Texas Classic Bridge Railing
For more information of a technical nature you may contact Mr. Mark Bloschock, P.E. at TxDOT, telephone 512-416-2178, or via email at MBLOSCHO@dot.state.tx.us.
The intended use of the Texas Classic Bridge Rail design was for park settings, historical areas, and urban locations where a historic feel or aesthetic design was desired by the owner/client. The 411 rails are intended for highway bridges, but at low design speeds only. Testing under NCHRP Report 350 supported and confirmed this type of restricted use.
Bridge Railing Construction MethodsA local bridge contractor assembles the bridge material components by nailing the disposable foam block-outs in place against the reusable forming board used to define the back surface of the bridge rail. This is to hold the foam in place during the installation of the re-bar.
After the rebar is placed, the other side of the forms, containing another piece of forming board, is assembled against the front surface of the foam insert. At that point the completed assembly is joined with a Taper Tie, a bolt which is tightened to hold the foam in place. The foam is supplied in a slightly oversized thickness to allow for sufficient tightening to keep the foam in place during the concrete pouring.
Each of the three designs is also available in two heights, requiring either a 28″ (tall) block-out or a 21″ (short) block-out. A bid letting request will likely appear in the form of “lineal feet of bridge railing”; so to estimate the number of block-out parts that will be required, use an estimate of one piece of foam for approximately every 18″ of bridge railing – i.e., a 120 lf. bridge railing (both sides) will use approximately 80 blockouts. Typically the railing designs will be designated as item C-411 (28″ height) or item T-411 (22″ height) on the bid sheets.
Concrete Form Release AgentsConcrete form release agents are used by contractors to assist in the foam removal process after the bridge railing is poured. The Expanded Polystyrene blockouts we manufacture are sensitive to solvents, so solvent-based release agents are not recommended.
To facilitate block-out removal from the cast concrete bridge railing, it is recommended that the foam piece be treated with a non-solvent release agent. Call us for suggestions and price quotes on the block-outs at 1-800-333-3626. Since the bridge railings are poured on site, proper environmental considerations are advised for block-out removal and disposition. The use of traditional solvents, such as gasoline, is likely to be prohibited. We have tried a sample of DUOGARD II, a water-emulsion form release agent, and found it safe to use with our blockouts.It is manufactured by W.R.Meadows, Inc of Elgin, Illinois. DUOGARD II can be applied to the foam in a thin film by spraying, mopping, or brushing. W. R. Meadows has manufacturing facilities across the US and Canada, with local distributors serving concrete industry contractors. For additional technical information, or to learn the name of a distributor covering your area, call 1-800-342-5976.
After removal of the foam blockout a slight white residue is likely to remain on the surfaces of the bridge window. It can be removed quickly and easily using a portable high pressure water washer.
Removing the foam blockoutsThe bridge window design for the Texas Classic Bridge rail uses a one-piece foam blockout that essentially gets locked in place by concrete as the railing is poured. Removal can be a challenge, even after thoroughly coating the foam with a release agent.
Experienced bridge builders have offered us several different approaches for blockout removal, but the most effective method seems to use a couple of short pieces of rebar as handles, with a piece of (~10 gauge) wire in between. One of the pieces of rebar is pushed through the foam blockout near the top. The wire is then pushed through the opening and attached to the rebar. So you end up with a rebar handle on both sides of the bridge window, with wire in between. Then use a sawing action around the inside of the window to release to foam. Obviously this depends on having good access to the outside of the bridge rail.
At that point the foam piece can be pushed out. This final removal has been accomplished using a 4 x 4 as a ram – attached to a rubber-tired loader bucket. The foam is pushed out in a single piece, which minimizes the amount of foam residue blowing around. Good environmental practice suggests placing the foam pieces in plastic bags for disposal.
If you’ve had a good pour, with good vibration, you should see very little evidence of air bubble, voids, or honeycombs in the concrete. But there can always be a small residue of white – which can easily be cleaned with a high pressure portable washer.
Finally, and depending on the bridge rail specification you may leave the railing as is – or perhaps apply a one-rub finish. Another common alternative is to paint or stain the concrete. Builders we have talked with have developed similar methods that work, and have improved their productivity in the process.