PARKING STRUCTURE TOPPING SLAB

[PT99]

THIS IS A MULTI LEVEL TYPICAL PARKING STRUCTURE (OPEN SIDES) WITH PRECASET DOUBLE T's. I AM CONSIDERING FOR TOPPING SLAB TO USE 1 1/2" THICK LATEX MODIFIED CONCRETE WITH 6X6 W2.9XW2.9 WWR. ANY COMMENTS. LOCATION IS SOUTHERN US.
ANY SUGGESTIONS?

 

[ANE91]

GOOD LUCK. MAKE SURE THE DTS AREN’T OVERSTRESSED.

 

[ANE91]

Also PCI books should have all this already worked out in their tables. All that potentially changes with your topping is transformed section properties and weight.

 

[PT99]

Thanks,
We are replacing the topping that was there, but my real question is, would you put W2.9 WWR in 1 1/2" thick LMC?

 

[rlmengineer]

I would be concerned with chloride intrusion and section loss in the reinforcement inside the double tee beams. I would recommend a forensic assessment before doing anything.

 

[PT99]

This is 1960's structure. We have spalled areas at beam ends and exposed strand there also, but strand is not corroded. Surprisingly we are not seeing any rebar stirrups suggesting either plant or design error or did they just do it that way then? Corrective work will be to add Sika corrossion inhibters to exposed strand steel or any rebar if we find any, and patch with L&M Duracrete. Topping to redone with LMC. (any comments on how LMC holds up. This is multistory open sided garage.

 

[BridgeSmith]

On a bridge deck for a highway bridge, we wouldn't attempt to reinforce an 1 1/2" overlay. Most likely, we'd use hydrodemolition to scarify and roughen 1/4" (minimum) of the surface and remove any loose and degraded concrete (it also cleans up the steel nicely, without damaging it). Then we'd place a 1 1/4" concrete overlay, either latex modified or silica fume modified, at the contractor's option. So far, those have been fairly durable, even on Interstate 80, which carries 2000+ trucks per day, most traveling 70+ mph, so it takes a beating.

 

[ANE91]

Corrective work will be to add Sika corrossion inhibters to exposed strand steel or any rebar if we find any, and patch with L&M Duracrete.

Consider also adding sacrificial zinc nodes at these locations. The problem with both approaches is that the corrosion will simply continue beyond the immediate repair boundaries, if the source is left unaddressed.

Topping to redone with LMC. (any comments on how LMC holds up. This is multistory open sided garage.

Latex-modified concrete is awesome. Dense; relatively lower shrinkage; good bond properties…

Nothing inherently wrong with adding WWR, but be clear in its purpose. If it’s intended to restrain crack width/distribution, then consider it in conjunction with your aggregate size/gradation, paste content, and water content. I would probably not spec it, though, as it’s another locus of near-surface corrosion and spalling. Parking garage maintenance is already difficult.

 

[KootK]

I vote no on the WWR:

1) Firstly, it's another corrosion vector as others have mentioned.

2) Secondly, I don't believe that WWR will even be effective for crack control here. A thin topping, bonded continuously to a substrate, will have these characteristics:

a) Good crack distribution by virtue of the shear slip restraint provided by the substrate bond and;

b) Shrinkage cracks that are not much bigger at the top than they are at the bottom because of how thin the topping is.

3) The WWR might be handy for diaphragm action but that's another kettle of fish.

Note that my intent was to sketch a "good" condition below, even if it looks like the reverse.