While searching for articles on building turnouts, I stumbled across the Haworth Engineering site. Mr Haworth certainly has a bullet proof roadbed, as explained in the following two articles: Track Laying and Asphalt.
His layout is featured in the current (June 2015) Garden Railways. There are other articles that are worth reading, as well.
Really nice asphalt. I wonder if it has enough give in it for thermal rail movement?
I am not sure of this is the same stuff that I have. So far I have only used it to improve Bachmann 1:22.5 coal hopper loads and two static display open cars, quite successfully I believe.
I do intend to use it around my flag stop as platforms, building surrounds and in one or two other locations. I does have a ‘springy’ feel to it particularly as it is used in areas where children play, which means their falls are somewhat cushioned - more so than concrete.
The asphalt idea is a good one for making stepping areas that don’t look like stepping areas. Now in 1890 there wasn’t asphalt parking lots and roads but there was dirt roads and dirt “parking” areas. Using fine brown rock like he mentions would allow for hard surface areas that look like period features and scenery as opposed to landscaping and a rock or a paver stuck somewhere.