Concrete Crack Sealant required

[hemis]

I am designing a reinforced concrete pavement-light (see link). The light consists of a grillage of thin beams set at 150mm c/c. I want to maximize the structural opening.

Due to deflection, the concrete cracks in the ribs at a short span (1.9m). If I ignore deflection, I could achieve a span closer to 3m but at these spans, the concrete has certainly cracked. I intend to control the size and spacings of the cracks using a fibre in the concrete (polypropylene seems favourite at the moment) but I need to find a way to seal the cracks. The cracks should be microns wide - I am working on the math.

My idea is to coat the moulds used to form the concrete ribs with a material that would bond with the concrete and form a waterproof barrier at the cure stage and remain flexible as the concrete cracks. The sealant would soak into the concrete and remain permanent. I have heard of some waterproof barriers that work by bonding at the cure stage.

Or maybe a material that could be added to the concrete that would enhance the cracking?

I would prefer not to have to coat the ribs after construction but I will if no other solution exists.

Has anyone any materials that I may research, please?

Daniel

 

[PanelGuy]

Look at a waterbased PolyUrethane Dispersion (PUD). These are used lately as the overcoat on laminated floor. Witcobond makes one that is 30% solids, dries and is really a thermoplastic urethane (more like a hot melt then) so can be reheated and made tacky. But the 296 has a modifier that when the system is heated to over 275F it polymerizes and turns in to a more permanent thermoset. It is still rubbery.

You could probably coat a mold, lay up, heat it and it will bond in the surface and then polymerize at the higher temperature.

 

[hemis]

PanelGuy

Thanks for the link. I have written to Chemtura for some technical advice. I attach a technical sheet for an aqueous PUD. Can this material be added to the concrete mix or would that be very expensive?

 

[hemis]

Sorry. The tech sheet

 

[PanelGuy]

Interesting idea...sort of a rubberized binder for the cement. It is all water based so should be compatible. I really don't know that much about the concrete chemistry, but with the Polymer concretes out there, it is probably doable. Actually with an exothermic concrete you could probably get the stuff to polymerize nicely either in the binder or as a surface coat.

If you did both you could put it in as a mold coating and guarantee it all bonds together and seals.

Good luck!

 

[hemis]

Thank you PanelGuy