SrVaro
Structural
- Oct 19, 2010
- 53
I am working on a small portion of a large industrial rebuild project. My portion has been designed for approximately 3 months, and now the PM is stating a construction schedule that I feel is not possible.
My portion of the project was to design a replacement concrete pit for a rail unload station. The new pit is 7'-8" wide x 16'-6" long x 4'-9" deep. The pit was required to be designed to support a fully loaded rail car across the 7'-8" direction. The walls are 13" thick with reinforcement each face and the base slab is 12" thick with a double mat. I am very comfortable with the wall design under normal construction time tables.
I am now being told the construction schedule is 140 hours, just under 6 days, to be fully functional again. This would include demo of the old concrete pit, excavation for the new larger pit, form work, pouring, curing, and the placement of the mechanical equipment within the pit. At the end of the 140 hours, the pit will be fully loaded with the rail car.
When I stated this schedule is not possible, the response was to use early strength concrete. The concrete design requires 3000 psi at 28 days, therefore I specified 4000 knowing that the construction would be completed earlier than 4 weeks, so I would still have the required concrete strength.
I do not think it will be possible to get 3 day concrete at 3000 psi. Even with using all the following:
- type III cement
- no fly ash
- tenting the area and using steam curing
Especially since this will be a special design fix there will not be any previous testing data, therefore per chapter 5 of ACI the cylinders will need to be tested for at least f'c + 1000 = 4200 psi.
Are there any suggestions, comments, or similar that could help them achieve their goal? Any assistance would be greatly appreciated.
My portion of the project was to design a replacement concrete pit for a rail unload station. The new pit is 7'-8" wide x 16'-6" long x 4'-9" deep. The pit was required to be designed to support a fully loaded rail car across the 7'-8" direction. The walls are 13" thick with reinforcement each face and the base slab is 12" thick with a double mat. I am very comfortable with the wall design under normal construction time tables.
I am now being told the construction schedule is 140 hours, just under 6 days, to be fully functional again. This would include demo of the old concrete pit, excavation for the new larger pit, form work, pouring, curing, and the placement of the mechanical equipment within the pit. At the end of the 140 hours, the pit will be fully loaded with the rail car.
When I stated this schedule is not possible, the response was to use early strength concrete. The concrete design requires 3000 psi at 28 days, therefore I specified 4000 knowing that the construction would be completed earlier than 4 weeks, so I would still have the required concrete strength.
I do not think it will be possible to get 3 day concrete at 3000 psi. Even with using all the following:
- type III cement
- no fly ash
- tenting the area and using steam curing
Especially since this will be a special design fix there will not be any previous testing data, therefore per chapter 5 of ACI the cylinders will need to be tested for at least f'c + 1000 = 4200 psi.
Are there any suggestions, comments, or similar that could help them achieve their goal? Any assistance would be greatly appreciated.
