Concrete Pad Questions

[Jerry D]

We have a cover all building (metal arches with white poly cover) that we are building.

We want a concrete pad inside and an apron outside. Inside is 40x80 and apron would be 40x20 roughly.

Contractor says 30mpa with wire mesh inside

32 mpa with 6% air with 10mm rebar on 3ft centers for apron outside

The building is unheated. Thoughts?

[expedition]

Wire mesh is garbage . Rebar 16 to 18 inch centers

[lannie]

Preparation for the pad is as important as the pad itself.
Get a compacted base built using 3/4" road crush 8" deep and a 1000 lb plate tamper. Use water sparingly to get 98% compaction. When this is done start working on the actual concrete. Have a plan on everything before you put the crush down including drains if used or slope on pad etc.

[Parker Hale]

Ditto on the rebar, and 3' spacing in the apron is not enough. Should be 16"-18" as well.

[Trochu]

What are you using the facility for? Heavy loads? As indicated by expedition, 3' off center seems like pretty large spacing. For mild loads, 10M seems reasonable. Most floor slabs don't have air added as a smooth finish is desirable and air literally adds air bubbles to the mix. That being said, most floor slabs are in heated buildings and air adds flexibility to the concrete, which in theory will reduce the cracking as the floor heaves with the frost.

[expedition]

Concrete inside an unheated structure should have the same consideration and construction as your apron. I recomend air and light broom finish.

[Smokinyotes]

I’m not a cement guy but the smoother you have it the easier it is to sweep. My shop is 40x60 and I have wire mesh with 10mm rebar. Make sure you saw cut it to prevent cracking

[Jerry D]

Building is just storage and parking tractors etc. Small tractors 60hp size and less. Hobby farm.

[Redneck 7]

If I was going to build this pad and apron for my shop, I’d go 2x6 for forms, 2” slope to a center sump in the floor with or without a drain. I’d do 16” centres with 15 mm rebar, 30-40 mpa concrete, little air wont hurt, steel finish inside and a broom finish outside, 2” slope away from the door. Saw cuts would be a definite.

So 5” thick slab and 15mm rebar, if you don’t want to pay for 15m rebar you can go with 10m but I’d go 12” centres.

[expedition]

Originally Posted by Smokinyotes

I’m not a cement guy but the smoother you have it the easier it is to sweep. My shop is 40x60 and I have wire mesh with 10mm rebar. Make sure you saw cut it to prevent cracking

True . Unheated concrete should have air entrainment to greatly increase freeze thaw durability . Whwn you trowel air entrainment can cause spalling.

[Bassett]

Originally Posted by Redneck 7

If I was going to build this pad and apron for my shop, I’d go 2x6 for forms, 2” slope to a center sump in the floor with or without a drain. I’d do 16” centres with 15 mm rebar, 30-40 mpa concrete, little air wont hurt, steel finish inside and a broom finish outside, 2” slope away from the door. Saw cuts would be a definite.

So 5” thick slab and 15mm rebar, if you don’t want to pay for 15m rebar you can go with 10m but I’d go 12” centres.

I second this, only thing i would add as we do it everytime at work is a 12-16" x 2" deep thickening around the edge of slab and apron with double perimeter bars.

[Ice Fishing Maniac]

Unheated interior building should have Air Entrained concrete.

Ask your concrete supplier to provide "Dura-mix" product. Its an ARMCA industry standard class mix for exterior exposed concrete / non-heated buildings slabs. HS Mix Type with 5-8% Air Entrainment, 80mm Slump and 30-35 MPa if I remember correctly.


As mentioned, light broom finish - you cannot power trowel finish air entrained concrete.

10-15M bar at 12-16" o/c will be good.

As mentioned clay subgrade and gravel base prep is very important. 98% compaction SPDD at Optimum Moisture content for clay and for the crush gravel - keep the moisture on the crush gravel lower than Optimum.

Make sure to have good drainage away from your building footprint.