Intumescent paint - concrete interaction

[bkal]

As a modification of the existing steel structure, parts of it will need to be encased in new concrete walls / slabs. The steel structure has been treated with intumescent paint to provide fire required protection. The modification does not require composite action of the existing steel and the new concrete. Are there strong reasons to either remove the intumescent paint before concreting, or would it be preferable to leave the paint in place.

 

[KootK]

When the intumescent paint heats up in a fire event, it's going to expand and exert an outwards pressure on the concrete, encouraging the concrete to spall off. Will the concrete actually spall off at the given cover? Will the concrete cover prevent the intumescent paint from ever seeing enough heat to initiate expansion? I don't know the answers to either of those questions. As such, I would either find out those answers or default to having the intumescent paint removed.

 

[dik]

Can anyone provide some information on this? I was not aware that intumescent paint had any effect on concrete.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[jayrod12]

I don't think the paint itself affects the concrete provided there's no confinement aspect as described by Koot. As I understand it, when intumescent paint heats up it expands to provide a thermal barrier between the heat source and the base material. In the example Koot provided if the paint on the top (or embedded) portion of steel were to expand it could have negative effects on the concrete by putting pressure in directions that it is unable to resist.

 

[dik]

Thanks jay... I've never heard that it could assist with spalling. Adhesion and cohesion is way too low, I would have thought.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[jayrod12]

I liken it to frozen drinks. With no confinement, nothing bad happens. If confined, you go out to your car to an exploded pop can all over the inside.

 

[HTURKAK]

Pls provide more info ... what will be the concrete cover thk ? is this an outdoor application ? what is the reason for the modification? did you conduct a corrosion survey ?and will you provide some descriptive sketches ?..

The intumescent paint is applied on steel primer and with a decorative top coat..

My concern is, corrosion could develop under the paint and the future concrete cover will just hide and may continue rather than stopping..

 

[bkal]

Thanks to everybody for responses. The issue is actually an existing steel column which will go through a new (to be built) slab. I was also concerned about confining the paint from expansion, but I have no idea what level of pressure would that impose. Another option is to remove the intumescent paint locally and box out the area close to the penetration. HTURKAK - I have also raised a concern regarding corrosion.