Full Curing Time of Concrete

It is important with how much moisture content your coating will adhere. Google "curing time for concrete" and how dry it is. How hard comes second after 7 days. Mechanically the concrete will be strong enough to deal with the "load". The adhesion of your coating is a unreleased water content that can create a vapor tension under your coating and loosen it up. It depends on the nature of the coating too. PU can handle some moisture. Epoxies less. Follow the instructions and if a sealant is necessary, apply it.

Thanks dvmdsc for the input.

But my point is that, the Inspection Department insisting us to apply the bitumen coating after full curing time which is 28 days after placement of concrete. Our concern here is, it will delay our job. Besides our interpretation is we can apply bitumen after 7 days of concrete placing.

aCres

It sounds as though the ambiguity of "Full Curing Time" needs to be addressed by the engineer of record and not the "Inspection Department". Don't let the tail wag the dog!

May require a revision of the specification or change order. At the very least, the intent of the parties should be made clear. With re-formulation of many bituminous coating products to comply with VOC restrictions it might be wise to consider using a penetrating sealer as soon as possible. Consider application of the sealer to waterproof the surface and totally eliminate the 'Bituminous Coating" all together. This sealer will stop evaporation, provide for internal curing enhancement, reduce shrinkage and curling and leave you with a waterproofed surface.

If the coating was specified to waterproof? OK, that's done! And if "Full Curing" is determined to be seven days, that is fine also. Once you have applied the sealer and waterproofed the surface it doesn't matter if it's 7, 28, or 120 days!! The sealer I use is ready for the next phase in construction after 48 hours. Test the surface for waterproofing affect after 48 hours and move on! You can backfill or apply a coating without counting days.

Thank you Glenn Summers, KJK/USA, Lehman57, Tamu, cwarner7_11 and Guest.

By the way Guest, that's the recommendation of the Inspector(QC) before applying the coating. The coating is there already and he wants us to remove it. Remove??? OMG! Quality People.

129CBRider it is a spread footing of a warehouse building.

Here is the Standard were relying in...

This standard covers the minimum mandatory requirements for surface
preparation, coatings application, and coatings materials selection for the
concrete surfaces in industrial facilities both onshore and offshore.

Exception:

Coating of above ground/atmospheric concrete structures is not required, unless
otherwise specified in other standards and project documents.

This standard shall not cover water-proofing materials designed to slow or
prevent chloride ion attack or carbonation, or to address the decorative finishes
utilized for concrete buildings. It does not cover the concrete repair materials
prior to coating such as sealers and synthetic membranes sheets.

The objectives of concrete coatings are as follows:

a) Protection from chemicals.
b) Protection from wear, abrasion and impact.

c) Mitigation of steel reinforcement corrosion.

d) Mitigation of fouling.

aCres

The jurisdiction can request information from the engineer, but the building code allows them authority to supercede the engineer. This may simply be a clarification that the regulatory agency needs, and a RFI could address that. However, the ultimate authority is the local regulatory jurisdiction. If the building depatrment wants 28 days and feels it is for the protection of the public or the City, the engineer may need to talk to them. If they don't agree, he will try to negotiate. He may be able to get them to change their minds. However, the engineer of record on private projects general has an agenda oriented supporting his clients interests. Unless his client will own and oerate the facility, like the big box stores do, then the Regulatory agencies tend to be suspect of the design engineers when they promote more rapid or cheaper actions on behalf of the cleint and the contractor. At which point the regulators may bring in their engineers, and all of this staff time will be charged to the developer.

In project specifications, I frequently see the verbage "28 day full compressive strength" or "28 day cure duration".

My experience is that you can walk on it 24 hours after pour.

My interpretation of the specification verbage is don't - drive on it, drag anything across it, drop any sharp objects on it, pour any liquids on it (rain seems to be OK after the initial 12 to 24 hours), or seal coat it for 28 days.

I believe the theory behind this specification is that while concrete cures within 24 - 48 hours, the water used to mix it continues to evaporate, leach, (whatever term you wish) for up to 28 days after pour, that being the reason not to seal coat - all excess moisture must be allowed to escape first.

wall or floor?

floor/slab

I believe the theory behind this specification is that while concrete cures within 24 - 48 hours, the water used to mix it continues to evaporate, leach, (whatever term you wish) for up to 28 days after pour, that being the reason not to seal coat - all excess moisture must be allowed to escape first.

I'm not a concrete person, but I thought it was just the opposite: that the water evaporated relatively soon, but that curing (a chemical process) continued even after 28 days for standard concrete. (Then there is the high early strength stuff!)

Nor am I a concrete person so I can not agree or disagree with you but you may very well be correct.

I was only giving my interpretation of the specification based on discussions I had with the concrete contractor.

Concrete will continue to cure for years, but the majority of the curing , and the ultimate strength for design will be achieved by 56 days, unless it is a early strength mix design. 28 days of curing should get the strength to within 10% of the ultimate strength. The set time is only 90 minutes. Water can evaporate for the whole period curing, because concrete cures through chemical reaction with water. If the water all evaporated the reaction would stop. So it is not a question of water or not, but of how much. Some compounds are very sensitive to moisture on the substrate.

Text book answer to the question, perfect.....might add that some years ago in the UK we undertook an experiment on concrete strengths and found strength gain on 20 degree cured specimens after 5 years

To test concrete for full curing my painter tapes a 24 inch square piece of plastic sheeting on the concrete wall or floor. If there is any condensation after 24 hrs the concrete is not cured. I would also call the manufacturer for technical advice. Take a shortcut and risk material failure and rework. Which is way more than the cost to do the original job.

everything depends on air temperature, humidity and how many of the over 700 additives they can add to a concrete mixture they used to make it cure different ways.

If it was hot and dry when they poured it they may have had the plant add retarder to slow it down so they could get a good finish on it.

Yes, the plastic/tape test is the safest.

The label on the can of bitumen should give you the most info on how long it has to cure.

I read in a concrete newsletter years ago its best to keep it watered down as long as possible as I'm assuming water curing. They recommended at least a month so whatever coating keeps in moisture hopefully does the trick. So an extremely important fact is keeping it moist for a very long time really increased the strength and life of it by a very large factor. Hopefully it can be done with the right coating in your case.

This will help you cure much faster:

http://www.sika.com.au/cmc/Datasheets/tds/SikaRapid1_tds.pdf

Bitumen? Are you doing a road surface? If so, just lay your concrete and go over with the bitumen 7 days later. But!! Cover the concrete with plastic etc after your pour it. Remember concrete goes off after 1 hour unless you slow it down with a retarder. If the mix is coming in trucks, clock the time from premix to site and check if they used a retarder for long journeys. Don't allow the driver to add water when he gets to the site. It should come out of the mixer like thick sauce, not slop the workmen want to make their life easier.

GA from me

Same here - GA!

Concrete continues to cure as long as there are 3 things:

1. Unhydrated Cement

2. Water

3. Proper temperature, (not freezing)

Old concrete in foundations that are buried in moist ground, are incredibly tough and hard to demo!

The Hoover Dam is still curing!

Bap

Hello Sir, Your question can be very tricky but let's understand the objective here. Your climax remote is Full Curing Time.

Curing enables concrete to attain full hydration that will propel the maximum strength required of the concrete. With above in mind, Full Curing Time technically should be 28-days, however, sometimes we add an additive in the concrete mix to attain an early strength and that also reduces the curing time too.

thanks JC

JC,

We're not adding any additive here. If it is 28 days(Full Curing Time), meaning we did a wrong job.?

aCres

What does it say for "application instructions" on the can?

Hi Acres,

Full curing of concrete: When Portland cement is mixed with water, a chemical reaction occurs, called "hydration" at a certain temperature, between 10 to 20*C. It's completion influences the final strength, durability, and density of the concrete. In shortly, maintain concrete "saturated with water".

Originally the water is in excess to obtain fluidity and workability. It's important to maintain water level in excess during curing time to obtain calcium silicate hydrate.

Hydration can go to 28 days or more.

Coating can be applied before gel formation of calcium silicate hydrate, 30 minutes to one hour, as membrane-forming curing compound or other coatings that maintain water at desired level.

I suggest to apply coatings as soon as possible, no more standing water on the surface, before gel formation of calcium silicate hydrate, which interfere in adhesion between cement and coating. Waterbourne is preferable for easier blending of materials, and followed with coating which retain water as long as possible. Water vapour permeability is the lowest being the best.

Everyone must test coating before the start of a project, Gil.

@ Yusef1

Direction of application in the can, is not my concern here. I need your help if what is your interpretation of Full Curing Time of concrete. Thanks

aCres

P.S. Thanks Guest for the input

Well that is easy then. It takes 28 days to fully cure ordinary concrete. If the application instructions demand that you wait until it is fully cured, you must wait 28 days. Thats how to do it right. Nobody on this forum will advise you to do it wrong. And nobody here will give you permission to violate your local building code. That being said, the usual procedure around here is to rush the job unmercifully. They do that around here all the time, pouring, waterproofing and back filling walls within a week. How much can you get away with? Well, that would be between you and the inspector. There may be different codes, or different waterproofing materials than bitumen involved though, so your local inspector will be the one to make the final decision. Information gleaned from an internet forum is not likely to mean much to an inspector.

I cannot see how waterproofing a wall too soon would damage the concrete underneath in any way. But maybe the person who wrote the specification knows something I don't. (I would love to receive a link to a study on this topic.) I always waterproof with a mastic plastic based material (similar but perhaps not identical to bitumen based roofing tar), nail up dimpled plastic, and backfill, but purely by accident, there is always so much to do around a job site that I have always waited more than a month to get around to that particular job. My experiences are clearly not usual, or even applicable to your situation.

Keep me, and us updated.

Regards

@ Yusef1 and Guest, thank you very much.

Also to everyone who give their idea.

aCres

P.S. Before I had a doubt that we are wrong and the inspector is right. As what I observed in our discussion here, I conclude that he(inspector) is 100% percent correct based on standard. And we are willing to rectify our job.

Well he may not be right, but he has the jurisdictional authority, and really can only be superceded by his engineering supervisors, which could cost more time that it is worth. You could possibly confront him with your design engineer and attempt to get him to change his decision, it may work. however, it could backfire in the long run and he could be much more attentive to your work in future efforts.

You don't mention the class of concrete and I will guess its structural since a QC is making you do the 28 day dance which is for the ASTM reading crowd. Any mix design needs about 3 days for the chemicals to do the activation needed to combine and gain strength. A waterproofing solution such as STABLECRETE that penetrates and seals the water will allow immediate continuation of the work but most QC inspectors don't have the education. Nor most Engineers. Hydration is kept in the concrete and cure will reach design strength in very little time, and then continue to gain strength for many months. Perhaps years depending on the admixtures. Make it simple and use a penetrating waterproofing product and continue the work. Don't use water cure or wax based products. These cause dusting and actually impede the concrete matrix to becoming uniform. Check this out..... www.StableCrete.com

Actually, unless the concrete company delivering the mix desires to have an overstength design, the mix may reach as low as 10% below design strength at 28 Days. Even at 7 days it will be substantially below design strength, and at 3 it might only be at something like 50% of design strength or less. Engineers who have experience with concrete design and testing can easily tell you this. Ultimate strength can be tested at 56 days assuming the mix fails the 28 day test. So some mixes may not reach within 10% of design strength even within 28 days.

Not here in Florida, if not close (70%) to design on the 7 day break its torn out. I have 45 years experience as the QC inspector for a large multistate Consulting Engineer, also launch pads at NASA need to have the strength in 3/4 days for continued work in place. We don't dilly-daly with 28 days water cure. Admixtures are the way to proceed. Older methods have proved to be costly when work is impeded. We have cooled hydration with liquid nitrogen too. I am talking about structural concrete not "sidewalk" concrete or thrust block application. Also if the aggregate is a high strength river rock then the matrix will be extraordinary strong in less time. Don't forget the Stablecrete waterproofing that penetrates not just covers the surface. Most important step.

I need to include- we use a early high early strength mix design and Super plasticizer for the placements. Stablecrete is the only one in the market that penetrates, accelerates strength and waterproofs thru-out. All the others are coatings and don't last. Calf and Japan earthquake designers told us about it.

Faster construction means Money in the bank. Most contracts are for normal construction and when a contr can pull a job in 4 months quicker. Everybody is happier. Green initiative is heavy here too.

Just finished a 3 million gal tank in a month thanks to Stablecrete application. 4'' thick floor.

I am not really sure what you are trying to say here. But it is apparent the QA testing should not have impated your construction. 3 million gallons would be a small communities water storage tank, so I am guessing you are referencing the floor thinckness because it was so thin? high early strength can save you a few days, not months. 60 foot tall concrete silos have walls and floors thicker than 4 inches and can be built in a couple of months including subgrade stabilization, the concrete placement takes about a month on this and the pressures on the concrete at the bottom can be substantial. 4 inches is admittedly pretty thin for any structural concrete for a large structure. However, the thickness has a lot to do with the pressures on the floor, and i guess it could be a shallow tank. The concrete pours on such structures are actually quite rapid, it is the reinforcement placement time, forming and other things that take the time. You can pour a lift along a wall about every 3 days if they can get the steel installed, inspected and approved. The lift height frequently is limited more by the confining capacity of the forms, obviously steel slip forms make this much easier and faster as well as allowing higher lifts.

Hi RPR,

Here or not here, NASA launch pad or "sidewalk", multistate experience or just a guy who make "dilly-daly" job with 27 days water cure, is the man at work.

Acres asked a simple and valueable question and many people answered with good or excellent way to teach him/her what is full curing period of concrete.

All personal knowledge means nothing to Acres but simple and clear explanations are welcome.

We thank you for your complete knowledge and long-time experience in this matter but the next time don't push waterproofing products because nobody asked for it. With respect for you, your age, and all older and latest methods, thanks again, Gil.