A new technology promises to dramatically extend the service life of precast concrete bridge piles by dramatically improving their corrosion resistance by using carbon fiber reinforced polymer (CFRP) grid.
U.S. Patent 8,677,720, “Precast concrete pile with carbon fiber reinforced grid,” describes a composite support structure with a plurality of support strands surrounded by a CFRP mesh and encapsulated by structural concrete. The support structure provides high corrosive resistance in additional to various advantages in withstanding compressive, tensile and shear loading as compared to carbon steel spirals commonly used in piles today.
AltusGroup, a partnership of precast concrete manufacturers dedicated to innovation, intends to market the novel technology as a CarbonCast® product line extension into the pile market sector – its first major foray into the DOT and transportation segment. The CarbonCast brand is already associated with CarbonCast Enclosure Systems for building exteriors and CarbonCast Double Tees for structured parking. All CarbonCast products use C-GRID CFRP grid from Chomarat NA, LLC, as a carbon fiber composite reinforcing material.
Conventional steel spirals and reinforcing bar that the C-GRID will displace are commonly used in piles today. Carbon steel can demonstrate extreme corrosion with repeated exposure to wet and dry cycles common in the splash zone of a pile where it is most susceptible to impact, damage, and cracking. When steel corrodes, it expands in volume and causes deterioration of associated concrete. The presence of salt in coastal and marine environments often amplifies the possibility and speed of corrosion which is a major identified problem by many DOTs.
CarbonCast Piles’ C-GRID CFRP reinforcing offers exceptional corrosion resistance to prevent deterioration and spalling, extending the life cycle of the element and reducing maintenance costs. The CarbonCast Pile system incorporating CFRP grid offers a combination of precast manufacturablilty and favorable composite product economics that alternative carbon-fiber based corrosion-resistant materials cannot match currently. Extensive testing of CFRP structures within the industry is currently ongoing in search of the ideal cost effective technology.
According to the American Society of Civil Engineers’ 2013 Report Card for America’s Infrastructure, more than 200 million trips are taken daily across deficient bridges in the nation’s 102 largest metropolitan regions. One in nine of the nation’s bridges is rated as structurally deficient, while the average age of the nation’s 607,380 bridges is 42 years. Most have a design life of only 50 years.
Through improved design and enhanced materials such as CarbonCast piles, civil engineers can target a service life of 75 to 100 years or more. AltusGroup plans to target the commercial construction sector of the market served by various regional precaster’s for initial technology commercialization while working closely with many of the state DOT’s which have coastal zones and exposure conditions and are in need of improved and enhanced durability.
Initial testing of the pile concept and confinement of CFRP grid versus steel spirals was done by Dr. Sami Rizkalla, of the North Carolina State University Constructed Facilities Laboratory in Raleigh, N.C. Subsequent testing (including pile load testing and driving in know soil conditions) was done by the Florida DOT – Marcus H. Ansley Structures Research Center Laboratory in Tallahassee, Fla. Various CFRP product research and testing is ongoing in the sector across the U.S. and Canada.