Natural vs Synthetic Fiber Reinforced Polymer

Concrete technology as a branch discipline of technology requires increase in the degree of specialization and consolidation of the fiber material in the cement matrix form composite materials. It requires knowledge of the concepts related to the interaction between the fiber and adhesive cement, mortar or matrix concrete that influence the production and nature of the product. The scientists and engineers have been actively exploring to find the materials that will be used as replacement of conventional materials that can provide a feature best new design and innovation to enhance the material.

The development of fiber technology is in the line with the development of knowledge of the material. Following the high demand and innovation in applying fiber, the fiber technology has produced various kinds of fibers potential for commercialization. Participation fiber reinforcement in concrete, mortar and cement adhesive work to improve the engineering properties of many based materials such as fracture resistance, bending strength and resistance to fatigue, impact, thermal shock or chipping. Consolidation of materials in the form of cement mortar or concrete has become an attraction as a building material because it is inexpensive, has the resilience and has a compressive strength and stiffness sufficient for restructuring. However, the disadvantages are located on fragile nature, tensile strength and impact of the weak as well as receptive to moisture movement. Hence, reinforced by fibers that have enhanced capabilities offer a suitable alternative, practical and economical to overcome the lack of features of conventional concrete or mortar.

Elements of a fiber is a continuous filament in the form of an express term sheet or spreadsheet form. Fibers can generally be categorized into three types : synthetic fibers, natural fibers and mineral fibers. Synthetic fibers are man-made fibers. It is based chemicals such as petrochemicals and synthetic fibers derived mostly from nylon, polyster, aerylic polymer and polyacrylonitrile fibers used to make fiberglass. There is also a bundle of fibers that make the polymer chain is as strong as aramid and chain bond length as dyneema.

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While natural fiber derived from natural sources, from plants and animals. Plant fibers are cellulose and lignin-based stacks such as cotton, jute, coir, oil palm bunches, flax and so on. It can be obtained from seeds (cotton, kapok), leaf (pineapple, banana), leather plant (jute, kenaf, rattan, hemp), fruit (coconut, palm) and straw (rice, wheat, barley, grass). Next, animal fibers derived from protein particles like silk and wool. For mineral fibers, it derived from the earth’s crust and it happens naturally. It is based on asbestos fibers (chrysotile, amosite, crocidolite, tremolite, actinolite, anthophyllite), ceramic fibers (glass wool, quartz, aluminum oxide, silicon carbide) and fiber-metal (steel, aluminum).

However, both of natural and synthetic fiber reinforced concrete have their own challenges and weakness. Nothing is being done without deficiencies. Synthetic fiber however has more challenges than natural fiber because of its production. Future development of natural and synthetic fiber reinforced polymer concrete will make us want to investigate more about them.

OBJECTIVES

• To know about polymer concrete and why fiber being reinforced in it.
• To describe the characteristics of natural and synthetic fiber reinforced polymer concrete.
• To describe the challenges in environment while using both composite materials in construction.
• To describe the future development in both composite materials.

LITERATURE REVIEW

POLYMER CONCRETE AND ITS CHARACTERISTICS

Polymer concrete is a composite material in which the binder consists entirely of a synthetic organic polymer. It is variously known as synthetic resin concrete, simply resin concrete or plastic resin concrete. Because the use of a polymer instead of Portland cement represents a substantial increase in cost, polymers should be used only in applications in which the higher cost can be justified by superior properties, low labor cost or low energy requirements during processing and handling. It is therefore important that architects and engineers have some knowledge of the capabilities and limitations of polymer concrete materials in order to select the most appropriate and economic product for a specific application.

Polymer concrete consists of a mineral filler such as an aggregate and a polymer binder which may be a thermoplastic, but more frequently, it is a thermosetting polymer. When sand is used as a filler, the composite is referred to as a polymer mortar. Other fillers include chalk, gravel, limestone, crushed stone, condensed silica fume (silica flour, silica dust), quartz, clay, granite, expanded glass, and metallic fillers. Generally, any dry, non-absorbent, solid material can be used as a filler.

To produce polymer concrete, a monomer or a pre-polymer which mean a product resulting from the partial polymerization of a monomer, a hardener (cross-linking agent) and a catalyst are mixed with the filler. Other ingredients added to the mix include plasticizers and fire retardants. Sometimes, silane coupling agents are used to increase the bond strength between the polymer matrix and the filler. To achieve the full potential of polymer concrete products for certain applications, various fiber reinforcements are used. These include glass fiber, glass fiber-based mats, fabrics and metal fiber. Setting times and times for development of maximum strength can be readily varied from a few minutes to several hours by adjusting the temperature and the catalyst system. The amount of polymer binder used is generally small and is usually determined by the size of the filler. Normally the polymer content will range from 5 to 15 percent of the total weight, but if the filler is fine, up to 30 percent may be required.

Polymer concrete composites have generally good resistance to attack by chemicals and other corrosive agents, good resistance to abrasion, have very low water sorption properties and good marked freeze-thaw stability. Also, the greater strength of polymer concrete in comparison to that of Portland cement concrete permits the use of up to 50 percent less material. This puts polymer concrete on a competitive basis with cement concrete in certain special applications. The chemical resistance and physical properties are generally determined by the nature of the polymer binder to a greater extent than by the type and the amount of filler. In turn, the properties of the matrix polymer are highly dependent on time and the temperature to which it is exposed.

The viscoelastic properties of the polymer binder give rise to high creep values. This is a factor in the restricted use of polymer concrete in structural applications. Its deformation response is highly variable depending on formulation ; the elastic moduli may range from 20 to about 50 GPa, the tensile failure strain being usually 1 percent. Shrinkage strains vary with the polymer used. For example, high for polyester and low for epoxy-based binder. It must be taken into account in an application.

A wide variety of monomers and pre-polymers are used to produce polymer concrete. The polymers most frequently used are based on four types of monomers or pre-polymer systems : methyl methacrylate (MMA), polyester pre-polymer-styrene, epoxide pre-polymer hardener (cross-linking monomer) and furfuryl alcohol.

Table 1 : General Characteristics And Applications of Polymer Concrete Products

Poly (methylmethacrylate)

General Characteristics

Low tendency to absorb water. As a result, high freeze-thaw resistance ; low rate of shrinkage during and after setting. Outdoor durability and good chemical resistance.

Typical Applications

Used in the manufacture of façade plates, stair units and sanitary products for curbstones.

Polyester

General Characteristics

Good adhesion to other materials, relatively strong, good chemical and freeze-thaw resistance but have high-setting and post-setting.

Typical Applications

Because of lower cost, widely used in panels for public and commercial pipes, buildings, floor tiles, stairs, various precast and cast-in applications in construction works.

Epoxy

General Characteristics

Strong adhesion to most building materials, low shrinkage, good creep and fatigue resistance, superior chemical resistance and low water sorption.

Typical Applications

Epoxy polymer products are relatively costly. They are mainly used in special applications including use in mortar for industrial flooring, skid-resistant overlays in highways, epoxy plaster for exterior walls and resurfacing of deteriorated structures.

Furan-based polymer

General Characteristics

Composite materials with high resistance to chemicals which most acidic or basic aqueous media, strong resistance to polar organic liquids such as ketones, aromatic hydrocarbons and chlorinated compounds.

Typical Applications

Furan polymer mortars and grouts are used for brick such as carbon brick and red shale brick, floors and linings that are resistant to chemicals, elevated temperatures and thermal shocks.

Source : Blaga, A. and Beaudoin, J.J., (1985). Polymer Concrete. Canadian Building Digest published November 1985.

THE CHARACTERISTICS OF FIBER AND TOUGHNESS CONCEPT

Characteristics of fiber in use to hardened concrete :

Fibers should be significantly stiffer than the matrix which has a higher modulus of elasticity than the matrix.

Fiber content by volume must be adequate.

There must be a good fiber-matrix bond.

Fiber length must be sufficient.

Fibers must have a high aspect ratio. Means that they must be long relative to their diameter.

Toughness is defined as the area under a load-deflection (or stress-strain) curve. Adding fibers to concrete greatly increases the toughness of the material. That is, fiber-reinforced concrete is able to sustain load at deflections or strains much greater than those at which cracking first appears in the matrix.

NATURAL FIBER REINFORCED POLYMER CONCRETE AND ITS CHARACTERISTICS

Potential use of natural fiber reinforced concrete in the application of natural fibers has long attracted the attention of researchers. Various researches has been conducted in many countries for a variety of mechanical properties, physical performance and durability of materials reinforced by natural fibers. Natural fibers are categorized as organic waste from plants such as fiber coconut, sisal, bagasse, jute, wood dust and so on.

Natural fiber reinforced concrete is essentially a special concrete where it contains fibers with a small diameter, independently and randomly distributed in the cement matrix. Uniform distribution in the cement matrix, contributing to an increase in the tensile and resistance to cracking, impact and improved the ductility values ​​for the good aspects of energy absorption. Although many types of fibers were used as reinforce material in concrete, the use of natural fibers had long been in existence and there is a lot of evidence of the usage of these fibers in the history of civilization. Nature has given human the fiber reinforced material in the form of wood, bamboo and other plants. The use of straw in mud bricks and horse hair in the mortar has the potential of natural fibers.

Only in the late 1960s and early 1970s, research began to study the potential use of various types of natural fibers as reinforcement material in the slab concrete and cement-based composite materials. Natural fiber reinforced cement or concrete products that use fibers such as coir, sisal, sugar bagasse, bamboo and so on have been produced and tested in more than 40 countries. For economic reasons in developing countries where natural fibers is so much available, it is demanding for construction industry players to enhance the usefulness of these resources in an effective and economical as to introduce composite materials for residential use and others.

Basic needs use of natural fibers as reinforcement material in concrete matrix is ​​tensile strength and high elastic modulus, the bond between the matrix and fiber, good chemical composition, stable geometry and good durability.

SYNTHETIC FIBER REINFORCED POLYMER CONCRETE AND ITS CHARACTERISTICS

Synthetic fibers are man-made fibers resulting from research and development in the petrochemical and textile industries. There are two different physical fiber forms: monofilament fibers, and fibers produced from fibrillated tape. Currently there are two different synthetic fiber volumes used in application, namely low-volume percentage (0.1 to 0.3% by volume) and high-volume percentage (0.4 to 0.8% by volume). Most synthetic fiber applications are at the 0.1% by volume level. At this level, the strength of the concrete is considered unaffected and crack control characteristics are sought. Fiber types that have been tried in concrete matrices include : acrylic, aramid, carbon, nylon, polyester, polyethylene and polypropylene.

The characteristics is depend on the types of synthetics used to reinforced with polymer concrete. Different fiber has different properties. Adding carbon fiber decreased the unit weight of polymer concrete. Carbon fiber provides much higher compressive strength, flexure strength and ductility of polymer concrete. PVC and polypropylene fibers did not significantly influence the compressive strength and gave the lowest pulse velocities and modulus.

NATURAL VS SYNTHETIC FIBER REINFORCED POLYMER CONCRETE : CHALLENGES

The challenges of polymer concrete are the monomers of polymer can be volatile, combustible and toxic. Initiators, which are used as catalysts, are combustible and harmful to human skin. The promoters and accelerators are also dangerous.

Natural fibers are emerging as lightweight, low cost, and more environmentally rather than synthetic fibers in composites. This is because :

• natural fiber production has lower environmental impacts compared to synthetic fiber production.
• natural fiber composites have higher fiber content for equivalent performance, reducing more polluting base polymer content.
• the light-weight natural fiber composites improve fuel efficiency and reduce emissions in the use phase of the component, especially in auto applications.
• end of life incineration of natural fibers results in recovered energy and carbon credits.

A compound reinforced with natural fibers is not only low density, low-cost, and abrasion resistant, it also offers an absence of toxicity and better dimensional stability.

Polyester raw material releases high amounts of carbon dioxide. This rapidly increases global warming, which is why polyester and other synthetic fabrics are widely discouraged. The other reason is that some synthetic fabrics come from non-renewable resources such as oil. Eventually rise of these synthetic fibers usage have been causing environmental problems such as dumping and recycling. In addition, glass fiber can cause acute irritation of the skin, eyes, and respiratory tract. Mainly concerns have been raised for long term disease such as cancer and lung scarring. Moreover, when released, glass fiber does not decompose and hence again it results in environmental pollutions, as well as, threaten animal life and nature along.

Therefore, one of the solutions is using natural fibers instead of synthetic fibers in developing composites materials as they are renewable. Also the consumption of renewable resources would provide positive image for sustainability of green environment. Natural fibers are less harmful to the environment and the society because they are derived from plants and animals which are more eco-friendly. Products which manufactured from natural fabric eventually dissolves into the earth. Plant and animal based fabrics are a part of the evolutionary process of life. They return to the earth to return once more to life.

Synthetic fibers are more harmful to the environment because they are enhanced with chemicals. Polyester and nylon fabrics are made from a substance which creates nitrous oxide. Materials that are labeled petrochemical, flame retardants, nylon, acetate and non-wrinkle are all chemically treated. Chemicals which used for the manufacture of synthetic fabrics is harmful and can enter into the water supply and cause health problems. Also workers who are continuously exposed to dangerous chemicals are at risk for developing auto-immune diseases and disease of the lung. Products made from petrochemicals take years to break down, creating a constant need for landfills. Synthetic products that are disposed into the ocean are a threat to marine life. The threat to aquatic animals will eventually precipitate a food shortage.

Although, synthetic fibers may offer softer fabrics and more durable materials, the long term effect on the environment far outweigh any advantages. The high cost of petrol along with global awareness of how natural fibers improve overall quality of life will help motivate manufacturers to find more innovative ways to utilize natural fibers.

NATURAL VS SYNTHETIC FIBER REINFORCED POLYMER CONCRETE : FUTURE DEVELOPMENT

Synthetic : Although not investigated extensively, the use of two or more fiber types in the same concrete mix is considered promising. The decision to mix two fibers may be based on the properties that they may individually provide or simply based on economics. Considerable improvement in the load deflection response was observed mixing steel with polypropylene fibers. In a more recent study, steel micro-fibers (25 microns in diameter and 3 mm long) and carbon micro-fibers (18 microns in diameter and 6 mm long) both in mono- and hybrid- forms were investigated. In the mono-form, steel fiber provided better strengthening than the carbon fiber and carbon fiber provided better toughening than the steel fiber. Interestingly, in the hybrid form (in combination), they both retained their individual capacities to strengthen and toughen. It appears possible, therefore, that by properly controlling fiber properties and combining them in appropriate proportions, one can actually tailor-make hybrid fiber composites for specifically designed applications.

Natural : Environmental awareness and depletion of the petroleum resources are among vital factors that motivate a number of researchers to explore the potential of reusing natural fiber as an alternative composite material in industries such as packaging, automotive and building constructions. However, their applications are still limited due to several factors like moisture absorption, poor wettability and large scattering in mechanical properties. Among the main challenges on natural fibers reinforced matrices composite is their inclination to entangle and form fibers agglomerates during processing due to fiber-fiber interaction. So, the research on natural fiber is being done by mercerization treatment on mechanical properties enhancement of natural fiber reinforced composite or so-called bio composite. It specifically discussed on mercerization parameters, and natural fiber reinforced composite mechanical properties enhancement. It was found that the most parameters used in mercerization treatment were alkali concentration, fiber soaking temperature and fiber soaking duration. Although similar types of reinforced fiber are used, it could give different values in its final composite mechanical properties due to different parameter setting during a mercerization treatment process. Therefore, there is a significant need to conduct further work focusing on main effect and interaction effect of mercerization parameters setting toward enhancement of natural fiber reinforce composite mechanical properties.

CONCLUSION

In conclusion, natural fiber reinforced polymer concrete has more environmentally characteristics than the synthetic one. But, in the context of advantages, synthetic fiber reinforced polymer concrete has more than natural. Both of them have their own advantages and disadvantages. Because of several characteristics of natural fibers such as moisture absorption, poor wettability and large scattering in mechanical properties, thus it makes reinforcement with polymer concrete a bit less advantageous. Future works will be needed to improve the properties of both natural and synthetic fiber reinforced polymer concrete included with environment impacts.