《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

HIGH PERFORMANCE APPLICATIONS OF FIBERS 665 stage of development. They are indicated with an (-$0.004/b ) even for the lowest-cost fiber), and asterisk. The properties utilized, application per- processability(measured in terms of workability formance improvements, and cost advantage or for concrete mixing and casting). In special prod justifications are also included for each applica- uct lines, such as thin roofing tiles and other tion. In this table, the nature of how the FrC has thin-sheet products, as well as in FRC protective been used is identified by the symbols n= non- shields and other products that can tolerate structural, Ss= semistructural, and S= struc- higher cost for additional performance needs tural. Many applications lie in the gray zone be- larger amounts of fibers have been used. Exam tween nonstructural, semistructural, and struc- ples include SifCon(slurry infiltrated concrete tural applications. The classification is therefore invented in the United States and used in airfield somewhat subjective. Even so, it is clear that at pavements) and CRC(compact reinforced con the present time, straight structural applications crete, invented in Denmark and used in safet of FRC are in the minority, but growing vaults). These FRCs have fiber content ranging It is noted that most fibers currently in use are from 5% to 20%. Special processing techniques either steel or polypropylene fibers. These are are required. SIfCON requires bedding of fibers relatively low-cost fibers and generally satisfy the into a concrete form followed by infiltration of the composite property needs and the concrete ele- fiber bed by a high w/e ratio mortar slurry. CRC ment performance needs as described above requires high frequency vibration applied directly Glass fibers have been used extensively in wall to a dense array of steel reinforcements to reach panel type applications. However their real/per cceptable material compaction. For thin-sheet ceived problems in durability appear to have products, the Hatchek technique is common in slowed down their market expansion, at least for processing the composite with high-content fibers the near future. A number of litigation cases in which serve as the main reinforcement in such the United States involving time-delayed crack- products ing of wall panels with glass fibers have added to One of the major drawbacks in many current concerns by end-users. Other fibers used in large FRC applications is that the development of the quantities include cellulose fiber, often used as FRC is often decoupled from the design of the processing aids rather than for their reinforcing concrete element. Furthermore, the detailed ef- capability. As is well known, asbestos fibers (often fect of fiber addition to the composite property, used in thin-sheet elements)are increasingly dis- and hence to the performance improvement of the placed, at least in the United States and in many concrete element is often not quantified. Instead countries in Europe, because of carcinogenic decisions on the choice of fibers and the fiber health hazard potential. Newcomers on the mar- content chosen are often reflections of experience ket for concrete reinforcements are Metglas on the part of the user. Unfortunately, this often (amorphous metal), carbon, and certain high-per- leads to results that fail to meet expectations. A formance polymer fibers. Metglas is produced in good example is the use of steel fibers in pave- France and its applications appear mostly limited ments. Many successful uses of fibers in pave to france at the present time. Production of car- ments have been reported, in some cases even bon and polyvinyl alcohol (PvA) fibers is cur- with the pavement thickness reduced. However, rently led by Japa nese manufacturers, although just as many cases have shown disappointing re- ome production facilities of these fibers have sults. There are a variety of ns for this to the last few years been started up in China. Each happen. The loading condition(environmental or of these fibers has their limitations. For example, mechanical)can be different, e.g., for pavements most carbon fibers are brittle (low bending located in different states. Because of this, there strength or tensile strain capacity), and some is a certain amount of luck factor involved in studies have suggested durability problems in successful applications. A ramification of this re- composites reinforced with certain PVA fibers. sult is that users become disenchanted over the However, manufacturers of these fibers are con- use of fibers The lack of systematic design guide- tinuously advancing the properties of these fibers lines and mixed experience in FRC applic to so that some of these problems may be expected to concrete elements are responsible for slowing the be overcome in the future spread of FRCs to even broader industrial appli- In most applications, fibers are used in less cations, despite their many advantages as de- than 1% by volume. Fiber content in FRC is lim- scribed above ited by cost(cost of fibers are much higher than Although the current application of fibers in Portland cement 03/1b )and aggregates concrete elements is limited in scope, it appears to

stage of development. They are indicated with an asterisk. The properties utilized, application per￾formance improvements, and cost advantage or justifications are also included for each applica￾tion. In this table, the nature of how the FRC has been used is identified by the symbols N 5 non￾structural, SS 5 semistructural, and S 5 struc￾tural. Many applications lie in the gray zone be￾tween nonstructural, semistructural, and struc￾tural applications. The classification is therefore somewhat subjective. Even so, it is clear that at the present time, straight structural applications of FRC are in the minority, but growing. It is noted that most fibers currently in use are either steel or polypropylene fibers. These are relatively low-cost fibers and generally satisfy the composite property needs and the concrete ele￾ment performance needs as described above. Glass fibers have been used extensively in wall panel type applications. However their real/per￾ceived problems in durability appear to have slowed down their market expansion, at least for the near future. A number of litigation cases in the United States involving time-delayed crack￾ing of wall panels with glass fibers have added to concerns by end-users. Other fibers used in large quantities include cellulose fiber, often used as processing aids rather than for their reinforcing capability. As is well known, asbestos fibers (often used in thin-sheet elements) are increasingly dis￾placed, at least in the United States and in many countries in Europe, because of carcinogenic health hazard potential. Newcomers on the mar￾ket for concrete reinforcements are Metglast (amorphous metal), carbon, and certain high-per￾formance polymer fibers. Metglas is produced in France and its applications appear mostly limited to France at the present time. Production of car￾bon and polyvinyl alcohol (PVA) fibers is cur￾rently led by Japanese manufacturers, although some production facilities of these fibers have in the last few years been started up in China. Each of these fibers has their limitations. For example, most carbon fibers are brittle (low bending strength or tensile strain capacity), and some studies have suggested durability problems in composites reinforced with certain PVA fibers. However, manufacturers of these fibers are con￾tinuously advancing the properties of these fibers so that some of these problems may be expected to be overcome in the future. In most applications, fibers are used in less than 1% by volume. Fiber content in FRC is lim￾ited by cost (cost of fibers are much higher than Portland cement (; $0.03/lb.) and aggregates (; $0.004/lb.), even for the lowest-cost fiber), and processability (measured in terms of workability for concrete mixing and casting). In special prod￾uct lines, such as thin roofing tiles and other thin-sheet products, as well as in FRC protective shields and other products that can tolerate higher cost for additional performance needs, larger amounts of fibers have been used. Exam￾ples include SIFCON (slurry infiltrated concrete, invented in the United States and used in airfield pavements) and CRC (compact reinforced con￾crete, invented in Denmark and used in safety vaults). These FRCs have fiber content ranging from 5% to 20%. Special processing techniques are required. SIFCON requires bedding of fibers into a concrete form followed by infiltration of the fiber bed by a high w/c ratio mortar slurry. CRC requires high frequency vibration applied directly to a dense array of steel reinforcements to reach acceptable material compaction. For thin-sheet products, the Hatchek technique is common in processing the composite with high-content fibers which serve as the main reinforcement in such products. One of the major drawbacks in many current FRC applications is that the development of the FRC is often decoupled from the design of the concrete element. Furthermore, the detailed ef￾fect of fiber addition to the composite property, and hence to the performance improvement of the concrete element is often not quantified. Instead, decisions on the choice of fibers and the fiber content chosen are often reflections of experience on the part of the user. Unfortunately, this often leads to results that fail to meet expectations. A good example is the use of steel fibers in pave￾ments. Many successful uses of fibers in pave￾ments have been reported,3 in some cases even with the pavement thickness reduced. However, just as many cases have shown disappointing re￾sults.4 There are a variety of reasons for this to happen. The loading condition (environmental or mechanical) can be different, e.g., for pavements located in different states. Because of this, there is a certain amount of luck factor involved in successful applications. A ramification of this re￾sult is that users become disenchanted over the use of fibers. The lack of systematic design guide￾lines and mixed experience in FRC applications to concrete elements are responsible for slowing the spread of FRCs to even broader industrial appli￾cations, despite their many advantages as de￾scribed above. Although the current application of fibers in concrete elements is limited in scope, it appears to HIGH PERFORMANCE APPLICATIONS OF FIBERS 665

Table I FRC Industrial Applications Performance Applications Ve(%) S? Properties Utilized Cost reduction ement""full pp monofils SS MOR, toughness pete with steel n Shrinkage crack res. Durability Crackstop o shrinkage control steel n Wear resistance ability Less than complete Canada op rutting of Life-cost Denmark Stang. 94 SIFCON 0.75 nergy absorption Impact Fatigue Life-cost = n Elastic modulus Compatibility with substrate conerete N Toughness Reduced thickne Canada Johnston. 9 1.7-25 SS Toughness Denmark Ramboll ustrial Metglas Adhesion 3MPa. Self-leveling, Chem. Life-cost France Lanko MPa. MOR 12 Shock, abrasion Industrial floor steel Ductility isting base mage res from Rendering, flo PP N No need for sand Denmark screeding resist, crack stop ngth and Floors Slabs pp 0.1 Shrinkage crack re ife-cost 300K m2 Glavind enmark Stang, 94 replaces mesh, reduce nsitop Broc. liability metglas Chemical res Parking garage pp n Shrinkage crack re Durability No steel mesh Denmark mm thick slabs 16x8 Shrinkage crack res. Seis mic force red. Build, weight resion Ss Shrinkage crack res. Durability Replace steel rein Mufti et al. 93 hear resistance Curtain wall carbon CFRC Broe Transp. oost red. all panels Low density inless Clubhouse n shells 65Km2 uilding foundation cost

Table I FRC Industrial Applications Applications Fiber Vf (%) S? Properties Utilized Performance Improvements Cost Reduction Amount Appl. & Location Reference Pavement overlay* 35 m long, 10 cm thick pp 1steel 0.75 1 0.75 SS Shrinkage crack res. Tensile strain cap. Durability: no failure at joints Thick. red. to 1⁄2 No steel reinf. No cut joint Denmark Glavind, ’93; Ramboll Hannemann & Hojlund, ’92 Pavement 75– 175 mm thick steel 0.5–1 SS Shrinkage crack res. Flexural strength Durability? Greater joint spacing Canada Balaguru & Shah, ’92 Pavement* “full depth” Thin bridgedeck overlay pp monofils 1 SS MOR, toughness Impact resistance chemical resistance fatigue resistance Compete with steel fibers US Van Mier, ’95 Ramakrishnan, ’93 Pavement 200 mm thick, 80 m long pp 0.7 N Shrinkage crack res. Durability No steel No shrinkage control joint U.K. Crackstop News, No. 1, ’90 Pavement whitetopping 100 mm steel 1 N Wear resistance Durability Stop rutting of asphalt Noise reduction Less than complete replacement of flex. pavement Canada Johnston, ’95 Repair Pavement pp 1–1.5 N Toughness Interface bond Crack res. Delamination res. Life-cost Denmark Glavind & Stang, ’94 Repair Airfield pavement SIFCON steel 5 0.75 SS Toughness Interface bond Energy absorption MOR Tensile strain cap. Crack & spall res. Delamination res. Impact res. (dyn. load from planes) Fatigue res. Life-cost Simplicity in slip￾form paving Incr. in joint spacing Glavind & Stang, ’94 Balaguru and Shah, ’92 Germany Harex fiber broc. Repair Airfield runway patch steel ? N Elastic modulus COE Compatibility with substrate concrete Durability Life-cost US Balaguru & Shah, ’92 Repair Bridge substructure steel pp 0.3 0.2 N Toughness Fatigue res. Impact res. Reduced thickness Canada Johnston, ’95 Repair General pp 1 steel 1.7–2.5 SS Toughness Interface bond Crack res. Delamination res. Life-cost No shrink. reinf. Thick. red. Denmark Ramboll Hannemann & Hojlund, ’92 Industrial floor restoration Metglas 1 SS Adhesion 3MPa, Compress. 80 MPa, MOR 12 MPa Self-leveling, Chem. corr. res. Shock, abrasion, crack res. Life-cost France St. Gobain, Lanko Industrial floor rehabilitation Thin overlay steel 0.5 SS Ductility Toughness Long term bond to existing base Spall res. Damage res. from forklift Reduce production facility downtime Long term performance US Smith, R., ’95 Rendering, floor screeding pp ? N Shrinkage crack resist, crack stop Durability No need for sand 3strength and bond Denmark D. Davis, Danaklon lit. Floors & Slabs pp 0.1 n Shrinkage crack res. Toughness Durability Life-cost 300K m2 , Denmark Glavind & Stang, ’94 steel 0.3–0.5 “1 energy absopt., MOR, toughness Impact res. (dyn. wheel load form fork lift); Easy processing, High reliability Spall res. Fatigue res. replaces mesh, reduce labor, slab thickness, incr. joint spacing, faster construction, lower maint. cost Bache, ’92 Densitop Broc. Bekaert Broc. Metglas Chemical res. St. Gobain, Lanko Parking garage floor 150 mm thick slabs 16 3 8 m pp 0.9 N Shrinkage crack res. Durability No steel mesh Denmark Crackstop News, No. 1, ’90 Bridge deck slabs* pp 0.88 SS Shrinkage crack res. Shear resistance Durability Replace steel reinf., Caontrol corrosion Canada Mufti et al, ’93 Curtain wall panels carbon 2–4 SS Low density Strength Shrinkage crack res. Light-weight Seismic force red. Fire res. Dim. stability Durability Build. weight red. Found. cost red. Steel red. Transp. cost red. Erec. cost red. Constr. time red. Shape flexibility 300K m2 Japan CFRC Broc., Kajima Wall panels carbon 2 SS MOR Low density Avoid corner damage & cracking Durable against sunlight, heat and salt Increase design flexibility Light-weight Kitakyus hu Prince Hotel 12 tons Japan Mitsubishi Kasei Broc. Ando, Lightweight cladding panels skin 40,75 mm thick stainless steel 1.3 SS MOR Low density Durability, Res. wind load Sail Clubhouse Australia Fibresteel, Vol 4 No. 1, ’92 Thin shells & facades AR glass 4–5 SS Shrinkage crack res. Tensile strength Toughness MOR Durability Shape desg flex. No steel reinf. Low weight per unit area, building deadload, foundation cost 65K m2 , Denmark Glavind & Stang, ’94 666 LI

HIGH PERFORMANCE APPLICATIONS OF FIBERS 667 Table i continued Performance S? Properties Utilized Cost reduction Reference Tunnel linings ste Strength, MO Durability Energy absorption Better bonding to 3: Maage Broe Metglas >25 kg/'m Shoterete. St Gobain lit. Crack resistance ability fatigue re Van Mier et chem. resistance n Abrasion rs n Shrinkage crack res Poland s出mw 25-30K m. Glavind Stang, 94 Fiberbeton steel reinf. Bending load res Wall thick. rec Australia No. 1, 92 0.3-0.5 Bending load res. nical w/o wire- Belgium Dramix broe. steel 1.75 Bending load res ck. red to 2 Denmark oors Metglas S Ductility Lightweight, Replace steel, sam France St. Gobain lit. aname energ weight, lower cost Dsorption CRC steel High-cost Denmark nergy Absorp. steel? Ss Energy absorption Impact Plastic shrinkage Denmark SS Tensile Thermal shock re Belgium thermal shock resist Columns(RPC steel 2-4 s Strength, Toughness Seismic resistance Slender columns France Richard & Cheyney, Column/slab CRC steel S Toughness Short development Building system Van Mier et al S Truss members Netherlands van et al Roofing tiles 4-5 Life-cost enmark Glavind extruded or engi age crack res. Durability rength steel reinf. poss. Stang, 94 Light-weight Life-cost products for o steel reinf. po cladding Toughness Ferrocem N rst erack Life-cost Shirai and Ohama, 95 Pakeaging and Metglas n Microcrack resist dioactivity 300 yr containers St, Gobain lit. Stair treads PVA Rust resistance Light-weight (Kajima KaTRI Broe *Experimental

Table I Continued Applications Fiber Vf (%) S? Properties Utilized Performance Improvements Cost Reduction Amount Appl. & Location Reference Tunnel linings steel 0.5–1 S Strength, MOR Toughness Energy absorption Shrinkage crack res. Safety Durability Better bonding to underlay Maintain contour Water tightness Replace wire-reinf., No reinf. corrosion Constr. time & labor red. (with shotcreting) Thickness red. Constr. safety 80K m3/yr., Norway Skerendale, ’94 Horri & Nanakorn, ’93; Maage, M., ’94 Bekaert Broc. EE-fiber Broc. St. Gobain Broc. Metglas .25 kg/m3 Sewage network linings* Metglas SS MOR Crack resistance Corrosion resistance Durability Replace wire-mesh, labor, Reduce thickness Shotcrete, France St. Gobain lit. Drainage canal in tunnel CRC steel 6 S MOR fatigue resistance durability (100 yrs) non-conducting (elec. sys. of train) chem. resistance Thin cover 40K element 500x400x 40 mm3, Denmark Van Mier et al., ’95 Wear linings, hydraulic structures steel N Abrasion rs. Durability Life-cost Denmark Glavind & Stang, ’94 Underground railway system pp “sm. amt.” N Shrinkage crack res. Durability Poland Brandt et al, ’94 Containers agriculture process sludge purifying pp 2 SS Shrinkage crack res. Elastic modulus Durability Water-tightness Mat’l cost 2x thickness red. No cut joint’ No steel reinf. 25–30K m3 , Denmark Glavind & Stang, ’94 Fiberbeton R&S, Denmark Septic tanks steel ? SS MOR Bending load res. Wall thick. red., Labor & mat’l red. Mass & weight red. Cost less than mesh Australia Fibresteel, V.4 No. 1, ’92 Pipe* steel 0.3–0.5 SS MOR Crack res. Ductility Bending load res. Spall res. Corrosion res. Economical w/o wire￾mesh reinforcement Belgium Dramix broc. and design doc. Pipe* steel 1.75 SS MOR Bending load res. Wall thick. red. to 1⁄3 of normal Denmark Thygesen, ’93 Pedersen & Jorgen, ’92 Anti-blast doors military shelters Metglas ? S Ductility Lightweight, Dynamic energy absorption Replace steel, same weight, lower cost France St. Gobain lit., Dynabeton by Sogea Security products CRC steel 6 S Strength Ductility Energy Absorp. Impact Res. High-cost Denmark Bache, ’87 Vaults and safes steel 1–3 S Energy Absorp. Impact Res. Thickness reduction (;2⁄3) U.S. Balaguru & Shah, ’92 Tetrapods (dolosse) steel? ? SS Energy absorption Impact res. 30K m3 Australia Engineer update, ’84 Sea defense work concrete pp 0.9 N Plastic shrinkage crack res. Durability against wind/exposure 4 tonnes, Denmark Crackstop News, No. 1, ’90 Refractories Stainless steel ? SS Tensile MOR Thermal shock resis. Spall resist. Durability Reliability Belgium Bekaert Broc. Refractories e.g. lip rings for iron ladles, furnace hearths stainless steel ? SS thermal shock resist. U.S. Lankard, ’92 Columns (RPC in steel tube) steel 2–4.5 S Strength, Toughness Seismic resistance Slender columns France Richard & Cheyrezy, ’94 Column/Slab cast-in-place joint CRC steel ? S Toughness Short development length for reinf. Building system flexibility Denmark Van Mier et al, ’95 Truss-system* SIFCON ? S Tensile Compress. strength Truss members Netherlands Van Mier et al, ’95 Roofing tiles (extruded or Hatschek) cellul. pp wollas. 4–5 N Shrinkage crack res. Tensile strength Toughness MOR Durability Life-cost No steel reinf. poss. Light-weight Denmark Glavind & Stang, ’94 Thin sheet products for cladding asbestos cellul. pp glass PVA carbon varies N Shrinkage crack res. Tensile strength Toughness MOR Durability Life-cost No steel reinf. poss. Light-Weight Europe Bentur, A., ’95 Ferrocement column steel carbon 1 5 N First crack res. MOR Corrosion res. Durability Red. in crack width Life-cost Japan Shirai and Ohama, ’95 Pakcaging and storage nuclear waste Metglas N Microcrack resist. Contain radioactivity Durability 300 yr. containers France St. Gobain lit. Sogefibre Stair treads PVA 2 SS Low denstiy Strength Toughness Rust resistance Light-weight Boltable Life-cost Japan (Kajima) Yurugi et al, ’91 KaTRI Broc. *Experimental. HIGH PERFORMANCE APPLICATIONS OF FIBERS 667

be gaining ground with documented successes in ments in first crack and ultimate member various parts of the world. The sluggish growth in strength, impact resistance, and shear resistance FRC applications is influenced by many factors, If properly designed, fibers can add to member including: 1. the high cost of fiber compared with structural performance even when used together other constituents of concrete: 2. the cost-sensi- with conventional steel main reinforcements (re- tive nature of the construction industry; 3. the bars). Some highlights of these laboratory find mixed experience in the use of FRC in certain ings are summarized in the section below. applications; and 4. the unclear linkage between Currently, several construction projects are fiber and concrete element performance. Both contemplating the application of fibers in load end-users and fiber suppliers need to be realistic carrying concrete members. The concrete tunnel- in what each type of fiber can do to concrete ning project in Japan appears to be the most element performance. Research is needed to con- advanced one, both in time and in implementing tinuously improve the benefits brought about by the fiber load-carrying capacity into the design fibers, while reducing the cost of fiber applica- calculation. This project is described in a later tions. Users need to be educated that part of the section. This case, together with the laboratory fiber cost can be offset by reduction or elimination studies of FRC structural members, suggest that of other costs using conventional concrete without the a-8 relation is the most useful property char fibers. as described in this section. acterization of FRCs for structural design Means The cost pressure will always be present. One of FRC structural performance comparison are way of overcoming this pressure is to continu- indicated at the end of this section ously and systematically enhance the benefit/cost ratio. Structural load-bearing capacity of fibers appears to be a significant benefit reaching be. Laboratory Studies of Structural Applications of frc yond laboratory curiosity and emerging in indus trial settings at the present time Fibers designed There have been a large amount of laborator with this function in mind, with proper surface studies of applications of FRCs in R/C and pre- treatment for fresh(FRC rheological) properti stressed concrete structural members This sec- and hardened composite properties, can contrib- tion summarizes the highlights of these studies ute significantly to future advanced structural which demonstrate without a doubt that fibers members. The emerging trend of structural appli- can be effective in enhancing structural strength cations of frc is described in the next section and ductility in load-carrying members studies include members under fexural torsion, and combined loads. Additionally STRUCTURAL APPLICATIONS OF FRC tural component responses under cyclic load and bond property of reinforcing steel bars have also At present. despite much research in the labora- been studied. Most of these studies have been tory, the use of FRC in load-carrying structural limited to steel fibers. More detailed descriptions members is very limited. Using fibers to carry of the test methods and parameters as well as the load across cracks in a hardened concrete in original references can be found in Balaguru and structural design is still a novel practice. This is Shah.3 because of a lack of clear understanding in how In fexural r/c members the addition of fibers fibers contribute to load-carrying capacity, confu- improves the modulus of rupture (bending sion between material and structural strengths, strength). Especially in over-reinforced concrete lack of structural design guidelines for FRC mem- beams, the significant gain appears to be in the bers, uncertain cost/benefit ratio, and insufficient enhancement of post-peak structural ductility material property specification, characterization, (Fig. 6), a quantity valued by structural and test standards. These deficiencies not only for safety reasons. This ductility improvement limit the broader use of fibers in structural appli likely a result of the delay in compression crush cations, but also make it difficult for fiber suppli by pression strain capacit ers to optimize their fibers for concrete structural due to fiber reinforcement. The potential for over- reinforcement is greater when higher strength Research findings in the last decade clearly steel or FRP(fiber reinforced plastic rod)is used establish that ductility of certain structural mem- as reinforcement. For under-reinforced beams or bers can be greatly enhanced with the use of beams with no main reinforcement at all, flexural fibers. In addition, fibers generally favor improve- strength enhancement and post-peak ductility

be gaining ground with documented successes in various parts of the world. The sluggish growth in FRC applications is influenced by many factors, including: 1. the high cost of fiber compared with other constituents of concrete; 2. the cost-sensi￾tive nature of the construction industry; 3. the mixed experience in the use of FRC in certain applications; and 4. the unclear linkage between fiber and concrete element performance. Both end-users and fiber suppliers need to be realistic in what each type of fiber can do to concrete element performance. Research is needed to con￾tinuously improve the benefits brought about by fibers, while reducing the cost of fiber applica￾tions. Users need to be educated that part of the fiber cost can be offset by reduction or elimination of other costs using conventional concrete without fibers, as described in this section. The cost pressure will always be present. One way of overcoming this pressure is to continu￾ously and systematically enhance the benefit/cost ratio. Structural load-bearing capacity of fibers appears to be a significant benefit reaching be￾yond laboratory curiosity and emerging in indus￾trial settings at the present time. Fibers designed with this function in mind, with proper surface treatment for fresh (FRC rheological) properties and hardened composite properties, can contrib￾ute significantly to future advanced structural members. The emerging trend of structural appli￾cations of FRC is described in the next section. STRUCTURAL APPLICATIONS OF FRC At present, despite much research in the labora￾tory, the use of FRC in load-carrying structural members is very limited. Using fibers to carry load across cracks in a hardened concrete in structural design is still a novel practice. This is because of a lack of clear understanding in how fibers contribute to load-carrying capacity, confu￾sion between material and structural strengths, lack of structural design guidelines for FRC mem￾bers, uncertain cost/benefit ratio, and insufficient material property specification, characterization, and test standards. These deficiencies not only limit the broader use of fibers in structural appli￾cations, but also make it difficult for fiber suppli￾ers to optimize their fibers for concrete structural applications. Research findings in the last decade clearly establish that ductility of certain structural mem￾bers can be greatly enhanced with the use of fibers. In addition, fibers generally favor improve￾ments in first crack and ultimate member strength, impact resistance, and shear resistance. If properly designed, fibers can add to member structural performance even when used together with conventional steel main reinforcements (re￾bars). Some highlights of these laboratory find￾ings are summarized in the section below. Currently, several construction projects are contemplating the application of fibers in load￾carrying concrete members. The concrete tunnel￾lining project in Japan appears to be the most advanced one, both in time and in implementing the fiber load-carrying capacity into the design calculation. This project is described in a later section. This case, together with the laboratory studies of FRC structural members, suggest that the s–d relation is the most useful property char￾acterization of FRCs for structural design. Means of FRC structural performance comparison are indicated at the end of this section. Laboratory Studies of Structural Applications of FRC There have been a large amount of laboratory studies of applications of FRCs in R/C and pre￾stressed concrete structural members. This sec￾tion summarizes the highlights of these studies, which demonstrate without a doubt that fibers can be effective in enhancing structural strength and ductility in load-carrying members. These studies include members under flexural, shear, torsion, and combined loads. Additionally, struc￾tural component responses under cyclic load and bond property of reinforcing steel bars have also been studied. Most of these studies have been limited to steel fibers. More detailed descriptions of the test methods and parameters as well as the original references can be found in Balaguru and Shah.3 In flexural R/C members, the addition of fibers improves the modulus of rupture (bending strength). Especially in over-reinforced concrete beams, the significant gain appears to be in the enhancement of post-peak structural ductility (Fig. 6), a quantity valued by structural engineers for safety reasons. This ductility improvement is likely a result of the delay in compression crush￾ing by increasing the compression strain capacity due to fiber reinforcement. The potential for over￾reinforcement is greater when higher strength steel or FRP (fiber reinforced plastic rod) is used as reinforcement. For under-reinforced beams or beams with no main reinforcement at all, flexural strength enhancement and post-peak ductility 668 LI