ML19275A042
| ML19275A042 | |
| Person / Time | |
|---|---|
| Site: | Wolf Creek  |
| Issue date: | 07/05/1979 |
| From: | Frederick Brown ARMY, DEPT. OF, CORPS OF ENGINEERS |
| To: | Seyfrit K NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| References | |
| WESSI, NUDOCS 7908300597 | |
| Download: ML19275A042 (8) | |
Text
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i lJ O DEPARTMENT OF THE ARMY
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WATERWAYS EXPERIMENT STA ION, CORPS OF ENGINEERS P. O. BOX 631 VICKSBURG. MISSISSIPPI 3918o WESSI t 5 JUL 79
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Do c$d E' 3 7At So-WA Mr. Karl V. Seyfrit, Director Region IV l
U. S. Nuclear Regulatory Cocmission j
Suite 1000 611 Ryan Plaza Drive Arlington, TX 76012
Dear Mr. Seyfrit:
f In accordance with Interagency Agre ment No. NRC-05-79-266 received here on 20 June 1979 and subsequently executed, petrographic work was done.
i Twenty copies of the report of the results of this work are attached (Incl 1).
The report shows that the results of this investigation agree with the PCA findings as given in reports transmitted by the Kansas Gas and Electric l
Company to you and to your Washington office on 28 February and 13 May 1979 l
respectively.
Specifically our results indicate that the concrete samples representative of test cylinders giving low values in the compression tests are of comparable quality to that in the specimens giving the normal strength values.
This is as discussed by Mr. Alan D. Buck of this office with Messrs. Crossman and Seidel of your office during the week of 18 through 22 June 1979.
Sincerely yours,
(
l 1 Incl (20 cy)
F. R. BROWN As stated fwd sep Engineer Technical Director 2032 135 7 90830 051~7
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e Corps of Engineers, USAE Petrographic Report Structures Laboratory Waterways Experiment Station P. O. Box 631 Vicksburg, Mississippi
- U"IY 1979 Project Examination of Concrete Samples from Wolt Date Creek Reactor Containment Building Base Mat, Kenses ADB
Background
1.
The design strength at 90-days age of the concrete in the base mat
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portion of the Wolf Creek Plant is 5000 psi.
When it became apparent that I
this requirement was not met an investigation was started to determine the l
cause.
The low strength cylinders were tested late in 1977.
The Construc-tion Technology Laboratories of the Portland Cement Association (PCA) examined fragments from some of these cylinders during 1978 and the early part of 1979 and issued several reports.
Those dated 27 Februar and 25 April 1979 were studied as part of the present investigation.,2 In general, their conclusion was that they could find no significant differ-ences between the concrete from the low and normal strength cylinders and l
that the low strengths were probably due to factors other than the quality of the concrete.
2.
By Interagency Agreement No. NRC-05-79-266 received 20 June 1979 the U. S. Nuclear Regulatory Commission (NRC) requested the U. S.
Army Engineer Waterways Experiment Station (NES) to make a petrographic examina ;
tion of concrete thin sections prepared by the PCA and to report the results.
Fragments of cylinders were also examined.
Samples 3.
On 19 June 1979 Messrs. D.11. Campbell of the PCA and C. R. Oberg of the NRC delivered 41 thin sections to WES for examination. A list of those cections as identified by the PCA is shown below:
t PCA Compressive Slide Cylinder
- Age, Strength, No.
No.
days psi 1
6503 90 4190 2
6850 90 6640 3
6444 90 4640 4
6784 90 4730
'S
.6696 90 4280 6
6546 90 3270 7
6606 90 4340 8
6767 90 5850 9
6558 90 5380 10 6599 90
?
11 6540 90 4329 12 6659 90 5390 13 6785 90 4830 14 6671 90 4370 9C b, )i,,
}3h d
15 6551 90 4290 16 644411 90 4640 (Continued) j, -,C
/* WES FORM No.
1115 Rev Feb 97
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PCA Compressive Slide Cylinder
- Age, Strength, No.
No.
days psi 17 6794 28 4860 18 6771 28 5410 19 6752 28 4460 20 6561 28 5680 21 6700 28 4790 22 6735 28 4190 23 6718 28 4320 24 6717 28 4990 25 6651 28 5130 26 6640 28 4530 27 6586 28 5200 28 6583 7
4000 l
29 6543 28 5570 i
30 6531 28 5020 31 6490 28 4190 32 6424 28 4270 33 6509
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34 6534 90 4660 35 6557 90 4180 36 6563 90 4620 37 6587 90 4670 38 6672 90 5230 39 6713 90 4630 40 6737 90 4520 41 6714 90 4370 In addition, on 27 June 1979 f ragments of four broken 90-day cylinders were received at UES for examination.
These cylinder f ragments are identified below:
No. of Correspondirn Cylinder Compressive Strength PCA Thin Section No.
at 90-day Age or Slid 6546 3270 6
6557 4130 35 6659 5390 12 6767 5850 8
Test procedure 4.
Dr. D. II. Campbell of the Construction Technology Laboratories of the PCA is the petrographer who made the petrographic exanination at the PCA.l* 2 11e spent 19 June and part of 20 June 1979 at WCS as an of ficial observer and to discuss his thin sections.
Part of this time was used to verify that there was accord on recognition of the various phases one would encounter in thin sections of concrete.
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5.
It is always desirable to make a petrographic examination of good or normal concrete in comparison with concrete of questionable quality.3 In this case cylinders of low and of normal strengths 'were available as both thin sections and cone. rete f ragments; both were used to make compara-tive examinations.
The pairs of thin sections that were examined are I
I shown below:
PCA Thin Age of Compressive Section Cylinder
- Breaking, Strength, j
No.
No.
days psi 28 6583 7
4000 18 6771 28 5410 19 6752 28 4460 20 6561 28 5680 6
6546 90 3270 2
6b50 90 6640 1
7 6606 90 4340 12 6659 90 5390 1
6508 90 4190 38 6672 90 5230 6.
All of the 41 thin sections were examined with a polarizing microscope.
7.
Portions of the four concrete cylinders were examined visually and with a stereomicroscope. The bulk of this exanination was made by examining fresh fracture surfaces at 20X.
The intent was to look for evidence of alkali-silica reaction or any other abnormal features.
Fragments of nicro-scopic white catcrial believed to be alkali-silica gel were removed from pieces of cylinders 6659 and 6546 with a dissecting needle and examined with a polarizing cicroscope as powder immersion mounts in a liquid with a refractive index of 1.544.
8.
A sawed surface of low strength cylinder 6546 and of normal strength cylinder 6767 was ground smooth and exanined with the stercomicroscope.
9.
Another sawed surface of the same two cylinders uas etched for 30 seconds in dilute hydrochloric acid and theri exanined visually and with the stereomicroscope for possible rims on the carbonate coarse aggregate particles.
10.
Representative portions of mortar from low-strength cylinder 6546 and normal-strength cylinder 6659 were used to prepare cement paste con-centrates which were then examined with an X-ray dif f ractometer using nickel-filtered copper radiation.
The cement paste was prepared by slight crushing of nortar follo <ed by passing over a 150-pm (No. 100) sieve to concentrate paste in the smaller size material.
This material was then ground to pass a 45-pm (No. 325) sieve before it was X-rayed.
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Results
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11.
The appearance of the concrete in the fragmentc of the four cylinders (6546, 6557, 6659, 6767) was similcr.
The paste was gray with a slight
/
l glimmering vitreous luster rather than chalky or dull, which is of ten
'e indicative of concrete in poor cow 3 tion.4 12.
There was no evidence of abnormal features such as detrimental alkali-silica or alkali-carbonate rock reaction in the, concrete fragments.
Microscopic appunts of white, porcellanout gel-like maCerial were observed in one void in cylinder 6546, in two voidy in cylinder 6557, and in two voids in cylinder 6653. This material wr s so small that it usually was "not,
detectable by r.he ur. aided eye.
Examination of some of this material from cylinders 6546 and 6659 in powder immers!on mounts with a polarizing
( ;'
microscope showed it to be largely amorph'eus with a refractive index below I
1.544.
This material is alkili-silica gel.
Its presence. indicates that there was a small a=ount of alkali-silica reaction in both the low and normal strength concrete. The likelihood of detrimental alkali-silica or alkali-carbonate rock reaccion o: curring is considered negligible since low-alkali portland cement w as u!.ed An thim concrete.* 'fhis level of indication of ' alkali-silica rea?. tion is regarded as normal for a 2y,
concrete made using aggregates co ttaining silica stored.,in, water for agesi of as long as 90 days.
'i 13.
Neither the smoothe nor the e/.id-etched surfaces of concrete from cylinders 6546 and 6767 indicated any abnormality with either saeple,.
The exanination of the 5 ybir.s of 14.
Thin section examia2tions.
thin sections representing low-and normal-strength concrate_ did not reveal significant differences nor did the examinatian of c the other 31 sections of concrete reveal any significant features that would explain the low strengths of some cylinders.
15.
The typical thin section$1rdicated a dense, well consolidated concrete made with a carbonate coarse aggregate, a natural sand, and ~ portland cement.
No admixtures such as fly.ish were recognized.
The paste was a mixture of calcium silicate hydrate, calcium hydraxide, and unhydrated cement grains that seemed to be appropriate 's amount.
The calcium vilicate -hydrate is not specifically recognizable 'by * :nmination of thin sections of concrete although its presence is reality inferred. The comparative examinations did not suggest dif ferent amount.9 of cement or of water between the different samples.
Some of the thin sections were carbonated, or small areas were missing, or the epoxy resin was contaminated with small crystals that crystallized from the resin. LThese defects are common, are not
- Information furnis'aed by Mr. C.
Oberg of the NRC, 4
b 2 f39 s
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considered sisnificant, and did not?secur preferentially witi the lower st rength.v.ancrete.
No reacted sand grains or opal-bearing sand grains were rece;gnf z:d in these thin sections.
16.
The comparison of the X-ray diffraction patterns of concentrated l
l' cement paste from low strength cylinder 6546 and normal strength cylinder l
6659 indicated general similarity.
l
' Disensslaa 17.
K. Mather has described a similar uttuation involving low strength 3
concret: cylinders.
She pointed out that the pertinent questions in such
{
a case are:
a.
What-_ nrocesses could cause the observed resu3 ts, in this case low strength?'
b.
What evideace would these processes Icate i, the concrete?
These problems inclvd.c' excessive air content, too little cenent, tno much water, and early frrezing.
13.
While there could be other processes these illustrate the logic to follow.
In the present case freezing is not an applicable consideration s!nce the cylin'ders.;heuld all have been protected before testing.
In add iti.on, early freezing would ledve ice crystal imprints which were not
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found by the present. examination.
Excessive air content, too little cenent, or execssive water have been ruled out by the PCA data.1, 2 Houever, the present examination would have founi such conditions if they were present.
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Thus, the comparative examination of the five pairs of thin sections i
represencing Tow-and normal-strength cone :ete and also the examination of concrete fra3ments of low-and nornal-strength concrete by eye and with a stercomicroscope was specifically designed to detect such differences as described or other differences.
Mien this type of comparative examina-tion of what should be the saua concrete separated by strengths of 3270 psi (cylinder 6546) and 6640 psi (cylinder 6850) at the sane age does not reveal a signiricant difference this strongly suggests there is no real dif ference between the concretes and that the problem is not with the concrete per se.
Conclujions 20.
Since comparative examination of concrete thin sections and of concret e f agments ' representing low-and normal-strength concrete did not reveal signifi ant differences and since the texture and structure is c
typic,1 of relatively high-strength concrete, it is concluded that the indic ited low strengths are invalid and that all of t his concrete is of comparaale quality approximately as indicated by the higher strength exampl( s.
This suggests that the indicated low strengths vere probably due to one or more failures to follou current standards of good practice in test ing.
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21.
Since the concrete quality appears to be as intended the concrete i
should provide the inten< led service.
22.
These findings are in agree tent with th-se reported by the PCA Construction Technology Laboratories.1, 2 2032 1A1 6
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REFERENCES 1.
PCA Construction Technology Laboratories petrographic report dated 27 February 1979, proj ect CT-0407, 2.
Ibid, 25 April 1979.
f 3.
Mather, K., " Petrographic Examination," in Significance of Tests and Properties of Concrete and Concrete-Making Materials, ASTM i
STP No. 169-B, pp 132-145, 1978.
l 4.
ASTM C 856-77, " Standard Recommended Practice for Petrographic Examination of Hardened Concretc," Note to Table 2, Part 14.
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