The sustainable use of wood for rail ties requires chemical treatment to increase service life and maintain structural integrity. Treatment can only be applied after lengthy air-seasoning to reduce moisture content in wood, but seasoning leaves ties exposed to attack by decay fungi for up to a year. One factor affecting the rate of decay is proximity to soil contact. The height of sills used to raise untreated ties above ground contact while drying is mandated by national standards to be 12 inches, but there is little research examining the effects of deviating from this height on decay risk.
This study examined the effects of varying sill height on colonization by decay fungi and flexural properties of black gum and red oak ties. The objective was to relate sill height with populations of decay fungi and to changes in wood strength during air-seasoning. Sampling of blackgum railroad ties from the Koppers plant in Guthrie, Kentucky at three time points during seasoning showed that the incidence of decay fungi increased at an even rate over time with little or no difference attributed to distance of stacks above the ground. Red oak ties sampled three times over 11 months showed that red oak yielded few decay fungi for 6 months followed by a rapid increase in fungal populations. Stacks of red oak and blackgum had completely different fungal populations and colonization rates despite being stored in close proximity.
Changes in fungi colonizing ties and their effect on tie properties were not strongly related to height between 6 and 33 inches, and there was no relation to sill heights of 6, 8, or 12 inches.
Isolates of decay fungi recovered from ties were evaluated for decay potential and produced a wide range of decay capabilities. Blackgum ties were colonized most by white rot fungi, while red oak ties were colonized by both white rot and brown rot fungi. Many cultures isolated from blackgum had weak decay capabilities.
The results indicate that decreasing sill height from 12 to 6 inches had no significant effect on fungal colonization or timber properties of the two species evaluated.
Key Words: Railroad ties, crossties, blackgum, red oak, fungal colonization, air-seasoning, decay, decay out of ground-contact.