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Nanotechnology reveals carbon’s full performance potential in concrete

Littleton, Colo.-based EdenCrete Industries enters 2017 ramping up production of a liquid admixture that has demonstrated in field trials and early commercial applications a capacity to strengthen concrete at levels sufficient to reduce rebar and portland cement requirements. Dosed at 0.25 gallon to 4 gallons per cubic yard, which typically equates to approximately 3 ounces to 130 ounces per 100 lbs. of cementitious material, the EdenCrete admixture embodies quintillions (one million trillion) of carbon fiber-like tubes, or nanotubes, per gallon. EdenCrete Industries has developed a method to safely transfer carbon nanotubes in admixture form to concrete customers without any risk of health concerns; the resulting product dictates packaging solely in liquid form.

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EdenCrete carbon nanotube (above) measures about 20 nanometers in diameter. Engineers estimate that a gallon of EdenCrete admixture contains one quintillion—1 x 1018 or one million trillion— carbon nanotubes, shown in cement paste (below) at 76,200x magnification through a helium ion microscope. MICROGRAPHS: EdenCrete Industries
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The nanotubes are multi-walled structures of individual carbon nanofibers, whose single-atom thick walls exhibit honeycomb patterns typical of carbon compounds viewed at nano scale. NANOFIBER SCHEMATIC: Massachusetts Institute of Technology

EdenCrete Industries is the North American subsidiary of Perth, Australia-based Eden Innovations Ltd., whose scientists characterize their carbon nanotubes as cylindrical structures comprising bundles of graphene having single-atom wall thickness. The EdenCrete admixture’s multiple-walled nanotubes have estimated diameters of 20 to 40 nanometers and lengths of 100 to 300,000 nanometers. Ounce for ounce, they are nearly 120 times stronger than steel and 30 times stronger than bulletproof Kevlar.

In concrete mixtures, the nearly pure (> 99.5 percent) carbon nanotubes bond to hydrating cement particles, creating millions of flexible, strong bridges throughout the matrix. They likewise enhance interfacial transition zone bonds between the cement paste and aggregate, netting superior pullout capacity and greater aggregate fracture at failure. When compared to conventional plain or reinforced concrete, a slab or structure bearing the EdenCrete admixture at recommended dosages exhibits lower permeability; greater resistance to wear and shrinkage cracking and curling; higher ultimate tensile and compressive strengths; improved durability and resistance to chemical attack; and, lower tendency of steel corrosion. At the top dosage of a 4 gallons/yd., the agent has consistently increased concrete compressive strength by more than 30 percent at 7-, 28- and 56-day intervals. Results vary depending upon the mix design.

Neutral and non-reactive, the admixture has no impact on fresh concrete properties, especially workability and finishability, and can be used in mixes bearing all standard chemical agents. Although a thin black liquid, EdenCrete has a negligible effect on color in ordinary portland cement concrete. In white cement concrete mixes with integral coloring agents at 2-3 percent dosage, the admixture dosed at 3-4 gallons/yd. has a negligible effect on finished slab or surface color. Applications include bridge beams and suspended slabs warranting higher than normal tensile and flexural strengths; corrosion-prone structures such as bridges, locks and water distribution facilities; walls where congested steel is a concern and hampers proper consolidation; plus, industrial warehouse floors, runways or loading docks where high resistance to abrasion and minimal shrinkage are critical.

MORPHING METHANE

EdenCrete Industries operates the only commercial facility for Pyrolysis, a process in which methane (CH4), or natural gas, is broken down into its hydrogen and carbon constituents without carbon dioxide byproduct. The process and companion reactant yield carbon in the form of nanotubes or nanofibers, each exhibiting strength characteristics significantly higher than steel. Eden Innovations owns the Pyrolysis process, which it developed with the University of Queensland.

EdenCrete Industries plans to expand a charter Colorado plant’s annual capacity from just over 100,000 to 2 million-plus gallons of the namesake admixture by mid-2017, while building an even larger Pyrolysis operation on a 140-acre greenfield site in Georgia. The capital investments follow early admixture field trials and demonstrations with ready mixed producers plus local and state agencies. EdenCrete Industries Inc., Littleton, Colo., 303/468-1705; www.edencrete.com


GEORGIA DEPARTMENT OF TRANSPORTATION

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Augusta Ready Mix supplied 16 yd. of EdenCrete concrete for a trial slab on Interstate 20. GDOT has observed strong performance of the carbon nanotube-reinforced concrete, especially compared to a plain control specimen.

METROPOLITAN ATLANTA RAPID TRANSIT AUTHORITY

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Argos USA supplied 200 yd. of EdenCrete ready mixed for bus-routing pavement at the Metropolitan Atlanta Rapid Transit Authority Brady Mobility Transportation Facility.