Pouring new concrete over exisitng
Pouring new concrete over exisitng
(OP)
I have a client that wants to pour a 3" slab over the top of an existing slab on grade. The new slab is for a change in elevation only (no structural purpose). The existing slab has been in place for 30+ years and is currently used for industrial purposes.
I am going to have them clean the existing slab with a power washer and then have them apply a bonding agent to the existing slab an pour the new slab over the top.... but I am a little concerned with having the new slab bonded to the existing. It almost seems as if I want the new slab to be free from the slab below (to allow for proper shrinkage). What do others do in this instance.
I am going to have them clean the existing slab with a power washer and then have them apply a bonding agent to the existing slab an pour the new slab over the top.... but I am a little concerned with having the new slab bonded to the existing. It almost seems as if I want the new slab to be free from the slab below (to allow for proper shrinkage). What do others do in this instance.






RE: Pouring new concrete over exisitng
So, adopting what you can from this and it will work great. Remember a dry old surface will allow the cream to soak into the old for a better bond.
RE: Pouring new concrete over exisitng
RE: Pouring new concrete over exisitng
RE: Pouring new concrete over exisitng
RE: Pouring new concrete over exisitng
RE: Pouring new concrete over exisitng
RE: Pouring new concrete over exisitng
RE: Pouring new concrete over exisitng
And get something in writing as to if cracking is a concern.
Also look into topping cements or gypcrete or leveling mixtures that can go to that thickness...?
RE: Pouring new concrete over exisitng
RE: Pouring new concrete over exisitng
For a bonded overlay, or one that is not intentionally debonded, make your mix as "non-shrink" as possible (i.e., keep cement content low, keep W/CM low, use a polycarboxylate water reducer, biggest large aggregate as feasible) and make sure the old concrete is SSD or you allow enough water into the mix for what will be sucked out by the old slab.
In any case, be sure to cure the new work well and plan so you do not get curling, which will happen is you put plastic between the slabs (curls up due to exposed surface drying) or if you allow the old slab to suck moisture out of the new one (curls down as the bottom of the new work dries.)
While you could tool joints, it's probably better to do early-entry sawcuts. These cuts will reduce curling related cracks.
RE: Pouring new concrete over exisitng
As you see I differ as to what happens if a plastic barrier is at the bottom. Most noticeable for those is the finishers get mad having to wait way past quitting time to do their job. Setting is slower. I have not seen interior slabs on moisture barriers curl.
RE: Pouring new concrete over exisitng
I guess if you asked 10 engineers the proper way to do this you would get 10 different answers.