Concrete Cracking Question

Brapbrap

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For all you concrete experts out there, question for you:

I had my driveway extended about 2 weeks ago and one of the sections developed a crack literally while the concrete was setting. Now the contractor said this is normal for Georgia and it would only be superficial and "probably" shrink. Fast forward to today and it appears to not only have widened (can fit at least 4 bills @ 0.10922mm = 0.43688mm), but is also chipping and completely through the slab. Is this a shit job that I need to pursue in getting them to fix it or am I the asshole? Unfortunately I do not know how they laid it as I have work all day and can't babysit contractors to make sure they do there work.
Picture 1: crack within 2 days of project end (~04/29)
Picture 2-4: crack as of today (05/13)

20220428_172329.jpg20220513_121057.jpgsignal-2022-05-13-12-26-01-391.jpg20220513_125225.jpg
 
Pretty lame excuse. It could be cut out and if they drilled rebar into the existing joints then it should be good. I'm guessing they didn't pull the mesh up as they were pouring, assuming they used mesh. I had a new driveway put in a couple years ago but it was done correctly and in 75' there isn't one crack. Had a very big truck on it a couple weeks ago and still no cracks.
 
No expert, but if they do try to repair it I assume they'd just cut out that section and pout it again. That would lead to more expansion joints which may just as unsightly as the crack.

Ironically, the owner came by and said exactly that.
 
Pretty lame excuse. It could be cut out and if they drilled rebar into the existing joints then it should be good. I'm guessing they didn't pull the mesh up as they were pouring, assuming they used mesh. I had a new driveway put in a couple years ago but it was done correctly and in 75' there isn't one crack. Had a very big truck on it a couple weeks ago and still no cracks.
I thought so to. My guess is that it is on a slope and it wasn't compacted/leveled sufficiently enough to prevent a crack. They used mesh. I live in a pretty rural area, so it's one of those, "deal with what you have" situations.
 
That happened to me with a previous house. I assumed it wasn't compacted properly as it was from a time that they couldn't build the houses fast enough... It cracked, I left it alone, and it didn't change significantly in 10 years. I eventually filled it with flexible filler along with all the other joints to stop the weeds from popping up!
 
This is not a what could be called a small cosmetic crack which can be present in the very top layer due to the finishing bringing the fines to the top. Caracks in the surface which are very small/superficial are usually caused due to a curing agent or just water was not used to help the concrete cure or correctly said let the cement hydrate evenly.

This is by no means minor or acceptable and will get worse. The reason if you will notice this crack goes all the way through the slab. What will happen now is moisture is allowed to ingress in this crack there will be moisture and when driving over the crack in this condition will actually cause hydraulic action in the subgrade which will eventually tun into a void underneath. Additionally with water and the freeze thaw cycle expanding the moisture when frozen will only further degrade the structural integrity of the slab.

Another cause could be the concrete itself was defective and by that, I mean it was poured using too much water to facilitate easy placement (high slump), the design mix was not correct or possibly the concrete was allowed to get too old before being placed. This allows the hydration or curing process to start too soon and when the concrete is being placed or poured it is actually tearing itself apart during the placement or pouring process.

The pictures nor your narrative address the subgrade and how it was prepared prior to the placement or pouring of the slab.

Hope this helps a little. I did testing and quality control including on site sampling, slump control and the setting up of the batch plants to ensure the proper mix was being used. Correct moisture and also ensuring the proper amount of air entrainment (prevents cracking in the freeze thaw cycle when moisture is present in the fully cured product) is present by use of an additive is critical in the fresh mix. This for both the small and large aggregate is critical when setting up the batch plant. Ever notice when going by a concrete mix plant you see the stockpile of both small and large aggregate having water by sprinklers being applied?
 
Concrete contractors are notorious for cutting corners. Make sure your base has been compacted--this varies dependant on soil conditions. I always spec out 3000 psi concrete. Up-to a 5 slump is OK. Don't let your contractor add water on the job! Excess water evaporates and your concrete shrinks and cracks. Cut the concrete the following day. Max 10 ft by 10 ft. Stay off of the concrete for 10 day after it is poured with anything heavy. 4 inch thick for normal cars/light pickups. 6 in for anything else. Add rebar for extra insurance.
 
If the crack appeared as it was hardening then it's most likely a shrinkage crack which shouldn't happen with the proper mix and slump. If the surface is starting to chip and spall as well then it's probably the mix.

As far as the mix goes it could be a multitude of things:

Finisher added way too much water on site
Batch plant didn't put enough cement in the mix - this happens quite often
Batch plant put too much fly ash in the mix

If the base material under the driveway is poor or not compacted well it will only exasperate the failure of a poor mix.

There is one redi-mix company here that is notorious for thinning their mud with fly ash. 3,000 mix breaking at 1200 - 1500 in 28 days type mixes.

Is this the only major crack in the driveway?
 
Just to be fair here as a note-------there are admixtures that when used will increase the slump temporarily called superplasticizers. Back when I was in the industry in the early 80's I have added thousands of gallons of this product sold by Gifford Hill (link below) to 10's of thousands of cubic yards of concrete on site in the Redimix trucks. There have been advances chemically with this technology over the last 40 years lol but this is what I used.


Point is and there are well meaning people here who are speaking about a product that is quite technical even though it seems simple on the surface when you think about how long it has been used. Slump which is how the plasticity/workability of the concrete is measured. Example when adding the SP to the mixer on site it would take about 2 minutes of mixing to make a 4 slump a 7 or 8 slump. This will save labor obviously and time not to mention cut down the use of the vibrators to help the concrete move during placement. The vibrator is used Incorrectly can cause the large aggregate to separate from the fresh mix and cause the small aggregate (sand) along with other fines to come to the top. This is not good for the structural integrity of the cured product either.

Just as a point----to say Never allow water to be added to a mixer when it arrives is a silly statement with out knowing all of the facts. Just as ONE example. The batch plant has a person we called the "batch man" that controlled all of the weights and measurements on the scales before adding to the trucks. IF for example, trucks started arriving with a 2 slump on a large pour and it was supposed to be a 5 would call back to the plant on the radio and ask for the % moisture to be taken in the sand large aggregate. There are aggregates such as expanded shale used in lightweight concrete that required storage in a silo with constant moisture saturation.

Ok getting into the technical side too much but just know that it can be complicated. Anyone know why ice plants were built and used during the building of Hoover Dam? ;)
 
...Ok getting into the technical side too much but just know that it can be complicated. Anyone know why ice plants were built and used during the building of Hoover Dam? ;)
You know your stuff Dave. Right on the money.

They used ice because the heat generated from curing that much concrete would take forever to cool down naturally. They had to cool sections as they went or they would never finish.
 
You know your stuff Dave. Right on the money.

They used ice because the heat generated from curing that much concrete would take forever to cool down naturally. They had to cool sections as they went or they would never finish.
Ahhhhh you are on the right track! The sections being poured were so large and the temperature internally caused by the hydration process of the cement would cause the product to damage itself because of the excess heat generated. The internal temperature of the interior parts of the dam were still over 100 degrees in 1984. Complete hydration takes a long time when huge areas are poured at once. :)
 
Just to be fair here as a note-------there are admixtures that when used will increase the slump temporarily called superplasticizers. Back when I was in the industry in the early 80's I have added thousands of gallons of this product sold by Gifford Hill (link below) to 10's of thousands of cubic yards of concrete on site in the Redimix trucks. There have been advances chemically with this technology over the last 40 years lol but this is what I used.


Point is and there are well meaning people here who are speaking about a product that is quite technical even though it seems simple on the surface when you think about how long it has been used. Slump which is how the plasticity/workability of the concrete is measured. Example when adding the SP to the mixer on site it would take about 2 minutes of mixing to make a 4 slump a 7 or 8 slump. This will save labor obviously and time not to mention cut down the use of the vibrators to help the concrete move during placement. The vibrator is used Incorrectly can cause the large aggregate to separate from the fresh mix and cause the small aggregate (sand) along with other fines to come to the top. This is not good for the structural integrity of the cured product either.

Just as a point----to say Never allow water to be added to a mixer when it arrives is a silly statement with out knowing all of the facts. Just as ONE example. The batch plant has a person we called the "batch man" that controlled all of the weights and measurements on the scales before adding to the trucks. IF for example, trucks started arriving with a 2 slump on a large pour and it was supposed to be a 5 would call back to the plant on the radio and ask for the % moisture to be taken in the sand large aggregate. There are aggregates such as expanded shale used in lightweight concrete that required storage in a silo with constant moisture saturation.

Ok getting into the technical side too much but just know that it can be complicated. Anyone know why ice plants were built and used during the building of Hoover Dam? ;)
Good info!! Both the general process and Hoover Dam history...
 
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