Concrete topping for hollow core floor slabs

[PG35]

Are bonding agents typically used to bond the topping to the slabs? If so, what product is recommended. I've seen the topping crack and delaminate from the slabs a few times. In a current job, the concrete is the finished floor. The owner is concerned.

I want to use a bonding agent, WWM and Fibremesh 150. The floor is to have a polished finish.

Any insight will be appreciated.
Thanks,
P

 

[hokie66]

Using bonding agents can be tricky; sometimes if not done well, they can actually work as bond breakers. As a structural topping over hollow core slabs, generally all that is required is that the surface be clean. If not clean and free of laitance, high pressure water cleaning is the best method. Give the surface time to dry before placing the topping.

You need to reinforce the topping to control drying shrinkage and temperature cracking, and if the floor is to be polished, I doubt that light WWF is enough. Either use heavy WWF or a mat of bars.

I don't think that fibremesh will be beneficial. Your concrete troweling should close any plastic cracks, and I think the fibres will interfere with a satisfactory polished finish.

 

[SperlingPE]

Is the topping to be composite?
The top of the planks should be roughened to help bond with the topping.
I don't see mesh as a great benefit.
WWM for drying/shrinkage or bars.
Make sure that you take into account the camber in planks when you specify the topping thickness.
Take into account the thickness of a mat of bars when specifying your topping thickness.
The location of yoru reinforcing is important to performance of the slab. Don't let it get placed at the bottom of the topping slab.
If plank and topping are to act as a diaphragm, confer with your precast supplier concerning connections.

 

[lkjh345]

Generally, no bonding agent is required for the composite topping. The roughened surface of the top of the PC plank is adequate to transfer the horizontal shear between the two materials.

Agree with SperlingPE that accounting for the plank's camber is very important when deciding on topping thickness.

 

[PG35]

Bonding agent may not normally be required but I want to ensure threre will be no problems. The slabs are already installed and have been finished smooth.

 

[JLNJ]

There is some data that the "as cast" condition from the plant is adequate to get composite action for the topping.

That said, I don't like to rely on composite action due to the uncertainty of the camber and therefore the unknown net section thickness at mid span. If you are fixed on applying some sort of topping I believe that a cement paste scrub is all that is recommended.

It seems to me that when I looked thoroughly into all this, PCI was awkwardly silent on who is responsible for specifying the conditions for proper bonding. Not finding satisfaction in the PCI specs, I began forcing the precaster to decide if he needed to make the slab composite and if so making him responsible for specifying the precast-to-topping application method.