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Phil
Phil, Mechanical Engineer
Category: Home Improvement
Satisfied Customers: 5489
Experience:  Retired contractor, 51 years experience
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I had a driveway poured in the second week of July and after

Customer Question

I had a driveway poured in the second week of July and after about two weeks noticed a crack in it that goes thru the width and depth. Is this something I should have inspected by an expert or be concerned about?
Submitted: 11 months ago.
Category: Home Improvement
Expert:  Phil replied 11 months ago.
Welcome to Just Answer.

Concrete shrinks when it cures. With larger slabs cracks are entirely unavoidable. Generally expansion joints and troweled in separations are installed to control cracking to pre planned patterns. (such as with sidewalk sections etc).

There can be errors made in creating the slab however, and in compacting the base the slab is poured on, that can cause cracking and later problems that are beyond normal cracking.

This is an article on that topic CLICK HERE.

Tell me a bit about the slab... how thick is it, and what work was done to the ground prior to pouring the new slab... was gravel placed? How thick was the gravel base? Was a roller or tamper used to compact the base before the slab was poured? Was the concrete delivered in a ready mix truck, or was it hand mixed on site?

Does the slab look good, was it finished properly, are the edges neat and professional... how it looks tells us a lot about how the rest of the slab may have been constructed.

Generally speaking however, a slab done well in all other aspects, that develops a crack or two, is entirely normal.

Let me know, we can go from there.

Phil


Customer: replied 11 months ago.

Hello Phil, Thank you for taking the time to help me with this issue. I understand what you are saying about crack being unavoidable, but the Contractor has lied about so many things I wanted to get a real experts advice on this before I make my final payment to them. Troweled in separations were used but the crack formed away from them. What was defined in the work estimate was very detailed about what you ask. They specified:




Concrete Amount: 7.5 cu. Yds.


5. Concrete Quality: 6 sacks – Pea Gravel


6. Concrete Finish: Combination Broom/Stamped Concrete


7. Color Preparation: N/A


8. Main Color: Natural


9. Second Color: As a Release Agent – Dark Grey


10. Aggregate type: 3/4” gravel Class II – 2” thick (1.5 cubic yards)


11. Rebar: 24” On Center


12. Forms: 2x4


 



  • · Excavate 4” of existing soil or 8.5 cubic yards of soil with. Haul dirt to the nearest landfill.


 Grade the area before setting all the forms and compact as needed.


 Any extra dirt will be hauled away to the nearest landfill


Scope of Work:


1. Set the wood forms for the driveway and bender boards to replace the mow strip


2. Add the base material


3. The base preparation is the most important part of the entire process. Appropriate base material, thickness, and compaction are essential to ensure your installation will last a lifetime.


4. We will add and prepare (2) two inch of Class II Road Base. Once the base has been set, we will dampen the base down, and compact it until we reach a compaction level of 95%. At this point i.e. if you drive with your car over the prepared base, you will not see any tires indentations mark, as it is literally hard as a rock, which is exactly what we need.


5. We will use a plate compactor and firmly compact the gravel base material. For best results we will compact no more than 1" of the base rock at one time. This is crucial as we do not want to have any air gaps in our system. If you skip this step, it will lead to undulations later on.


6. Install the forms at a rate of 24” O.C.


7. Use barricades and cones to secure an area on the street for the Concrete Pump and Ready Mix Truck.


8. Pour concrete with pump


9. Finish.


10. Come back 48 hours later to remove forms and release



Pictures of the base look different than what was stated in that I see a lot of clay ground with a few rocks on top per square area. Maybe you can see if the ground looks compacted as to me it doesn’t before they pour the concrete. The thickness from top to gravel measures 4 inches. The ground was excavated using a small bulldozer that took up vegetations and soil in an area that was designed for RV usage as an unpaved driveway. They tore out my gutter drains that ran underground from my house under the lawn and down to the sidewalk. They left that as is and now this gutter drain terminates under the new driveway at ten feet and 15 feet from the sidewalk. This is a separate issue I was wondering what effects of water pouring under the new driveway will have during our rainy Winter season. From pictures I have it doesn’t look like much gravel was put down before pouring the concrete but when inspecting it just now it does look like there was gravel put down at some point in time. The concrete was mixed in a ready mix truck (cement mixer) then delivered on site poured into a vehicle that pressurized it enabling it to flow thru a black flexible tube that was used to direct the concrete to the exact spot it was needed.



The overall appearance of the slab is very professional with curved edges at the top and a nice finish and stained with a sealer applied to it.



The crack is roughly 1/16 inch wide at its widest point for about half of the width of the slab and the rest of the way it is more of a fine crack paper thick.



I just wanted to be sure that such a crack is not an indication of some type of pending failure in the future. Ed

Expert:  Phil replied 11 months ago.

Hello again Ed. * If* the slab is indeed 4" thick with rebar on a 24" grid pattern (they did not specify the size, hopefully it was #3 or #4 rebar)..and laid as professionally as it appears it was, the crack itself would fall into the normal range and is likely nothing to be concerned with.

There is not much we can do to insure that 2" of gravel was indeed placed and compacted as it should have been at this stage.

The slab thickness cannot be reliably measured at the edges because of the way the base is thinned out at the edges near the forms... it is the center thickness of the slab that is crucial. Were you there to measure that as the concrete was poured?

If the slab is no actually 4 inches thick, there will be problems later, and that crack could indeed be a precursor. You can rent an impact drill with a 3/8" inch bit and drill a few spots on the slab to determine its thickness. You can back fill the drilled holes with grout when you are finished.

If you drill the slab drill it very slowly so that the bit does not push a chunk of concrete out the bottom and make the slab look thinner than it actually is... if you drill it slowly enough, with the drill set on rotation only or only slight impact.. you will get a clean hole through the slab.. notice how far the drill bit penetrates before it breaks through... a survey firm would use a 1" core drill for such a test. that would allow a closer inspection and verification of the 2" crushed rock base.

-------

The roof drains cannot be allowed to run under the slab and then terminate under the slab as well... if thats the case, it will indeed turn out to be fatal flaw in fairly short order.

You need to look at other options for the roof drains, do not allow that situation to persist at all. I did not get any pictures with you post.

Let me know what you think. we can go from there... as long as you rate my ongoing comments *positively, I will hold the question open without any time limit for you.

Thanks!

Phil

Phil, Mechanical Engineer
Category: Home Improvement
Satisfied Customers: 5489
Experience: Retired contractor, 51 years experience
Phil and 4 other Home Improvement Specialists are ready to help you
Customer: replied 11 months ago.

Hello Phil,


 


I measured the grid pattern using magnetics and found out that center to center the grid is closer to 17.5 inches. This would seem to be a stronger rebar than on 24 inches, correct? From the pre poured pictures the rebar looks like the #4 being about ½ inch in diameter.


 


Because the crack goes threw the width and depth of the slab at that point, I would think that this indicates a problem while a crack going only part way would not. Is my assumption incorrect?


 


There are many open faces of the slab so if a 2 inch gravel thickness is needed for structural integrity I will take measurement at several points to see if this is the average thickness.


 


No, I was not present during pouring I viewed parts of it from my window, but having a business keeps me tied up most of the day.


 


Measuring the slab thickness in a drilled out section is a good idea I do have the tools to do this, but may take awhile to get to as business is suffering from this issue.


 


Thank you for telling me about the termination of the roof drains under the slab. I am aware of some Hydrogeology processes and introducing two sources of water under a slab o concrete makes me wonder if the slab will shift or crack and parts separate.


 


As for pictures I haven’t posted any and was not aware that could be done.


 


Yes, I am positive about your help and plan on leaving positive feedback and a tip for your services.


 


I think that hiring a local expert much like yourself to do an evaluation and provide me with a report on their findings would be the best something I would like to do. Do you know of anyone in my area, zip 95688 that can do this? I tried Googling and the yellow pages but that technique requires the process of elimination, so a referral would be beneficial.


 


Thank you, Ed

Expert:  Phil replied 11 months ago.
Hello again Ed,

All such cracks go all the way through, it is the nature of how concrete shrinks when it dries.. its most likely not an issue if the slab is indeed 4" thick.

You cannot measure anything regarding the slab from the exposed edges. Because the fill is sloped down toward the bender boards and forms at the edges and is generally always higher inside the perimeter.

You can rent a impact hammer and bit to drill the test holes... minimum 1 hour or half a day rental would do it. Cost about $50 for a smaller one.

Tell me which direction you are from the center of the nearest city and i can find you an inspector most likely (zip codes don't search in those regards)... cost of the inspection will be $300 or a bit more. I am not so sure that would be worth it given that you can drill your own test holes without much problem.

Let me know, we can go from there.

Phil
Customer: replied 11 months ago.

 


Hello Phil,


 


I’m half way between San Francisco and Sacramento along the I-80


 


Thank you for your help, Ed

Expert:  Phil replied 11 months ago.
Hello again, this is the closest I can find that can look over all aspects of the job, including the drain issues. He gets very high ratings and will very likely know or have heard of the contractor that did your work.. that will tell him a lot about what corners might have been cut.

He is about 40 miles away from your midway point (Fairfield California) however.
Call him on the phone first, see what he says...



3871 Piedmont Ave #13, Oakland, CA
(510) 655-3409 · jimgardnerconstruction.com
4.97 reviews ·
french drain · drain pipe · stamped concrete · retrofitting · earthquake
"He subcontracted the concrete slab and walkway installation and finishing to a highly skilled team and also referred me to a stucco contractor whose ..." -


In Fairfield either of these outfits will be worth talking to.

1743 Sycamore Dr, Fairfield, CA
(707) 422-4630
Category: Concrete Contractors
"After having a fence installed years ago I remembered the great service we ..." - insiderpages.com

PO Box 411, Fairfield, CA (707) 712-2978




Customer: replied 11 months ago.

Did I provide a positive feedback? I can't remember, Ed

Expert:  Phil replied 11 months ago.
Hello again Ed, you did indeed provide an 'excellent' feed back. Thanks! Let me know how all this turns out if feel like it, I am concerned that the roof water drain stops under the slab, that will create mud under the slab, the concrete will loose support and will fail without solid support.

our server has bugs and will not let me disable my signature file, just ignore it please.
thanks


Phil
Customer: replied 11 months ago.

That is my biggest concern too. Thank you for reminding me about the feedback. I do appreciate your help and guidance, Ed

Expert:  Phil replied 11 months ago.
.stay in touch.

Phil

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