19 Oct 10 17:31
For a new multistory concrete building, I am placing a 4" thick lightweight concrete topping on top of the normal weight structural slab at various locations (the required "depressed" area accounts for 70-80% of the floor plate, hence the entire structural floor is set at 4" down and the other 20-30% is brought back up to finish floor line by topping).
The flooring sitting on this topping will be terrazzo, ceramic tiles, and carpeting.
I am attempting to do the following:
1. The 4" lightweight topping will be reinforced with welded wire mesh to control shrinkage crack because there will be no control joints.
2. Specify the largest practical maximum size aggregate and/or the highest practical coarse aggregate content to minimize drying shrinkage.
3. Dowels will be located along the edge and at the corner of the topping area to reduce potential curling, or separation from the structural slab below.
4. Specify low strength, about 2500 psi, and low slump lightweight concrete topping.
I don't find many references or guidelines for such construction in ACI or PCA publications, and I appreciate it if anyone has any comments or suggestions on the approach listed above. Also, I am debating to see if there is any need to either roughen the structural slab or apply bonding grout before placing the topping as the structural slab below is still relatively green when this occurs. Thank you.