Recipe for strong concrete using ballast.

[epsilonGreedy]

Once the sun burns off last night's frost I intend to fill a shallow trench across the entrance threshold of my drive. The dimensions of the trench are 5.5 meters long 300mm wide and 225mm deep. When the concrete is semi set I will bed down a line of granite kerb stones laid flat on the surface of the setting concrete, these kerb stones are 75mm thick by 150mm wide.

 

Given the vehicle traffic passing over I assume a strong concrete mix is recommend and I have a pile of 10mm ballast left over from the cavity fill operation. I understand that a strong mortar has a 3:1 mix but since the lumpyness of ballast equates to less aggregate surface area to bond, a strong concrete has less cement.

 

In another thread @PeterWsuggest a 4:1 mix was strong but I might not have mentioned I was using ballast. The advice at the site below suggests 1 part cement to 6 parts ballast will equate to a strong concrete for paths and drives. The same site also says 1 to 8 would be good for foundations which is counter intuitive to me.

 

https://www.allmix.co.uk/much-ballast-need-mix-concrete/

 

Anyhow after that preamble what does the panel recommend? I am thinking 5.5 or 6 to 1.

 

He is my other thread discussing the need for the driveway entrance "speed bump".

 

 

[Mr Punter]

Between 1:6 and 1:9 will be fine.  Make sure you dig down the trench to remove any soft material.  Backfill with type 1 and thoroughly consolidate.  If the sub base is not wide and solid the concrete will not hold up. 

[epsilonGreedy]

1 hour ago, Mr Punter said:

Between 1:6 and 1:9 will be fine.  Make sure you dig down the trench to remove any soft material.  Backfill with type 1 and thoroughly consolidate.  If the sub base is not wide and solid the concrete will not hold up. 

 

 

Thanks. Having been mixing and filling for the last 30 minutes. I have mixed a touch stronger than 1:6, my theory is I am up against the clock and the freezing overnight weather so a stronger dryer mix makes sense to me. Not sure that is conventional building trade wisdom.

 

Got loads of hessian sacking to keep it snug and warm overnight.

Edited December 4, 2019 by epsilonGreedy