Late last week we had a new concrete driveway (120′ long) put in. The contractor poured the concrete over compacted stone and a wire screen. He said he would have a crew there the next day to cut the stress relief cuts (basically cutting the driveway into 10′ squares) – well the crew didn’t show up until 48 hours after they poured.
The question is – we have a couple cracks (one about 16′ long) that are not in the stress cuts – that concern us. Not being a concrete contractor – my guess is that they happened because the stress cuts weren’t cut soon enough. What should we do. The last thing I want is a driveway that separates – living in Chicago the temperatures swing quite dramatically and my guess is that will affect the driveway over time. My GC says it is normal and that the concrete won’t separate, so don’t be worried. My insticts tell me differently – should we be concerned?
Let’s assume that it needs to be repaired/replaced – how would that be done?
Replies
I don't think the 48 hour delay is the cause of the cracking. The purpose of the control joints they sawed into the concrete is to control where the cracking would occur. Even cracking at the control joints wouldn't typically show up so quickly- more likely after a few seasons of freeze-thaw and with traffic on the driveway. After only 48 hours, I doubt anyone has driven on it. Subgrade prep is often the culprit for failing pavement but only with the addition of the weight of traffic on the pavement and, again, you wouldn't have had that yet.
My only thought as to what could have caused cracking so early on is the frequency of expansion joints. You didn't mention any- did they install them? If not, that might by your problem. I sure wouldn't buy the contractor's line about not worrying about it. Cracking within the control joints is totally normal (and hardly visible) but you shouldn't get them anywhere else- at least not for a long time. I'd insist on replacment of the affected areas and have him take out the concrete back to the next control joint so it doesn't look like a patch job. There are fillers available for concrete but with the job newly installed, I wouldn't accept a bandaid solution.
My WAG is that there was too much water in the mix.
SamT
Sleepless in Columbia.
Diurnal rhythm? What songs did they do?
The crack will appear where the loads of concrete was last poured and where the next one started. It will also crack between where one part of the slab was in the sun and in the other in the shade.
If the ground under the driveway was fully compacted, the crack will not tip up or grow.
Another tip: Tree roots love to go under slabs, especially if the dirt is loose or sand.
Sungod,
If this were your new driveway - what would you do? Would you ask the concrete contractor to remove and replace the section (bordered by the stress cuts) of concrete that has the crack - or would you live with it?
If the color is uniform, I would rant and rave, make sure the saw cuts were more than 1" deep and then negotiate a $200 discount AFTER the concrete supplier was paid. I never seen a contractor pay for driveway removal and replacement. I have seen contractors let the cement company lein the homeowner.
If you want to make it real official, the recommendations for timing and placement of control joints can be found in a document called ACI 302, published by the American Concrete Institute. I do not think I would be as gracious as settling for $200 personally. Internal stresses may have also developed and exhibit themselves at a much later date.
" I never seen a contractor pay for driveway removal and replacement. I have seen contractors let the cement company lein the homeowner."
Jst had to throw in my two cents:
The broom finish on my last driveway flaked and came up in little chunks as I was shovelling snow off it (poured in about August and a March snowfall) I called the placer to look at it, he called the supplier because he figured the batch was probably too watery. They had both been paid in full months ago. Next thing I know, they broke out the affected portions, and replaced them. The colour doesn't match at all, but it does look better than a disintegrating surface with the aggregate showing.
No invoice ever arrived from either.
Fez
p.s. I am a GC and this house was my own. That may have tipped the scale in my favour.
Mike,
Having read the previous posts I thought I needed to put in my 3 cents. First off let me say that I poured concrete full time for seven years an have several hundred driveways out there. Now as to your problem with cracking. First the idea as another poster said that shrinkage cracking wouldn't show up for the first winter is ridiculous. The reason that the driveway cracked that soon is that it was not cut soon enough, period. It should have had at least three cuts done with a jointer when the concrete was wet. these should have been across the norrow portion of the drive. You stated that the drive was a 120 feet long. In this case most of the shrinkage is occurring from one direction. And it occurs in a hurry, like in the first 12 hours after the pour. It will continue to occur until the concrete is cured (28 days) but the bulk of it occurs very quickly.
Speaking from experience I can tell you that my crew and I have experienced cracking showing up when we went back the next morning to cut the drive poured the day before. this mainly occurs on the long straight sections of the drive which are usually not more than 16 feet wide at best and may be quite long in order to get to the road. for this reason we started cutting several control joints with a hand jointer when the concrete was wet after which we would finish the cuts with the saw the next day.
Usually if we placed them every 30 feet or so it would keep the drive from cracking anywhere else overnight.
AND I CAN ASSURE YOU THAT MANY TIMES WHEN WE WENT BACK THE NEXT MORNING THE CONCRETE HAD CRACKED ON THE JOINTS
sometimes it would open as much as a 1/4 inch. And for the poster who said the concrete was too wet , it is possible but it ain't necessarily so. 48 hours on a driveway is way too long before cutting it.
that being said just because the driveway is cut does not mean that you will not experience cracking somewhere other than on a control joint. You can do everything by the book and still have it crack randomly, no matter how stiff you pour it or how well the sub grade is prepared.
Your guy should have cut it the next morning and put some control joints in by hand when he poured it but that does not mean it would have remained uncracked.
concrete is funny stuff and if you want to make millions then you can invent a 'crete that will not crack. Ain't anyone succeeded in doing so yet.
As to making them repair it: your only leverage is that they didn't cut the control joints in a timely manner. If you want to try to make an issue of that then go for it but your best bet would be to let it go and maybe try to get a small credit for it. If you make them tear out the affected areas and replace them the color will never match. If I were you I would just live with it.
If the base was prepared as well as you stated yo should not have any heaving problems. If you do they will affect more than the cracks.
In closing there are thousands of drives out there with a few cracks which have remained very servicable and still look nice, not to mention they beat the heck out of blacktop. Let it go. You have far more important things to worry about.
Hope this helps
Mark
Mark,
Thanks for the great post. This is the information that I was looking for. I think my strategy will be to get some extended security that this crack won't become an issue later (shortening the life of the driveway) - in the form of a extended guarantee.
Thank you
Mike ,
You are quite welcome, I just couldn't let this thread go by. There are few subjects out there with as much misinformation floating around as the subject of concrete. I'm glad to help.
mark
Extended guarantee.....how about " Fireproof, Theftproof, and guaranteed to crack" It's concrete, it's a few gazillion year old technology, that in my opinion is WAY to hard of work for WAY to little money especially in residential flat work. But it beats a gravel drive.
I don't think MikeB is looking for a "perfect" driveway with no wayward cracks -- he's just worried about the worst case scenario. Perfectly normal concerns and he came here to get some good advice which I think he has.
But this points out what has been discussed here many times. AFTER the work is done, you are pretty well screwed if it's not done right. Whatever it takes to fix the problem probably will not be worth it. The time to address potential problems is BEFORE they occur with references, discussions about exactyly what will be done (how's & why's). This will irritate many contractors, but not the best ones.
professor, I am about to have an 22' x 80' drive done. They are proposing redwood control joints since it will have a pebble finish. We have agreed on using rebar on 3' centers instead of wire mesh, and a minimum thickness of 5" My fill (clay gravel with a 4" topping of crushed rock) has been in place for about...... a year? This is our "forever" home. What are your thoughts? (besides I'm way slow moving)Never be afraid to buy the best -- you'll always be happy with it!
Rusty,
I don't have any issues with the redwood in your situation since you are doing an exposed aggregate finish which is a horse of a different color. I would make sure they place the wood to form the joints in an appropriate manner. In this case I would say one board down the middle placed to divide the driveway in two (longways) which would be 11 feet in (22 foot wide drive). This is fine for a 5 inch drive. Even for a 4 inch drive which is supposed to be (technically ) 10 by 10 blocks the 11 foot spacing would work fine
Along the 80 foot direction I would place them at tenfoot intervals. Your base should be fine especially having been in place for a year. It has obviously been well compacted by now. The rebar grid should be fine as well. I would recommend Fiber in most instances but in your case it would be a liability with the exposed aggregate finish. It would be an eyesore until it wore off of the surface.
You should look at some work the contractor has already done (if you haven't already) and if it looks good then go for it. It sounds like he knows what he is doing to me.
Good luck
Mark
Mark,
Your insight on this is appreciated. One thing you didn't mention is that there are differences between control joints and expansion joints. The point of my e-mail was that nothing was even said about expansion joints which led me to my question of were there any at all? I don't claim to be an expert and am not saying that anything you said is wrong, but the shrinkage you're talking about is due to the curing of the concrete, right? Wouldn't that have been accomodated if expansion joints were installed?
My understanding was always that control joints are installed to control where load-induced or subgrade-related cracking occurs and are not intended to handle expansion/contraction issues. Based on the immediate appearance of cracks, it seems to me that these cracks are related to the curing of the concrete and the apparent lack of expansion joints. Your feedback is appreciated.
Edited 6/25/2003 12:42:16 PM ET by stonebm
Hope you don't mind if but in and try to help, thanks.
The only places linear (drives, sidewalks and roads) exterior flatwork needs Expansion joints are adjacent to structures or other independent objects.
On these types of pours, the initial contraction (usually in the first 12 hours) will create and remain seperated enough to handle future expansion. This being said, the second major reason for sealing joints is to keep the joint free of objects that would inhibit future contraction and expansion of the slab.
>>>shrinkage you're talking about is due to the curing of the concrete, right? Wouldn't that have been accomodated if expansion joints were installed?
the immediate appearance of cracks are generally related to contraction caused by concrete curing. Concrete will always crack when poured on large areas. Control joints are the best way to consolidate these cracks, expansion joints may work in theory, however if there is no vertical restraint (smooth dowel bars) the two adjacent slabs may tend to misalign vertically and create a more undesirable bump.
Stone,
Ward has answered your question pretty well already. But I will add my three cents.
The purpose of what is commonly (and incorrectly ) called an expansion joint has nothing to do with cracking. That is solely the job of control joints. An expansion joint should be called an ISOLATION joint. It's purpose is to provide a buffer between dissimilar materials. If it is placed in the middle of a pour it can ACT as a control joint. Control joints should be installed as soon as possible as most of the crack causing shrinkage occurs very quickly after the concrete is poured. On long narrow pours such as driveways and sidewalks control joints should be installed with a jointer while the concrete is still workable. This is because most of the shrinkage is ocurring in one direction so tremendous pressures can develop.
I am not a believer in the use of expansion joint material for use in the middle of a pour. I have seen many driveways which have been pushed apart at the expansion joint lines over the years, some quite severely. Expansion joint material is basically a form of celotex with a little more asphalt in it. It does not hold up to the weather for an extended period of time. And as a result it allows dirt and debri to build up in the joint, which is then pushed apart by the expansion created during freeze - thaw cycles, which opens up the joint for the further entry of more dirt, which freezes and expands, more dirt, more expansion and soon the two sides of the joint have been pushed apart sometimes as much as 2 inches . Additionally when this material is used in the middle of a pour then the two sides of the joint have no aggregate interlock to help in the transfer of loads from one side of the joint to the other. This is not a desirable situation.
The best defense for the inhibition of random cracking is the timely placement of control joints in the correct places and spacing. The second best defense is the use of fiber reinforcement in the concrete. This will not replace control joints but it helps greatly in the prevention of micro cracks which have a tendency to become big cracks. It also reduces the surface permeablity of the concrete which is highly desirable. It also helps with abrasion and dent resistance. And since it is mixed in the concrete it is always in compliance unlike wire mesh. Wire will do you no good if it is on the bottom of the pour and not pulled up correctly. Even with a conscientious effort being made to place wire in the pour correctly, it is still hard to do it evenly thruout the pour. And for the record every time I have removed concrete with wire in it it has always been on the bottom and not doing much good.
Now, I can already hear those of you who are big on wire screaming your lungs out. To you I say if you want to use wire then use it. but I have researched the benefits of both and have almost 3oo drives out there with fiber in them, not to mention several hundred garage floors. And I have had EXCELLENT results with it. You will never convince me that wire is as good. I know better.
One last thing in regard to the technique used during the pour and the finishing of exterior concrete.
First don't pour"Swamp water" , but don't be fooled into trying to pour a 4 inch slump in hot weather either, unless of course you have an awful lot of experienced help available. The best thing to do is to get the concrete to a workable slump immediately, I like a 5.5 to 6 inch slump , AND GET IT THE HECK OFF OF THE TRUCK!!
PREFERABLY WITHOUT ADDING MORE WATER!!!
I have watched guys fight it trying to pour too stiff and then wind up retempering and adding water 4-5 times. The actual water cement ratio in the last third of the load might be a 12 slump by then . So they are fooling themselves Far better to get it workable from the get-go and then get it DOWN!! You can talk about all the Lab tests you want but this is the real world not a controlled environment.
Secondly the concrete should never be touched with a steel trowel but only with a float or bullfloat. And even then it should not be overworked. What happens is that this beats out all the air-entrainment from the surface which is just where you need it. I you remove the airentrainment you then have a surface that is extremely vulnerable to deicers and freeze -thaw cycles. Bullfloat it nicely and broom it is the preferred method. Or you can do a swirled finish with a handfloat. BUT DON'T TROWEL IT!!!!
Hope this helps
Mark
I-64 in souther Illinois has sections of roadway that run 1-2 miles in length before they have an expansion joint. And those are at bridges or overpasses.
However, I have not stopped in 75 MPH travel and gotton down on the road to see if they have any control joints cut in them or not.
They do....that's not a mistake, it's rustic
My finisher, well Mike, as he will remind anyone who asks, " Guarantee, aw heck, I'am the last person who is going to touch this concrete, I have no control over the other previous elements involved in this stuff. You have the driver, distance from batch plant, the individual who batches the stuff, all the materials involved, ie sand rock and cement. Then there is the weather, wind, sun, humidity,,, etc.( there is an awful lot of "etc" in this concrete stuff in my opione) No, I won't guarantee anything." He is a great finisher, and he is very busy, always. If you have a flat driveway, with a good finish, a few cracks, I'd say your driveway is fine. Jim J
I am with the gang that believes you would be less satisfied with the slab removed and replaced. Leave it in place.
The reinforcing (steel mesh presumed) should be continuous over the affected areas. Even if the patch was doweled and grouted to the surrounding pavement, IMHO you would have less integrity in the drive.
Agreed the cracks are most certainly caused by the delay of installing the control joints. A slab this size (more than 12' sq for 4" thick) will almost certainly crack. The control joints contain these cracks in an orderly fashion. By delaying the cutting, it cracked randomly, probably not any more than if the joints were installed in a timely fashion.
If you believe a fix is required, ask the contractor to route and seal the random cracks.