length of coir fiber
4.2.2. Diameter of coir fiber
4.2.3. Density of coir fiber
4.2.4. Water absorption of coir fiber
4.3. Microstructure analysis
4.3.1. Surface morphological characterization
4.3.2. Energy dispersive spectroscopy analysis.
4.3.3. Fracture surfaces observations.
4.4. Thermogravimetric analysis
4.4.1. Residual weight
4.4.2. Derivative weight
4.4.3. Heat flow
4.5. Mechanical properties
4.5.1. Tensile strengths
4.5.2. Young‘s modulus
4.5.3. Elongation at break
4.7. Conclusions of chapter
5.1. Introduction
5.2. Mix-Design of low cement content in mortar for extrusion
5.2.1. Mix design of an extrudable mortar.
5.2.2. The water content in clay mortar
5.2.3. Influence water content on cement mortar.
5.2.4. The formulation of an extruded fiber reinforced composites.
5.3. Morphologies of fresh fiber mortar composite
5.4. Rheology properties of fiber mortar composite extrudability
5.4.1. Fiber content and fibers length on torque
5.4.2. Fibers content and fibers length on yield stress.
5.5. Rheology model
5.5.1. Relative yield stress as a function of the fiber factor
5.5.2. The proposed rheological model to predict yield stress
5.5.3. Validation the rheological model.
5.6. Conclusions of chapter
6.1. Introduction
6.2. The aspect surface of screw extrusion.
6.2.1. Surface of extruded mortar
6.2.2. Surface of extruded composites
6.2.3. Surface of mold and extrusion
6.3. Orientation fibers in screw extrusion.
6.3.1. Longitudinal
6.3.2. Transversal
6.4. Mechanical performance extruded composites.
6.4.1. Compressive stress-strain of extruded composite
6.4.2. Tensile stress-strain of extruded composite
6.4.3. Stress-strain of molded and extruded sample behavior
6.5. Failure modes.
6.5.1. Failure modes in compression
6.5.2. Failure modes in tension
6.6. Mechanical models
6.6.1. Compressive strength behavior
6.6.2. Tensile strength behavior
6.6.3. Compressive modulus behavior
6.6.4. Tensile modulus behavior
6.6.5. Density behavior
6.6.6. Strain Behavior
6.7. The conclusion of the chapter.
7.1. Introduction
7.2. Mechanical characteristics of fiber composite behavior
7.2.1. Compressive strength behavior
7.2.2. Tensile strength behavior
7.3. Damage Evolution.
7.3.1. the compressive strength of extruded composites
7.3.2. Composites extruded on tensile strength
7.4. Microstructure
7.4.1. Fractography
7.4.2. Interfacial transition zone.
7.5. Micromechanical models.
7.5.1. Micromechanical models for tensile strength.
7.5.2. Micromechanical models for compressive strength
7.5.3. Comparison between models and experimental results
7.6. Conclusions of chapter
8.1. Conclusions.
8.2. Further Research.


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