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`Home > Carbon fibre grid improves precast concrete
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`Carbon fibre grid improves precast concrete
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`(Published on January - February 2008 – JEC Magazine #38)
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`JOHN M. CARSON DIRECTOR COMMERCIAL DEVELOPMENT TECHFAB, LLC
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`As a replacement for conventional steel reinforcing, carbon fibre grid can dramatically improve many aspects of concrete
`performance. It had been used primarily in concrete for rehabilitation applications, everything from bridge decking to
`balcony repairs to industrial floor retopping to roof renovation. It delivered outstanding resistance to corrosion, adding
`years of durability to the projects.
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`Several forward-thinking companies have explored the initial use of carbon fibre grid in precast concrete for large concrete
`elements such as facade panels, walls and parking garage components that are manufactured in a factory and then
`shipped to a job site for erection.
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`In 2005, five precasters along with C-GRID™ manufacturer TechFab LLC formed AltusGroup, a partnership dedicated to
`expediting the development and commercialization of precast concrete using C-GRID carbon fibre grid reinforcing.
`Because precasters’ market areas are limited by the cost effectiveness of transporting the heavy concrete pieces, their
`willingness to share the technology with other AltusGroup members enabled the development of the building industry’s
`first-ever national brand of precast concrete in the United States: CarbonCast.
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`Metromont Ex-1027, p.1
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`Since introducing the technology nearly four years ago, AltusGroup members have realized significant progress in
`promoting the acceptance of carbon fibre grid reinforced precast concrete. It has been used on nearly 200 projects ranging
`from 30-storey condominiums to 75,000- seat sports arenas.
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`Why precast concrete needs reinforcing
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`Concrete is strong in compression but weak in tension. Reinforcing steel compensates for this weakness, but it requires
`extra concrete covering it to develop its strength and to help protect it from the elements that cause corrosion. There are
`two types of reinforcing: primary and secondary. Primary reinforcing resists tensile stresses induced by external loads,
`such as gravity, seismic events, and wind loads. It typically takes the form of rebar, prestressing strand, or post-tensioning
`cables. Secondary reinforcing – usually a mesh or grid, or occasionally loose fibres placed in the mix – controls cracks
`caused by shrinkage or thermal loading on the surface.
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`In terms of rebar and mesh, common carbon steel is the least expensive material, though its price is rising. Carbon steel is
`strong and generally easy to work, but it still rusts, even when galvanized or epoxy coated. When steel corrodes, it doubles
`in volume, causing cracking or spalling. When wet, it may also cause staining. Naturally, any cracks in the concrete will
`accelerate the ingress of moisture, causing even more havoc. As a result, a structure’s performance and aesthetics suffer
`over time.
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`Nonetheless, for decades steel has been the reinforcing material of choice for precast concrete. Until recently, no other
`material made major inroads. Advancements in industrial-grade carbon fibre production have made it a costeffective
`alternative to steel mesh reinforcing for precast concrete structures.
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`Reinforced precast products manufactured with epoxy-coated carbon fibre grid are extremely competitive from a cost
`perspective with conventional precast products that employ steel mesh for secondary reinforcement. Carbon fibre
`effectively eliminates concrete cover requirements, enabling new precast product designs that reduce the materials used in
`fabrication. After factoring in savings on raw materials, reduced transportation costs, reduced superstructure demands,
`time saved on-site, improved insulation qualities, speed of erection, and other system benefits, using epoxy-coated carbon
`fibre grid reinforced precast products will likely result in long-term cost reduction.
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`Precast applications
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`Precast concrete can be cast into hundreds of forms and shapes. To realize the benefits of carbon fibre on a significant
`scale, the precasters in AltusGroup have centred their efforts on large structural and architectural components for buildings
`and parking structures, namely high-thermalperformance wall systems and pretopped double tees. The use of carbon fibre
`grid reinforced precast has also been explored for multi-family residential applications, including highrise condominiums.
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`Architectural cladding panels
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`Ranging from 152.4 to 304.8 mm thick, architectural cladding panels feature a carbon fibre grid reinforcing in the face, or
`the side that comprises a building’s exterior. Because carbon fibre will not corrode like steel mesh, precasters can use less
`concrete to protect the reinforcing – up to 66% less. Less concrete means less weight, leading to savings in picking and
`lifting costs related to construction cranes and building substructure. And their design can provide R-values up to steady-
`state R-20.
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`High-performance insulated wall panels
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`Vertically installed insulated sandwich wall panels can be used for both nonstructural and load-bearing applications.
`Manufactured in thicknesses from 152.4 to 304.8 mm, widths to 4.57 m and heights of 15.24 m or more, CFRP composite
`grid is used for shear transfer between the inner and outer wythes. With its relatively low thermal conductivity, epoxy-
`coated carbon grid maintains essentially 100% of the insulated wall panel’s core R-value, generates an even insulation
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`Metromont Ex-1027, p.2
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`profile without hot spots or cold spots on the interior wall surface, and provides a truly structural composite panel for added
`strength and reliability.
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`Pretopped double tees for parking structures
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`In pretopped double tees, carbon fibre grid replaces conventional steel mesh reinforcing in the flange, or deck. Because
`carbon fibre does not corrode, parking garages do not face long-term flange degradation from cracking and spalling. No
`corrosion in the flange means precasters require less concrete cover to protect the reinforcing – reducing weight up to
`12%. They also eliminate the need for sacrificial barrier coatings on the steel, corrosioninhibiting admixtures, and sealants
`on the deck surface. Sealant re-application every five years is avoided, too, saving money in long-term maintenance costs.
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`Multi-unit residential applications
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`Load-bearing and non-load-bearing CarbonCast ribbed residential wall panels weigh up to 60% less than conventional
`precast panels and offer value-added insulation performance of up to R-13. They are specially designed to make drywall
`furring with metal studs quick and easy. They can be formed or finished to simulate stucco, brick, stone and even
`clapboard siding.
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`Applications
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`The promise of CFRP technology has been borne out by nearly 200 applications in the past three years. Several projects
`are highlighted below to illustrate how architects and building professionals have begun to embrace the concept.
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`The 31-storey Symphony House, a breathtaking $125 million, 163-unit
`condominium in Philadelphia, features CarbonCast architectural wall panels that
`deliver a traditional aesthetic sensibility and a remarkable 60% weight reduction
`of precast members.
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`The weight reduction provided two benefits to the owner. First, the restrictive
`building site necessitated a tower crane to lift the 770 exterior panels into place.
`The CarbonCast panels were easily accommodated by the crane, even at the
`more distant corners of the building.
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`In addition, the lightweight panels reduced load on the floor slab where they were
`mounted and on the rest of the reinforced concrete structure, all the way down to
`the sizing of the foundation. Further, the thinness of the panels and the reduction of the structure provided more interior
`floor space and better apartment layouts. To accommodate the architect’s colour selection, precast panels were fabricated
`with a red-pigmented, sandblasted finish meant to evoke the feeling of brick, but without the expense or limited colour
`range of brick or other systems.
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`Constructed from CarbonCast highperformance insulated wall panels, Georgia State University’s 2,000-bed four-building
`student housing complex is the largest privately funded university housing complex in the nation. The aesthetically
`pleasing wall panels greatly reduce mildew risk because concrete inhibits water penetration. In addition, using the precast
`wall panels eliminated the drywall, eradicating any potential food source for mildew and mould.
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`The panels deliver R-12, attained by 101.6 mm of expanded polystyrene sandwiched between two 63.5 mm thick concrete
`wythes. The inner and outer wythes were connected using thermal-efficient C-GRID carbon fibre trusses. Compared with
`the original design, the increased R-value enabled the university to save $700,000 in HVAC costs. And cost savings will
`only increase over time as the annual utility and maintenance costs will be significantly less.
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`Metromont Ex-1027, p.3
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`The new Lucas Oil Stadium, Indianapolis, Ind., will feature
`an insulated, brick-inlay architectural facade with
`CarbonCast highperformance insulated wall panels. The
`project will require over 37160 m2 of limestone-finished
`architectural precast featuring blasted accents and
`embedded brick.
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`With C-GRID shear grid reinforcement connecting the 76
`mm wide interior and exterior concrete wythes, the panels
`will maximize energy efficiency and reduce the possibility
`of condensation and mould. As the system’s rapid
`installation does not compromise its clean lines and
`exacting detail, construction time and cost savings are
`anticipated. Additionally, the prestressed panels allow
`longer spans – another costsaving aspect of the system.
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`Conclusion
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`The construction industry has quickly been learning what other markets have known for years: carbon fibre is a material
`that can impart numerous benefits to end-products. The use of carbon fibre reinforcing in precast concrete signals a shift
`toward its use in new construction after years of success in rehabilitation applications. And considering a new focus on
`energy efficiency, the insulation benefits of carbon fibre reinforced precast is more attractive than ever.
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`Each new structure stands as a testament to carbon fibre’s viability as a reinforcing material. With about 1 million m2 of
`carbon fibre reinforced precast erected or in development just over four years after the technology’s introduction, it is
`evident that architects and engineers are quickly embracing the numerous benefits that this technology can deliver.
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`While carbon fibre is universally acclaimed for its strength as a primary material – witness its use in aerospace, automotive
`and wind energy applications – carbon fibre also has a remarkable capacity to make other materials stronger. The same
`high-strength characteristics that make it desirable for demanding applications render it ideal as a reinforcing material.
`Nowhere is this property more evident than with concrete.
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`More information: www.altusprecast.com
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`Metromont Ex-1027, p.4
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`Links
`[1] http://www.jeccomposites.com/knowledge/international-composites-news?f[0]=field_theme:33
`[2] http://www.altusprecast.com
`[3] http://www.jeccomposites.com/user?destination=print/knowledge/international-composites-news/carbon-fibre-grid-improves-precast-concrete
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`Metromont Ex-1027, p.5
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