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UHPC Placement

Review placement techniques that help achieve proper flow, fiber alignment, moisture retention, and full consolidation during UHPC pours.
  1. On placement day, several techniques will help achieve a high quality UHPC pour. Each item can be constructed and available on site prior to placement day to facilitate a smooth experience.
  2. If an overfill is specified in the project, furring boards of the specified thickness can be placed along any UHPC location exposed to the deck to provide a backing for the extra material.
  3. If more than one batch of UHPC will be used to fill a continuous volume, headers can be placed to separate each section. This ensures UHPC will not flow out of a completed location until new material is ready to continue pouring. The headers can be removed immediately as the next batch is ready. Rodding may be needed between adjacent sections to appropriately intermix batches.
  4. UHPC should be placed in a continuous manner to prevent cold jointing. Each new batch should be placed in a location adjacent to the most recent pour. While filling each section of the bridge, pour the UHPC in one location and allow it to flow down the joint or other volume for approximately 10 feet. Then, move the pouring location to the end of the current flow and begin pouring again into existing UHPC. This will provide the best fiber alignment within the UHPC and intermixing between pours.
  5. Fresh UHPC is often transported from the mixing operations to the bridge placement site in buckets or mobile concrete buggies but is ultimately cast in a location with a relatively small opening to the bridge deck. Constructing a trough or funnel can assist buggy operators while moving material from their buckets to the placement location. This will help prevent UHPC from being spilled on the bridge deck, minimizing wasted material and cleanup efforts.
  6. Top forms and head buckets are needed to finish the pour. Top forms can be made of plywood and nailed or weighted down on top of each UHPC location. They protect fresh UHPC from losing moisture due to evaporation from the sun and wind, as well as hold material from flowing out of volumes at lower elevations as the UHPC sets. Head buckets are built integrally with the top forms, matching a port hole in the bottom of the bucket with one cut in the top form. As the top forms are placed, a little extra UHPC is placed in each bucket, forming a pressure head that allows entrapped air to escape and the UHPC to fully fill each location.
  7. Formwork can be removed 24 hours after placement is completed. Grinding operations, if applicable, can begin when the UHPC has reached the construction load strength specified in the project plans. This is frequently set at 14,000 psi and achieved in 3 to 4 days. Field cast cylinders should be used to verify the required strength has been met before loading the bridge.