Compaction of Fly-Ash?
Compaction of Fly-Ash?
(OP)
Has anyone seen the placement of fly ash where the fly ash is compacted? I thought the fly ash comes in the form of flowable fill which does not need compaction. Please comment.
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RE: Compaction of Fly-Ash?
When mixed with soil, I always recommend that the resulting mixture be field tested based on strength not density; since the fly ash tends to result in a somewhat lower density than soil alone. But very high stiffness and strength.
RE: Compaction of Fly-Ash?
To make a useful construction material out of fly ash, agents such as lime or cement are added to stabilize it (such as flowable fill).
Fly ash contains the concentrated heavy metals from coal which can contaminate groundwater. Lime or cement "lock" the these contaminants in place and make the use of flowable fill environmentally acceptable.
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RE: Compaction of Fly-Ash?
RE: Compaction of Fly-Ash?
Several new power plants came on line that included stack scrubbers, which produce their own industrial by product - scrubber residue. The company began to mix scrubber residue with the fly-ash, bottom-ash, LKD blend and continued to deliver this to market. Seemingly all continued to go well.
Several months later (after construction completed) a poltergiest appeared at these projects. Buildings began to crack, doors failed to close and walls/slabs began to crack. Needless to say, there was a huge problem!
A cottage industry was born! What was happening. . . .
Here is the summary: Flyash mixtures when blended with lime can be very effective. If, however, there is a source of sulfur (i.e., in the case of the scrubber residue), a damaging reaction occurs in the presence of moisture; the development of ettringite. Any of you concrete guys know about ettringite; however, in a fill pad there is a different dynamic. The ettringite crystals in the pore spaces of the fill create a jacking force that is quite impressive! We measured heave of 6 to 9 inches in some slabs.
My advice: If you are using coal combusion by-products confirm for yourself that the product does not contain appreciable quantities of sulfur. I'd limit the total concentration to under 0.5 percent of the total dry mass. However, to be safe take your odometer and do a swell test and run it for 30 days (i.e., if there is any sulfur in the overall product).
These were HUGE lawsuits!
f-d
¡papá gordo ain’t no madre flaca!
RE: Compaction of Fly-Ash?
RE: Compaction of Fly-Ash?
RE: Compaction of Fly-Ash?
It wouldn't be a baseball field in NC, HAH!
i hear once you get to 1st the hard part is over and it's all downhill from there!
RE: Compaction of Fly-Ash?
f-d
¡papá gordo ain’t no madre flaca!
RE: Compaction of Fly-Ash?
One sieve analysis shows that over 80 percent is finer than #200 sieve. This was obtain from a field sample. I do not have any data from the supplier.
RE: Compaction of Fly-Ash?
Good luck.
f-d
¡papá gordo ain’t no madre flaca!
RE: Compaction of Fly-Ash?
RE: Compaction of Fly-Ash?
RE: Compaction of Fly-Ash?
RE: Compaction of Fly-Ash?
RE: Compaction of Fly-Ash?
In my previous assignment, given that the fly ash was being "confined" on all sides by an outer clay layer (and the base was clay as well), then the grounwater level, eventually, even with good measures installed, would eventually rise up and may, then, create a situation of saturated subgrade under the roadway (bathtub effect). This would not be a good thing. I had thought that, say, 1/2 way up to 1/3 way up the embankment, one could lay horizontal pvd wick drains within the embankment which would daylight out of the clayey confining layer and would therefore maintain the maximum groundwater "mounding" at a prescribed and suitable level.