Bringing a CBR of 87 to 90

[boxman1]

I work for a small road construction company. I am not an engineer but my boss has tasked me with a project. The quarry we use has gravel with a CBR of 87 and we need a CBR of 90. I need to find a solution that will do this before the gravel reaches the construction site. I have come up with using a pug mill and adding nickel slag to the gravel. Does this sound right? I also need the ratio of gravel to slag mixture. If someone can help, it would be greatly appreciated.

 

[fattdad]

I bet there is another sample from the same quarry that has a CBR of 93 maybe even 102. Have a lab run another test or two.

f-d

¡papá gordo ain’t no madre flaca!

 

[BigH]

Can anyone tell me the real difference between 87 and 90? Between 80 and 90? Mmmm

 

[fattdad]

BigH: My point exactly! You take some large aggregate and measure the load to advance a piston 0.1 inch. Heck, move the piston over a quarter inch and you may increase the value from 87 to 92.

For the purpose of the original post, if you are dealing with a stupid spec, I'd do several CBR tests and then use an average. I'm not even sure I'd bother with the soak.

One item that comes to my mind is how is the sample being prepared? Is there a Emax and Emin so you can prepare the sample to some relative density? Any "Proctor" approach to sample preparation would be seemingly meaningless.

Good luck,

f-d

¡papá gordo ain’t no madre flaca!

 

[oldestguy]

Take a good look at your quarry. Most of them have differing rock beds of different quality.

Can you move about the site and use material from areas where the rock is harder?

As to blending, do you have areas where the blasting was done and large harder stuff (in large blocks) can be separated off and then crushed?

As to ratio, it would appear trial mixes are needed.

However, first run more tests on what you have as has been advised above.

 

[civilperson]

Run a sieve analysis and then scarf off the over represented fraction to make a uniformly graded mix. Run the CBR on the modified mix.