If you're making "concrete" abutments and tunnel portals, styrene can be used to either represent concrete or as a material to make moulds. I use .060" styrene, bought as 4'x8' sheets, for either. If you use it to represent concrete, you need to layer it to get the effect you want (buttresses, curbs, or whatever relief you require) and then paint it to suit. If you use it to make moulds, you should first sketch out on paper the shapes you require. Unless the shape is very simple, the mould should be designed in two or more parts to facilitate removal of the finished part. I usually cast bridge abutments in place on the layout, whereas piers are easier to do at the workbench. If you go to the Photo Forum, I have several posts that show various "concrete" structures. Probably the best one to view, as far as variety goes, is entitled "A mysterious move...".
The first bridge that the train crosses has poured-in-place abutments and workbench-poured piers, the second bridge has workbench-poured abutments, (not visible) and piers. The tunnel portal is sheet styrene, as is the long retaining wall by the coal dealer's yard near the large station. There is also a bridge, not shown, that has high concrete piers that are installed across the uneven bottom of a wide ravine. To make these, I made one styrene mould, in two pieces. The piers are tapered on all four sides and are of varying heights. The mould consists of one piece encompassing two adjoining sides of the pier and the second piece the other two sides and the top. There are a few aligning tabs glued onto the outside of the mould so that the two halves don't become misaligned during the pour. I use a paper towel to lightly coat the inside of the mould (before assembly) with vegetable oil. After assembly, the halves are secured with elastic bands and the mould stood upside down on a convenient work surface. I made this mould tall enough for the tallest pier required. For the shorter piers, I made a pencil mark inside the mould and filled only to the line, allowing a little extra height for carving to suit the site. Because the piers are shortened at the bottom, the profile at the top remains constant across the length of the bridge. Rather than Hydrocal, I used a patching plaster called Durabond 90. It sets firm in 90 minutes, and over the course of a day or two, depending on the thickness, becomes harder and less brittle than Hydrocal. If you want to carve stone detail on this stuff, do it before it gets really hard.
I hope that this is of some assistance.
Wayne
