frost protection sidewalks 2

[costace]

I am familiar with ASCE 32 and FPSF design methods. However, the site contractor proposed XPS under sidewalks and claims that he has seen less cracking as a result of this. The contactor whispered this into the municipal owner's ear and the owners want to include this in the proposed cement concrete walks. I exhausted my search to find design methods for this to no avail. Methods exist for footing and slabs, but not walks. For XPS to provide benefit, it needs to extend about 4ft beyond the edge of walk.

Has anyone heard of XPS frost protection under concrete walks in the Northeast US and if yes, please comment.

 

[oldestguy]

Let's say you have a sidewalk out there with no insulation under it. In winter will it make any difference if the walk heaves along with the lawn along side? Probably not. Then, with insulation under the walk, you have a depressed walk while adjacent land is higher. I'd not like that.
The only place I'd insulate under a walk is where it enters a building.

 

[MotorCity]

I have not heard of this approach being used for sidewalks. I suppose that theoretically it would work, but does not sound practical to me.

 

[MTNClimber]

I would say you're better off having a good, non-frost susceptible base material under your sidewalks. XPS for sidewalks sounds expensive (and odd) if you're doing the entire street. Maybe less weird if you're doing 10'-25' of sidewalk... but still odd to me.

 

[oldestguy]

Here is a true story. At a small village with new construction of a main road at the entry into town some "great thinker engineer" decided the bad subgrade would heave badly in winter. So his design called for preventing a lot of heave by placing the thin base course on a layer of insulation. Worked great. No heaves. However one rainy day the temp was at or below freezing. So the rain stayed wet on the road just outside of town, but it froze on the insulated part in town. So in comes the traffic at highway speeds hitting a glare icy road. You guessed it, many pile ups. Ya fix one problem and cause another.

 

[MTNClimber]

Ha, that's great! Sometimes it's best not to re-invent the wheel.

 

[amlinerrichard]

There must be in excess of 50,000,000 feet of uninsulated sidewalks in the Northern tier of states. If it ain't broke, don't fix it.

 

[geotechengineer1]

It sounds like the site contractor has had a visit from the XPS salesman who has offered him a weekend at a "training course" in Vegas to make some XPS sales.

 

[aeoliantexan]

I have used XPS under sidewalks and pavements in the Midwest over silty clays. Applications included sidewalks that must meet the doorsill grade, sidewalks transitioning to supported floors over basements in plazas, sidewalks and wider slabs in parks next to pools where the water table is high, the pool floors and walls, and pavements at parking garage entrances. Basically, anywhere that a modest amount of frost heave would create a tripping hazard, keep the door from opening, or cause cracking because one edge was doweled to the structure. My rule of thumb at the latitude of Omaha was one inch of closed cell Styrofoam reduces heave, two inches prevents it.

 

[darthsoilsguy2]

Generally speaking... this is BS. The only benefit that really could be happening is that you are placing a homogeneous semi-compressible layer of unfreezable material beneath the subgrade and the slab that could cushion the slab against differential heaving from non-homgeneous soils with variable drainage conditions.... But that has nothing to do with insulating the ground to prevent freezing. In fact, without extending the insulation beyond the walk's edge you could end up with differential freezing at the subgrade elevation and the walk will need to span like a beam until the central zone freezes. Whether the benefit of putting a semi-compressible filler below the slab outweighs the negatives of having variable near surface freezing is a dice roll

Our frost depth is 5 ft. Standard design in this area is sidewalks over 18" of compacted gravel and keep the fine soils (#200 sieve) limited below 5%.