[logan176]

I am putting down a concrete walkway in front of my house. The walkway will be 3.5' wide and about 25' long. I have already dug down and compacted the soil, then I added 4" of item-4 and compacted that too. Now I'm getting ready to set up my forms, lay down the wire mesh and rebar, then add the 3000 psi concrete that's being delivered.

The one obstacle I have is a pvc sump pump discharge pipe that runs through the path (see picture below). The pipe is 1.5" in diameter. My original plan was to take a 3" pvc pipe and trim off the bottom so that the larger pipe covers the discharge pipe. I figured that if the original pipe was encased in concrete and I ever had to work on it, the larger pipe would allow me to slide out the smaller one. However the pipe is close to the surface. If I stay with my original plan there would only be 2-3 inches of concrete on top of the pipe. I'm worried that the pipe will create a weak point and crack the concrete.

A friend I spoke to suggested that I remove the item-4 from around the larger pipe and let the concrete fill the area. But I wanted to check in with you guys before going forward. Does anyone have any ideas to help me with this pipe issue?

[hkstroud]

How far is it from the walk to where the pipe exits the ground and what is the grade. In other words, how much digging would you have to do to lower the pipe 2 " and still have it drain properly?

You want to maintain the 4 inches of concrete or you will almost assuredly have a crack.

[logan176]

My front yard is flat. The pipe exits into a storm drain that is about 20 feet away. From the walkway to the storm drain the pipe only slopes down about 4 inches. Since my storm drain is shallow I did not have many options with the pipe.

Do you think I should remove the 3" PVC pipe that I placed over the discharge pipe? I know I had a good reason for putting it there but without it I can put another inch of concrete over the pipe.

[hkstroud]

Yes, while sleeveing the pipe under the walkway seems like a good idea is is in reality not that advantageous. It is the kind of thing I would do, but when you think about it it is not going to do you much good. The only problem you will ever have with the pipe is that it might get clogged. Highly unlikely but it might. If it did you would snake it out. If you ever had to replace the pipe, having the sleeve would be nice but tunneling under the walkway would not be a problem.

If I had to choose between weakening the concrete in the walk and having the sleeve, I would give up the sleeve. I might slip on a piece of the foam pipe insulation on the discharge pipe, just to prevent a puncture by gravel or abrasion as the pipe vibrates or expands and contracts.

[logan176]

Harold,

I'm going to follow your advice and remove the sleeve. I also like the insulation idea. At first I thought that the insulation would stick up as much as the sleeve, but then I figured that the insulation would compress undr the weight of the concrete.

Since I am going to remove the sleeve I might run into one more issue. When installing the discharge pipe I had to join two pieces of pipe and the joint is right under the walkway. Should I replace the section of pipe that runs under the walkway with a section of pipe that doesn't have a joint? This change would remove the one joint in the middle and put a joint on either side of the walkway.

[hkstroud]

I wouldn't bother. That joint is just as strong as the pipe. Remember this is just a drain line, no pressure. Even if you had a leak wouldn't make any difference, just a little more rain water in the ground. Pipe insulation should raise the top of the pipe only about 1/2"

[logan176]

Okay, next problem... high temperatures. The temps in New York have been hovering around 100 degrees. That along with an injured wrist during jack hammering have slowed things down. I only have one more week before I go back to work. Temps seem like they will hold strong in the high 80s and low 90s.

I've been reading up on pouring concrete in high temps. I know I need to have the concrete delivered early in the morning or towards the evening so that the temps are at their lowest. Since my walkway is about 30 feet long, I will have my father-in-law helping to pour and trowel. I will have two 10'x10' foot tents set up over the walkway to keep the concrete cool. I will also put down 4 mil poly to cover the concrete while it hardens.

Do you guys have any other suggestions for pouring concrete in 90 degree weather? Tips on preventing surface flaking/scaling are also welcomed. Thanks.

[hkstroud]

Talk to concrete supplier about additives that slow down the drying process. Depending on everybody's skill, strength and stamina, and the excess temperature, you might want to have additional help. A person can tire out very quickly in high temperature and humidity conditions.

[KISS]

Harold about covered it. Here is something that might help: http://agbiopubs.sdstate.edu/articles/ExEx1006.pdf

This goes against the advice of delivering in the morning. It suggests later in the day. Keeping it cool and preventing evaporation is key.

And:
The more people you have for the pour, the smoother it will go.

The PDF also suggests wetting the forms.

Let us know how it turned out.

[smearcase]

The previous posts have covered everything very well. I'll just say that the presence of the pipe and the thinner concrete cover will cause a serious crack in this set of circumstances, so, doing all you can to make it better will help.
You mentioned scaling and flaking and the best way to avoid that is to not overwork the concrete when finishing the surface. The tendency is to keep working smoother and smoother which brings water to the surfaces and dilutes the water/cement ratio, and at the surface is the worst place to do that. Sprinkling water on top is even worse.
During hot weather, in most states bridge decks have to be placed during the wee hours (I can't remember exact times but usually in darkness) and ice is also added, and retarders.
It sounds like a little over one cubic yard of concrete. I would start at daybreak or at least befoe 9 AM, get it placed and cover with wet burlap as soon as you can without damaging surface which won't be long in these temps. I would keep covered and wet for 7 days.
It has probably been mentioned but thoroughly wetting the stone base right before the placing of the concrete is critical to keep moisture from being drawn from the mix.
I realize you are not doing a bridge deck but the specs that have evolved for bridge decks came about from attempting to deal with the same conditions you will encounter. If I couldn't move the pipe I think I would dig out under the pipe (6" below) for about one foot each side of pipe, put in some 2' long rebars (2" up from bottom as encasement of the bar is critical). You will still get a crack because of the pipe but this may prevent a big crack and settlement resulting because of the crack. A "dummy" joint tooled in about 1/2" deep above the pipe may control the location of the crack. The earth "step" under the pipe may also help keep the crack from continually widening from expansion. The only way to eliminate the problem is to get the pipe out of the concrete. There are other ways of dealing with these pipe issues but the costs might be undesirable.

[smearcase]

I should have added. Check with the concrete supplier to determine what hours you can get delivery without paying a premium.

[logan176]

Okay, I spoke to the concrete supplier. They said they do not mix in additives when the temps get hot... they only use additives when the temps are too low. They also said that they will try and deliver in the morning (no deliveries past 2pm on Mondays) but it depends on their schedule.

With regards to the pipe, I took off the sleeve and raised the gravel around it. I should have the full 4" of concrete on top of it. I also added the foam insulation over the pipe so it doesn't puncture when the sump pump kicks on.

Here is one of the websites I've been pulling information from. The site uses 2x4s for the forms, but I wanted a full 4" slab so I ripped down 2x6s. I also used a compactor instead of the hand tamper. Here's the site:

Google Image Result for http://www.concretenetwork.com/images/walkway-form.jpg

Another question I have has to do with wooden floats vs. aluminum floats. If I remember correctly, the aluminum float will give me a smoother finish... however that smoother finish might bring too much water up to the surface and I'll be brooming the concrete anyway. So for this application should I use a wooden float or an aluminum one?

[smearcase]

You are really doing your homework. I think you will get a great job.
4" over the pipe is great but it will still tend to crack. Can you just go over the pipe and not embed it? That is to say, so that the movement of the concrete (exp/contr.) won't be affected by the pipe? 4" sidewalk is sufficient under normal conditions. It would also allow you to replace the pipe without damaging the sidewalk in the future.
I would still make sure a dummy joint is placed over the pipe, perpendicular to the centerline of the walk.
I am not a finishing expert but I think I would use a metal float.
My earlier comments about extra depth and rebar under the pipe are not relevant if you have that much concrete over the pipe.
You might or might not want to use an edger to lessen spalling. I think your most critical step will be determining when to broom and get it covered and kept wet.
There are also liquid curing compounds that can be sprayed on, but you would have to check the manufacturer's recommendations, especially or you are having 95 degree temps like we have been experiencing. If you can keep it wet, water can't be beat.

[logan176]

Smearcase, I can't really move the pipe because its slope is so minimal as it is. If I moved the pipe down further I would create a spot for the water to pool, possibly creating a cracking situation in the cold months. When you say embed the pipe do you mean to dig down around it so that it is completely encased in concrete?

Any tips on the timing of the brooming and cooling. I think I'm going to use burlap instead if the 4 mil poly to keep the surface damp and cool.

[smearcase]

I wasn't clear. Let me try again.
4" concrete is good for normal sidewalk and you say you can get 4" on top of the pipe. If you are doing 4" walk, you are good to go. You haven't said or I might have missed it--what depth sidewalk have you set up for?
Let's say 5" and 1" of the top of the pipe would be in the concrete. I would use several layers of tar paper or easily available expansion material to break any bond (not much) between the concrete and the PVC, in case you have to pull it out later, and a half inch or so will act as an expansion joint. if you use 1/2' expansion material, you may have to use short pieces parallel to the walk---up over the hump, extra long and anchored in the grade.
If the top of the pipe is flush with the bottom of the concrete (4" sidewalk) you can just use some tarpaper or nothing.
I intended to say that if you can AVOID embedding the pipe that will be to your advantage because the whole slab will be able to move and reduce the extent of cracking. I would still put a dummy joint perpendicular to the walk, centered on the pipe (measure the center of the pipe and perpend. Both ways)
Don't emded it if you don't have to. If you HAVE to, use the expansion material and make a cushion around the pipe.
If it's 80 or 90 degrees you will probably need someone to start brooming before you are done placing and screeding, depending on how close the truck can get. For brooming timing I suggest you search "brooming concrete" as it looked like some good advice there. I will only say--if you get a lot of liquid and mortar moving around, it is too soon, and it can be easily refinished, try again in 10minutes. Keep testing especially in this weather. The brooming is for friction. If you wait too long, you'll get none.
For burlap, dampen it first (not soaked) and put it on when you can press on the surface with no penetration, and then poly. After about an hour, if it is dried out, spray (mist) the burlap until it is quite damp and cover it. Check and when it dries out again, test the surface, should be hard--saturate it and keep it saturated for as long as you can--a week is good if possible.
These are just my opinions based on inspecting bridge and highway construction and I haven't done that for 6 years. There may be new products or methods that I am not up on.

[smearcase]

Correction. I should have said tarpaper (maybe 3 or 4 layers) instead of 1/2 inch expansion material) especially on top of the pipe. That extra depth of concrete (about 12.5% more) over the pipe is more valuable than the thicker expansion material.

[Stratmando]

I often see Magnesium Floats?
Before you pour, think if you need any Conduits or chases for Water, sprinklers, landscape lighting, Electric Gate conduits etc.

[KISS]

Hey guys. This has been a very interesting thread. Thank you.

ABout the only concrete work I ever did was gluing a chunk of concrete that broke off and then a spot repair under the ground to prevent it. A pocket was created in the pour where water froze and chipped a corner off the cement. Now, you can't even tell the repair has been made.

I've done re-pointing of bricks including a chimney.

And recently, I buried a 4" piece of PVC UNDER a sidewalk.

I did help a high school classmate (went to trade school) during high school to pour a basement, but that was decades ago.

I'm currently doing just as ambitious project: Drainage.

It's proceeding in phases.

Phase1: Educate, design, permits, procurement
Phase 2: swales and berms. One swale isn't final and the other will have to be destroyed and re-built. But, they have already proven helpful.
Phase 3: 40' trench (~18d x 10 W) with two catch basins, pop-up, under sidewalk and a pop-up. One catch basin is at the end of the swale. The other picks up a gutter.
(almost done)
Phase 4: Grade and plant grass seed.
Phase 5: Add underdrain and another catch basin and grade (re-swale)
Phase 6: Final swale grading and seed.

Phase 5 & 6 might wait until fall or next summer.

[logan176]

I wasn't clear. Let me try again.
4" concrete is good for normal sidewalk and you say you can get 4" on top of the pipe. if you are doing 4" walk, you are good to go. You haven't said or I might have missed it--what depth sidewalk have you set up for?

My current setup is a 5-6" item-4 base that has been compacted. Originally the base was 4 inches but after writing to you guys I added two more inches so that the pipe was completely covered. The 4" concrete slab will now sit on top of the base and will be completely above the pipe. This way if the concrete and/or the ground shifts, the slab will not have the pipe interfering.

I don't know what kind of truck will be delivering the concrete. I highly doubt the truck will have one of those long arms that can reach my walkway from the street. So I recruited my father-in-law (who's very handy) and another friend to help. My buddy and I will man the wheel barrows while Dad screeds. The forms go up today and the concrete comes tomorrow. Thanks for all the help. I will post pics when I can.

[smearcase]

Every concrete truck I have seen has about 15 to 20 feet of chute which locks together in smaller sections. Many won't drive onto your property unless you sign a release of liability.
Go easy on the water added by the driver. It is easier to work it with more water but the ultimate strength goes down with every extra gallon. It is possible (not a good practice) to add water if it is too stiff but you can't get it back out, if you have too much!
I would consider renting a bobcat loader if I had to do it in 90 degree temps. But I'm old!
Everything sounds good.
Keep it saturated as it cures and I don't think you can do much better.