I have a customer who called me the other day about a little bridge on her property washing out. The "bridge builder" set 2x2x6 concrete blocks (mafia blocks) for abutments and then just poured 4" slabs for approaches and a suspended 4" slab to cross. Now the water has eroded under one of the approaches. Ideally would be to break out the slab, cut it down solid and backfill with compacted gravel and repour the slab, costwise thats not feasible. My thought is to cut out either side of the approach slabs and set blocks to reinforce and protect them, which will also give me a "diversionary structure" to channel the water. Then cut a hole in the washed out approach slab and run flowable fill under it to fill the void and make it solid. Here's the hard part... I've never dealt with flowable fill and don't know anything about it. Will it set up under an existing slab given time to set and cure? I'm open to suggestions. Thanks John
We use a lot of flow able fill behind building retaining walls, under foundations, in tough backfilling spots, when adding new services under building walls, etc. A one bag mix will yield more strength than compacted structural fill and will flow great. We normally core drill a few holes to vibrate thru dependent on size of the void to fill. If underwater, different placement methods are needed but still easily done and the cure strength is the same.
Been around a lot of it and there should be no problems curing it one job I was on we were pumping 300' down and filling in an abandoned coal mine
just don't forget as the name implies it's (flowable) any crack's or hole's in the walls it will blow out so make sure every thing is button up tight if it's a very big hole you may be better off to pour it in lifts better safe than sorry
I dont have any experience with flowable fill.... What does this stuff cost? I assume it comes from the local concrete suppliers?
It depends on the sack per yard cement content. I use it from time to time and order one sack per yard. Five sack concrete runs about $80 per yard here and the last time I ordered one sack flowable fill it was $50 a yard. When I lived in Cali we called the mix "sand slurry", but that was quite awhile ago. The term "flowable fill" sounds like a more marketable term.
Runs about $90 dollars here when bid with project concrete. 5 bag runs about $115. Should be at about 80% of normal concrete. Comes out in the redi mix truck just like normal concrete, only about at a 9 to 10 slump.
Thanks for the replies and information guys. I love this site for the huge amount of noncompetitive friendly advice that's here. I figured about 8.5 yards to fill the void under the approach slab. This seems like the best, easiest, most cost effective solution to someone else's half hearted attempt. Thanks guys John
Back in the day, we had a job to abandon a old storm sewer line and we use "flowable Fill, we just pulled the mixer up to a manhole and let her rip, Like old-iron-habit said the slump was around 9 - 12 and I think ? we dump around 25 yards down the manhole, but there were a couple problem the biggest was air displacement of the flowable fill in the pipe we had to make a couple changes to the bulkhead at the end of the line. I think that the fill we used was only a 2 bag mix with only a sand mix.
Sometimes if you get a void that never fils. If you get a bleeder like that, let it set up and try again.
If possible try and put a small vent in it-that will take care of the air-if necessary pour some and then wait a couple of mins and pour again-it will work just fine