Required Concrete Exposure for Boat Ramp

[HK2013]

Howdy folks!

I was wondering if anyone had any advice on the required concrete properties for a slab on ground boat ramp. The ramp is going to be half submerged and in an area where yearly ice is possible. The way I read Table 19.3.1.1 and 19.3.2.1 in ACI 318-14, since the ramp will be exposed to freezing and thawing cycles and frequent exposure to water (F2); I would need to specify a min F'c of 4500psi and air entrainment. The client (Civil Engineer) is hesitant to do this as he is worried that it will be difficult to procure the higher strength concrete in rural areas.

Any thoughts or advice?

 

[JAE]

Technically a boat ramp slab-on-grade / or pavement / isn't covered under ACI 318. (see 1.4.7)
But that said, I think the issue is still a concern that icing over time would deteriorate a less robust concrete mix.

So the client would be faced with two options:

1. Use a lower strength (3,000 psi?) concrete and then have a shorter ramp life span where spalling and general deterioration would commence earlier and ramp replacement might be needed in 5 to 10 years.
2. Use a higher strength (4,500 psi) concrete and pay the up front difference but perhaps have a slab that lasts 15 to 20 years.

The life spans I put above are very subjective and that is the challenge that you have to overcome to justify the higher strength concrete.



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[TehMightyEngineer]

Precast 5000 psi+ with corrosion inhibitor, galvanized or epoxy coated rebar (one of the few times I feel it makes sense to use coated bars), stainless steel ties and pins connecting the ramp sections.

I'm biased as our plants make these but I honestly believe that there is very little reason to go away from precast concrete for anything but the most unusual of boat ramp setups.

Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

http://www.americanconcrete.com

 

[SlideRuleEra]

Ramp in salt water or fresh water?
How do you plan to place concrete for the submerged portion of the ramp? Cofferdam?

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[HK2013]

I was thinking the same thing about the durability.

Fresh water, we are planning on a cofferdam during construction.

 

[SlideRuleEra]

HK2013 - I like your specs, 4500 psi, air entertained concrete.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[HK2013]

SlideRuleEra - By our estimate, the cost difference would probably be on the order of 8% of the concrete material cost for the higher strength concrete. We have provided this information and the risks involved to our client along with our recommendation of 4500psi, air-entrained and will see what they decide.

Thanks for the responses evryone! Cheers!

 

[Ron]

Yes...SRE is correct. Air entrainment is necessary. 4000 to 5000 psi compressive strength is in the right range.