ML18003B069

Forwards Addl Info Re Concrete Curing Requirements (Fsar,Section 3.8,App A),In Response to Structural Engineering Branch 841001 Request

ML18003B069
Person / Time
Site:	Harris
Issue date:	02/25/1985
From:	Zimmerman S CAROLINA POWER & LIGHT CO.
To:	Harold Denton Office of Nuclear Reactor Regulation
References
NLS-84-456, NUDOCS 8503070457
Download: ML18003B069 (14)

Text

REGUL ORY INFORMATION DISTRIBUTI SYSTEM (RIDS)

ACCESSION NBR:8503070457 DOCsDATE: 85/02/?5 NOTARIZED:

NO DOCKET FACIL:50-400 Shearon Harris Nuclear Power Plant~

Unit 1i Carolina 05000400 AUTH,NAME AUTHOR AFFILIATION ZIMMERMANiS.R, Carolina Power-8 Light Co, RECIP ~ N'AME*

RECIPIENT AFFILIATION DENTON~H ~ R ~

Office. of Nuclear Reactor Regulationi Director:

>>r

SUBJECT:

Forwar ds addi info re concrete curing requirements (FSARiSection 3.8iApp A)iin response to Structural Engineering Branch 841001 requests DISTRIBUTION COOK'00 1D COPIES RECEIVED LTR

'NCL SIZE'o TITLE: Licensing Submittal:

PSAR/FSAR Amdts 5 Related Correspondence NOTES:

'RECIPIENT ID CODE/NAME NRR/DL/ADL NRR LB3 LA INTERNAL: ACRS 41 ELD/HDS1 IE/DEPER/EPB 36 NRR ROEgM ~ L NRR/DE/CEB 11 NRR/DE/EQB 13 NRR/DE/MEB, 18 NRR/DE/SAB 24 NRR/DHFS/HFE840 NRR/DHFS/PSRB NRR/DSI/AEB 26'RR/DSI/CPB10 NRR/DSI/ICSB 16 NRR/DSI/PSB 19 NRR/DSI/RSB 23 RGN2 EXTERNAL: BNL (AMDTS ONlY)

LPDR 03 NSIC 05 COPIES LTTR ENCL 1

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RECIPIENT ID CODE/NAME NRR L83 BC BUCKLEYiB 01 ADM/LFMB IE'ILE>>

IE/DQASIP/QA821 NRR/DE/AEAB NRR/DK/EHEB NRR/DE/GB, 28 NRR/DE/MTEB 17 NRR/DE/SGEB 25 NRR/DHFS/LQB 32 NRR/DL/SSPB NRR/DSI/ASB NRR/DS I/CSB 09 NRR/DS I/METB 12 N

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C!XQK Carolina Power & Light'Company KB 3 5 iSSS SERIAL:

NLS-84-456 Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation United States Nuclear Regulatory'ommission Washington, DC 20555 SHEARON HARRIS NUCLEAR POWER PLANT UNIT NO.

1

DOCKET NO. 50-400 CONCRETE CURING REQUIREMENTS

Dear Mr. Denton:

Carolina Power

& Light Company hereby submits additional information concerning concrete curing requirements at the Shearon Harris Nuclear Power Plant.

This attached information is submitted in response to NRC Structural Engineering Branch questions transmitted by letter dated October 1,

1984

'f you have further questions or require additional information, please contact me.

Yours very truly, S

R.

mmerman anager Nuclear Licensing Section GAS/ccc (776GAS)

Attachment cct Mr. B. C. Buckley (NRC)

Mr. S.

B. Kim (NRC-SEB)

Mr. G. F. Maxwell (NRC-SHNPP)

Mr. J.

P. O'Reilly (NRC-RII)

Mr. Travis Payne (KUDZU)

Chapel Hill Public Library Wake County Public Library Mr. Daniel F ~ Read (CHANGE/ELP)

Mr. Wells Eddleman Mr. John D. Runkle Dr. Richard D. Wilson Mr. G. 0. Bright (ASLB)

Dr. J.

H. Carpenter (ASLB)

Mr. J. L. Kelley (ASLB) 850307DOCK 05000000 0a57 850225 PDR A

FtDR A

411 Fayettevilte Street o P. O. Box 1551 o Raleigh, N. C. 27602

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ENCLOSURE

Response

to NRC Questions Concerning Concrete Curing (PSAR Section 3.8, Appendix A) uestion 1

The amendment states that there has been engineering data available to justify the alternative requirements for concrete curing.

Please provide such data.

Response

1 Attached is the written justification to address the revision in curing requirements.

The "engineering data" requested

("research" referenced in Amendment ll) is part of the attached justification.

uestion 2

The amendment provides minimum'emperature and moisture requirements for the first three days out of seven day curing.

Provide the requirements for the fourth through seventh day.

< If there is no requirement during these

days, provide justification.

Res onse 2

Implementation criteria Item 3 in the attached justification provides the requirements for minimum temperature and moisture for days 1 through 7.

(776GAS/ccc)

Exce tion to CC-4240 Curin Recommended Action:

Approve the field practice of allowing the cure period to be extended at least one full day for each day of deficient cure for all weather conditions, subject to the following provisions:

• Note:

"Cure" refers to both moist cure and/or temperature protection.

1.

The concrete temperature may not drop below 32'F during the initial 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> following placement.

In-place strength tests will be conducted should this occur.

2. If the concrete temperature drops below 40'F during the first 3 days after

placing, the field shall verify that the in-situ strength of the concrete exceeds 0.7 f'c before discontinuing curing operations.

Revision of the FSAR to include incorporation of the exception to ASME/ACI-359 with justification in order that a cure extension be allowed for each day of deficient cure.

+Curing requirements of specification CAR-SH-CH-6 will continue to be enforced in that moist cure and temperature protection above 50'F will still be applied.

Inspection requirements on site, however, require that moisture and temperature be checked at the most unfavorable position.

While virtually all placements have average temperatures of 50'nd above, by checking in a particular unfavorable spot, it is often possible to find nonconforming conditions.

The intent of the exception is to provide the field a corrective action for these spot deficient cure violations.

Justification:

1.

Curing of containment concrete is governed by ASHE/ACI-359, 1975 Winter

Addenda, Subsection CC-4240.

This document requires that containment concrete be, maintained above 40'F in a moist condition for the first 7 days following placement.

Present Ebasco specification CAR-SH-CH-6,Section II, requires that the concrete be maintained above 50'F for 7 days; this requirement is much in excess of the 40'F protection requirement which is considered adequate by the ACI Committee.

Therefore, condition 2 in Recommended Action is justifiable as only temperatures below 40're considered low enough to inhibit strength gain to an unacceptable degree.

Condition 2 will ensure that ASHE/ACI-359 curing and strength gain criteria are being complied with.

2.

Condition 1 of Recommended Action will guarantee that the concrete shall not suffer irreparable damage caused by frost heave caused by frozen concrete.

Concrete which has been placed for 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> will gain in excess of 500 psi during this period.

Concrete experts have published literature which states that concrete which has reached a compressive strength of 500 psi will not be permanently damaged by subfreezing temperatures.

Therefore, unless concrete is frozen within the first 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> after placement, no irreparable damage will occur.

The curing process will be (776GAS/ccc)

slowed down due to low temperatures, but this can easily be regained with an extension of cure to ensure that the concrete has gained

.7 f'c.

Any concrete which has sustained freeze damage will be evaluated on site for conformance to design requirements.

3.

ACI-306 lists minimum protection periods for durability.

The intent of this chart in ACI-306 is not to infer that concrete which does not receive the minimum protection will lack adequate durability later on during the service life of the structure.

Rather, this chart is intended to give minimum protection periods to supply immediate durability to the concrete by ensuxing that the concrete reaches sufficient strength to resist freezing and thawing deterioration soon after placement.

Durability is primarily aided by two factors:

Air entrainment and low permeabilities.

The higher the strength of concrete, the lower the M/C ratio is generally, and therefore the concrete has a lower permeability.

Our site mixes have sufficiently low M/C ratios such that the durability is ensured because of the low permeabilities.'hese low M/C ratios also ensure a rapid strength development such that minimum immediate durability requirements are met to <resist freeze-thaw provided the concrete reaches

.7 f'c before cure is discontinued.

4.

The dashed line portion of the attached curve indicates that probable anticipated worst temperature cure conditions for site concrete during cold weather conditions.

These conditions would result when concrete is allowed to drop to 33'F within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> of placement and is subsequently cured the first 7 days at 33'P.

Between day 7 and day 14, the concrete temperature is maintained at 50'F (in order to rectify the initial 7 days of 33'F cure one day of cure extension for each day of deficient cure).

Beyond day 14 all protection would be removed and it is assumed the concrete temperature would return to ambient temperatures of 33'F for the duration of the initial 28 days.

The dashed portion of the curve is superimposed using the 50'F and 33'F curves.

Most recent statistical analysis. of concrete mix design M-72 (used on the majority of site concrete operations Class AA 5,000 psi. design strength) indicates a mean value of 5,968 psi for a total of 219 28-day moist cure laboratory compressive cylinder tests.

It is thus evident that at 28 days, only an 8% reduction in strength is realized due to worst probable site cure conditions as opposed to the ideal cure period of 50'F for the entirety of 28 days.

In summary, while the difference in compressive strengths is large, early in the cure period for concrete cured at 33'P and 50'F, this difference becomes quite small as the concrete approaches an age of 28 days.

Thus, the design strength of the concrete will ultimately be easily reached even assuming worst probable site cure conditions.

In addition, a liberal overdesign of site mix H-72 (and other site concrete mixes) assures that design strength will be reached even under adverse cure conditions.

(776GAS/ccc)

Also attached is data taken from Concrete Technolo y by D. F. Orchard, Applied Science Publishers Ltd., London, Copyright

1979, pp.

234 and 235.

This data indicates that concrete subjected to freezing temperatures as early as 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> after placement suffers negligible freeze damage.

Im lementation Criteria:

1.

The concrete temperature shall not be allowed to drop below 40'F during the initial 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> following placement.

2. If,the concrete temperature drops below 50'F anytime during the first three (3) days after placing, the field shall verify that the in-situ strength of the concrete is not less than 0.7 f'c before discontinuing curing operations.

3. If the concrete temperature drops below 50'F or interruption in moist curing occurs anytime during the first seven (7) 'days after placing, the curing period shall be extended at least one full day for each day of deficient (temperature or moist) cure.

(7 76GAS/ccc)

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Elfeet ol'aIloing concrete to dsy hefore it has fullycured.

but this point was not noted by Waters). The rise and I'all in strength on drying and subsequent wetting can be repeated any number of times.

It is thus evident that. even ifproper curing is not effected, exterior concrete should eventually reach the same strength as concrete which has been caret'ully cured, as periods of wet weather will give it the necessary moisture, but that ifinterior concrete is not carefully cured, there willbe a loss in strength. Lack ofproper curing at an early age may ofcourse lead to serious shrinkage cracking, especially in thin slabs.

FREELING OF FRESH CONCRETE Itwas found by McNeeset2 that in the absence ofentrained fliirl'.theloss of-

strettgth due to f6edtlg de)endk'ei thiIIIixingtettlperategkfd Ifo(flsootf!

the oyrictete Is froihh'hhecttstitlII.IfIt'8 illowed t() set fdr'6i$'.1 h sefl'3re!

freezing, the lo'sg ()fg(IetIIIthoh be as il'Iuch as 50'Per celithit'thIgiPPettri.

to be'abou( the Inllximumloss pbssibfe under any cotlditionkiIfItis placed

't a temperature of 24'C (75'F) and is not subjected to severe freezing conditions within about 6h, very little loss of strength results. If the temperature ol'the concrete when placed is only 4'C (40'F) even a freezing tcmpcrature as mild as -4'C (25'F), il'applied immediately, produces a

'onsiderable loss ofstrength. Ifthc concrete is completely frozen before it has scl and is subsequently thawed at 24'C(75'F) it still loses about 45 per cent of'its strength. Thc intensity of the freezing tcmpcrature and the time f'r which it is applied appears to have little effect once freezing has occurred. After frcczing and Ihawing, the concrete appears to gain strength normally with age. about the same perccntagc loss of strength being 234 maintained throughout the curing period. Some ofthe results obtained by McNcese are given in Table 6.lll.

It seems probable that, provided thc area above freezing point of the curve of temperature of the 1'reshly placed concrete against time exceeds a certain value depending probably on the kind ofcement, then no loss of strength willresult due to freezing but McNecse does not appear to have investigated this point in detail.

Storing of Concrete by Freezing The storing ofconcrete by 1'reezing has been suggested's a way ol'moothing out the testing load. Iffreezing is adopted, samples taken can bc transported to and tested at a central laboratory instead of on a

construction site and they can bc stored at the laboratory until it is convenient to test them. The sample ofconcrete is placed in an insulated container and solid carbon dioxide placed between thc sample and tlie

~ insulatlona Itwtfsfound accessary to top upwith solid caihflfdioxidkevery.:

&thtyilphe'sailnapIe e6uld be thasfte'd out Yvhcn wit'a(4f by pfacing ItIkhot';

Hi(el',or'bettet'.&thln4mIIIby mict'xf(vavcs.Thecdncret'e%ai'then ttsed for'::.

IIiaklngthe test hpehmeni which were cured aIId tesited'lit'thcdrdin~ way.

'-.. The samples do not appear to have suffered in any vtay although storage periods extended to up to 5 days.

I THE EFFECT OF DELAYED PLACING OF CONCRETE A review of availablc information on the c,ffects of delayed placing of concrete and some additional experimental evidence has been given by Zictsman.s It is well agreed that there is an increase of strength and a decrease in slump ifa period clapscs between mixing and placing of the concrete. Varying figures are given, however. for thc amount ofchange in

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>32 PI hIN CONCRETE lCRAP. 7 Clthr. 7]

PhCTORS hFFECTIh'C CONCRETE STREKCTIIS 133.

Rppen to '"e frozen concrete ifit were subjected

.ng temperature: after freezing?

It often happens on construction that concrete is frozen a day or two after p)acing ind the question is raised, ss hethcr the concrete willever develop strength.

H. 4tf. Fitch'eports that ifthe concrete is given a day Thnt.E 7-1.CoMPA'nls~oN oF TllE RATE$ or GAINlso STREicsTtt or Cotc-ORFTc CURED AT VARIOUS TFatrERATURES Values, lb. pcr sctunre inch 100 90 80 70 eo 50 40 rf Ct Wg;Sr, ttCen Cn acr OVaZa! 70t.

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al. 70'F. it, willbegin to tfcvclop strength at thc normal rate upon bciitg thatved out.

Results shown in Fig. 7-6 are similar to (ho. e

. eettrcd by Fitch.

A study of all his tests'esults leads I"i(.h to conehidc that if the freezing period is omitted in the plotting of the age-strength curves, the curve will be essentially the same as though thc concrete had never been frozen.

Curing before and after freezing was done in the usual moist stor'age room

. at 70'F.

Results secured by Fitch for all series of the same mix

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A. O. Timms and N. H. Withcy'onducted tests with initial curing periods of tet, pcf', 1 and 3 days, using a standard and two high-carly-strength

cemcnts, and with three different mater contents.

Results for thc standard portland cement are shotvn in Fig, 7-8.

Results for thc high-early-strength ccments arc similar, but the strengths developed in thc initial curing periods at 70'F. are higher.

Thew investigators found that "subse-

'Eifcct of Lorr Curing Tcmpcrnturcs on the Strength of Concrete,"

Waiter's thesis (1933) at the University of illinois.

'"Tcmpcrnture Effects on Compressive Strength of. Concrete,"

Proc.

hm. Concrric Inst., Voh 30, pp. 159-180 (1931).

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(From Timcns anrf Il'ifhctt, "Tcmpcrntccrc Egectc on Comprcccirc hlrcngth of Concrrfr." Proc..4m. Cnncrctr fart., Vof. 30. pp. 150-150.)

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