Engineers from the National Institute of Standards and Technology in Gaithersburg, Md., report a nano-sized additive whose potential to slow chloride
Engineers from the National Institute of Standards and Technology in Gaithersburg, Md., report a nano-sized additive whose potential to slow chloride ion and sulfate ingress could double the service life of concrete slabs and structures exposed to deicing compounds, seawater and active soils. Chlorides and sulfates cause internal structural damage within a concrete matrix, leading to cracks and weakening over time; and, NIST officials note, curtailing ion transport reduces maintenance costs and lowers the risk of catastrophic failure.
Instead of denser and less porous concretes, which have been prone to cracking, NIST engineers focused on a project called viscosity enhancers reducing diffusion in concrete technology (VERDICT). Rather than change the size and density of matrix pores, they opted to change the viscosity of the solution in the concrete at the microscale to reduce the speed at which chlorides and sulfates enter a finished slab or structure. They turned to food-processing additives used to thicken recipes; among compounds tested was xanthum gum, a salad dressing and sauce ingredient that also gives ice cream its texture.
NIST researchers find the additives can be blended directly into the concrete with current chemical admixtures, yet observed better performance when the additives are mixed into the concrete by saturating absorbent, lightweight sand. A nonprovisional patent application was filed in September, and the technology is available for licensing from the Institute, which is part of the U.S. Department of Commerce. Additional information on VERDICT can obtained from Terry Lynch, NIST Office of Technology Partnerships, [email protected]; 301/975-2691.