CTLGroup developed specifications and drawings for the repair of a concrete switch deck of a 35-year-old coke drum support structure in Carson, California. The project was prompted by the early failure of several previous repair efforts. The repair material delaminated from the existing base concrete, exposing corroded reinforcing steel and presenting hazardous conditions for workers on the deck.
The repair had to take place while the coker remained in full operation. The concrete is exposed to temperature cycles where the maximum temperature exceeds 310°F, with 5-hour intervals between cycles. Therefore, the time available to perform the repair was limited and the material had to cure during the cycles. The work involved:
- Mix design for a cementitious repair material suitable to install without greatly disrupting operations. The material needed to set fast with high bond strength and low permeability to minimize future corrosion of the steel reinforcement.
- Examine samples for microcracking and carbonation of the original concrete.
- Develop repair specifications and drawings to address concrete removal, temporary shoring, concrete formwork, reinforcing steel, substrate preparation and cast-in-place concrete repairs.
- On-site consulting during the repair work, evaluating the effectiveness of surface preparation, verifying steel placement and form construction, assessing concrete mix and measuring bond strength after placement and curing.
CTLGroup evaluated the performance of the repairs over a 10-month period. The coker was never taken offline due to requirements of the rehabilitation and the repairs performed very well.