Concrete Topping Repair

[KHoff]

I am working on a project that is currently under construction that includes a three story wood framed apartment building with an underground parking garage framed with precast (hollowcore planks and inverted tees). The precast is topped with minimum 2" thick composite concrete. A rectangular precast beam was used over the overhead door at the garage entrance. This beam was recently hit with construction equipment, causing damage to the precast beam and concrete topping over the beam. The precast engineer is handling repairs to the beam, but I am being asked to provide a repair detail for the topping. Loose concrete has been chipped away, exposing a fairly significant amount of concrete topping lost (see attached picture). To further complicate the issue, a sill plate for an exterior wood stud wall will have to be anchored to the concrete at the location of the repair.

Here is my initial thought for the repair:
1. Drill & epoxy threaded rod into sound concrete for anchorage of the sill plate. Protect threads during concrete repair.
2. Drill & epoxy dowels along edge of concrete repair area. Lap dowels with continuous rebar at short ends of repair area.
3. Apply repair product such as LATICRETE L&M.
4. Bolt sill plate down with previously installed threaded rod.

I am going back and forth on using a repair product as listed above or using a modified concrete mix. I have concerns with pouring concrete due to the variation in the thickness and issues with aggregate size.

Please let me know if you have any thoughts or suggestions. I appreciate any input.

 

[KHoff]

Another picture...

The damage is worst at the ends of the precast beam, but it extends the full length of the beam.

 

[oldestguy]

One way I have added a new layer of concrete to a concrete parking garage deck after the deteriorated salt deteriorated stuff has been removed and all dust blown off is the following.

Leave the old concrete as clean as possible and as dry as possible. Have the new concrete ready for applying. Smear on, with a broom a paste made from Portland cement and water. Add the new patch concrete and cure as normally you would. If you doubt the bond capability, later take a core therefrom and use a hammer and chisel to "break" the core at the joint. All my experience at this resulted in a break in some other place, not the joint.