scope:

INTRODUCTION

Historical aspects

Since ancient times, fibers have been used to reinforce brittle materials. Straw was used to reinforce sun-baked bricks, and horsehair was used to reinforce masonry mortar and plaster. A pueblo house built around 1540, believed to be the oldest house in the U.S., is constructed of sun-baked adobe reinforced with straw. In more recent times, large scale commercial use of asbestos fibers in a cement paste matrix began with the invention of the Hatschek process in 1898. Asbestos cement construction products are widely used throughout the world today. However, primarily due to health hazards associated with asbestos fibers, alternate fiber types were introduced throughout the 1960s and 1970s.

In modern times, a wide range of engineering materials (including ceramics, plastics, cement, and gypsum products) incorporate fibers to enhance composite properties. The enhanced properties include tensile strength, compressive strength, elastic modulus, crack resistance, crack control, durability, fatigue life, resistance to impact and abrasion, shrinkage, expansion, thermal characteristics, and fire resistance.

Experimental trials and patents involving the use of discontinuous steel reinforcing elements-such as nails, wire segments, and metal chips-to improve the properties of concrete date from 1910 [1.2]. During the early 1960s in the United States, the first major investigation was made to evaluate the potential of steel fibers as a reinforcement for concrete [1.3]. Since then, a substantial amount of research, development, experimentation, and industrial application of steel fiber reinforced concrete has occurred.

Use of glass fibers in concrete was first attempted in the USSR in the late 1950s [1.4]. It was quickly established that ordinary glass fibers, such as borosilicate E-glass fibers, are attacked and eventually destroyed by the alkali in the cement paste. Considerable development work was directed towards producing a form of alkali-resistant glass fibers containing zirconia [1.5]. This led to a considerable number of commercialized products. The largest use of glass fiber reinforced concrete in the U.S. is currently for the production of exterior architectural cladding panels.

Initial attempts at using synthetic fibers (nylon, polypropylene) were not as successful as those using glass or steel fibers [1.6, 1.7]. However, better understanding of the concepts behind fiber reinforcement, new methods of fabrication, and new types of organic fibers have led researchers to conclude that both synthetic and natural fibers can successfully reinforce concrete [1.8, 1.9].

Considerable research, development, and applications of FRC are taking place throughout the world. Industry interest and potential business opportunities are evidenced by continued new developments in fiber reinforced construction materials. These new developments are reported in numerous research papers, international symposia, and state-of-the-art reports issued by professional societies. The ACI Committee 544 published a state-of-the-art report in 1973 [1.10]. RILEM's committee on fiber reinforced cement composites has also published a report [1.11]. A Recommended Practice and a Quality Control Manual for manufacture of glass fiber reinforced concrete panels and products have been published by the Precast/Prestressed Concrete Institute [1.12, 1.13]. Three recent symposium proceedings provide a good summary of the recent developments of FRC [1.14, 1.15, 1.16].

Specific discussions of the historical developments of FRC with various fiber types are included in Chapters 2 through 5.