Adding walkway to existing work


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Old 12-28-14, 11:31 AM
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Adding walkway to existing work

Hi,
Several years ago I put in a flagstone over concrete entryway and recently I realized that I should have also put in a flagstone walkway adjacent to the driveway. So I'm tackling that now and my concern is with regards to bonding it to existing work.

Of course I will bond to the existing entry at the top of picture. I plan to put in a few epoxied rebar in addition to the bonding adhesive. The rebar may be overkill but there is a slight downward grade and I'm afraid that the whole slab may pull away from the entryway.

At the red mark on the picture, the brick grout line has steadily cracked probably due to the driveway settling. This is why I'm not sure if I should bond to the driveway. I could put epoxied rebar but leave out the adhesive or even use a tar paper to create a control joint between brick and flagstone surface. Currently though I'm planning to bond it with rebar and adhesive because I think even if there is some settling the crack will occur at the boundary. A control joint between brick and flagstone won't look very good
At the bottom of the picture is the city sidewalk and I won't bond to that and I'll probably knock off the cement that escaped the bottom of the form and place tar paper against the existing sidewalk.

Of course I will be putting down wire reinforcement for the concrete. The soil is highly compacted clay.

I'm using 3/8" rebar and quickcrete says you only need to drill the hole a couple of inches deep - this seems kind shallow?

Thanks for any comments

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Old 12-30-14, 04:54 AM
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new conc won't ' bond ' to existing conc unless you use an epoxy bonding coat,,, why rebar tie bars ? w/no expectation of frost, we'd use expansion jnt material to aid during expansion due to high heat temps based on where you are,,, don't understand why you're planning on welded wire mesh,either how many square feet is this work ? how thick ?

you MAY want to groove in a contraction jnt
 
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Old 12-31-14, 11:04 AM
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Contrary to a previous opinion, epoxy is not the only bonding agent for adhering new concrete to old--back in my DOT days, I specified and monitored the use of neat Portland cement slurry as a very effective bonding agent, both on smaller substructure enlargements/repairs and even complete concrete bridge deck overlays. Believe me, if it hadn't worked, we would not have continued to use it for dozens of years. The trick is to not let the brushed-on slurry dry before adding fresh concrete. The slurry is also very effective for bonding rebar dowels.

I'm not sure of a need for steel mesh for such a small pour, as small placements rarely require it. I would replace the sickly-looking lath stakes holding the curved bender board form with more substantial 2 x 4 stakes (and more of them), as the bender board will develop more curves than Jane Mansfield during concrete consolidation, if just the existing stakes are used.
 
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Old 01-02-15, 03:58 AM
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my response is based on exp gained from dot & fed work when/if new conc had to be bonded to old,,, never saw specs allowing portland slurry altho i saw it many times on private work applied as bdge notes to surface saturated existing conc - never public jobs, tho,,, we shouldda worked in OR
 
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Old 01-02-15, 04:10 PM
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Poor stadry--you need to get out more. Doing so would definitely improve your wattles.

Some DOTs learned that the most expensive products aren't necessarily the best or most practical ones for meeting their needs. Section 51 of my 1984 Caltrans Standard Specs specifies that neat Portland cement is to be used as a concrete bonding agent. Which means they (and I'm sure quite a few other states) have been using it for more than 30 years. My first experience using it was in 1976, on concrete bridge deck overlays in NM.
 
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Old 01-04-15, 01:28 AM
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you leave my wattles alone in '76, we repair'd the a10-warthog parking apron surface spalls @ willow grove nas, pa - only epoxy allowed as cement slurry bonding coats had failed,,, honestly never thought it would work as materials were too dissimilar to properly meld but i was neither engineer, specifier, nor contracting officer,,, iirc, we did get a change order approved to substitute master builder's ' set45 ' ( magnesium phosphate ) after 33% completion w/bid mtls & the change worked much better imho + saved the pa air natl guard $$$,,, even including tearing out & replacing the 33% completed work - another change order !

same thing that year w/usn's colts neck weapons resupply docks in nj - only epoxy,,, the navy wasn't as open to either mtl change OR saving $$$,,, but we got paid !
 
 

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