Pouring concrete into footings and creating a padstone at the same time

[Glee]

Hi

I am due to pour concrete into these footings and as you can see the pour also creates a padstone underneath existing concrete floor to support a steel column which will be load bearing. The concrete will be poured to about half up the existing floor slab. Do I need anything underneath the existing floor slab like a bonding agent before pouring the new concrete?

all help appreciated 

Edited January 28 by jack
Changed title

[Redbeard]

What is the pipe? How will it be protected and how will it interfere (if at all) with the integrity of your foundation?

[Russell griffiths]

Who designed it, what do they say. 
 

Imho it’s not normally done like that. 
pouring any concrete under something will result in the concrete dying and shrinking back from the slab you are trying to support. 
 

in the underpinning world you would normally pour the concrete and leave it 50-75mm low, you allow the concrete to go sufficiently hard and then fill the void with a structural dry packing, this dry pack is rammed in so firmly that you use a club hammer and block of timber to ram the mortar packing in, smashing and smashing untill it won’t take another trowel full. 
this dry pack doesn’t shrink on drying because it has such a low water content. 
 

the other method is a liquid structural grout, again the concrete is poured leaving a 10-15 mm gap, this gap is filled with a very liquid high strength grout, you will need to block the gap up with timber and leave a small opening to pour it into. 
 

all depends really on how crucial this floor is for supporting this steel post. 

[Glee]

16 minutes ago, Redbeard said:

What is the pipe? How will it be protected and how will it interfere (if at all) with the integrity of your foundation?

That’s just an acrow prop

[Glee]

13 minutes ago, Russell griffiths said:

Who designed it, what do they say. 
 

Imho it’s not normally done like that. 
pouring any concrete under something will result in the concrete dying and shrinking back from the slab you are trying to support. 
 

in the underpinning world you would normally pour the concrete and leave it 50-75mm low, you allow the concrete to go sufficiently hard and then fill the void with a structural dry packing, this dry pack is rammed in so firmly that you use a club hammer and block of timber to ram the mortar packing in, smashing and smashing untill it won’t take another trowel full. 
this dry pack doesn’t shrink on drying because it has such a low water content. 
 

the other method is a liquid structural grout, again the concrete is poured leaving a 10-15 mm gap, this gap is filled with a very liquid high strength grout, you will need to block the gap up with timber and leave a small opening to pour it into. 
 

all depends really on how crucial this floor is for supporting this steel post. 

Thanks that is immensely helpful and appreciated 

[Redbeard]

22 minutes ago, Glee said:

That’s just an acrow prop

 

Ah! Thank you. I could not see its base-plate. 

[Tosh]

if you're coming halfway up the slab I would've thought a few holes and some rebar to tie existing foundation and slab to new pour.