RCA as a Structural Fill 1

[joeskin]

Does anyone have any experience using Recycled Concrete Aggregate as a subbase for a building foundation? Have a situation where the proposed building is to be constructed in an area that contains peat. The contract calls for removal of all peat and replacement in controlled compacted lifts with clean fill. Contractor wants to use RCA with a modified proctor of 115.4 pcf. The material is approved as a DGA for DOT applications. The excavation is to be 10 feet deep surrounded by peat. I am concerned that the friction angle may allow the material to fail against the compressible material, not mention the numerous environmental concerns in our state. Any help would be great!! At the 11th hour and I need to make a decision.

 

[cbosy]

It is used all the time here in Chicago. You should go at least 10 ft past the building with it at the bottom of the cut with a minimum of 95% modified. It usually is dry of optimum and needs some water.

 

[fndn]

I agree with cbosy. Just ensure that all the peat and water is removed. You'll end up with a large hole due to cave ins of the side walls. Also a lot of times, the aggregate supplier has clean and not so clean recycled concrete.
Watch the first few trucks and reject any loads that contain wire mesh, rubber and miscellaneous fill material. Lastly, you should avoid having 5" plus size chunks since this will create voids in the lifts and screw up your compaction test results later. By the way, because of the cement in the recycled concrete aggregate, you'll get something like 16% for moisture content and that will be fine.