CHAPTER 4 APPLICATIONS OF COMPOSITES IN CIVIL ENGINEERING V. M. Karbhari SCOPE OF THE STUDY It is essential that this chapter be prefaced with the note that the subject of this chapter was initially not considered as being of sufficient importance to warrant a separate chapter in the report. However, it turned out to be the important point of difference between new developments in the U.S. and those in Japan. Although it was known to some in the panel that the Japanese composites community had been making strong overtures to the civil engineering area over the past five years, the magnitude of their commitment to this new and emerging market was simply not comprehended. This chapter thus is intended to only briefly touch upon the subject, as a full and comprehensive treatment would be beyond the scope of the present report. This should, however, be in no way construed to suggest that the study did not unearth a large body of useful information; rather the amount was so large that it was viewed as being overwhelming for the overall report. INTRODUCTION Before beginning a brief description of Japanese activities in the civil engineering area, it is worthwhile to list the reasons behind the rapid development and growth of this area in Japan, where despite efforts by U.S. companies such as DuPont, Hercules and Dow over the past decade, very little real advance (in terms of market penetration) has been seen in the U.S. 1. A shortage of skilled labor combined with an aging workforce This presents a special challenge to Japanese construction firms in retaining their global position. Simplified construction methods, resulting from the use of lighter materials that are easier to handle and can be largely prefabricated, are major drivers pushing the use of composites. 2. Societal preoccupance with neatness and aesthetics The potential of having cleaner work sites while simultaneously increasing the capability of integrating form and function with aesthetics makes the use of composites and advanced materials attractive. 3. The predominance of a marine environment Japan's major urban and industrial centers are all within a marine environment that makes corrosion of steel a constant problem. The constant deterioration of steel and even wooden structures provides a strong impetus for the use of corrosion- and degradation-resistant materials. 4. Growth in population and the corresponding increased demand on transportation and related infrastructure Infrastructure in Japan has been overwhelmed by a level of usage not foreseen. In addition to previous poor design and construction practices that resulted in accelerated deterioration, lack of large spaces for expansion has led to the search for innovative solutions. 5. Earthquakes and seismic activity The need for lighter construction materials and more seismic resistant structures has placed high emphasis on the use of new and advanced materials that can not only decrease dead weight but can also absorb the shock and vibration through tailored microstructures. Similar objectives are seen for retrofit/rehabilitation/strengthening of pre-existing structures that have to be retrofitted to make them seismic resistant, or to repair damage caused by seismic activity. 6. Close link between materials suppliers and construction industry A major barrier to the acceptance of composites by the construction industry in the U.S. is the lack of connection between the materials suppliers and construction industry at a level higher than salesman/potential customer. The keiretsu structure has already forged strong business links between these groups in Japan, whereby each has the potential for using the other as a demonstration of capabilities or as a quick and ready resource center. 7. Research and development laboratories in the civil construction area Whereas large construction companies in the U.S. have no R&D centers, there are as many as 15 such centers in Japan -- funded and managed by individual companies. Thus the search for and the development of new and improved materials begins with the company rather than from the outside, thereby increasing its acceptance. 8. Codes and regulations A significant difference between procedures in the U.S. and Japan is that the construction industry is far less curtailed by codes and regulations in Japan than it is in the U.S. The flexibility afforded to them in experimenting with new materials and structural forms is higher. This in no way should be taken to mean that they are any less responsible or liable than their U.S. counterparts; rather, Japanese companies feel individually responsible for the structures they build. However, it is much easier for them to build without completely qualifying the materials of construction as long as viability has been proven. The time taken to get through the bureaucracy is also often much less. 9. Positioning and global competitiveness Japanese construction companies and the materials industry were quick to realize that the reduction in defense spending would lead to enormous opportunities for application of composites in the infrastructure area, and began to commit their resources at an early date, so as to gain a competitive edge. The competitive position of Japanese construction companies in the international arena (especially in the Middle East) has also made it possible for them to initiate the use of new materials earlier (such as the use of carbon fiber reinforced concrete in the Al-Shaheed monument in Iraq by Kajima Corporation). 10. The critical need to find a use for carbon fiber Although carbon fiber is produced worldwide, Japanese companies have been more aggressive not only in finding new markets, but also in trying to develop them (the use of the keiretsu and more advantageous code regulations no doubt are factors as well). This may in part be due to the higher overall carbon fiber production capacities in Japan as compared with those in the U.S. 11. Willingness to establish demonstration sites Materials suppliers in Japan appear to be more willing to use their own structures as demonstration sites for their products (Shimizu through the use of NEFMAC in their building, Mitsubishi Kasei and Tonen Corporation through the use of carbon fiber for rehabilitation, etc.) than their U.S. counterparts. Part of this is no doubt due to codes, but a large part is in essence their willingness to make major investments towards long term goals, rather than being tied to quarterly earnings (as in the U.S.). This chapter discusses the use of advanced composites in Japan in grid-type structures. Other uses, including short and continuous fiber, cable-typed elements, 3-D and grid structures, and applications in retrofit and rehabilitation will be covered in future publications by this author. This was found to be the best way to maintain the original focus of this study, which was composites in general and not just civil infrastructure applications. The development of the civil engineering market will also be discussed. It should, however, be noted that the cost-competitiveness of the products compared to traditional construction material is based on claims that the panel did not attempt to check, and hence should be treated with a degree of caution. However, it is clear that the Japanese are far ahead of the U.S. in the development (and in the capturing) of this new market and are steadily increasing their lead. Rather than present a detailed list of the motivation and background for the use of composites in infrastructure, the interested reader is referred to Karbhari (1993) and Ballinger (1992). In the context of this report, we discuss pertinent developments in the area of grid-type structures. GRID-TYPE STRUCTURES Although a majority of developments in the area of composite reinforcement for concrete have focused on the investigation of composite rebar, it must be stressed that the specific form is not the best application of composites, due to reasons related to bond development. In this section, we describe a representative 2-D grid structure called NEFMAC (New Fiber Composite Material for Advanced Concrete) as shown in Figure 4.1. Figure 4.1. Schematic of NEFMAC Grid - Graphics File ***.GIF NEFMAC is a grid-type reinforcement for concrete structures. It consists of high-performance fibers such as glass, carbon, aramid, and hybrids, impregnated with resin systems ranging from vinylesters and other thermosetting resin systems to thermoplastics. Besides the inherent corrosion resistance, the grid form itself is advantageous in that the intersections provide anchorage and mechanical interlock in the concrete, facilitating good stress transfer. Again, due to the non-corrosive and alkali resistant (based on resin selection) nature of the grid, cover requirements are reduced, resulting in lighter slabs and other concrete elements. A listing of applications is given at the end of this section. NEFMAC is produced by the NEFCOM corporation -- a cooperative venture between Shimizu Corporation and Asahi Glass Matex Company (formerly Dainihon Glass Industrial Company). The actual method of production is shown in the schematic in Figure 4.2, and is termed "pin winding." The process is similar to filament winding in that individual fibers/tows are placed in prespecified patterns after being impregnated in a wet-bath. The process is a semi-batch type operation, unlike the continuous operation of forming NESTEM geosynthetic material for soil reinforcement. In the NEFMAC process a series of continuous fibers are dispensed from individual creels by a mechanical system, through a wet-bath to be deposited by two orthogonal traveling (winding) heads. The heads are moved at synchronized speeds that define the size of the grid. Successive movement of the heads results in fiber cross-over and placement of interlocking layers until the desired content/cross-sectional area is achieved. The process is currently capable of line speeds as high as 2 m/min in continuous mode, with about 200 m(2) of grid produced per hour. Cure is achieved through the use of either infra-red or ultraviolet heat sources assisted by peroxide catalysts in the resin system. Post-cure is conducted at room temperature. A list of primary characteristics and their resulting features is given in Table 4.1. Figure 4.2. Schematic of the Pin-Winding Process - Graphic File ***.GIF Four basic types of NEFMAC are available based on the type of fibers used. A comparison of gross properties is given in Table 4.2 and representative stress-strain profiles are shown in Figure 4.3. A wide variety of fiber types are used within these broad classes, the details of which are given in Table 4.3. Table 4.1 Principal Characteristics of NEFMAC CHARACTERISTICS FEATURES/ADVANTAGES Non-corrosive Improved durability and needs less concrete cover resulting in lower thickness and weight Excellent Depends largely on resin selection. Improved resistence to durability and ease of use in conditions alkalis, acides where damage/deterioration by salt, chemicals and chemicals or extremes of cold are expected. Continuous fibers Good performance attributes without local "wrinkling" as seen in pultruded rods. Easy fabrication of hybrids. Non-magnetic Electromagnetic transparency resulting in ease of use in ospital and for rooms where electromagnetic transparency is required. Light-weight Specific gravity of less than 2 - results in ease of transportation and placement. Also results in overall lighter structures. Tailorability Due to potential for hybrids and shaping, grids can be made to easily follow contours such as for tunnel linings. Figure 4.3 Typical Stress-Strain Profiles - Graphic File ***.GIF Table 4.2 Main Types of NEFMAC Based on Reinforcement Type (Vinylester Resin Based) TYPE FIBER SPECIFIC TENSILE TENSILE MODULUS GRAVITY STRENGTH OF ELASTICITY kg/mm(2) kg/mm(2) A Aramid 1.28 130 5,700 C Carbon 1.42 120 10,000 G Glass 1.70 60 3,000 H Glass/Carbon 1.65 53 3,700 Hybrid þ Figure 4.3. Typical Stress-Strain Profiles - Graphic File ***.GIF Table 4.3. Details of Fiber Type - Graphic File ***.GIF It is interesting to note that the range is wide and includes fibers manufactured in Japan (Torayca - Toray Industries, Besfight - Toho Rayon Company, Technora - Teijin) and abroad (Kevlar 49 - DuPont). The hybrid, using a combination of glass and carbon, is designed to have a proportional limit and bi-linear stress-strain profile, similar to that of steel. Other hybrids such as high strength or high-modulus carbon and aramids are also available, based on specific needs. The size of a NEFMAC grid is given by specifying the area of the bars and the interval spacing. Figure 4.4 gives a detailed schematic of the grid with details of geometrical specifications. Figure 4.4. Geometrical Features of NEFMAC - Graphic File ***.GIF The cross-sectional area varies from 32 - 3806 mm(2) for glass, carbon and aramid based NEFMAC grids, and from 284 - 3806 mm2 for hybrid grids. Typical interval spacings are 25, 50, 75, 100 and 150 mm (nominally 1, 2, 3, 4 and 6 inches). Although the standard profiles are flat panel-type structures, L and curved profiles are also available, as are full 3-D cage type structures that include shear reinforcement. Standard specifications of the NEFMAC grid are given in Table 4.4.1 Within the limits of this chapter we will briefly review the use of NEFMAC in three applications: (1) slabs, (2) shotcrete reinforcement in tunnels, and (3) 3-D reinforcement in beams. Table 4.4 Standard Grid Specifications (Available Commercially) FIBER TYPE BAR NO. SECTIONAL MAX. LOAD STANDARD AREA (mm(2)) CAPACITY WEIGHT (tonf) (g/m) Aramid A6 16.2 2.1 21 A10 36.2 4.7 46 A13 60.0 7.8 77 A16 92.3 12.0 118 A19 136.0 17.7 174 Carbon C6 17.5 2.1 25 C10 39.2 4.7 56 C13 65.0 7.8 92 C16 100.0 12.0 142 C19 148.0 17.7 210 C22 195.0 23.4 277 Glass G2 4.4 0.26 7.5 G3 8.7 0.52 15 G4 13.1 0.78 22 G6 35.0 2.10 60 G10 78.7 4.7 130 G13 131.0 12.0 220 G16 201.0 17.7 342 G19 297.0 510 Carbon/Glass H6 39.5 2.1 65 Hybrid H10 88.8 4.7 147 H13 148 7.8 244 H16 223 12.0 368 H19 335 17.7 553 H22 444 23.4 733 Slabs NEFMAC reinforcement has wide application in concrete slabs due to its corrosion and chemical resistance, its light weight, and its need for significantly less cover. A comparison of the behavior of the reinforcement types used in one study is shown in Table 4.5, and a schematic of the slab reinforcement is given in Figure 4.5. Table 4.5 Comparison of Reinforcements REINFORCEMENT MAXIMUM YOUNG'S MODULUS STRAIN AT MAX. LOAD (tons) (kg/mm(2)) LOAD (æm) Glass Fiber in Vinylester 2.23 2,910 23,100 ³ Glass/Carbon Hybrid in Unsaturated Polyester 2.09 4,990 14,900 Glass/Carbon Hybrid in Vinylester 2.22 4,590 14,800 ³ Steel Mesh 1.80 18,100 15.1* * = % Elongation An overall comparison of behavior is given in Figure 4.6, which also shows the effect of temperature. It was concluded that deflections in NEFMAC were comparable to those with steel until 600øC, with almost no recognizable differences. The Japanese code for allowable deflection is also met by the NEFMAC grids at the one-hour fire resistant levels under specific design details. Shotcrete Reinforcement in Tunnels NEFMAC shows considerable potential for use as reinforcement of shotcrete in tunnels because of its corrosion and chemical resistance, its light weight, and its ease of forming to fit curvatures. A typical M-þ curve comparing NEFMAC reinforced and welded wire fabrics reinforced shotcrete panels is shown in Figure 4.7. Since the reinforcing material is placed along the center plane in such applications and the reinforcement ratio is small, the maximum load coincides with cracking load, irrespective of the kind of reinforcement. NEFMAC would appear to be better because of the advantages stated earlier. Table 4.6 gives a listing of the applications of NEFMAC in shotcrete between May 1986 and June 1987. It is significant that no failures have been observed so far, and it should be noted that under some of the prevalent conditions, metallic reinforcement would have degraded due to corrosion and/or chemical attack resulting in overall failure/cracking of the structural element. Figure 4.5. Details of the Test Slab - Graphic File ***.GIF Figure 4.6. Stress/Strain Behavior of NEFMAC as a Function of Temperature/Time -- Graphic File ***.GIF Figure 4.7. Comparison of M-þ Behavior - Graphic File ***.GIF Figure 4.8. NEFMAC Grid - Graphic File ***.GIF 3-D Reinforcement in Beams It is possible to create 3-D cages of NEFMAC that are analogous to the steel reinforcement cages comprised of longitudinal and shear reinforcement as in Figure 4.8. Tests in fatigue have demonstrated that NEFMAC has a fatigue strength equal to or greater than that of a reinforcing steel bar. Applications NEFMAC is currently claimed to be effective for use in: 1. Tunnel supports and supports for storage containers 2. Airport facilities such as runways and aprons 3. Roads and bridge structures 4. Marine and offshore structures 5. Power plant facilities 6. Architectural features and structures such as exterior walls, handrails, etc. Table 4.6. Representative Use of NEFMAC in Existing Structures in Shotcrete - Graphic File ***.GIF Table 4.7 gives a comprehensive overview of the applications of NEFMAC, and shows its versatility of use. A number of claims have been made regarding the overall cost-effectiveness of NEFMAC as compared to steel grids. An example of this is the construction of the new Shimizu building, where it was claimed that although the cost of materials was higher, significant systems-level savings were achieved due to the factors of weight (i.e., no need for specialized lifting equipment, the increased ease of placement of the structure, improved life cycle, and lower overall structural weight). However, no hard evidence has yet been seen to prove the claims as such. It must be stated that the advantages and potential for systems- level cost savings (even on a purely acquisition cost basis) make this a very attractive use of composites in the civil engineering area. Table 4.7. Applications of NEFMAC - Graphic File ***.GIF