Hemp fiber adds to FRP buzz

Carbon, glass and basalt fiber manufacturers are improving their concrete market prospects by pursuing certification for fiber reinforced polymer (FRP) reinforcement. FRP bar and tendons offer compelling alternatives to traditional reinforcements for bridge decks, pavements, marine structures and other conditions whose chemical exposure invites steel corrosion. FRP is also attracting attention for its potential to lower embodied carbon in finished concrete. That characteristic reflects lower energy intensity in production and transportation when the lightweight product is measured against steel. 

The American Concrete Institute’s recently organized NEx: An ACI Center of Excellence for Nonmetallic Building Materials is teaming with the American Composites Manufacturers Association (ACMA) on FRP bar or tendon plant certification (note page 36). A formal program abiding American Association of State Highway and Transportation Officials certification guidelines would augment FRP reinforcement stakeholders’ value proposition for department of transportation engineers. 

Concurrent with the NEx and ACMA undertaking, a new research and certification group seeks to advance composite reinforcement for non-building concrete in North America and beyond. Incorporated last month, the FRP Institute for Civil Infrastructure will serve as the focal point for research, testing, material certification and education (note page 38). Spearheading the Institute is a 20-member (State) DOT Board and National Precast Concrete Association veteran Rich Krolewski. “Our DOT representatives are committed to a material verification program that will create standards, inspect and audit manufacturing facilities, and provide training,” he explains. “The goal is to give DOTs confidence in adding FRP producers to their qualified producer lists.”

While most concrete-grade FRP has entailed carbon, glass or basalt, another fiber type has surfaced thanks to provisions in the 2018 Farm Bill. It allows states to designate acreage and certify growers for industrial hemp crops. Researchers at the Institute for Energy, Built Environment, and Smart Systems (EBESS), a recent addition to the Rensselaer Polytechnic Institute in Troy, N.Y., view hemp as yielding some of the plant kingdom’s strongest fiber, matching glass fiber pound for pound. One of the charter EBESS projects centers on innovative, cost-effective hemp processing technologies—leading to development of a conventional concrete rebar alternative. 

RPI Assistant Professor of Architecture Alexandros Tsamis and Professor of Mechanical Engineering Dan Walczyk seek to develop machines that can separate fibers from the inner, woody hemp plant core without adversely affecting mechanical properties of the former. Targeted machinery and methods could net a natural fiber-reinforced thermoplastic rebar. Measured against steel rebar, hemp fiber reinforcement would represent a replacement of significantly lower embodied carbon, but one imparting comparable or better service life when factoring corrosion-free performance.

“A major focus of the Institute for Energy, the Built Environment, and Smart Systems will be to create products that drive decarbonization of the construction industry, in this case by helping to incorporate industrial hemp into New York infrastructure,” says Acting Vice President for Research Robert Hull.

RPI officials reviewed the potential for hemp fiber-based concrete reinforcement last month during a “Seed to City Hemp Initiative” workshop, aimed at supporting Empire State construction, manufacturing and agriculture interests. The event was tied to the New York State Hemp Plan, which now counts nearly 800 authorized growers and approximately 30,000 acres registered for the crop. Plan participants are bound by strict U.S. Department of Agriculture terms confining crops to industrial grade hemp use and calling for destruction of plants whose tetrahydrocannabinol, or THC, levels test above a certain threshold.

Work at EBESS and other public or private entities could align hemp fiber—extracted from plants that have minimal value to those inclined to medical or recreational cannabis consumption—with the reinforcing alternatives that the FRP Institute and NEx/ACMA aim to embed in mainline concrete. 

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