Freeze-thaw Durability of Composite Materials

About the report:

Composite materials, produced from polymer resins and high strength fibers, have the potential to be widely used in construction because of their corrosion resistance and high strength-to-weight ratio, However, such environmental factors as extreme temperature fluctuation and water absorption adversely affect the material properties of composite materials produced from polymers. Cycles of freezing and thawing temperatures magnify the effects of water absorption. For use in highway structures, composite materials must be as durable as steel and concrete. Therefore, the behavior of composite materials subjected to cycles of freezing and thawing needs to be characterized. Two commercially available composite systems, both reinforced with fiberglass and produced by the pultrusion process, were studied. One system was produced with isophthalic polyester, the other with vinyl ester. Coupons were cut from plate stock and placed in a solution of water and 2% sodium chloride and subjected to cycles of freezing and thawing. Periodically, coupons were removed and tested in flexure to failure. Flexural strength values at various numbers of freeze-thaw cycles were compared to the strengths of virgin coupons. Prior to destructive testing, coupons were tested to determine the dynamic modulus of elasticity. Dynamic modulus values at various numbers of freeze-thaw cycles were compared to virgin values. Results indicate a significant loss of flexural strength (20% 30%), rigidity, and toughness after 300 cycles. Data from dynamic modulus measurements when compared to modulus of elasticity calculations taken from load-deflection data, may not be an appropriate measure of durability for composites.

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