Extending Existing Mat Slab

[RM87]

Hello folks,

Does anyone have any suggestions with extending an existing mat slab?

The mat slab is 15" deep with #5 @ 16" O.C. E.W. T&B, and I'm wondering if my initial impression of doweling #5X18" @ 16" O.C. T&B and continuing the reinforcing would be acceptable? There are no significant loads on this extended section.

Any recommendations on how I should detail the joint?

Thank you,
R

 

[SlideRuleEra]

One detail that has been used for decades for pavement is a reinforcing steel dowel grouted (or epoxied) into drilled holes in the face of the existing slab. Dowels are spaced on the existing slab face, along a line at the center of the face. At this location existing rebar does not interfere with the dowels. The existing slab face is cleaned and roughened. A bonding agent may be applied to the existing concrete face. New concrete is cast directly against the existing slab face. An expansion cap is not needed on the end of the dowels, since there will be no movement between the existing and new concrete. Don't connect the new and old rebar - drilling that close to the surface and bottom of the slab can cause unwanted cracking. For a 15" slab, I would consider using #8 rebar dowels, say 24" long (half in new and old slabs), spaced 16" on center. Here is a sketch:

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[RM87]

Thanks a lot.

 

[RM87]

As a note for future reference to anyone using this thread as informational:

I detailed the doweling of 2 rows of #5 bars in a staggered formation to try to avoid inducing crack lines. I had those dowels fully develop in tension. The reason for the two rows was to resist any sort of localized settlement between the two slabs with the intent that they would serve as a pseudo-couple.