In place density of 3/4 Crushed stone
In place density of 3/4 Crushed stone
(OP)
We have compacted 3/4" crushed stone for a leveling course prior to concrete placement. The compaction was tested using a nuclear density machine. He used the "back scan" option. Doesn't that give you a direct reading of the in place density rather than a value to compare to the lab density or(Proctor)?





RE: In place density of 3/4 Crushed stone
For determination of in-place density, use a direct volume replacement method such as the rubber ballon method (hard to find these days. You can also use the sandcone method, but you'll have to isolate the voids in the gravel by using Saran wrap to line the hole. Make sure the Saran wrap is loose so that the sand conforms to the particle surfaces.
RE: In place density of 3/4 Crushed stone
Ron is correct that nuclear density testing on clean rock is inaccurate at best.
The choice between backscatter and direct transmission can be governed by the layer thickness. Most meters on backscatter only test the upper 4 inches.
RE: In place density of 3/4 Crushed stone
RE: In place density of 3/4 Crushed stone
RE: In place density of 3/4 Crushed stone
Keep in mind also that the dry rodded unit weight is done in a confined "bucket". Loosely placed gravel has little or no confinement and no cohesion, so you're not really comparing apples to apples.
RE: In place density of 3/4 Crushed stone
I attached a photo of the 3/4" stone which was placed and compacted. There is approximately 2 feet of this stone. It is placed directly on rock. There is a 15' x 34' x 3' deep 4000 psi reinforced concrete footing over this. I am very comfortable with the integrety of the structure. Would you concur?
RE: In place density of 3/4 Crushed stone
I have monitored placement of clean gravel on numerous projects. Our standard requirements are maximum lift thickness of 6-8 inches and a minimum of 3 passes with a vibratory compactor. Generally, it's for backfilling building foundations under sidewalks or lawn areas.
RE: In place density of 3/4 Crushed stone
Structural integrity goes to a lot more than just a leveling course of gravel, so I won't go there.
RE: In place density of 3/4 Crushed stone