Problem
Concrete exposed to cyclic freezing and thawing temperatures is susceptible to damage. It is commonly accepted that hydraulic, osmotic, and crystallization pressures develop when ice forms in the pore structure of concrete leading to internal micro-cracking. The internal damage reduces the durability by decreasing overall compressive strength, increasing susceptibility to water and ion ingress, and increased susceptibility to additional freeze-thaw damage. The default method used to mitigate freeze-thaw damage in OPC concrete since the 1930s has been through the creation of an entrained air void system via the addition of air entraining agent (AEA).
Research into other methods include super absorbent polymers to create properly sized and spaced voids, supplementary cementitious materials and nanoparticles for reducing porosity, hydrophobic materials to reduce water ingress, and polymeric fibers for containment of crack propagation. Nature produces antifreeze proteins (AFPs) and antifreeze glycoproteins (AFGPs) to allow a variety of cold climate species to survive. Although AFPs display excellent antifreeze properties, they are currently not an economical option due to limitations in production and they are known to lose functionality in the highly basic and ionic environment of concrete. There are a variety of polymeric materials that have shown ice recrystallization inhibition with PVA being the most widely studied.
Solution
The chemical functionality of PVA mimics the highly hydroxylated carbohydrates of AFGPs. PVA is soluble in water but requires mild heat to go into solution. To this end, a more soluble polymer like polyvinyl alcohol-polyethylene glycol graft copolymer (PEG-PVA) is of interest. PEG-PVA is composed of 75% PVA and thus it is expected it will display IRI activity. Researchers at CU Boulder found that PEG-PVA provided freeze-thaw resistance comparable to air entrained concrete with a hardened state air content less than 3%. The low air content suggests that the freeze-thaw resistance could be attributed to something other than an entrained air system.
The addition of PEG-PVA was found to increase fresh state air content and slump compared to unmodified concrete. However, X-ray computed tomography has shown that hardened state air content was less than that of fresh state for PEG-PVA modified concrete and was equal to that of unmodified concrete. Which indicates that fresh state entrained air due to PEG-PVA addition is not stable and air gets released during concrete consolidation. PEG-PVA-modified and AEA samples were proven to improve freeze and thaw resistance as indicated by relative dynamic modulus, durability factor, and length change. Addition of PEG-PVA at a concentration of 0.066% was found to have no influence on compressive strength compared to AEA which experienced 6.25% reduction.
Market Application
This has potential applications for construction and other relevant industries.
What's Next?
This technology is available for exclusive and non-exclusive licensing.
Nicole Forsberg: nicole.forsberg@colorado.edu
