concrete specimen initial cure 1

[msucog]

i've thumbed through a few threads that mention initial cure of concrete specimens/cylinders. i occassionally run across jobs where low breaks show up and the contractor tries to blame the testing firm for the low break since there is no storage box on site. unless the specifications or client specifically direct me to provide a storage box on site, it falls back on the contractor to provide such a box since they are responsible for their site, storage of all materials on the site, and protection of the materials on site. and as usual, the supplier and contractor try to throw us "under the bus". the issue is usually resolved because the contractor provides a storage box, they reduce placement times, and they improve onsite handling of the concrete. i have many construction jobs going on very near this site and none of those guys are experiencing the same problem. so i'm interesting in some other opinions on here since i'm sure contractors, suppliers, engineers, testing firms etc visit this site.

i've got a job that has many low breaks. the low breaks are typically within 500psi of the design strength (but too many low breaks to satisfy the aci low break criteria). the passing breaks are all very marginal and usually within 300psi of the design strength. low breaks started showing up at the beginning of the job prior to the temps being high (highs were about 80-85). the contractor said that the low breaks were due to the testing firm not storing the samples properly. i told the project team that we will gladly store the samples where directed at the jobsite and can put them in a storage box once one is provided by the contractor. (if no box is available, we attempt to cover the samples with a box or semi-bury the cylinders to get them out of the sun. we also use plastic bags or plastic tops on the cylinder molds). and on a side note, we learned the first round of low breaks was due to the wrong mix being sent to the jobsite--correct id number on the tickets but the plant had the wrong mix in their system. i have also learned that the particular plant is having difficulties with batching consistency. so, we cored the area at 70 days old and the core breaks were 100-350 psi higher than the design strength. the contractor stated that "we reviewed the break results and all the results are passing therefore the cylinders must be made incorrectly". i tried to be political and said that i reviewed the results and they looked reasonable to me given the age and strength--in other words, i didn't make personal attacks like the contractor is making toward me.

they finally provided a storage box so we've been placing the samples there. the low breaks are continuing with the passing results still marginal. now they're saying that the testing firm is responsible because we're not keeping the initial cure temps regulated (in their storage box). anyone have any thoughts on how to be political about this without calling the contractor an idiot? i have maintained that we cast and test the cylinders in accordance with astm but that we're not responsible for the initial onsite storage conditions since it's not our jobsite. i also noted that aci says that the placement times should be reduced in hot weather but the contractor continues to simply say we're leaving samples in the sun and not following astm (by leaving them in the sun, he means the storage box they provided is in the sun but implies we're leaving the cylinders laying out in the sun).

a little more background: the placement times vary from 1 hour to 2 hours. concrete temps at the time of placement vary from 80-96 degrees. slumps are generally 5-6" range with occasional 8". 7 day breaks are typically about 50-70% of design strength (3000-3500psi) and the 28 days are 85-110% of design strength. 56 day strength are typically only 10% higher than the 28 day strengths. ~70 day old core breaks are typically 101% to 120% of design strength.
a little more background: these guys are very difficult to deal with since during the masonry work, they had never heard of building code requirements and were ready to fight when they were told to cover their materials onsite and to consolidate grout. we have not been extremely picky over the masonry inspections since the architect is pretty lax about the requirements and required inspections. in other words, the contractor is doing his best to be difficult and get back at us because of his own lack of knowledge of the requirements.

any thoughts on the best way to get this settled so that i can get on with work?

 

[boffintech]

It is an absolute must to get this issue resolved at the earliest possible time and to get the backup of the EOR and the owner (the client).

Response to team:

An environment created by climate controlling equipment and facilities suitable for strength test specimen Initial Curing complying with the requirements of ASTM C-31 is not available on site.

The lack of on-site Initial Curing facilities exposes strength test specimens to harsh extreme weather conditions potentially detrimental to specimen performance (strength gain) which may result in the reporting of inconsistent and/or less than accurate strength test values.

An Initial Curing facility for concrete strength test specimens is not in our scope of work. Per the project specifications, as outlined below, Initial Curing facilities are the responsibility of the contractor:

ACI-301 SPECIFICATIONS FOR STRUCTURAL CONCRETE
1.6.3 Testing responsibilities of Contractor
1.6.3.2 Duties and responsibilities—Unless otherwise specified in the Contract Documents, the Contractor shall assume the duties and responsibilities given in 1.6.3.2.a through 1.6.3.2.g:
1.6.3.2.d Provide and maintain adequate facilities on the project site for safe storage and initial curing of concrete test specimens as required by ASTM C 31/C 31M for the sole use of the testing agency.

 

[msucog]

i agree. if the issue was simply who is going to buy a few bucks of ice per day to put in a storage box, i'd have no problem with providing that if the owner requested it (heck, that's only a few bucks per day). but the issue remains that if i am responsible for the specimens while they have to remain on site, then i will need to camp someone out to stay with the box.
this whole thing is ridiculous to begin with but the contractor is just looking for something to put the blame on someone else and their taking cues from the supplier (they even emailed a link from the ready mix website that says it's the testing lab's responsibility). i've got jobsites all over (one 300 feet from this site) and they're all going smoothly because the field procedures are much better on the part of the contractor. i actually have one site about 5 miles away the contractor doesn't want to bother with a box at all and they've been doing just fine. they did have one marginally low break and the supplier brought out a cooler with an ice bath. we actually stuck an extra one of our cylinders in his cooler just to see what happens due the different initial curing. for the 28 day breaks, 2 sets had the iced cylinders 100-150psi lower, 1 set within 50psi, and 1 set had the iced cylinder 250 psi higher. the range and scatter was identical to all the previous breaks. however, on that particular job, the contractor knows it's not our problem and have been great to work with.
thanks for the reference location. i knew it was out there somewhere but i could not recall where exactly it was. that will save me some time monday. the specs on this job say the contractor is responsible for providing safe areas to perform tests and storage of samples but i guess the contractor didn't read that part (they apparently didn't bother to read the statement of special inspections or general notes either).
i've been trying to keep from kicking the contractor but they're leaving me little choice. i was hoping they would motivate themselves to improve their placement techniques instead of dumping on me. i have little respect for contractors that cut corners but i have absolutely no respect for contractors that cut corners and then point fingers at everone else instead of acting like grown men and accepting responsibility for their own actions.
thanks again

 

[boffintech]

"i was hoping they would motivate themselves to improve their placement techniques instead of dumping on me."

Seriously? Have you been out in the hot sun with the cylinders to demonstrate the detrimental effects of being in extreme heat for too long?

Motivating themselves to do better is not in the genetic code of contractor DNA.

 

[msucog]

i had a talk with these guys and project team back before they started having low concrete breaks. when the foundation masonry work started, i went round and round about covering the masonry materials to protect from rain and blistering sun. i went ahead and mentioned that they should be up to speed on hot weather construction for both masonry and concrete work or they might see problems arise once they got in to summer. i even told them that i am available to try and answer any questions they might have. they have never once called except to argue that there is no such thing as consolidating grout.

and i'm well aware of contractor's mentality as i once worked as a contractor for one of the largest contractors in the world (let's just say that i've got insight in their minds). now, as an engineer for the testing firm, i refuse to do their jobs for them--contractors are paid to at least know basic construction techniques. i attempt to educate contractors that are willing to listen when ever possible. i have the foresight to know that i will see the same contractors again and again (especially on school projects) and i would rather try to help the contractors help themselves in order to make my job easier down the road. this particular contractor has taken it personally because they have never been exposed to IBC requirements and think everyone is picking on them. they've now got a vendetta against me because i won't simply sign off on their work. they threw out the line, "i've been doing this for 30 years..." ha, they even said something to the effect of "yep, this code stuff is just way too conservative. it's all because of those crappy contractors that cut corners."--i just chuckled and told him that i would agree with that statement about crappy contractors to some extent.

and i did try to talk with the superintendent on the jobsite about some of the problems and he pretty much blew me off. as i said, i've been trying to keep from having to kick the contractor in front of the entire project team, but i think the time for trying to be helpful has past.
thanks again for the 301 reference.

 

[civilperson]

Insulated storage boxes are STANDARD, add a recording thermometer if you wish to provide data for protection against claims and suits, (with heat source or cold block as necessary).

 

[DarthSoilsGuy]

just a side note:

"we reviewed the break results and all the results are passing therefore the cylinders must be made incorrectly"

Did you core your cylinders? oh wait those were broken.
i'm guessing that letter wasn't sealed by a PE!

When dealing with contractors like this, what bothers me the most is the gut feeling i have that they would not honorably report the facts if the roles were reversed. Also, when was "made" in question, hasn't it always been about curing? (oh no, that could be associated with our on-site super..., or oh no, that could mean that the cylinders could be representative of something on-site that wasn't cored. or Oh no, What the @#$% was I talking about?) What about all the "good" breaks made by your firm. logic has the contractor s$#$canning those too.

Don't take it personally, the project manager is probably playing hardball so that they don't get "negotiated" into paying for the additional testing. The super is probably just being a d!@k b/c he usually doesn't have to waste his time babysitting his masonry subs on other jobs without special inspections, or because he has had 30 years of training in this field.

here's what i would do:
Buy an air conditioner with a thermostat (also the hi-lo thermometer you should have there anyway if you don't) and connect it to the contractor's power before the report goes out.

write a report to all about the structural concrete involved. Establish that the concrete in those areas meets the project specifications and requirements of ACI-301 based on the review of laboratory and field testing of concrete both during placement and in-situ.

At this point i would discuss how the core testing does not invalidate the results of concrete testing on this project to date or in localized areas. (some people would dwell on this, i keep it simple. point being a general attack on testing methods like that one is an attack on the entire project testing)

Then describe the initial curing as Boffintech writes. Say it has been addressed temporarily by your firm. Seal it and ship it.

of course, it needs to be fact-checked, short, and written better than above, but you get the point.

crap. this thing is too long. i've been nibbling on it in my back browser all day.

adios
dsg

 

[msucog]

lol...thanks. i thought about it all weekend and decided to just pull the trigger on the contractor. i sent a copy of the page out of 301 and noted that the specs reitterate 301. i did stick a little jab saying that since the contractor was so insistent on having a cooled storage box (and since that was the only problem in their opinion) that perhaps they would immediately implement the necessary procedures to make that happen. i even noted that i didn't go down this road when it came up before because i thought that the contractor had realized he was wasting time and not really addressing the issue. we'll keep on keeping on and hopefully the issues will disappear off my desk...they're down to one last slab pour. maybe the contractor will work with us instead of against us to maybe be more productive...i won't hold my breath though.

 

[msucog]

update: had a meeting today. testing firm, supplier, contractor, engineer, architect, owner, and contractor. even after they saw 301, they kept saying we were responsible for initial curing. i just laughed. funny thing is that they complained the box (box they provided by the way) was sealed off and was baking the specimens. the whole issue of the box came up because they said the low breaks were due to the specimens not being in a box. the supplier threw out that they made companion cylinders next to our tech one day, stored them in a manmade tent and their 7 day breaks were 5200 while ours were 2400 for a 3500 slag mix (i saw malarky that they got 5200--that's higher than any of the submittal breaks and higher than most submittal 28 days breaks). again, the low breaks were happening before the box and we were shading the cylinders with our manmade tents but changed becuase the contractor claimed the low breaks were due to no box...go figure. come to find out that the mix was changed without a submittal submitted. also, we got another job where the same mix from the same plant is used for footings. the mix is 3000 and all this jobs breaks are roughly 2700-3300. on the other job, knocking out 4000+ all day long. the contractor is now going to supply a water bath buried in the ground and shaded (iced is necessary). i'm willing to be the supplier will bump up the cement and the strengths will shoot up. i'm going to make companion cylinders to store in the current box for funnzies. i'm also going to request all the batch tickets to see how much of what is in the mix.

 

[BigH]

Very tricky - just a quick query. What about the test results of other projects that the ReadyMix supplier is working on? Any problems with them? What does the Ready Mix suppliers QC programme show? It is good point on something like this to have the records of high-low initial curing.
It is interesting that Neville (Properties of Concrete - Chapter 7) indicates that "The loss of strength at 28 days seems to be directly related ot the loss of water which occurred during the first 3 days; the temperature (20 or 40 deg C (68 or 104 deg F) has no effect." (Referenc P. Nischer, General report: effects of early overloading and insufficient curing on the properties of concrete after complete hardning, in Proceedings of RILEM International Conf on Concret of Early Ages, Vol.II pp 117-26, (Anciens ENPC, Paris, 1982). Neville has a relationshipo of loss of strength vs mass of water loss (percent) ranging from 100% at 0 loss to 25% at 5% loss - and the storage at 20 or 40 degC both straddle the trend line. - so the question may be of how much water loss was there in the initial curing time? Just a thought

 

[msucog]

i did check across our jobs to see about the mix design. we have one other job going on right now with the footing mix on their site. i talked with the tech and he said the contractor hasn't provided a box so the cylinders are just set on the slab in the blazing sun (they try to cover with cardboard box whenever possible). their breaks look "typical" with 7 day's being 65-75% and 28 days being 4000-4500psi. as far as our cylinders on this site, the specimens are in plastic cylinder molds and covered with plastic bags and sealed with rubber band. the box was more of a winter box since it closed in and had insulation inside. our guy did place another piece of insulation on top of the box so that the top and sides would be shaded. (but no air flow going through the box).
we did look at the statistical data across the different mixes for the job. it looks like the mix is consistent (whether it's strong enough is another argument but i have not seen anything jump out that would suggest it wouldn't work). the tests results also look consistent. both of those referring to aci 214.
again, the box that the contractor is now using was just being used 100 yards away on an adjacent job by another contractor for the same client. the concrete total was about 4x as much with different supplier and had 3 or 4 low breaks total (only had to core two of those and they came up ok).
the one thing i'm not sure about is what admixtures are being used. maybe once i see the batch tickets i'll see something there. i'm hoping that we can just narrow it down to initial curing but my gut feeling says that's not it. i've seen cylinders initially stored under brutal conditions and not see drastic changes in the breaks, but there again, i have no other explanation for this scenario. one thing that we should be seeing if initial curing is the problem would be that the strengths would be taking off fast at first. there coming in 50-65% at 7 days. let's say the box is getting up to 120 degrees. i would expect the cement to take off and the strength sky rocket for the 7 day break and then flatten off for the 28 day. also if the other job with the same mix is having no problems with less than optimal initial curing, i'm left with two suspects as far as i can tell: the contractor's onsite efficiency and admixtures (or batch plant errors). some of the low breaks are showing placement times of right at an hour and temps in mid 80's so that doesn't seem to be the entire culprit (maybe partial). since the batch plant did send out the wrong mix and inside sources tell me that particular plant has had control problems, my gut tells me that's going to be the source of the problem but we'll see what the data shows. i would much rather it be the initial curing and storage box since we work all over with that supplier (i probably shouldn't really care since they throw us under the bus every chance they get but still i'd rather not throw gas on the fire).
as far as the moisture loss after initial curing, that should be easy enough to measure. with the new storage trough, we should be able to make a comparison between the moisture loss from the two different storage methods. bigh, any thoughts on how much moisture loss is possible with specimens in plastic molds and sealed with plastic bags (assume the box hits say 120 with no air flow)?

 

[DarthSoilsGuy]

just throwing out a couple more things on your aug 18 post.

you may already know this now, but if not it's worth knowing or could help other people who use this post.

there are some references to some of the mixes having slag. Blast furnace slag and fly ash are pozzolans <sp> that have a secondary reaction with concrete hydration byproducts for increased strength (along with some other benefits). since it is a secondary reaction, the concrete strength development time can exceed and usually exceeds the 28-day standard test cycle because it doesn't kick in until those byproducts are available. (you still have to test and meet code/spec at 28-days when you use pozzolans in a mix.) But, IF there are pozzolans in the original concrete described in your post, there is an argument that the 70+ day field core tests would indicate that your 28-day breaks are more accurate than not. Especially so if they are having problems batching.

also, for all you testers out there that haven't read the ACI 301 Structural Concrete - Duties & Responsibilities of the Contractor. there is are some other good items in there. the contractor is responsible to:

1.6.3.2.b
"Furnish any necessary labor to assist Owner's testing agency in obtaining and handling samples at the project site or at the source of materials"

What that means.... We're going to have to work out some other way than having our tech going up and down stairs with 5 gallon buckets of concrete, and yes it's your problem.

 

[msucog]

well, i think i've broken one of the riddles on the job. that majical 5200psi cylinder the supplier made was likely miscalculated. we just could not believe the 5200 number so we looked at it for 30 minutes and finally it clicked. we happened to back calculate the strength based on the cylinder size they typically use. they usually use 4x8 molds but they used 6x12 on this date to match ours. they put the break load in the spreadsheet but forgot to change over the area. 5200 drops down to ~2200 or so (right in line with ours). there were two sets made and both fall within about 100psi of our results. i still haven't seen the new results sent out to the team to clear up the issue. the supplier and contractor basically tried to pin us to the wall in front of the architect, engineer, and owner yesterday and now they're sandbagging clearing up their main arguement. i suppose we'll be making a few phone calls tomorrow if they don't own up to it. we knew something was wacky since the highest 28 day break was only 5500 so their results were way out of range.
fly ash not allowed on these jobs. we're going to make 4 extra cylinders on next pour. 2 will go in the box that's been used. 2 will go out on the open slab in the sun. the regular 4 will go in the tub. we should be able to make a reasonable assessment of the results based on 1 7 day and 1 28 day compared to the regular set. i'm willing to bet it's negligible. it's starting to point awful hard at the supplier or mix.

 

[boffintech]

KILL THE BOX.

ASTM C-31 does NOT require a box. What is required is a environment between 60-80F <6Ksi and 68-78F >=6ksi without loss of moisture.

ASTM C-31 "The storage temperature shall be controlled by use of heating and cooling devices, as necessary."

Wooden boxes sitting in the sun are like ovens!

If they thought 24 hours of heat was detrimental to strength gain why not try leaving the cylinders at the job-site for the full 48 hours that ASTM C-31 allows for Initial Curing.

 

[msucog]

I agree that the box is more suited for cold weather storage. The only reason it was brought over is because the contractor and supplier maintained that the reason for the initial low breaks was because we (the testing firm) had not provided a box. I kept telling these clowns it was not my responsibility. Finally, the owner (in an attempt to help) got the contractor on the same site (but different job) to bring over the box they had used. I'm sure the temperatures got up to 120, but I have never seen a big strength loss due to temperature. Our samples are protected to minimize moisture loss and the box had layers of shading (due to our tech's trying to keep it from being an oven). Either way, I didn't build the box and I don't personally care if they use a box. I just about fell out laughing in the meeting when the contractor said "well why didn't the testing firm tell us to change the box. the damn thing is baking the cylinders." everyone had an odd look on their face and was thinking, it is your box so go fix it.
i'm 99% sure the supplier screwed up their calculations and so the results will be less than 100psi off of our results.
the only other deviation from the mix i see is that there's no #89 stone. instead, they bumped up the #57 stone. i'm not a mix design guru but i wouldn't think that would be killing the strengths. anyone else have an opinion?

 

[msucog]

well, i think this is going to turn out ugly. the supplier says that the results are good. 300lb cement going to get 5000+ at 7 days...malarky. wouldn't the samples that were baking get higher faster? it's a 3500psi mix! i guess the supplier wants to be generous and give away a 5000 high early mix as a 3500 normal mix. highest 28 day break was 4500 with the average around 3800 for slab and 3200 for footings. highest 7 day was 2500 and average was 1900 or less. i guess we will go to plan b since we're not getting any help to find the problem...

 

[BigH]

msucog - perhaps consideration and evolution from an adversarial point of veiw to one of permitting someone to "save fac" might be in order?
You are correct; they are wrong and off base - is there not a way to turn this out so they don't lose face? Think like an Asian.
I am NOT saying to back down - but there are two paths you can take - the Nolan Ryan fast ball - down your throat - or the Gaylord Perry "goop" ball that slips and slides - gets to the catcher all the same but follows a different path. The batter can always then feel exonerated for striking out due to the "goop" (or in the case of Hoyt Wilhelm, the knuckler). Ryan gives him no such option. A thought.

 

[msucog]

i don't intend to call the man a liar on the record. results are what they are. but in this case, it's very plain to see what has happened.
the supplier works for the contractor, so the contractor is probably directing him to keep his mouth shut. the best route for the supplier to take is to break the 28-day cylinders and report them as they really are (which should be around 3500psi if they break like the rest have for the job). then, their able to say, "yep, the first break sure did look odd and it appears that it was weird". that way, we don't have to call them out and completely embarrass them in front of the entire team (and county).
we'll do our correlations between the storage box, open air and water bath initial cure with all of our own samples. i am fairly certain i know what the results will be. hopefully, since the supplier is a very large one and reputable, i'm hoping they will take the high road and either say to throw out their results or bring out real 28-day breaks. it's going to be hard for them since they (along with the contractor) essentially tried to discredit all of our results and our company in the meeting with the county. we'll see if they get a new attitude and work to change and correct the situation. there's a small question mark in the back of a few people's minds about my company/personnel because of these clowns and i don't intend to leave it that way. i'll give them the opportunity to do the professional thing and save face at the same time...but the clock is ticking.
(and i'm sure nolan has intentially beaned a few players in his day too--gotta be careful since they might charge and beat your ____. "the best defense is a good offense")

 

[dirtsqueezer]

Do you live in Las Vegas? I heard there's still mob activity out there.

This situation would drive me absolutely up a wall. I'm impressed that you're dealing with it so well. Where did the supplier cure there specimines initially? If they came up with 5000+ @ 7 days, which is ludicrous given the difference with your results, and the core for that matter, you could just ask them how they did it, do it the exact same way. If you don't get that 5000+, you can just ask them why the heck not. Not only that, but you're the testing agency. They're not on record for this, you are. It's your responsibility to get the right results. Though I'd say when involved in this type of war, best to arm yourself with a hi-lo thermometer and record on your break sheet. Then there's nothing they can say about it.

Sounds like you're dealing with a crime ring or something. I'd say you're going way overbudget on your patience and effort spent, though it may go a long way for the next time you deal with the same contractor/supplier.

 

[msucog]

they cured their specimens under a lean-to style tent made of a sheet of plywood leaning over against a pallet of brick (in other words, home made tent just like we were doing at first until they supplied a box). we're going to put a hi-lo thermometer in the water bath. we'll also stick one inside the box and one outside the box with the extra cylinders we're making next time. i wouldn't normally go through all the trouble but these clowns have tried to damage our image with the county. we do quite a bit of testing for this county, so i'm doing my best to make sure these allegations don't stick...so far i'm certain everyone is on our side--besides, the owner said in the last meeting "well this is my testing firm and their results are the only ones that matter on this project".

we had to core more footings last week and while we were on site, the supplier came out and ran a windsor probe (isn't that about pointless). they mentioned that they ran some on the previous sections back during the meeting. we and the engineer told them that was useless. we said it's plausable if you've correlated the results back to core breaks. so i suppose they're planning on using our core breaks as the correlation. here's the kicker, they ran a set of 3 shots at one location and left. we suggested that they run multiple trials at all 4 places that were being cored that day (4 seperate low breaks from different days). they declined and left. the core ended up having about 2 inches of grout on top of the footing. no wonder the guy in the field said his windsor probe results were 3500-4000psi (grout has been breaking at 4500 at 28 days).
the supplier and contractor are bracing themselves for a lawsuit in case they're told to rip out the concrete or to give a credit of some sort to the client since the client didn't get what he paid for.
as far as being over budget, the only good aspect about this whole deal is that the client does not set budgets with us for this very reason. they know that we're out there protecting their butts and trying to see that they get a good product. a few thousand dollars to us saves them many many times that. during the grading on this project, i already saved them well over 20,000+ cy of pay rock due the contractor and surveyor errors, so you can almost say they owe me one.