《复合材料 Composites》课程教学资源（学习资料）第一章 复合材料基础_复合材料民用 Large Volume, High-Performance Applications of Fibers in Civil Engineering

Large Volume, High-Performance Applications of Fibers in Civil Engineering VICTOR C. LI ACE-MRL, Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, Michigan 48109 Received 8 November acce Nouem ber 2000 ABSTRACT: This article presents an overview of fiber applications in cementitious composites. The socio-economic considerations surrounding materials development in civil engineering in general, and fiber reinforced cementitious materials in particular appliations are fibers are used in these applications, are documented. An attempt is made to extract common denominators among the widely varied applications. The R&D and industrial trends of applying fibers in enhancing structural performance are depicted. An actual case study involving a tunnel lining constructed in Japan is given to illustrate how a newly proposed structural design guideline takes into account the load carrying con- tribution of fibers. Composite properties related to structural performance are de cribed for a number of FRCs targeted for use in load carrying structural members Structural applications of FRCs are currently under rapid development. In coming years, it is envisioned that the ultra-high performance FRC, with ductility matching that of metals, will be commercially exploited in various applications. Highlights of such a material are presented in this article. Finally, conclusions on market trends are drawn, and favorable fiber characteristics for structural applications are provided o 2002 John Wiley Sons, Inc. J Appl Polym Sci 83: 660-686, 2002 Key words: FRC, ECC; fiber; composites; structure INTRODUCTION Fibers are generally used in one of two forms short staple randomly dispersed in the cement The use of fibers to reinforce a brittle material can tious matrix of a bulk structure, or continuous be traced back to egyptian times when straws or mesh used in thin sheets. In recent years, some horsehair were added to mud bricks. Straw mats attempts to weave synthetic fibers into three-di- serving as reinforcements were also found in mensional reinforcements have been made In ad- early Chinese and Japanese housing construc- dition, fiber-reinforced plastic rods are currentl tion. The modern development of steel fiber rein- entering the market as replacement of steel bar forced concrete may have begun around the early reinforcements. Beyond cementitious matrix, fi- 1960s, preceded by a number of patents. Poly- ber-reinforced plastics are finding increasing use meric fibers came into commercial use in the late in the civil engineering industry. However, this 970s, glass fibers experienced widespread use in article will focus only on the material with the the 1980s, and carbon fiber attracted much atten- currently largest consumption of fiber--randomly che early 1990s oriented fiber-reinforced cementitious matrix (ce- ment, mortar, and concrete) materials (hereafter Contract grant sponsor: National Science Foundation. breviated as FRCs). Based on industrial sources, the amount of fibers used worldwide at Joumal of Applied Polymer Science, Val. 83, 660-686(2002) o 2002 John wiley Sons, Inc. present is estimated at 300, 000 tons per year, and

Large Volume, High-Performance Applications of Fibers in Civil Engineering VICTOR C. LI ACE-MRL, Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, Michigan 48109 Received 8 November 2000; accepted 18 November 2000 Published online 15 November 2001; DOI 10.1002/app. 2263 ABSTRACT: This article presents an overview of fiber applications in cementitious composites. The socio-economic considerations surrounding materials development in civil engineering in general, and fiber reinforced cementitious materials in particular, are described. Current FRC appliations are summarized, and the where, how, and why fibers are used in these applications, are documented. An attempt is made to extract common denominators among the widely varied applications. The R&D and industrial trends of applying fibers in enhancing structural performance are depicted. An actual case study involving a tunnel lining constructed in Japan is given to illustrate how a newly proposed structural design guideline takes into account the load carrying con￾tribution of fibers. Composite properties related to structural performance are de￾scribed for a number of FRCs targeted for use in load carrying structural members. Structural applications of FRCs are currently under rapid development. In coming years, it is envisioned that the ultra-high performance FRC, with ductility matching that of metals, will be commercially exploited in various applications. Highlights of such a material are presented in this article. Finally, conclusions on market trends are drawn, and favorable fiber characteristics for structural applications are provided. © 2002 John Wiley & Sons, Inc. J Appl Polym Sci 83: 660–686, 2002 Key words: FRC; ECC; fiber; composites; structure INTRODUCTION The use of fibers to reinforce a brittle material can be traced back to Egyptian times when straws or horsehair were added to mud bricks. Straw mats serving as reinforcements were also found in early Chinese and Japanese housing construc￾tion. The modern development of steel fiber rein￾forced concrete may have begun around the early 1960s, preceded by a number of patents.1 Poly￾meric fibers came into commercial use in the late 1970s, glass fibers experienced widespread use in the 1980s, and carbon fiber attracted much atten￾tion in the early 1990s. Fibers are generally used in one of two forms— short staple randomly dispersed in the cementi￾tious matrix of a bulk structure, or continuous mesh used in thin sheets. In recent years, some attempts to weave synthetic fibers into three-di￾mensional reinforcements have been made. In ad￾dition, fiber-reinforced plastic rods are currently entering the market as replacement of steel bar reinforcements. Beyond cementitious matrix, fi- ber-reinforced plastics are finding increasing use in the civil engineering industry. However, this article will focus only on the material with the currently largest consumption of fiber—randomly oriented fiber-reinforced cementitious matrix (ce￾ment, mortar, and concrete) materials (hereafter abbreviated as FRCs). Based on industrial sources, the amount of fibers used worldwide at present is estimated at 300,000 tons per year, and Contract grant sponsor: National Science Foundation. Journal of Applied Polymer Science, Vol. 83, 660–686 (2002) © 2002 John Wiley & Sons, Inc. 660

HIGH PERFORMANCE APPLICATIONS OF FIBERS 661 is projected to increase. In North America, the plications of FRCs are currently under rapid de- growth rate has been placed at 20% per year. velopment In coming years, it is envisioned that However, it should be pointed out that FRC re- the ultrahigh-performance FRC, with ductility mains a small fraction of the amount of concrete matching that of metals, will be commercially used each year in the construction industry exploited in various applications. Highlights of ibers may have been originally introduced in such a material are described in the section enti n attempt to "strengthen"the matrix, without tled Strain- Hardening Cementitious Composites consciously distinguishing the difference between In the final section, conclusions on market trend became generally recognized that the most signif- placed on the need for fiber and surface charac cant effect of fiber addition to the brittle cemen- teristics most suitable for the ensuing applica titious matrix is the enhancement of toughness. tions and performance needs of future FRCs For most FRCs, this means the capability of the material to carry tensile load, albeit at a decreas- ing level with opening of a crack after its forma- SOCIOECONOMIC CONSIDERATIONS tion. For certain FRC with continuous and/or high-fiber volume fractions, the ability of fibers in Civil infrastructures are organic, in the sense substantially increasing the tensile ductility has that they grow with the years. The Akashi-Kaikyo been recognized since the work of Aveston et al. Bridge in Kyoto, Japan, recently completed in However, it is only in recent years that such duc- April 1998, has the longest suspended span(1990 tility accompanied by strain-hardening can be de- m) of all bridges in the world. At 450 m, the rived by a moderately low amount of randomly Petronas twin Tower in Malaysia(completed in oriented discontinuous fibers(e. g, less than two 1996)is the tallest building in the world. No volume percent) by carefully tailoring the matrix, doubt these records will be shattered in the near interface, and fiber via the help of micromechan- future. Behind this growth is the development of ics. As a result, a new class of economically viable, advanced construction materials field processable, high-performance damage-tol Unfortunately, when put in perspective, civil erant material is emerging. Emphasis on compos- and building engineering materials development ite tailoring also brings with it the need to control does not have a good track record, in comparison fiber characteristics to meet the performance with other industries. Part of the reason comes need and economic constraints in construction ap- from the lack of cooperation/coordination between plications of this new type of FRO the construction industry and the construction n the next section, broad socioeconomic con- material supplying industry. Especially in the siderations surrounding materials development United States, joint research and development in civil engineering in general, and fiber rein- between materials suppliers and the construction forced cementitious materials in particular, are dustry is relatively nonexistent. Such fragmen- described. The section entitled Current Applica- tation between materials development and infra- tions of FRCs summarizes current Frc applica structures is not conducive to the healthy growth tions worldwide and documents where, how, and and maintenance of our societies infrastructures why fibers are used in these applications. An at- The negative impact of this stance on construc- tempt is made to extract common denominators tion productivity, durability, and public safet among the widely varied applications. Most cur- cannot be underestimated rent use of frcs is in nonstructural or. at most The magnitude of our infrastructure need is semistructural applications. The following section enormous. Put in economic terms, about 10% describes the research and development and gross domestic product derives from infrastruc dustrial trends of applying fibers in enhancing ture construction worldwide. In the United States structural performance. An actual case study in lone, infrastructure construction is a $400 bi volving a tunnel lining constructed in Japan is lion industry involving 6 million jobs. We have given to illustrate how a newly proposed struc- approximately $17 trillion worth of infrastruc ural design guideline takes into account the load- tures in place. Advanced construction materials carrying contribution of fibers Composite proper- must contribute to the organic growth of our new ties related to structural performance are de- infrastructures, and at the same time, contribute scribed for a number of FRCs targeted for use in to maintaining the health of our infrastructure load-carrying structural members. Structural ap- inventory. The implications of advanced civil en-

is projected to increase. In North America, the growth rate has been placed at 20% per year. However, it should be pointed out that FRC re￾mains a small fraction of the amount of concrete used each year in the construction industry. Fibers may have been originally introduced in an attempt to “strengthen” the matrix, without consciously distinguishing the difference between material strength and material toughness. As the study of FRC evolved into a scientific discipline, it became generally recognized that the most signif￾icant effect of fiber addition to the brittle cemen￾titious matrix is the enhancement of toughness. For most FRCs, this means the capability of the material to carry tensile load, albeit at a decreas￾ing level with opening of a crack after its forma￾tion. For certain FRC with continuous and/or high-fiber volume fractions, the ability of fibers in substantially increasing the tensile ductility has been recognized since the work of Aveston et al.2 However, it is only in recent years that such duc￾tility accompanied by strain-hardening can be de￾rived by a moderately low amount of randomly oriented discontinuous fibers (e.g., less than two volume percent) by carefully tailoring the matrix, interface, and fiber via the help of micromechan￾ics. As a result, a new class of economically viable, field processable, high-performance damage-tol￾erant material is emerging. Emphasis on compos￾ite tailoring also brings with it the need to control fiber characteristics to meet the performance need and economic constraints in construction ap￾plications of this new type of FRC. In the next section, broad socioeconomic con￾siderations surrounding materials development in civil engineering in general, and fiber rein￾forced cementitious materials in particular, are described. The section entitled Current Applica￾tions of FRCs summarizes current FRC applica￾tions worldwide, and documents where, how, and why fibers are used in these applications. An at￾tempt is made to extract common denominators among the widely varied applications. Most cur￾rent use of FRCs is in nonstructural or, at most, semistructural applications. The following section describes the research and development and in￾dustrial trends of applying fibers in enhancing structural performance. An actual case study in￾volving a tunnel lining constructed in Japan is given to illustrate how a newly proposed struc￾tural design guideline takes into account the load￾carrying contribution of fibers. Composite proper￾ties related to structural performance are de￾scribed for a number of FRCs targeted for use in load-carrying structural members. Structural ap￾plications of FRCs are currently under rapid de￾velopment. In coming years, it is envisioned that the ultrahigh-performance FRC, with ductility matching that of metals, will be commercially exploited in various applications. Highlights of such a material are described in the section enti￾tled Strain-Hardening Cementitious Composites. In the final section, conclusions on market trends are drawn, and favorable fiber characteristics for structural applications are provided. Emphasis is placed on the need for fiber and surface charac￾teristics most suitable for the ensuing applica￾tions and performance needs of future FRCs. SOCIOECONOMIC CONSIDERATIONS Civil infrastructures are organic, in the sense that they grow with the years. The Akashi-Kaikyo Bridge in Kyoto, Japan, recently completed in April 1998, has the longest suspended span (1990 m) of all bridges in the world. At 450 m, the Petronas Twin Tower in Malaysia (completed in 1996) is the tallest building in the world. No doubt these records will be shattered in the near future. Behind this growth is the development of advanced construction materials. Unfortunately, when put in perspective, civil and building engineering materials development does not have a good track record, in comparison with other industries. Part of the reason comes from the lack of cooperation/coordination between the construction industry and the construction material supplying industry. Especially in the United States, joint research and development between materials suppliers and the construction industry is relatively nonexistent. Such fragmen￾tation between materials development and infra￾structures is not conducive to the healthy growth and maintenance of our societies’ infrastructures. The negative impact of this stance on construc￾tion productivity, durability, and public safety cannot be underestimated. The magnitude of our infrastructure need is enormous. Put in economic terms, about 10% of gross domestic product derives from infrastruc￾ture construction worldwide. In the United States alone, infrastructure construction is a $400 bil￾lion industry involving 6 million jobs. We have approximately $17 trillion worth of infrastruc￾tures in place. Advanced construction materials must contribute to the organic growth of our new infrastructures, and at the same time, contribute to maintaining the health of our infrastructure inventory. The implications of advanced civil en￾HIGH PERFORMANCE APPLICATIONS OF FIBERS 661

ineering materials in the world economy are sig. large amount of materials used in construction the negative impact(through energy consumption There are a number of unique characteristics of and pollution)on our environment can be signif- civil/building engineering materials which set icant. However, we can enable sustainable infra them apart from those used in other industries. structures to be developed by using more recycled These characteristics include materials (e. g, fly ash, silica fumes, and waste bers (or seconds) in infrastructure with en- Low cost-for example, concrete costs $o 1/kg hanced durability (in contrast to eye contact lens which cost n summary, construction materials can, and $100,000/kg) should, play an important role in our infrastruc- Large volume application-e. g, on a ture development and renewal. The obvious im- wide basis. 6 billion tons of concrete pact on society in economics, public safety, and half billion tons of steel are used in the environment must be recognized structure construction annually Durability requirement--our infrastructures generally are designed for much longer life CURRENT APPLICATIONS OF FRCS than consumer goods, e.g., most bridges are Most current applications of fibers are nonstruc designed with a 75-year service life,com tural Fibers are often used in controlling (plastic pared with an automobile with a typical de- and drying) shrinkage cracks, a role classically sign life of 10-20 year played by steel reinforcing bars or steel wire- Public Safety-it goes without saying that mesh. Examples include floors and slabs, large the general public will not tolerate failure of concrete containers, and concrete pavements. In infrastructures. The experiences from the re- cent Northridge earthquake in the United general, these structures and products have ex- States and the Kobe earthquake in Japan tensive exposed surface areas and movement con- straints, resulting in high cracking potential. For serve important lessons such applications, fibers have a number of advan- processed into infrastructures. Construction These include: (a) uniform reinforcement distri workers generally do not have the same kind bution with respect to location and orientation, of training ceramics engineers have. This im- (b)corrosion resistance especially for synthetic plies that the material, if processed at a con- carbon, or amorphous metal fibers, and(c)labor struction site, must be tolerant of low-preci- saving by avoiding the need of deforming the re- sion processing. inforcing bars and tying them in the form-work Thich often leads to reduction of construction The above unique characteristics need to be time. Elimination of reinforcing bars also relaxes bserved when developing advanced construction constraints on concrete element shape. This func- materials. They may be regarded as overall con- tional value of fibers has been exploited in the straints. Only materials meeting such constraints curtain walls of tall buildings. The Kajima Cor will be successfully adopted in the real world. For poration ( Japan) has taken advantage of fibers i FRC, the first two constraints on cost and appli- the manufacture of curvilinear-shaped wall pan cations in large-scale structures imply that fibers els valued for their aesthetics(see, e. g Fig. 1). In cannot be overly expensive and must be used in some applications, the use of fibers enables the relatively small volume content elimination or the reduction in the number of Viewed in a more positive light, some of the cut -joints in large continuous structures such as above constraints also make materials serve as containers(Fig. 2) and pavements. Especially enabling technology for infrastructures. Proper pavements, joints are locations of weaknesses at selection of fiber and matrix materials is critical which failure frequently occurs. Thus, fibers have in producing durable infrastructures. FRCs with been exploited to enhance the durability of con- high ductility lead to safer infrastructures. Mate- crete elements. Some additional representative rials can even lend themselves to improving con- industrial applications of FRCs are shown in Fig struction productivity. For example, the replace- ures 3-5. These examples are chosen to illustrate ment of re-bars in reinforced concrete(R/C)struc- the wide range of fiber used(steel, glass, polymer, tures with FRCs have led to reduction in labor amorphous metal, carbon) and the international cost in construction sites. Finally, because of the nature of FRC applications

gineering materials in the world economy are sig￾nificant. There are a number of unique characteristics of civil/building engineering materials which set them apart from those used in other industries. These characteristics include: ● Low cost—for example, concrete costs $0.1/kg (in contrast to eye contact lens which cost $100,000/kg). ● Large volume application—e.g., on a world￾wide basis, 6 billion tons of concrete and a half billion tons of steel are used in infra￾structure construction annually. ● Durability requirement—our infrastructures generally are designed for much longer life than consumer goods, e.g., most bridges are designed with a 75-year service life, com￾pared with an automobile with a typical de￾sign life of 10–20 years. ● Public Safety—it goes without saying that the general public will not tolerate failure of infrastructures. The experiences from the re￾cent Northridge earthquake in the United States and the Kobe earthquake in Japan serve important lessons. ● Construction labor—materials have to be processed into infrastructures. Construction workers generally do not have the same kind of training ceramics engineers have. This im￾plies that the material, if processed at a con￾struction site, must be tolerant of low-preci￾sion processing. The above unique characteristics need to be observed when developing advanced construction materials. They may be regarded as overall con￾straints. Only materials meeting such constraints will be successfully adopted in the real world. For FRC, the first two constraints on cost and appli￾cations in large-scale structures imply that fibers cannot be overly expensive and must be used in relatively small volume content. Viewed in a more positive light, some of the above constraints also make materials serve as enabling technology for infrastructures. Proper selection of fiber and matrix materials is critical in producing durable infrastructures. FRCs with high ductility lead to safer infrastructures. Mate￾rials can even lend themselves to improving con￾struction productivity. For example, the replace￾ment of re-bars in reinforced concrete (R/C) struc￾tures with FRCs have led to reduction in labor cost in construction sites. Finally, because of the large amount of materials used in construction, the negative impact (through energy consumption and pollution) on our environment can be signif￾icant. However, we can enable sustainable infra￾structures to be developed by using more recycled materials (e.g., fly ash, silica fumes, and waste fibers (or seconds)) in infrastructure with en￾hanced durability. In summary, construction materials can, and should, play an important role in our infrastruc￾ture development and renewal. The obvious im￾pact on society in economics, public safety, and the environment must be recognized. CURRENT APPLICATIONS OF FRCS Most current applications of fibers are nonstruc￾tural. Fibers are often used in controlling (plastic and drying) shrinkage cracks, a role classically played by steel reinforcing bars or steel wire￾mesh. Examples include floors and slabs, large concrete containers, and concrete pavements. In general, these structures and products have ex￾tensive exposed surface areas and movement con￾straints, resulting in high cracking potential. For such applications, fibers have a number of advan￾tages over conventional steel reinforcements. These include: (a) uniform reinforcement distri￾bution with respect to location and orientation, (b) corrosion resistance especially for synthetic, carbon, or amorphous metal fibers, and (c) labor￾saving by avoiding the need of deforming the re￾inforcing bars and tying them in the form-work, which often leads to reduction of construction time. Elimination of reinforcing bars also relaxes constraints on concrete element shape. This func￾tional value of fibers has been exploited in the curtain walls of tall buildings. The Kajima Cor￾poration (Japan) has taken advantage of fibers in the manufacture of curvilinear-shaped wall pan￾els valued for their aesthetics (see, e.g., Fig. 1). In some applications, the use of fibers enables the elimination or the reduction in the number of cut-joints in large continuous structures such as containers (Fig. 2) and pavements. Especially in pavements, joints are locations of weaknesses at which failure frequently occurs. Thus, fibers have been exploited to enhance the durability of con￾crete elements. Some additional representative industrial applications of FRCs are shown in Fig￾ures 3–5. These examples are chosen to illustrate the wide range of fiber used (steel, glass, polymer, amorphous metal, carbon) and the international nature of FRC applications. 662 LI

HIGH PERFORMANCE APPLICATIONS OF FIBERS 663 Figure 1 Japanese curvilinear carbon-FRC curtain Figure 3 French Metglas FRC underground tunnel Durability is an important performance-en hancement characteristic in many industrial FRC applications. Naturally, durability has different connotations in different application contexts. For xample, for containers durability implies the lifetime prior to unacceptable leakage. For pave- Figure 2 Danish pp-FRC containers Figure 4 U.S. glass-FRC wall panels

Durability is an important performance-en￾hancement characteristic in many industrial FRC applications. Naturally, durability has different connotations in different application contexts. For example, for containers, durability implies the lifetime prior to unacceptable leakage. For pave￾Figure 1 Japanese curvilinear carbon–FRC curtain walls. Figure 2 Danish pp–FRC containers. Figure 3 French Metglas FRC underground tunnel linings. Figure 4 U.S. glass–FRC wall panels. HIGH PERFORMANCE APPLICATIONS OF FIBERS 663

at. eo in building foundation cost, hoisting ma- steel reinforcement, and transportation example, the Kajima Corporation claims a reduction In extern structural steel requirement of 4000 tons for the Tokyo Ark- Mori building which used 32, 000 m-of CFRC (carbon fiber FRC)wall panels. Reduction in construction time is highly valued (e. g, in fiber shotcreting of tunnel linings common in Sweden a and Austria) and represents major cost advan- tage in the construction industry There is no question that fibers lead to concrete element performance improvements in a wide range of applications, providing the benefit part of the cost/benefit ratio consideration. Apart from durability against shrinkage cracks, fibers are Figure 5 German steel-FRC airfield pavement. valued for their imparting the concrete element with energy absorption capability-often de- scribed in terms of their impact resistance(e. g ments, durability implies the repair time interval foors and slabs), and delamination and spall re- in order to maintain rideability. The cause of loss sistance (e. g, concrete structure repair). Other of durability is also very much dependent on the rformance improvements include corrosion and specific application and field conditions fatigue resistance. Repair of concrete structures appears to be a To achieve such performance enhancements sizable application of FRCs. This includes resto- two essential properties of FRCs are utilized. As ration of pavements, airfields, bridge decks, and replacements for steel reinforcements and joints floor slabs. With the decaying infrastructure cou- fibers contribute to the shrinkage crack resis- pled with increasing demand in their perfor nce property of the FRC Impact resistance per mance in most industrialized countries, it is ex- formance (and to a certain extent bending pected that the need for durable repairs will in- strength) is linked to the fracture toughness of crease over time. Fundamental understanding of the composite. Fibers are very effective in this durable repairs is lacking at present. However, it respect, much more so than in increasing compos is generally agreed that repair failures are often ite tensile strength or ductility( strain capacity) in related to mechanical property incompatibilit urrent frcs. IThe exception to this“rule”is between the repair material and substrate con- being realized in the laboratory; see Strain-Hard crete. Dimensional stability of the repair material ening Cementitious Composites below.] The and delamination resistance are often cited as shrinkage crack resistance and toughness prop- some of the controlling factors. Fibers can be, and erty of FRCs are well recognized and exploited in have been, used to advantage in this area current concrete element applications in the con- The adoption of new materials in the highly struction industry. Because of the utilization of cost-sensitive construction, building, and precast proved mechanical properties of FRC, some products industries(grouped together as the"con- the"con- dustrial applications can be considered semi struction industry hereafter) generally requires structural. These properties are needed to carry justification of cost advantage. The dollar value of dead loads, handling (or construction) loads, loads durability is difficult to quantify, but durability related to restrains from dimensional changes demand clearly represents one of the driving ete. Wall panels and some pavement applications forces in the use of fibers, especially when shrink- belong to this category. However, in most of these age crack resistance is considered. As mentioned applications, the fibers are not expected to con above, labor saving via elimination of joints or tribute to load-carrying function in the element re-bars provides extra financial incentives. Other Some examples of current industrial applica cost advantages in the use of fibers include ele- tions of FRCs are summarized in Table I. 7 This ment thickness and/or weight reduction, such as table provides a broad overview of wide-ranging in concrete pipes, pavements, and building cur- applications in different parts of the world. How- tain wall panels. In the case of building curtain ever, it is by no means exhaustive. Some of these walls, weight reduction can lead to significant applications are experimental, in the prototyping

ments, durability implies the repair time interval in order to maintain rideability. The cause of loss of durability is also very much dependent on the specific application and field conditions. Repair of concrete structures appears to be a sizable application of FRCs. This includes resto￾ration of pavements, airfields, bridge decks, and floor slabs. With the decaying infrastructure cou￾pled with increasing demand in their perfor￾mance in most industrialized countries, it is ex￾pected that the need for durable repairs will in￾crease over time. Fundamental understanding of durable repairs is lacking at present. However, it is generally agreed that repair failures are often related to mechanical property incompatibility between the repair material and substrate con￾crete. Dimensional stability of the repair material and delamination resistance are often cited as some of the controlling factors. Fibers can be, and have been, used to advantage in this area. The adoption of new materials in the highly cost-sensitive construction, building, and precast products industries (grouped together as the “con￾struction industry” hereafter) generally requires justification of cost advantage. The dollar value of durability is difficult to quantify, but durability demand clearly represents one of the driving forces in the use of fibers, especially when shrink￾age crack resistance is considered. As mentioned above, labor saving via elimination of joints or re-bars provides extra financial incentives. Other cost advantages in the use of fibers include ele￾ment thickness and/or weight reduction, such as in concrete pipes, pavements, and building cur￾tain wall panels. In the case of building curtain walls, weight reduction can lead to significant savings in building foundation cost, hoisting ma￾chinery, steel reinforcement, and transportation cost. For example, the Kajima Corporation claims a reduction in external wall load of 60% and structural steel requirement of 4000 tons for the Tokyo Ark-Mori building which used 32,000 m2 of CFRC (carbon fiber FRC) wall panels. Reduction in construction time is highly valued (e.g., in fiber shotcreting of tunnel linings common in Sweden and Austria) and represents major cost advan￾tage in the construction industry. There is no question that fibers lead to concrete element performance improvements in a wide range of applications, providing the benefit part of the cost/benefit ratio consideration. Apart from durability against shrinkage cracks, fibers are valued for their imparting the concrete element with energy absorption capability—often de￾scribed in terms of their impact resistance (e.g. floors and slabs), and delamination and spall re￾sistance (e.g., concrete structure repair). Other performance improvements include corrosion and fatigue resistance. To achieve such performance enhancements, two essential properties of FRCs are utilized. As replacements for steel reinforcements and joints, fibers contribute to the shrinkage crack resis￾tance property of the FRC. Impact resistance per￾formance (and to a certain extent bending strength) is linked to the fracture toughness of the composite. Fibers are very effective in this respect, much more so than in increasing compos￾ite tensile strength or ductility (strain capacity) in current FRCs. [The exception to this “rule” is being realized in the laboratory; see Strain-Hard￾ening Cementitious Composites below.] The shrinkage crack resistance and toughness prop￾erty of FRCs are well recognized and exploited in current concrete element applications in the con￾struction industry. Because of the utilization of improved mechanical properties of FRC, some in￾dustrial applications can be considered semi￾structural. These properties are needed to carry dead loads, handling (or construction) loads, loads related to restrains from dimensional changes, etc. Wall panels and some pavement applications belong to this category. However, in most of these applications, the fibers are not expected to con￾tribute to load-carrying function in the element. Some examples of current industrial applica￾tions of FRCs are summarized in Table I.7 This table provides a broad overview of wide-ranging applications in different parts of the world. How￾ever, it is by no means exhaustive. Some of these applications are experimental, in the prototyping Figure 5 German steel–FRC airfield pavement. 664 LI