ARCH CONCRETE EMBEDMENT
After the arches and decking have been set, the abutments can be completed.
When the foundations are done in multiple placements, the compressive strength of the prior placement must reach specification before the second placements occurs. Note that there are situations (i.e. with low or no water passages) where the arches can be embedded directly into the foundation within a single pour as shown below.
No other work operation on the deck beyond workmen walking on the deck can occur until the arch embedment concrete cures to the specified strength.
ARCH CONCRETE PLACEMENT
The concrete required in this operation is a self- consolidating concrete (SCC). The SCC mix includes a shrinkage compensating admixtures (SCA), a viscosity modifying admixtures (VMA), a hydration stabilizer (retarder) and a superplastisizer (high range water reducer). A mix design with proven performance needs to be submitted to the engineer for approval.
Flowability of the SCC mix is field tested by measuring slump flow. Typically slump flow (measured as diameter of the concrete spread) is between 24”and 30”.
A concrete fill box has been used successfully to facilitate the concrete operations through the fill hole at the apex of the arches. This fill box allows for flow control and topping off operations, while minimizing concrete overflow and spillage. A maximum of two workmen are allowed at the apex of the arch while it is being filled.
Vent holes are located 18”-24” on either side of the arch fill hole and must be unobstructed during concrete filling.
A continuous concrete arch fill operation is required. No partial truck load is allowed in an arch fill operation.
After the arch concrete placement, no other work activities are allowed for 48 hours. Only light foot traffic is allowed over the decking until the arches have reached their desired compressive strength.
DECK REINFORCING STEEL
Installation of the reinforcing steel for the decking, when specified, can begin after 24 hours of arch filling with concrete. PEX tubing has been successfully used as bar "chairs" to prop the reinforcing to its desired location.
When the non-reinforced deck option is used in the system, this step is omitted.
DECK CONCRETE PLACEMENT
Deck concrete placement can begin once the arches have cured as specified. Deck concrete is still recommended without reinforcement for drainage reasons. Under the unreinforced deck option, the concrete needs to only fill the deck troughs. A stiff mix with a low slump is recommended.
After the deck concrete has cured to its required compressive strength, work can begin on integrating the headwalls and the other subsequent operations of drainage installation, backfilling to grade, guardrail, and paving.
