Fibrous and Composite Materials for Civil Engineering Applications

R Fangueiro

• Publisher: Woodhead Publishing
• Year: 2011
• ISBN:
  9780857092526
• Topic: Technology & Engineering
• Subtopic: Civil Engineering
• Index: Technology & Engineering

The use of fibrous materials in civil engineering, both as structural reinforcement and in non-structural applications such as geotextiles, is an important and interesting development. Fibrous and composite materials for civil engineering applications analyses the types and properties of fibrous textile and structures and their applications in reinforcement and civil engineering.Part one introduces different types of fibrous textiles and structures. Chapters cover the properties of natural and man-made fibres and of yarns, as well as an overview of textile structures. Part two focuses on fibrous material use in concrete reinforcement, with chapters on the properties and applications of steel fibre reinforced concrete, natural fibre reinforced concrete and the role of fibre reinforcement in mitigating shrinkage cracks. In part three, the applications of fibrous material-based composites in civil engineering are covered. Chapters concentrate on production techniques and applications such as reinforcement of internal structures, structural health monitoring and textile materials in architectural membranes.With its distinguished editor and international team of contributors, Fibrous and composite materials for civil engineering applications is a standard reference for fabric and composite manufacturers, civil engineers and professionals, as well as academics with a research interest in this field.

• Explores the development of fibrous materials in civil engineering, both as structural reinforcement and in non-structural applications such as geotextiles
• Key topics include short fibre reinforced concrete, natural fibre reinforced concrete and high performance fibre reinforced cementitious composites
• A standard reference for fabric and composite manufacturers, civil engineers and professionals, as well as academics with a research interest in this field

Part I

Types of fibrous textiles and structures

1

Natural and man-made fibres: Physical and mechanical properties

M. De Araújo, University of Minho, Portugal

Abstract:

A fibre is a unit of matter characterized by flexibility, fineness and a high ratio of length to thickness. Because fibres have a high surface to volume ratio, they can be extremely strong materials. According to their origin, textile fibres may be classified as natural fibres, when they occur in nature in fibre form, and man-made fibres, when they do not occur in nature in fibre form. This chapter addresses the relationship between their structure and properties, and their use in civil engineering applications, such as road construction, bridges, non-structural gratings and claddings, structural systems for industrial supports, buildings, long-span roof structures, tanks, thermal insulators, etc.

Key words

fibres

modulus

strength

density

civil engineering

1.1 Introduction

A fibre is a unit of matter characterized by flexibility, fineness and a high ratio of length to thickness (Fig. 1.1).¹ As fibres have a high surface to volume ratio, they can be extremely strong materials.

1.1 Typical textile fibres: (a) flax, longitudinal view; (b) flax, cross-sectional view; (c) polyester, longitudinal view; (d) nylon 6.6, cross-sectional view.

Fibres are normally constituted by long and chain-like molecules known as macromolecules or polymers, which may be of organic or inorganic nature. These molecules are able to pack together closely to each other resulting in regions of crystallinity (Fig.1.2(1)). The degree of orientation of these regions is an important factor in determining the usefulness of a fibre for a particular application. There are other regions, however, where the molecules do not hold together and form random arrangements or amorphous regions (Fig. 1.2(2)). The crystalline regions provide strength and rigidity to the fibres, while the amorphous regions are responsible for flexibility and reactivity. The ratio of crystalline to amorphous material has an important influence on the properties of the fibres.

1.2 Model of molecular arrangement in nylon fibre:¹² (1) crystalline region; (2) amorphous region.

According to their origin, textile fibres may be classified as natural fibres, when they occur in nature in that form, and man-made fibres, when they do not occur in nature in fibre form. Within the latter, some are made of a natural polymer that has been spun into natural polymer fibres, and others are made of a synthetic polymer that has been spun into synthetic fibres.

High-performance fibres are mostly synthetic fibres that are engineered for specific applications that require very high performance in terms of strength, stiffness, heat resistance or chemical resistance. These fibres have generally higher tenacity and higher modulus than standard fibres.

There are also some inorganic man-made non-polymeric fibres such as metal threads.

Fibres are used in many civil engineering applications including road construction, bridges, non-structural gratings and claddings, structural systems for industrial supports, buildings, long-span roof structures, tanks, thermal insulators and so on.

1.2 Natural fibres

Traditional natural fibres, such as cotton, wool and silk, have tenacities in the order of 0.1–0.4 N/tex and initial moduli ranging from 2–5 N/tex. However, fibres such as flax, hemp, jute and ramie may have higher strength and stiffness. With the exception of silk, which was used in more demanding applications such as protective and parachute fabrics, they are all short fibres, and this hinders the conversion efficiency of the fibre’s strength into yarns and fabrics.

The usefulness of natural fibres in civil engineering applications (Fig. 1.3) is limited by their moderate mechanical properties. However, there may be advantages from using some of these fibres for the reinforcement of composites used as building materials. The low specific gravity of fibres like jute results in a higher specific strength and stiffness than glass fibres and this may be a benefit, especially in parts designed for bending stiffness. The tensile strength and modulus of jute are lower than those of glass fibres; however, the specific modulus of the jute fibre is higher than that of glass and, on a modulus-per-cost basis, jute can also be superior. The specific strength per unit cost of jute, too, approaches that of glass. The advantage of using jute fibres as a substitute for glass fibres, partly or in total, in the reinforcement of composite materials arises from its lower specific gravity (1.50) and higher specific modulus (11.46 N/tex) when compared with glass (2.58 and 10.85 N/tex respectively). Furthermore, the lower cost and the renewable nature of jute, requiring less energy for its production (approximately 2% of that of glass), make it an attractive reinforcing fibre in composites for some civil engineering applications.²

1.3 Typical stress–strain curves of cellulosic fibres: (1) flax; (2) jute; (3) fortisan; (4) tenasco.

1.3 Man-made fibres

1.3.1 Natural polymer fibres

Viscose rayon and acetate, which were amongst the first regenerated cellulose fibres, exhibited tenacities below 0.2 N/tex. The need to improve the strength of cellulosic fibres led to the development of continuous-filament rayon yarns (Tenasco), with a tenacity of 0.4 N/tex, which were used for tyre cords. Further improvements led to strengths of the order of 0.6 N/tex, with an extension to break in the region of 13%. Other developments led to fibres with higher stiffness, such as Fortisan, which was developed from highly stretching acetate yams which were subsequently converted into cellulose. This increased the tenacity to 0.6 N/ tex and the modulus to 16 N/tex. Another example is Bocell, which is a cellulose fibre spun from a liquid-crystal solution in phosphoric acid and has tenacities and moduli of the order of 1.1 N/tex and 30 N/tex, respectively.³

It should be noted that the extension to break of regenerated fibres is generally high, ranging from around 6–27%. The low to moderate mechanical properties of these fibres render their usefulness quite limited in civil engineering applications at the present time.

1.3.2 Synthetic fibres

The first synthetic fibre was a polyamide, generally known as nylon, which started to be marketed in 1938 and found applications in wartime technical uses. Its tenacity was in the region of 0.5 N/tex and the modulus 2.5 N/tex. Another synthetic fibre that followed was the polyester fibre (polyethylene terephthalate), which had a similar tenacity but a higher modulus of around 10 N/tex. Varieties of these fibres developed for industrial applications, such as ropes and tyre cords, exhibit tenacities over 0.8 N/tex for both nylon and polyester and moduli of 9 N/ tex for nylon and 12 N/tex for polyester.

Another fibre of increasing interest in technical applications is polypropylene. Its tenacity is in the region of 0.65 N/tex with a modulus of 7.1 N/tex and a specific gravity of 0.91.

Nylons, but especially polypropylene and polyester, are widely used in geosynthetics, and ...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Contributor Contact Details
• Woodhead Publishing Series in Textiles
• Part I: Types of fibrous textiles and structures
• Part II: Fibrous materials as a concrete reinforcement material
• Part III: Fibrous materials based composites for civil engineering applications
• Index