Advice on enlarging concrete bottom step


Hello,
I'm redoing my front porch stairs, the old stringers were encased in the concrete bottom step, not a good thing. I want to bolt a board to the top of the concrete and notch the bottom of the stringers to meet the board.
So I need to somewhat enlarge the step. It is about 66" L x 16" W x 12" D. The back side of the step is all rough concrete with large aggregate. The top of the step is a greyish material without aggregate; it is somewhat chipped and not particularly flat, so it could use redoing. Here's the procedure I've come up with, I'm looking for any comments or suggestions:
Remove any loose soil behind the step. Clean the backside of the step with a hose and brush. Drill 4 holes 6" deep into the back side of the step and epoxy in some 9" #4 rebar stubs projecting out 3". Form up to extend the step 5" (providing 2" cover on the rebar ends). Mix and pour 4-5 0.45 ft^3 bags of sacked concrete, poking it into all the voids. Leave the new concrete about 1" below the finish surface and allow to cure a day. Chisel the the top of the old step to roughen it up and remove 1/2" to 1" of material. Mix some non-shrink grout (e.g. CementAll) and pour a smooth finish surface at the desired pitch and elevation.
Thanks, Wayne
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Wayne Whitney wrote:

Wayne-
Sounds fine....I would add some cement to the sackrete or use the CementAll stuff in the green bag...not cheap but hardens harder & faster
cheers Bob
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You know, that is what everybody says, but why? Sakrete claims their "High Strength Concrete Mix" has a 28 day strength of 4000 psi. Is that not adequate? I will pay attention to the amount of water, I understand it is common to use too much.
Thanks, Wayne
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Wayne Whitney wrote:

'cuz sackrete is cheap & cement is the expensive component
and weak concrete is a problem downstream & a little extra cement is good insurance
hand mixed concrete is questionable....I've seen it from 2000 to 5000psi
4000 pis is more than enough.....if that's what you really get...gotta dry mix it well & not over water it...it's just easier to add some extra cement (like a single shovel per bag) or use the grren bag stuff (expensive but hard in no time & strong)
cheers Bob
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