Min. Compress. Strength of Flowable Fill in Parking Lot Application

[Jeng79]

What is the minimum compressive strength of flowable fill that would be recomended for a parking lot application? Our parking lot is generally for "cars-only".

There is underground utilities being added - the contractor is proposing using flowable fill CLSM instead of compacted back fill.

I did search and was not able to find a sufficient reference stating such a strength-nor a way to correlate a SPD to a CLSM compressive strength.

Any thoughts would be appreciated. Especially providing a good reference for us to review, which discusses the topic.

 

[cvg]

f'c less than 100 psi, 1/2 sack mix is plenty and far better than most compacted backfill. If mechanical protection is required for the utilities than use 1 1/2 sack mix, but be forewarned that you will not be able to easily dig up and repair the pipes later.

http://www.cement.org/basics/concreteproducts_clsm.asp

 

[Ron]

Agree with cvg...just enough cementitious material to give it a little strength, but still removable by shovel. 75 to 100 psi, max.

 

[Jeng79]

Thanks for the information. I am aware of the general maximum strength of 100psi or less to allow for future excavation - however I am interested in how low the compressive strength could be and provide sufficient performance as a sub-base? I still haven't been able to find that information or any concrete organization or DOT that specifies what the minimum compressive strength shoud be.

 

[cvg]

allowable foundation pressures are generally in the 1,000 to 3,000 psf range. CLSM with 25 psi compressive strength (generally the minimum supplied) provides about 3,500 psf, exceeding code allowable pressures for building foundations on soils. More often the strength is closer to 70 psi which is about 10,000 psf and is significantly stronger than most residual soils. You should be more worried about settlement than compressive strength here.

 

[Jeng79]

Exactly what I was thinking. Working back the uniform pressure, a very low compressive strenth flowable fill still provides a large equivalent bearing pressure.

I am more concerned about settlement/deformation of the pavement on the flowable fill. Especially thinking about a wheel load on the pavement section.

 

[Ron]

As others have noted, not much strength required. It is a subgrade consideration, not a base or surface consideration.

Keep the strength low, don't create "hard spots" in the pavement section and make it excavatable for future repairs.

 

[grabens]

I seem to recall using a soil-cement material as a pavement base course and specifying the soil-cement mixture be at least 300 psi. This is for projects in Central Florida.