Mix concrete on 0-32 crushed stone?

[Andreas A]

I'm going to cast a footing on bedrock for a retaining wall, on which I will later place the house's edge beam. Can I mix cement with 0-32 crushed rock or must I follow the instructions on the bag? I think that what it says on the bag, 0-8 gravel and pebble, becomes almost the same as 0-18. Maybe I'm completely off track.

Does anyone know?

 

[Fasting65]

The difference is that 0-8 concrete gravel has an even grading curve, which means there's an even distribution of 0-8 millimeter stone. If you use 0-32 crushed rock, the distribution throughout the range is a bit hit or miss. I remember my neighbor tried casting with 0-8 stone dust instead of casting gravel. It worked okay, but he tried some chemical from SIKA and the concrete got the "right" properties again.

 

[Krawk]

You're probably getting too little fine material with 0-32 crushed rock.
But it completely depends on what kind of rock has been crushed, whether the loader took from the top or bottom of the pile, etc.

Try mixing a wheelbarrow and see? You can easily measure the moisture content with a small scale and the kitchen oven.
The final strength is uncertain, but maybe that's not so important?

0-32 concrete will be quite laborious and stiff even if you get the gradation curve right.

If you need many cubic meters of concrete, it might be worthwhile to call and order a truck instead...

 

[Mats]

I have used both 0-8 plus 8-16 as well as 0-18 all-in-one for simpler castings and there is a difference between crushed and real casting gravel. The concrete becomes more homogeneous with real gravel.

For something as important as a house foundation, I would probably follow the sack's advice.

 

[Andreas A]

Now have the right gravel and crushed stone at home, there might be no shortcuts if you want the best results.