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
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
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
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
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
I’m half way between San Francisco and Sacramento along the I-80
Thank you for your help, Ed
Did I provide a positive feedback? I can't remember, Ed
That is my biggest concern too. Thank you for reminding me about the feedback. I do appreciate your help and guidance, Ed