Crossties – also referred to as railroad ties or wooden sleepers – have long been made out of wood.
Even though technological advances have paved the way for crossties to be made from other materials – including concrete, steel, and plastic composites – wood still makes up over 93% of railroad track applications.
Wood crossties are treated with a preservative before they are installed under the steel tracks that create the railway trains run on.
Benefits of Treated Railroad Ties
Despite the use of other types of materials for railroad crossties, wood remains the prevailing choice.
And with good reason.
Wood has a proven track record. It has great compressive and yield strength and, when treated with a wood preservative, can last 30 years or more.
Even when wood crossties are treated, they can have great environmental benefits, too.
Of course, a tree is the source of the wood manufactured to make a crosstie.
You’ve probably never thought of it this way, but solar energy makes that tree grow.
During this time of growth, the tree is absorbing greenhouse gasses.
But that’s not all. The tree the crosstie is cut from is a renewable resource and, once the wood crosstie has reached the end of its usefulness in the rail system, it can be recycled as a biofuel for the production of electricity.
Brief History of the Treatment of Crossties
The process of treating crossties with pressure dates back to the mid-1800s.
In 1838, crossties were treated with a mixture of bichloride of mercury. In 1848, the first treatment facility opened, using both bichlorides of mercury and bichloride of zinc.
Just before the 1900s, crosstie treating really took off when manufacturers starting using creosote (coal tar).
By the 1940s, all but about 10% of crossties used were treated with some type of preservative.
What Types of Wood Are Used for Treated Railroad Crossties?
Most of the woods used today for wooden crossties are hardwoods.
There are still some softwoods used, but they only make up a small percentage – approximately 4-6%.
According to the Railway Tie Association, about 50-60% of the hardwoods used are oak and hickory, while the other 40-50% are other mixed hardwoods, including cherry, walnut, hemlock, redwood and fir (Douglas and Spruce).
Preservatives Used to Pressure-Treat Crossties
The majority of crossties treated within the United States are preserved with creosote, but other preservatives are used, such as copper naphthenate, or ACZA.
Creosote not only acts as a preservative against decay, but it also helps to protect against wear of the crosstie itself.
With materials like concrete and composite plastics, this wear often is greater due to the lack of lubrication between the plate and tie.
As the train travels over the steel tracks – attached to the crosstie with steel plates – the plate connection tends to slide and cut into the crosstie’s surface.
As creosote is an oil-based preservative, the oil act as a lubricant and reduces the friction between the plate and the wooden tie. This reduces the plate from cutting into the tie.
In certain high decay zone areas, a dual treatment is used to preserve wooden crossties.
They are first treated with borate compounds, followed by creosote.
Borates serve a couple of different functions. First, they help to preserve the harder parts of the wood that creosote has difficulty penetrating.
They also add protection against decay while the crosstie is being air dried prior to treatment with creosote or other preservatives.
Where your crossties are treated matters
At Tank Fab, we provide you with the specialized equipment – such as autoclaves – you need to protect your wooden crossties from fungal and/or insect decay.
Our equipment will help you to preserve wooden crossties that railroads will be proud to install into their railway system.
How would your business be improved if you had a way to improve your processes?