I have dealt with CLSFF on a few occasions and can offer this advice
in response to your questions.
1. The strength of the CLSFF can be specified to whatever your project
requirements are. Strengths in the range of 50 to 150 psi are commonly
specified for piping backfill, so that the material can still be
excavated if need be. In a foundation backfill situation, you need to
specify the strength necessary to prevent shear failure in the CLSFF.
2. The compressibility of CLSFF is substantially less than most soil
materials as long as the applied stresses stay well below the failure
stress of the CLSFF. A compacted sand would have an elastic modulus in
the range of 50,000 psi. In comparison, if you assume a weight of
100pcf and a strength of 100 psi for a CLSFF and plug those numbers
into the ACI formula for concrete elastic modulus, you get 330,000
psi.
3. Since CLSFF is an engineered material that is proportioned and
mixed in the same manner as regular structural concrete, you should
expect the same degree of uniformity. If your design depends on a
certain strength, I strongly suggest that you have the design mix
tested prior to use at a testing laboratory and then have mortar cubes
(as opposed to regular concrete cylinders) of the material taken in
the field for lab curing and testing.
4.I would expect the variability of the CLSFF properties to be low as
long as you are providing the proper QA/QC testing.
5. I don't think that you should be considering the material to be
soil-like. It is a cementitious material and should be evaluated like
structural concrete, just much weaker. Effective stresses would be
inappropriate in my opinion.
If you do a search on the web for controlled low strength flowable
fill, you will find concrete companies are really pushing this
material and some of them have good data for your reference. They like
the material since its another chance for them to sell their products.
Contractors like it since its easy for them to use, pour it in and let
it set.
I feel that CLSFF is a preferable alternative to other pipe bedding
materials when you are concerned about seepage along a buried
pipeline. It may even completely substitute for seepage cutoffs if the
length of the piping is great enough.
I hope this is of use to you.
Martin Brungard, PE
Woodward Clyde
Tallahassee, FL
______________________________ Reply Separator _________________________________
Subject: Flowable fill, self compacting concrete, etc
Author: "Bleakney; Michael (DOT/STR)" <[log in to unmask]> at Internet
Date: 9/25/98 11:41 AM
Have any list members had experience with the material variously known as
flowable fill, self compacting concrete, etc?
I am considering its use as a structural fill material beneath a shallow
foundation. The thickness of fill required is such that a compacted
soil/aggregate fill will permit excessive settlement. The material would be
seasonally submerged.
The sort of things I would like to know about this material are:
1. What range of strengths can be expected?
2. What range of compressibility properties can be expected (elastic
modulus, subgrade modulus, etc.)?
3. How difficult are these properties to predict and control?
4. Is the variability of these properties very high?
5. For strength and stability considerations, is it best to consider
effective stress, drained, behaviour; total stress, undrained, behaviour;
or ????? Or should it be considered a soil, or soil-like, at all?
Any suggestions, or experiences, would be appreciated.
Michael R. Bleakney
Geotechnical Engineer
New Brunswick Department of Transportation
Structures & Materials Branch
PO Box 6000
FREDERICTON, NB
E3B 5H1
CANADA
Tel: (506) 453-2674
Fax: (506) 457-6714
E-mail: [log in to unmask]
