Simple weight box question?

[zmansmac]

I'm getting very close to turning the weight box design in my imagination into reality. But my head always spins when I look at all the different formulations of concrete mix in the local home improvement stores. I'm only looking at about 600 pounds and a lot of it will be scrap metal. So cost due to the number of bags I'll need is not an issue. So which is the best formulation for a tractor weight box?:confused3:

JohnZ
B7500

 

[dusty3030]

Cheapest sackcrete general purpose mix you can find, below is easy to use.
http://www.homedepot.com/Building-M...3&langId=-1&productId=100318511&storeId=10051

 

[Groo]

granite rocks are denser than concrete. fill it full of rocks first.