Manufacture and rehabilitation of guard-rail posts using composites for superior performance

Abstract

The objective of this research was to study the effectiveness of an external composite reinforcement in increasing the strength and durability of a conventional CCA treated wood post. Glass fibers (with excellent mechanical properties and low cost) in a polymer matrix were used for wrapping CCA treated wood posts. Six chemically different resins were screened, and a combination of HMR (Hydroxy Methylated Resorcinol) as primer and epoxy as adhesive was found to provide the best possible adhesion of the wrap to CCA treated wood. Wooden posts of 0.5 OD and wrapped posts of 0.6 OD, representing a scaled down version of the proposed posts were subjected to a 6-cycle aging procedure that involved application of vacuum and pressure under water. The wrapped posts were also subjected to freeze-thaw cycling in four different liquid media: (1) water (2) 3% salt water (3) acidic solution of pH 3 (4) alkaline solution of pH 13. The retention of flexural strength and stiffness of the wrapped posts after chemical aging was measured. Samples of dimensions 50 mm X 9 mm X 2 mm wrapped with 1mm thick wrap were also subjected to aging. The retention in strength and stiffness was measured and the service life was estimated. Results of flexure tests show that the strength of the wrapped post reduces due to aging. Results of DMTA (Dynamic Mechanical Thermal Analysis) show that freeze-thaw cycling and 6-cycle aging increase the Tg (glass transition temperature) and widen the glass transition region. After a service life of about 20 years, the stiffness of a wrapped post is predicted to be about 1.8 times that of an unwrapped wood post of the same age. Heating and freezing in liquid media causes more damage than heating and freezing in the absence of a liquid medium. Among the liquid media, it was found that the alkaline medium damages the epoxy matrix, the epoxy/glass interface and also the wood/HMR/epoxy bond. Acid medium primarily damages the epoxy/glass interface. Water diffuses easily through the epoxy matrix and primarily damages the epoxy/glass interface. Salt water damages the wood/HMR/epoxy bond. The performance in terms of flexural strength, modulus and rigidity was reduced the most by acidic medium, and the least by saltwater medium. There was no delamination at the wood/FRP interface under any of the aging conditions. It was concluded that under unaged conditions, the flexural rigidity of wood is improved by 162% due to composite wrapping. The technique of composite wrapping also shows a promise of improving the properties of guard-rail posts under actual field conditions. v

Manufacture and rehabilitation of guardrail posts using composite fabrics

“…This is used based on its advantage over other fabrics in terms of its cost. The mechanical properties are also relatively comparable to any other material for the given cost of the material (Anegunta, 2000, andLaosiriphong, 2000).…”

“…Commercial CCA treatments are also known to contain wax emulsions that greatly increase the water-repellancy of the treated wood as compared to untreated wood. This is due to the higher contact angle for the CCA treated wood (Anegunta, 2000).…”

“…....................................................................................................................91 One alternative is to use a smaller diameter wood post with Glass Fiber Reinforced Polymer (GFRP) fabric wrap than conventional wood post. The wrapped wood post is found to be cheaper than a steel post (Anegunta, 2000). Also, the wrapped wood post, compared to conventional wood post, is easier to install because it has smaller diameter.…”

“…These properties were retained throughout the aging period when exposed to dry heat or moisture at ambient temperature suggesting an appreciable durability of the composite material. Anegunta (2000) wrapped CCA (Chromated Copper Arsenate) treated southern pine dowels of diameter 0.5-inch with E-glass fabric (0-45 degree). The length of samples was 7.5-inch.…”