New Concrete Driveway Curing and Sealing Questions

[Caviller]

I had a replacement driveway poured recently. The main section is 5 inches of 6.5 bag concrete with fiber and wire mesh, poured 4 days ago. The ticket noted a 4 inch slump. Temperatures since then have been highs around 70 and lows around 50, with 50 percent humidity and mostly cloudy. The sidewalk and easement are 6 inches thick with no reinforcement, as per city code, poured yesterday with a 3.5 inch slump. Yesterday was also cloudy in the 70s, and in the 50s overnight. Both have full air entrainment as we do get road salt from Chicago area winters. The base should be well compacted from 25 years of a previous driveway, plus the added gravel and prep they did before pouring.

On a previous driveway at another house, I had been told to keep it wet for at least a few days to improve the strength of the driveway, especially at the surface. I was also told there are curing compounds that could be used instead. The contractor said neither was really necessary this time given the relatively low temperatures.

Is this good advice? Should I be doing anything at this point or is it too late to bother?

Temperatures are going to be highs in the 80s and lows in the 60s this week with somewhat higher humidity and mostly sunny. The contractor is supposed to apply some type of concrete sealer, presumably when they come to remove the forms later this week.

Any information greatly appreciated. I'd like to keep the surface looking as good as possible for many years, especially given the cold winters, freeze/thaw cycles and road salt used on the street that will invariably come onto the driveway. Keeping it constantly wet is not possible due to city watering codes, though I am permitted to keep it wet for a few hours in the morning and evening for the first week if that would help at this point.

Finally, I know cracks will appear at some point. Should they be filled or sealed somehow, or just left alone? I assume some of the cracks will appear in the control joints. Should those joints also be sealed or filled at some point to keep water and salt from getting into the slab?

Thanks!

[Richard J Kinch]

Keep it wet for up to a month, as in soaking wet under polyethylene sheeting. This develops the maximal strength. Water and that much time is required. It won't be ruined if you don't do this, but you won't get quite the full strength possible. Whether this additional strength is any practical difference depends on the application.

There is a lot of superstition about concrete, especially amongst contractors, but this is the simple scientific-engineering truth.

[DanG]

The curing compound or water treatment needed to start the moment the finishers were off the slab. Doing anything now is a waste of time.

The first 3 days are critical. Initial cure is 28 days.

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Keep the whole world singing. . . . DanG

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[wecolby]

!Alas minimalist contractors!

As soon as they poured, floated and finished the crete they should have applied a curing compound to the surface or used curing blankets

or something. As it has been said and as you well see it written: "Concrete does not dry. Concrete cures." Even if you dont use a curing compound or anything it cures but not necessarily well. What you dont want concrete to do is to lose water too quickly.

So its fiber-reinforced (good), and reinforced with wire mesh (gag). I prefer to use rebar. But nontheless, poor curing with loads of even rebar and fibers mixed in makes adversely affects quality and durability.

Hmmm. "In low temperatures, concrete cures slower" which means in plain Enrish: *its takes longer for the chemical reactions to take place that lend to concrete's strength.* It does not mean that concrete does not cure. But the 70s aint low temperatures for concrete. Its like this: on hot days you have to float and finish the crete faster. You have less time from pouring to floating to finishing the curing blanket, burlap, curing compound needs to be applied FASTER/SOONER. But this does not mean that one a 70s day curing is of no concern.

Read this.

As far as cracks go, expansion joints should be placed between abutting slabs of crete. Control joints should be cut every 10' or so. The size of the slab(s) are quite relevant. These control joints help control cracking because concrete cracks. The goal is to encourage (i.e. control* where it cracks) it to crack along control joints. Control joints are typically applied by scribing the joints (lines whose dept are at least 1/4 of the thickness of the slab) before the concrete hardens or they are cut into the hard concrete. Rebar + control joints + expansion joints + curing altogether make for a durable and long-lasting driveway. Poor curing can make the rebar, control joints, expansion joints all worth nada.

And btw, curing compounds...try to use one that is easy to remove from the surface of the concrete so that sealer can be applied directly to the concrete surface.

Typically concrete reaches maximum strength in 28 days. That does not mean that it cannot be utilized for 28 days.

[Yaofeng]

That is what i was going to suggest. Cover the driveway in large plastic sheets and keep it wet.

[Caviller]

Thank you all for the replies.

Unfortunately, I can't turn back time and make them do it another way. It's still unclear to me if there is anything I could have done after the fact (or even now) that would make any difference. The contractor did come back yesterday to remove the forms and clean up. They also applied a coating of "Eccocure VOX Cure & Seal". Obviously, I should have been a little more insistent about what they planned to do for curing before the pour.

Back to my original question- what action is required when the cracks do appear? Do nothing? Apply some sort of sealant to keep out water and salt? Does this vary if the cracks are within the control joints or not? Incidentally, the control joints are such that the driveway sections are about 8.5 feet by 11 feet. The expansion joints were added around the sidewalk and between the existing concrete garage and front walk.

I guess I'm stuck hoping that it cures properly enough for a residential driveway application. All this also leads me to wonder how much difference there is between proper curing and improper curing. Given the variability of contractors, along with homeowners who don't know what to specify, I'd expect to see a lot more newer concrete driveways in poor condition. I'm also starting to regret having spent twice the money on concrete instead of asphalt, given that concrete appears to require significantly more attention and expertise to get a long lasting driveway. That's not to mention the extra expense for the 5" of 6.5 bag concrete compared to the 4" of 5.5 bag concrete some contractors quoted and insisted was good enough. I guess it is if they cure it correctly.

Live and learn...

[default]

Minor nit: I'm pretty sure that concrete reaches it's *design* strength in

28 days, not it's maximum. And that this is because when they made up the tables for how strong concrete is, they tested the samples at 28 days..

--Goedjn

[Childfree Scott]

Exactly how big is this concrete pad and how much did it cost you?

Just curious.

[Richard J Kinch]

It's an exponential process. There is no "day". Cf Jerry Seinfeld and milk expiration.

[Yaofeng]

It is asymptotically approaching the maximum strength starting from pour. For practical purpose, 28 day strength is probably 90 to 95% of the maximum, I forgot the exact figure.

[wecolby]