Concrete placement to ramp slab - top-down, or bottom-up?

[Ingenuity]

A lively discussion on a job site recently.

Construction of a carpark ramp between a ground floor (recently constructed slab on grade) and an upper parking level (recently constructed with PT).

Ramp is RC slab and beam at a slope of 16% (approx 9 deg). Length of ramp is about 20m (66').

There is NOT fully continuous reinforcement in the top of slab - only mesh/fabric over the intermediate RC support beams.

Line pump concrete mix is 80mm (3") slump and 32MPa (4500 psi).

Question: Do you start placement of concrete from bottom of ramp or top of ramp?

Assuming that cost of a line pump vs boom pump hire is approx the same.

Interested in your opinion.

 

[dhengr]

Start placing from the bottom upward so the fresh conc. is somewhat self supporting during the placing process. And, the slump and rate of placement can be adjusted to facilitate in this also.

 

[madmantrapper]

I've never a slope that long but we always went from top to bottom. I'm not sure why. Even when we were doing steps or stair runs we went top to bottom.

 

[Ron]

Bottom to top... facilitates consolidation of the concrete.

 

[Ingenuity]

Thanks for the responses.

The replies from the jobsite from the engineers were bottom-up, to facilitate consolidation and be more self supporting, as others have commented above.

The jobiste contractor replies were top-down, to make it easier to "distribute" the plastic concrete down the ramp.

The contractor-types 'won' and they placed the ramp concrete from top-down.

But the engineers sort of won too, as in "we told you so" - the concrete slumped and resulted in 'plastic tearing' with full-depth slab cracking. Leaks like a sieve now.

 

[hokie66]

Stupid contractor. You don't move concrete that way. The engineers should have stood their ground.