See how to plan casting sequence, control placement timing, and avoid cold joints during UHPC pours on bridge projects.
When casting ultra-high performance concrete, it is important to carefully plan the casting sequence.
The bridge should be cast from the lower elevation toward the higher elevation. Fresh UHPC wants to flow downhill, potentially leaving unfilled pockets if casting begins at the high side. By first casting on the low side and immediately securing top forms, the UHPC is already in its preferred location. The top forms ensure it has resistance to the pressure head that will form as work moves up the bridge. This challenge will begin to resolve itself as the UHPC sets and no longer tries to move.
Most UHPC projects are designed without construction cold joints, unless otherwise stated. Controlling production and placement to avoid cold joints is therefore another key consideration. A plan should be made to match the volume of fresh UHPC coming out of the mixer at each batch to the volume of each placement location on the bridge, ensuring adjacent pours are cast as soon as possible before the previous UHPC sets.
Mobile concrete buggies are used to move fresh material from the mixer to the placement location, and the number of buggies needed will depend on the volume of the buggy and the volume of the mixer.