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Bendable thermoplastic composite reinforcements for concrete

News International-French

1 Mar 2019

Readily bendable thermoplastic composite bar and cable for reinforced and prestressed concrete revolutionizing the durability of construction.

Sireg (Arcore, Italy) and Arkema (Colombes, France) have joined forces to develop and manufacture composite reinforcement bars (rebars) for concrete as well as cables for prestressed concrete applications using the thermoplastic resin Elium by Arkema in place of conventional thermosetting solutions.

Composite rebars and cables do not rust or corrode, are relatively insensitive to snow‐clearance salts and chemicals used for de‐icing, and have an interesting weight to strength ratio. These properties already make them an economically viable and more effective alternative to epoxy‐coated steel rebars when life cycle cost is considered.

Figure 1: Glass/Elium composite rod

Figure 1: Glass/Elium composite rod

The use of composite reinforcement also allows the use of seawater instead of fresh water and the deployment of aggregates contaminated with salt in concrete mixing. The implications are significant for coastal or arid areas of the world where fresh water is scarce.

Key Benefits:
> Elium rebars can be re-heated and then bent, reducing the cost of custom shapes
> TP composites enable the assembly of rods into flexible cables
> Equipment for concrete precasting remains the same as used for steel strands
> TP composites for prestressing revolutionize the durability of construction

In addition, the recent publication of new standards paves the way for the wider use of composite rebars and cables in reinforced and prestressed concrete. This type of application is expected to grow significantly in the coming years and become one of the major fields of deployment for composites all around the world.

For instance, pultrusion represents 3% of the total North American end product market for composites and was estimated to be worth $790 million in 2016. Analysts predict a CAGR of approximately 5% to reach $1060 million by 2020, with construction and infrastructure the major growth sectors (source : ACMA, 2018).

Figure 2: Pultrusion of a Glass/Elium rod.

Figure 2: Pultrusion of a Glass/Elium rod.

The global FRP rebars market size is estimated at USD 53.04 million in 2016 and is projected to reach USD 91.00 million by 2021, at a CAGR of 11.40% between 2016 and 2021. The market growth is attributed to growing demand of FRP rebars from new, structurally deficient and functionally obsolete bridges in North America and also from other applications such as highways, bridges & buildings and marine structures & waterfront application. (Source Markets and Markets, 2016)

Based on the reactive liquid thermoplastic resin technology Elium, a new generation of rebar and cables was developed (Figure 1) that combines the qualities of composites with the new possibilities offered by the use of a thermoplastic matrix. Unlike most thermoplastic resins, Elium can be easily processed through traditional pultrusion using exclusively standard equipment (Figure 2).

Elium‐based rebars and cables can be re‐heated and easily shaped or bent, reducing the cost of supplying rebars with custom shapes. Moreover, the use of thermoplastic matrix open a way for GFRP recycling of spare part, with a potential strong reduction in environmental impact.

Concrete has intrinsically high compressive strength but limited tensile strength and brittle behaviour. The use of rebars provides the necessary tensile strength without inhibiting the formation of cracks. A much more efficient use of concrete is by inducing in it, at the time of construction, a state of compression at a level higher than the tensile stresses it will experience during its service life. This is the principle of prestressed concrete. For this reason, Sireg, Arkema and their partners, the University of Miami and the National Cooperative Highway Research Program (NCHRP), are concurrently developing a patented thermoplastic composite cable for prestressing concrete (Figure 3). This effort is co‐funded under the aegis of a US federal program with the oversight of the Florida Department of Transportation (see, NCHRPIDEA/MILDGLASS: GFRP strand for resilient mild pre‐stressed concrete,

Figure 3: Glass/Elium composite cable.

Figure 3: Glass/Elium composite cable.

The composite rods that by twisting make up a cable are made by pultrusion with a glass fibre reinforced Elium thermoplastic resin. The assembly, hot‐on‐hot, of the rods into the helical cable, as well as the packaging of very long lengths on reels, are made possible by the use of the thermoplastic resin Elium. As importantly, the chucks to be used as anchors during the tensioning process at the precast plant are the ones used for steel strands; thus, making the transition to a novel material seamless.

The use of composite materials for concrete prestressing (Figure 4) is a major innovation, revolutionizing the durability of concrete construction to an unprecedented level since its invention in the 1930s by Eugène Freyssinet.     

Figure 4: Concrete prestressed bridge girder.

Figure 4: Concrete prestressed bridge girder.

This innovation has been selected as a finalist for the JEC Innovation Awards 2019 in the Construction & Infrastructure category. The JEC Innovation Awards - organized by the JEC Group - are recognized as the industry’s most prestigious awards that identify, promote and reward the most innovative composite projects worldwide. The award winners will be announced during JEC World 2019 on 13 March at 4.30pm.

Arkema will showcase their innovation at JEC World 2019 at Booth V39, Pavilion 5. Their associated partners are Sireg, National Cooperative Highway Research Program – NCHRP, Sireg, University of Miami.