ML19242D750

Petrographic Rept,Project Examination of Concrete Samples from Reactor Containment Bldg Base Mat Ks Prepared by Army Corps of Engineers.Concrete Samples Are of Comparable Quality to Specimens Giving Normal Value

ML19242D750
Person / Time
Site:	Wolf Creek
Issue date:	07/02/1979
From:	ARMY, DEPT. OF
To:	NRC
Shared Package
ML19242D746	List: ML19242D749 ML19242D750
References
NUDOCS 7908170539
Download: ML19242D750 (7)

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Corps of Engineers, USAE .

Petrographic Report Structures Laboratory Uaterways Experi=ent Station P. O. Box 631 Vick sbu rg , Mississi;;i Project Examination of Concrete Sanples from Ld3TT Date A JUIY 1979 ~

u_Qreek Reactor Containment Building Base riat, Kansds ADB

Background

1. The design strength at 90-days age of the concrete in the base cat i portion of the Wolf Creek Plant is 5000 psi. When it became apparent that this requirement uas not cet an investigation was started to determine the cause. The low strength cylinders were tested late in 1977. The Construc-I tion Technology Laboratories of the Portland Cement Association (PCA) examined f rcgrents from sone of these cylinders during 1978 and the ea:1y part of 1979 and issued soveral reports.

Thosedated27Februar{,and 25 April 1979 vere studied as part of the present inve st iga t ion. 2 In i

their cenclusion was that they could find no significant differ-

! general, ences between the concrete frc= the low and nortal strencth cylinders and 1

that the low strengths were probably due to factors other than the quality of the concrete.

l 2. By Interagency Agreerent No. N'RC-0 5-7 9-2 66 received ?O June 1979 the l U. S. Nuclear Regulatory Commission (NRC) requested the L. S. Arcy .

' Engineer Uaterways Experiment Station (WES) to make a petregraphic exacina j i tion of concrete thin sections prepared by the PCA and to ceport the results.

l Fragments of cylinders were also enanined.

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. 3. On 19 June 1979 Messrs. D. H. Ca pbell of the PCA and C. R. Oberg of ,

I the NRC delivered 41 thin sections to UES for examination. A list of those i sections as identified by the PCA is shown below:

I j PCA Compre ssive i Slide Cylinder Age, Strength, No. No. days psi 1 6503 90 4190 2 6S50 90 6640 i 3 6444 90 4640 4 6784 90 4780 i 'S 6696 90 4280 l 6 6546 90 3270 I 7 6606 90 4340

! 8 6767 90 SS50 9 655S 90 5380 10 6599 90  ?

11 6540 90 4329 12 6659 90 5390 7 9 0 8 1 M "a "m' 13 67S5 90 4830 14 6671 90 4370

. 15 6551 90 4290 l 16 644411 90 4640 i

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Rev Feb 1970 ,r ,

PCA Conpressive Slide Cylinder Age, Strength, No. No. days psi 17 6794 28 4S60 18 6771 28 5410 19 G752 28 4460 20 6561 28 56SO 21 6700 28 4790 22 6735 28 4190 j 23 6718 28 4320 24 6717 28 4990 25 6651 2S 5130 26 6640 28 4530 1 t

27 65S6 28 5200 28 65S3 7 4000 29 6543 28 5570 30 6531 28 5020 31 6490 28 4190 32 6 24 28 4270 33 6509  ?  ?

34 6534 90 4660 35 6557 90 4130 36 6563 90 4620 37 6557 90 4670 ,

38 6572 90 5230 39 671 3 90 4630 40 6737 90 4520 41 6714 90 4370 In addition, or 27 June 1979 fragnents of four broken 90-day cylinders were received at WIS for examination. These cylinder f ragments are identified below:

No. of Correspondirn Cylinder Cenpressive Strength PCA Thin Section No. at 90-day Age cr Clide 6546 3270 6 l 35  !

6557 4180

• 6659 5390 12 6767 SS50 8 Test procedure

4. Dr. D. H. Ca pbell of the Construction Technology Laboratories of the, ,

PCA is the petrographer who cade the petrographic examination at the PCf.. ' -

He spent 19 June and part of 20 June 1979 at UES as an official observer and to discuss his thin sections. Part of this tine was used to verify that there was accord on recognition of the vario2s phases one vould encounter in thin sections of concrete.

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5. It is always desirable to cake a petrographic exanination of good or normal concrete in comparison with concrete of questionable quality.3 In this case cylinders of low and of nornal strengths were available as both thin sect ions and concrete f ragment s; both were used to take campara-tive examinations. The pairs of thin sections that were examined cre shown belew:

PCA 1hin Age of Compressive Section Cylinder Breaking, Strength, No. No. days psi 28 65S3 7 4000 18 6771 2S 5410 i

19 6752 28 4460 20 6561 28 56S0 6 6516 90 3270 2 6S50 90 6640 7 6606 90 4340 12 6659 90 5390 1 650S 90 4190 t

3S 6672 90 5230

6. All of the 41 thin sections Vere examined with a polarizing microscope.

7. Portions of the four concrete cylinders were exarined visually and with a sterconicroscope. The bulk of this examination was made by exatining f resh f rac ture surf aces at 20X. The intent was t o look for evidence of alkali-silica rcact ion or any other abnormal f eatures. Fragrents of nicro-scopic white caterial believed to be alkali-silica gel were removed froa pieces of cylinders 6659 and 6546 with a dissecting needle and exacined with a polarizing ticroscope as powder itrersion count s in a liquid with a refractive index of 1.544.

8. A sawed surf ace of low strength cylinder 6546 nad of normal strength cylinder 6767 was ground smooth and examined with the stereo:icroscope.

9. Another sawed surface of the same tso cylinders was etched for 30 seconds in dilute hydrochloric acid and then examined visually and with the stereomicroscope for possible rios on the carbonate coarse aggregate particles.

10. Representative portions of cortar from low-strength cylinder 6546 and nornal-strength cylinder 6659 were used to prepare ce=ent paste con-centrates which were then exacined with an X-ray diffractoncter using nickel-filtered copper radiation. The cement paste was prepared b-j slight crushing of mortar f ollowed by passing over a 150-um (No. 103) sieve te concentrate pas *.e in the snaller size caterial. This material was then ground to pass a 45-um (No. 325) sieve before it was X-rayed. , .

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Results

11. The appearance of the concrete in the f ragments of the f our cylinders (6546, 6557, 6659, 6767) was similar. The paste was gray with a slight glitsering vitreous luster rather than chalky or dull, which is often indicative of concrete in poor condition.4

12. There was no evidence of abnorcal features such as dettirental alkali-silica or alkali-carbonate rock reaction in the concrete fraprents.

Microscopic amounts of white, porec11anous gel-like na terial were observed in one void in cylinder 65;6, in two voids in cylinder 6557, and in two voids in cylinder 6559. This caterial was so small that it usually was not detectable by the unaided eye. Examination of some of this material f ror cylinders 6546 and 6659 in pouder innersion mounts with a polarizing -

nicroscope showed it to be largely acorphous with a r e f ra c t ive index below 1.544. This caterial is alkali-silica gel. Its presence indicates that there was a small annunt of alkali-silica reaction in both thc low and nor:21 strength concrete. The likelil: cod of detrimental alkali-silica or alkali-carbonate rock reaction occurring is considered negligible since low-alkali pertland cement was used in this concrete. ' This level of indication of alkali-silica reaction is regarded as norcal for any concrete cade using aggregates containing silica stored in water for ages of as long as 90 days.

13. Neither the s:cothed nor the acid-etched surf aces of concrete fro '

cylinders 6546 and 6767 indicated any abno ality uith either sanpie.

14. Thin section exa min a t i o_n s . The examination of the 5 pairs of thin secticas representing low- and nornal-strength concrete did not reveal significant dif f erences nor did the examination of the other 31 sections of concrete reveal any significant features that would explain the low strenqths of sere cylinders.

15. The typical thin section indicated a dense, well consolidated concrete cade with a carbonate coarse aggregate, a natural sand, and portland cement.

No adnixtures such as fly ash were recognized. The paste was a mixture of calciu silicate hydrate, calciu hydroxide, and unhydrated cecent grtins that see ed to be appropriate in arount. The calcium silicate hydrate is not specifically recognizable by examination of thin sections of concr2te although its presence is readily inf erred. The comparative examinations did not suggest d if f erent arounts of cement or of water between the different samples. So e of the thin sections were ca rbonated, or stall arcas were tissing, or the epoxy resin was contaminated with small crystals ,

that crystalliced from the resin. These defects are coccon, are not

• Infor ation furnished by Mr. C. Oberg of the NRC.

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considered significant , and did not occur preferentially with the lower strength concrete. L'o reacted sand grains or opal-bearing sand grains were recognized in these thin sections.

16. The co parison of the X-ray dif f raction patterns of concentrated cerent ;aste fren low strength cylinder 6546 and norcal st rength cylinder

'659 indicated general sicilarity.

Discussion i

17. K. Mather3 has described a similar situation involving low strengt concrete cylinders. She pointed out that the pertinent questions in such a case are: i i

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a. What processes could cause t he observed resul t s, in this case low strength?

b. What evidence would these processes leave in the concrete?

These problers include excessive air content, too little cerent, too much water, and early f reezing.  ;

i 1S. Unile there could be other proceases these illustrate the logic to ,

follot. In the present case freezing is not an applicable consideration  !

since the cylinders should all have been protected before testing. In I additica, early freezing would leave ice cr stal imprints which were not found by the present extrination. Excessive air content, too little i cement, or excessive water have been ruled out by the PCA data.1 -

t However, the present exacination would have fcund such conditions if they ,

were present.  !

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19. Thus, the comparative exanination of the five pairs of thin sections i representing low- and normal-strength concrete and also the examination of concrete frag =ents of icw- and nor:al-strength concrete by eye and with a stereomicroscope vas spec 1fically designed to detect such differences i as described or other differences. Uhen this type of co parative exacina-t!on of what should be the same concrete separated by strengths of 3270 psi (cylinder 6546) and 6640 psi 'scylinder 6850) at the saae age does not reveal a significant difference this strcngly suggests there is no real dif ference between the concretes and that the proble is not with the concrete per se.

Conclusions

20. Since co parative exacination of concrete thin sections and of concrete frag ents representing low- and normal-strength concrete did not reveal significant dif ferences and since the texture and structure is typical of relatively high-strength concrete, it is concluded that the indicated low strengths are invalid and that all of this concrete is of comparable quality approxinately as indicated by the higher strength exa ples. This suggests that the indicated low strengths cere probably due to one or nore failures to follow cirrent standards of good practice in testing.

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21. Since the concrete quality appears to be as intended the concrete should provide the intended service.

22. These findings are in agreement with these reported by the PCA Construction Technology Laboratories.1, 2 i

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. . l RE FERE!!CES

1. FCA Const ruction Technology Laboratories petrographic report dated 27 February 1979, p roj ec t CT-0407.

2. Ibid, 25 April 1979.

3. Mather, K., " Petrographic Examination," in Significance of Tests and Properties of Concrete and Concrete-Making Materials, ASTM STP No. 169-B, pp 132-145, 197S.

4. ASTM C E56-77, " Standard Reco:: ended Practice for Petrographic .

Exacination of Fardened Concrete," Note to Table 2, Part 14 '

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