Repair Concrete

Recently, I clipped my neighbor's concrete retaining wall with my 18 wheeler.  The woman is very understanding, and suggested that I fix it myself.  The portion I hit is the corner post, about 2' square and 3' high.  I knocked the corner off the upright and the beveled decorative lip at the top.  I worked in construction for several years and am comfortable working with concrete.  I know I should make forms and pack the concrete, but I have only done "new" work and am not sure how the repair will "stick".  Will any concrete bond adhesive work or is there a special type I should use? 

Reading the Q & A, I am not sure if this is the type question you are soliciting.  If not, I appreciate your time and any tips or references you can provide.  Thank you.,

 Enhaut, PA,  USA
R.,

 I am not very clear about the extent of the damage, but seems like you knocked off part of the corner post.

In general:

Remove all damaged concrete (chip it) until you have strong, rough surface.

Drill into the existing concrete for dowels.  I suggest drill 4 holes, at least 4" away from the edge (you don't want to knock-off the edges).  Get some #4 deformed bars and epoxy them into the holes.  That means that the holes should be 1/2" or slightly more, and 4-5" deep.  Have the dowels extend almost to the top of the post (1-2" below the top of the new concrete).

Use good, fluid epoxy.  Pour some epoxy (don't fill it) into the holes and then push bars in until epoxy overflows.  Let cure as recommended.

Any concrete bonding agent should be OK when you place the concrete.  Follow the instructions on the package. Use concrete mix with high cement content and better strength.  It will be more workable and stick better.

Make sure she understands that the new concrete will look different from the old...