Concrete Driveway 1

[RetMark]

My project includes adding a narrow strip of concrete (1.5' in width) to an existing drive fabricated of 12' x 12' panels, 4" thick, rebar on 12" centers. In order to minimize potential cracking, what sort of enhancements (high strength concrete, 5" or 6" thickness, extra reinforcement, etc.) might be considered? This drive is for auto traffic of typical (say 4000 lbs) size at low speeds.

Thanks to all for their helpful advice.

 

[racookpe1978]

Is the 1.5 foot (18 inch) added to go on the right, left, or "probably not driven on" or "one side, but then we will repaint the centerline divider"?

 

[Ron]

cut a control joint every 2 feet

 

[darthsoilsguy2]

What they said... but in my imagination the finished product seems a little out of place with the old and larger existing concrete panels... consider looking at a brick paver edging detail perhaps with running bond stretchers... granted, i don't know what the rest of the site looks like or your reasons for this to understand if that would make any sense with the bigger picture.

 

[LittleInch]

dowel into the existing concrete for the re bar for the extension?
Have some very good and compacted backfill
Extend the backfill beyond the edge of the new slab

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[RetMark]

Thanks to all for their helpful advice.

I would prefer to attach new pieces to existing as not wanting to create a problem on existing pavement which is crack free. If the new piece is doweled in would a control joint be added where the two pieces join?

 

[oldestguy]

A control joint is usually used for long ex0pansis that expand and contract. You don't need a control joint. However, it may be neater to trowel that joint for appearance sake only. If using dowels, be ultra careful to center the hole, because a 4" slab is pretty skimpy in strength there.

 

[bimr]

Steel reinforcing bars and welded wire reinforcement will not prevent cracking. Reinforcement is basically dormant until the concrete cracks. After cracking, it becomes active and controls crack widths by restricting crack growth.

As oldest guy stated, the slab is skimpy for installation of rebar. For welded wire reinforcement, the Wire Reinforcement Institute recommends steel placement 2 inches below the surface or within the upper third of the slab thickness, whichever is closer to the surface.

Unless the existing slab has an existing trowel edge, the new joint will not be neat.

Consider darthsoilsguy2 recommendation.

 

[RetMark]

Thanks again for all the helpful comments.

So to control the cracking, would a thicker slab (5" or 6") in the narrow section be beneficial? Also, is the type or selection of concrete significant?

 

[cvg]

recommend nothing less than 6 inches
good compacted gravel base
no reinforcement is probably needed
standard Class A (3,000 psi) concrete is adequate

 

[concretemasonry]

Minimums and local practices can exceed the "standard Class A (3000 psi)concrete" that is "adequate".

In some areas, for driveways, aprons, garage floors and some sidewalks, the unwritten standard is 4000 psi with 5% air for durability. Even if it is not written, a supplier may refuse to deliver something less is they sense it falls into those applications. The supplier does not want to get into a hassle later if it is not a contractor with good practices. - The sale of a load or two is not worth the later problem of the an undeliverable load of concrete.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.