Reinforcement Cover for Concrete Grade Beams

[pcronin]

I know that ACI 318 states in section 7.7.1 clear cover for "concrete cast against and permanently exposed to earth" clear cover is 3 inches. Are there any specific requirements or recommendations for a slab and grade beam system that will be cast against the earth, but the soil should settle below? Furthermore, if the slab system is placed on stone and a vapor barrier, does the 3" cover still apply? I am currently trying to maintain the 3" cover, however my reinforcement is getting heavy. Any suggestions on how I can handle this issue or references I may use will be greatly appreciated. Thank you.

 

[gerrytt]

Maintain 3" minimum once cast against soil, if using a vapour barrier on 2" minimum sand blinding, then you can reduce to 2" minimum. If reinforcement is heavy, use more spacers. If cast against stone, maintain 2" minimum between highest point on stone surface an rebar. Note concrete cover protect the rebars and settling is not going to be quantifiable.

 

[dik]

From my standard drawing notes (for Canada):

CONCRETE COVER TO REINFORCING SHALL CONFORM TO THE FOLLOWING U/N:
SURFACES POURED AGAINST SOIL 3.0 in.
FORMED SURFACES EXPOSED TO SOIL
BARS LESS THAN OR EQUAL TO 15M 1.5 in.
BARS GREATER THAN 15M 2.0 in.
TOP AND BOTTOM SURFACES OF SLABS 1.0 in.
FACE OF WALLS 0.75 in.
SURFACES OF BEAMS AND COLUMNS 1.5 in.

correct for proportional spacing