Compaction and CBR

[1354vahid]

I carried out some compaction and CBR tests on recycled aggregates accordig to BS and then, drawn the curves of Moisture content and Dry Densities curves. The curves for Compaction gives higher Moisture content and lower Dry density than the correponding curves in CBR test.In BS the Compaction tests are carry out on the samples passing the 31.5mm test sieve. but the CBR test are carry out on the samples passing the 22.4 mm test sieve. this is the reason that we must take the opposit result. based on my studies for smaller particles at the same aggregates the maximum dry densities becomes lower and the optimum moisture contents becomes higher. can you please help me or give me some references to find the why?
You will find my results in attached file.

Thanks

 

[Ron]

There should only be one specimen for each of the points on the moisture density relationship and the CBR curve. You should not run those as two separate M-D relationship tests.

When you plot the CBR curve above the M-D relationship curve, the moist content points will align. Only the Y-axis scales will be different.

 

[iandig]

You should also look at the overall gradings of the two materials. If you remove coarser material you will change the grading. The moisture in the compacted material acts as a lubricant to aid the packing of the material and also fills some of the voids. If the grading is different, so will the moisture content requirement. With finer soils you tend to need more moisture to compact the material with the same compactive effort, resulting in a lower dry density (maximum Dry Density - MDD).
Therefore different gradings using the same material will have different compaction curves.

 

[1354vahid]

iandig,
Thanks. As I said I concluded some converse results for recycled concrete aggregates. in smaller fraction (passing the 22.4mm for CBR) MDD was lower and OMC was higher than fracton of compaction test (passing the 31.5mm.

 

[Ron]

1354....your data sheet was blank. Re-post.