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.

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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 truckload is allowed in an arch fill operation.

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HEADWALL INSTALLATION

After the arch concrete placement, no other work activities are allowed for 24 hours.  Only light foot traffic is allowed over the decking until the arches have reached their desired compressive strength.

After the arches have cured for 24 hours, the headwall panels may be erected and braced into position.  Headwall options vary and details will be project specific.

BACKFILLING

Once the concrete deck has cured for 24 hours, the structure can be backfilled using maximum lifts of 12" with a maximum deviation of equal backfilling of 24".  Install drainage as necessary during backfill.  Attach fascia plate if necessary.

After backfilling is completed to finish grade, work can begin on guardrails and paving.