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RE: Shrinkage of flowable fill against a stone wall

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For what you have described, I would go for the first option.  For what it is worth the officially ACI ordained term for this stuff is Controlled Low Strength Material (CLSM). 
 
Secondly, you might want to consider the effect of the additional weight of the CLSM on the structure in general.  Try to avoid causing settlement problems with the added weight. 
 
You can specify relatively low densities with CLSM, but you can "fill" the space with expanded shale aggregate (very light weight) and cast a 4" concrete slab on top and have a reduced weight and cost.  I would still encourage the addition of the concrete walls along the back side to knit the masonry wall together.  I would also encourage a bond breaker of some sort to whatever you provide to fill up the space.  If the expanded shale is used, there is no need for the bond breaker except for the concrete cap slab. 
 
I would avoid shrinkage compensating additives.  Shrinkage compensating compounds are difficult to predict and begin by expanding the volume.  This can complicate matters.  Let the supplier know what you want with shrinkage (and expansion) and let him make some suggestions.  Controlling the amount of cement, fly ash, aggregate, and water are more effective.  You should also consider placing the CLSM in plan blocks similar to how a concrete dam is constructed.  This allows one block to shrink and you fill in with the adjacent block after the first one has undergone shrinkage. 
 
I just finished assessing a project where they filled a depressed area with concrete.  this added a lot of weight to the soil and caused a lot of settlement problems.... oops!

Regards,
Harold Sprague



Date: Tue, 5 Feb 2008 14:10:42 -0800
From: wilsonengineers(--nospam--at)yahoo.com
Subject: Shrinkage of flowable fill against a stone wall
To: seaint(--nospam--at)seaint.org

I am looking to fill a crawl space between stone foundation walls with flowable fill.  But I'm concerned about potential shrinkage of the flowable fill and pulling in on deteriorating stone walls.  One of the goals is to secure the walls at the inside and protect them from further deerioration.
 
Options we have considered at the stone are:
1. place an 8" concrete wall/curb on the inside of the stone to protect it and bind the cobbles together. Then fill the area between with flow fill.
2. drape a plastic sheet on the stone wall to prevent bonding.  This would also prevent the fill from filling all of the gaps in the stone.  Not ideal.
3. Fill holes in the stone with conrete patch and then fill with flow fill.
4. Just fill as is and not worry about the flow fill affecting the wall.
 
The fill will be about 40'x80', 12"-18" deep.  The foundations support triple wythe brick walls about 24' tall supporting the roof of a church.  The outsides of the walls are several feet below ground.
 
Am I overreacting about consequences?  Or is there a potential for damage at the interface between old and new? The 8" concrete curb would be a plus, especially if it is reinforced.  But is the extra cost necessary?
 
I appreciate any insite into flow fill curing behavior and opinions on our detail options.
 
Jim Wilson, PE
Stroudsburg, PA


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