|Written by Bob and Pat Canfield for Family Garden Trains|
The B&P Garden Railroad (B&P) - Part 5 - HDPE Roadbed Expansion in the Nevada Summer
Note: This is a follow-up to The B&P Garden Railroad Part 4. In addition, technical aspects of the following text will be best understood if you first read the Family Garden Trains Primer Articles regarding HDPE Flexible Roadbed by Paul Race, Bill Logan and Bob Zajicek.
If you'll recall, we decided in 2007 to build an Outside O Gauge railroad, using a raised roadbed made from HDPE fabricated into a ladder-like framework (see Paul and Bill's HDPE Roadbed article for an overview). By the end of Part 4, we had the HDPE roadbed built, track laid, power applied, and trains running.
Also, we noted that one of our biggest concerns, as we approached the hot summer months, was the issue of rail expansion, and the potential track damage it might cause.
Starting in the second half of May 2008, while much of the United States experienced heavy rain and severe flooding, Southern Nevada was unseasonably warm. For two straight months, our daytime temperatures were routinely five to ten degrees above normal. In early July, our daytime highs were between 110 and 115 degrees.
Due to the high temperatures, we did not do much additional work on the B&P during that heat spell. However, we observed an unanticipated track/roadbed phenomenon, that in hindsight seems to make sense, and which we believe is worth sharing.
Concerned about potential track damage caused by rail expansion, Bob has routinely inspected all B&P track. To our surprise we have seen no evidence of rail expansion. In fact, if anything, Bob observed that the rail gaps that he deliberately provided for, were greater, not smaller.
After many weeks of unusually high temperatures, some rail gaps became large enough to cause rail joiner connections to fail (see right). Another observation has been the failure of several of the glued HDPE spacers we placed between the two parallel roadbeds to ensure the 4.5" on center separation of our mainline tracks (noted in Part 2).
Our conclusion is that the HDPE roadbed has expanded in the high heat at a greater rate than the Atlas Nickel Silver Rails. We had secured each section of Atlas Nickel Silver Track to the HDPE roadbed with several, sometimes many, stainless steel screws, when Nevada temperatures were 20 to 30 degrees cooler. Based on our observations, we have concluded that the HDPE expanded at a greater rate than the Atlas Nickel Silver Rail, producing larger rail gaps, the opposite of what we expected at the hottest time of year.
However, based on other HDPE construction observations noted in Parts 2 and 4, this conclusion made sense to us. In fact, when we later had several relatively cool days (for July) back-to-back, the rail gaps shrank again, further supporting this conclusion.
Additionally, HDPE expansion is believed to be responsible for the failure of the glued HDPE spacer joints (see right). Our conclusion about using Gorilla Glue to add rigidity to HDPE joints, is that it performs well, if the joint is also mechanically fastened, e.g., with a screw. However, many glued joints that were not mechanically secured have failed.
Screws were not initially installed at many of these “spacer” joints because it was not feasible when joining two already completed ladder roadbed structures. Our fix has been to fabricate aluminum strips and fasten them to the underside of the two ladder roadbed sections (see below).
August, 2008 Update - Another thought on HDPE Joints that are "screwed" but not "glued." In our climate, a screwed HDPE joint is weakened in high heat, due to the softening of the HDPE and its inability to rigidly "hold" a threaded screw. A "screwed" joint *that is also* "glued" does not seem to fail, and the two HDPE pieces are "rigidly" connected.
The "Big" Picture - Again, as we noted in Part 4, if we were starting today, we would not use pure HDPE in an area with the climate extremes we experience here in the desert Southwest. Instead, we would use a Trex-type product (combination Plastic and Sawdust). This type of low maintenance decking material is less expensive than HDPE, and is readily available under a variety of brand names at Lowes, Home Depot, etc.
However, we are confident that we will be able to overcome the HDPE expansion issues and have a very usable Garden Railroad this Summer and Fall. The question is, what will happen if the HDPE roadbed contracts at a significantly greater rate than the Nickel Silver Rail in the winter, when our nighttime temperatures are often below freezing? Will we then experience the track damage that most Garden Railroaders experience as a result of summer rail expansion? We’ll let you know.
We hope our experience gives you some useful ideas and helps you plan your project more effectively. If we can answer any questions, please contact us through the Family Garden Trains Contact link. Just put the words "Questions for the Canfields" somewhere in your comments and Paul will forward them to us.
Bob & Patricia Canfield
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