ML072780500

Oyster Creek September 2007 Evidentiary Hearing - Applicant Exhibit 60, L. Bertolini, Et Al., Corrosion of Steel in Concrete - Prevention, Diagnosis, Repair, Wiley - Vch, Weinheim, Germany, 2004, Selections Describing Corrosion Rates.

ML072780500
Person / Time
Site:	Oyster Creek
Issue date:	09/20/2007
From:	Bertolini L, Elsener B, Pedeferri P, Polder R AmerGen Energy Co
To:	NRC/SECY
SECY RAS
References
05-219-LR, AmerGen-Applicant-60, RAS 14274
Download: ML072780500 (3)

Text

-DA.5 Lg7 APPLICANT'S EXHIBIT 60 Luca Bertolini, Bernhard Elsener *WILEY-VCH Pietro Pedeferri, Rob Polder Corrosion of Steel in Concrete "NO.

OFFERED by(ý U.S.UCLEA REGUATORY 2 lt*1 0

C-OMMISSI OfficiaI Exhibit No. (

ensee Intervenor NR .S. ff Other Prevention, Diagnos , DO nKM ljsDETI ontnesqSp, wnA//a USNRC Action Taken: AM D EJEq! WITHDRAWN Repair October 1, 2007. (10:45am) Reporter/Clerk. -

• OFFICE OF SECRETARY RULEMAKINGS AND ADJUDICATIONS STAFF .

Ter(iccb mc 5-E C -0 a.

3.2 Attack by Acids and Pure Water 57 by BSA. This stimulated new research into the biological origins [131, the identifi-cation [14], the influence of concrete composition [15] and possible countermea-sures. Some aspects will be treated here briefly.

Anaerobic conditions can occur in sewers due to long retention times of waste-water, e. g. unexpectedly due to uneven settlement, as illustrated in Figure 3.3; was-tewater in (completely filled) pressure mains becomes anaerobic after being trans-ported for a few hours. Liberation of the H 2 S formed is subsequently promoted by turbulent overflow of anaerobic sewage into aerobic parts of the system. Various types of thiobacilli develop colonies on the concrete surface, which have increasing tolerance for acidic conditions. The final type in this series is thiobacillus thi0oxi-dans (also called concretivorus), which is able to produce (and survive) sulfuric acid with concentrations up to 10 % by mass with a pH below i. The cement matrix is converted by the reaction with the acid to mainly gypsum and eventually, the con-verted layer of concrete falls off. Exposure testing for three years in sewers at Rot-terdam showed that the rate of attack can be as high as 3 mm per year, with insig-nificant differences between (both very dense) Portland and blast furnace slag ce-.

ment concrete [14]. However, high alumina cement showed superior behaviour

[16]. A particular sewer system can be tested for BSA by measuring the oxygen and sulfide contents of the wastewater and the pH of the concrete. surface (using colour-indicator, solutions). The presence of turbulent overflows must be checked and the sewage temperature taken into account [14]. Avoiding long re.

tention times is the best preventative design strategy. Adding oxygen, hydrogen peroxide or nitrate to sewage in order to counteract anaerobic conditions has been successful. In some cases, increasing the flow by connecting rain drainages solved the problem. In larg- sewer pipe elements, protection of concrete by poly-meric sheeting placed in the mould prior to concrete casting is used .as a preven-tative measure.

3.2.3 Attack by Pure Water Pure water, that is water with a low amount of dissolved solids, in particular cal-cium ions, acts aggressively towards concrete because it tends to dissolve calcium compounds. If the water flow rate is high, hydrolysis of hydration products con-tinues, because the solution in contact with the concrete is continually being refreshed. Initially, calcium hydroxide, the most soluble component of cement paste, is removed. Then other components are attacked, producing a more open matrix, making the concrete more penetrable to further attack by aggressive solu-tions. Eventually this will have, a deleterious effect on its strength. In the presence of cracks or construction defects, water can more easily percolate through the con-crete, aggravating the aforementioned processes.

The degree of the attack by pure water depends to a large extent on the perme-ability of the concrete, but its Ca(OH) 2 content also plays an important role. Con-crete types with a low level of Ca(OH) 2 , like blast furnace slag cement concrete, have improved resistance with regard to this type of degradation. In addition to

General Aspects 1000 Concrete heavily contaminated by chloride and 95-98% R.H.

e 100

.W 1007 Concrete contaminated by chloride and 90-95% R.H. or carbonated concrete and 95-98% R.H.

a) Concrete contaminated by chloride and 80-90% R.H.

... * . .orcarbonated concrete and:90ý95%

.. .R.H.

.2 Concrete contaminated by chloride and 50-80% R.H.

o or carbonated concrete and 70-90% R.H.

Concrete carbonated or contaminated by chloride satured by water or dry: R.H. < 50% (chloride),

RH. 70% (carbonation)

Concrete non-carbonated and without chloride Negligible Figure 4.2 Schematic representation of corrosion rate of steel in different concretes and exposure conditions (after [9], modified) 4.3 Consequences The consequences of corrosion of steel reinforcement do not involve only the ser-viceability or the external condition of the structure, but may also affect its struc-tural performance, and therefore its safety.

Reduction in cross. Tensile strength-section of rebars deraei Sdecrease in 0 Elongation Fatigue strength Cracking of Loss of bond concrete strength Effects of - Increase in corrosion corrosion rate u__________Concrete disbonding Hydrogen Brittle failure embrittlement of reinforcement Figure 4.3 Structural consequences of corrosion in reinforced concrete structures [10]

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