Retaining walls: Railroad ties vs. concrete blocks?

We have some retaining walls built using railroad ties. I don't know how long they've been there, since they were already in place when we moved in, but they are beginning to look as though it's time to replace them. If we replace them with new (actually old) railroad ties, how long are the new ones likely to last? What kind of timber is used for railroad ties? Anything we can do to make them last longer? -- creosote? The bottom course is actuually below ground level.
We are thinking seriously about using interlocking concrete blocks instead. Any thoughts on those?
Perce
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Around here (Atlanta), they sell different grades of used railroad ties. I'm sure the better ones last a little longer, but after 15 years, most RR tie walls start looking pretty ratty, and after 20 years, it would probably be replacement time.
The interlocking blocks are a good solution depending on how high you want a wall. Some of the smaller ones they only recommend for 2' or 3' walls. However, there are bigger, heavier ones that can go substantially higher. If you hire the work done, this is a fairly expensive option.
Poured concrete is another solution.
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That is what I'd use. Concrete last longer than wood. Just look at the Coliseum in Rome. Stone is there, wood is long gone.
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Percival P. Cassidy wrote:

There are RR ties and then there are RR ties. They are made from all kinds of lumber. I have 300 ft of retaining wall built from basically cull RR ties that is still standing after 20 years but I am surprised. I have posts that I just pulled after about 20 years in the ground. 3 of 5 were too rotted to reuse (one fell over, rotted at ground level). 2 would still grade #1.
Harry K
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Hi Perce:
When I built my 6' tall x 150' long retaining wall 8 years ago, I went through a similar decision. I ruled out RR ties because of the creosote. I considered building a wooden wall from 0.6 pcf CCA treated wood (which I would have had to specially order), but by the time I put enough material into it (including stainless steel bolts) to hold up for more than 20 years, it was just as costly to use interlocking concrete blocks. I chose to use a locally made product, called Metrostone, which are 20" x 12" x 8" hollow concrete blocks with a rough face on one side. They weigh 90 lb each, and are dry stacked, filled with washed gravel, and pinned together with rebar. It took me about 3 months of weekends to build it. After 8 years, it still looks like new, and I know it will always be there (barring major earthquake or armageddon). If I had made it from wood (even RR ties), I'd start wondering how much longer it would hold up in a few years.
Regards, John.
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