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LAFARGE STUDIES ON CORROSION PRINCIPLES HIGHLIGHTS

) Lafargeistheworldwideleaderin research of concrete in the sewer environment. the confidence that they need as the

and production of all types of Portland This effort has resulted in a clearer un- long-term solution. cement and Calcium Aluminate cement, derstanding of the path of H2S attack. *L.F.I. isthe parentcompany of LafargeCalcium known primarily by the trademark FONDUo. Test results of weight loss in a controlled Aluminates, and established the brand nameciment This position of leadership compelled and simulated sewer environment indicates Fondu Lafawe@. ~

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Lafarge to begin to investigate the need for cementitious binders to resist the attack and corrosion of municipal sewers.

By drawing on 4Oyears of field experience in conjunction with a major research effort, Lafarge Fondu International*, (L.F.I.), set out to understand the principles of the concrete’s attack and the mechanisms of corrosion found in municipal sewers. The goal was to explain why FONDUG- based concretes are so successful in these environments, compared to Portland cement concretes.

The Lafarge Group Research Facility has a staff of over 300, and has been working with leading universities in this field to identify the key factors for durability

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that FONDUo concretes give it’s users

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Concrete Prism and scored test cubes (1.8 x 1.8 x 2.10 cm)

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BACTERIAL CORROSION HYDROGEN SULFIDE (H2S)

1. H2S CORROSION MECHANISM

A Well-Known Phenomenon The waste water is itself rarely corrosive.

However, under reducing conditions, the decomposing organic materials in the water release the hydrogen sulfide (H2S)

. hit& k g e and

comes out of the solution in areas of

stations, out falls, ... +llrhll A- l:ll_ ---h-I-- -..--,--. tu iuul~i i t h v v IIIW i i i ~ i i i i ~ i ~ ~ , puiiipiiiy

General Bacterial Corrosion Principles

El Berka, Egypt. The junction chamber walls are made of Portland. After 10 years.

This H2S gas is heavier than air and piles up from just above the fluid level, dissolving in the moisture, on the concrete above the flow. It is oxidized here and promotes the development of a bacterial activity. This bacterium with the name “Thiooxydans,” or also known as concretivorus in the literature, produces sulfuric acid in its direct surrounding.

Concrete Prism in the bacterial chamber test room. ic

Bacteriological test done in relation with the Universiv of Hamburg. Pre-scored samples are above water level, at 86°F (3OOC) room temperature. A saturated humid atmosphere is maintained at 10 ppm of f

H2S. Concrete samples are covered with bacteria found in a natural sewer environment. In just one year, the test room can simulate eight years of Hamburg’s sewer corrosion.

2. CORROSION PRINCIPLES The first major point to remember is

that the mechanism of attack isvery different in the case of the well-known diluted acid corrosion and the acid corrosion resulting from the bacterium population even though the acid is the “same”: H2S04 (sulfuric acid). A. The diluted acid attackonly involves

sudden chemical reaction. Protons from the acid decompose the ce- ment paste hydrates. This reaction produces calcium salts (on Portland cement) and aluminum salts (on FONDUo cement). These salts are themselves re-dissolved (plus or minus rapidly according to their mineral resistance solubil- ities), exposing fresh contact sur- face which is attacked again. (This does not regard the contents of this particular document, and addi- tional information on this subject is available .)

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. - -. . . . 344 days of accelerated tests. SewperCnatTM is

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El Betka, Egypt. The junction chamberpipes protected with a LAFARGE lining. After the same 10 years, in a pH between 1 and 2, there have been no degradations and there is good strength.

B. The hydrogen sulfide attack involves many other reactions. The corro- sion phenomena is the result of several parameters. Due to the fact that the attack happens in ambient

0 humid air and not in a liquid, the- chemical mechanism of corrosion

in sewers is far different than the one shown in the classic diluted liquid tests. In the underground network, three players are involved:

the bacteria growth and activity; the resulting acid from bacteria; the concrete reactivity.

The “triangle interface” between these three players is the basis of the corrosion process. This phenomenon has been precisely analyzed and measured. The attack is linked with the following five effects: 1. BIOLOGICAL EFFECT

This is the part related to the bacterial growth and activity on the concrete surface. This is one of the most difficult parts to analyze in the phenomena. Accelerated tests reveal that after one year, the concentration of bacteria is almost similar on all of the samples, but the activity of the bacteria is lower on a FONDUo-based concrete than on a Portland-based concrete.

Tests in the bacterial chambershow that the lower weight loss (corrosion) is obtained wi th Se waerCoat TM.

pH levelgenerated by bacterium according to the material they live on. The pH generated by the bacterium on SewperCoatTM* ( ~ H z ) , is the less aggressive.

*SewperCoatTM is a ready-to-use mortar, produced by Lafarge, specially designed as a coating to resist H,S corrosion. (See the following paragraph on hydrogen test results.) 2. KINETIC EFFECT

This is the part related to the speed of the reactions in the system (pH decreases slowly over time). Dissolution and pre- cipitation of the mineral phases (salts) are, therefore, slowly reacting. FOND@ chemistry-based concrete is aimed at generating stronger resulting salts against the acid attack than Portland-based materials. 3. CHEMICAL EFFECT

In humid aerobic environments, chemical equilibrium is different than in liquids. 4. PHYSICOCHEMICAL EFFECT

This part is related to the microscopic dimension of the reactions. At this scale, the concentration and pH of the resulting acid are variable locally. Therefore, mineral phases are not attacked by an “homo- geneous concentrated”acid at the same time. (Mineral phases reaction is then not uniform). 5. HISTORICAL EFFECT

This is the part related to the life cycle of all the players (bacteria, acid, concrete). The actiutxrtake pace sfmuttanemsty and directly affect the different thiobacillus bacteria comportment. Therefore, the bacreriai coiony is more or iess ‘aggressive ’’ depending on the concrete that they live on. The activity of bacteria decreases with time on the FONDUQ concrete and increases on the Portland concrete.

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the ultimate protective reactive barrier against H2S corrosion.

3. CONCLUSION: A. The well-known method used to simul,

the H2S04 attack by immersing coupons into diluted sulfuric acid is not the relevant way to measure the corrosion attack found in sew- ers, for the following three reasons:

1. The bacterial parameter is not taken into account. (Pop u lat i o n/Act ivi ty level)

2. The kinetics of the reaction in place is not the same.

3. The liquid environment and the humid air environment do not lead to the same re- actions in the salt dissolution and precipitation process.

B. The corrosion mechanism is linked to the attack of the solid mineral- phases (hydrates). Salt reactions are the center of this microscopic level process:

Aluminum salts produced on the surface of FONDUo con- crete or SewperCmtTM tend to protect the concrete. The formation of calcium salts inside Portland concrete ac- celerates the attack by form- ing an expanding mineral called ettringite. (The excess of free lime highly favors this on-going disruptive _.

phenomenon.) C. In the range of a normal concrete

made in the state-of-the-art; poros- ity is not a major factor. The acid does not penetrate the concrete by the pores, but acts directly on the mineral phases. In that respect, sib ica fume does not significantly en- hance the corrosion resistance of concretes.

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D. Alkalinity level of the paste is not a major issue as well. The rate of at- tack is linked with:

the salt reactions which either protect the concrete by staying as a superficial reaction (reactive

FOND UWewpe rCoatTM) or by

being an internal penetration with an on-going expansive and disruptive phenomena (ettringite process with ) the different dissolution protective barrier effect of all Portland-based mix designs).

kintics of the hydrates, and

TEST RESULTS Hydrogen Sulfide (H2S)

The objective of these experiments was to compare the reaction of various cementitious materials to the sewer environment in a carefully controlled laboratory environment. (See the test room pictures.)

)Weight loss of the different materials tested. This one year test reveals figures which have been observed in El Berka, Egypt sewers in 10 years.

1. Cements Are Reactive Various optimum mix designs used in

Ordinary Portland Cement (O.P.C.) Type II Blast Furnace Slag Cement (B.F.S.C.) which is an improved Portland mix design used in sewers (40% O.P.C. Type Ill t 60% slag). FONDUo Cement

After one year, parameters monitored were the weight loss, the depth of attack,

x”&rrendsofattack. The Portland-based concrete with

siliceous aggregates deteriorated quickly, revealed by the high weight loss, and severe depth of attack. In addition, the trend of attack was actually increasing because of the disruptive ettringite phenomenon. The B.F.S.C.-based concrete improved the results but trend of the attack was still high.

The FONDUG-based concrete with )siliceous aggregates showed a very low weight loss and the trend for further attack

the industry were tested.

2. Aggregates Are Reactive Too

Mechanism of corrosion is due to the attack of the mineral phase, therefore, it is necessary tg analyze the paste itself (the cement and the aggregates).

LAFARGE’s research strategy was to formulate and test the ULTIMATE CEMENTITIOUS CONCRETE or MORTAR against this corrosion, by developing special synthesis reactive aggregates. The combination of the very corrosion resistant calcium aluminate cement and these special aggregates produces the ready-to-use product called SewperCoatTM.

This product, SewperCoatTM, reveals exceptional performance in such sewer environments. It has been proven to have exceptionally low weight loss and low depth of attack in controlled and actual sewer environments. In addition, the low trend is maintained by the “protective reactive surface barrier effect” formed by the reaction of the special mineral phases composing the mix.

Therefore, SewperCoatTM has been made available in a ready-to-use material in order to eliminate all questions on mix design and aggregates, of which both are involved in the final quality assurance needed by the customers.

Depth and trend of the attack Dhenomena.

3. Conclusion Hydrogen Sulfide (H2S)

FONDUO Cement is a proven cement which is an alternative solution to epoxy coatings, vinyls, and olefins “families” of resins (P.V.C. and H.D.P.E.) used in underground systems. r

We’ve placed 3,000 miles of ductile iron pipe with corrosion and abrasion resistant FOND@-based linings in the ground over the last 10 years.

Mastering the depth and the trend of attack (disruptive or reactive barrier) is a great progress in the understanding of the mechanism of corrosion.

The sophisticated solution ofpoly-vinyl chloride (P. V. e.), the high density poly-ethylene (H. D. P.E.) or epoxy urethane are the best materials against corrosion in theory, but in practice, these materials showed bondingproblems with the support they applied on and have a tendency to create pinnoies after tneir instaiiation. With only one bubble, or joint defect, the corrosion starts underneath the protective shield. With FOND@-based concrete, a reactive barrier effect is achieved due to the creation of protective salts on the attacked surface. With Se wperCoatTM concrete, the barrier is even more effective against corrosion.

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was not increasing as rapidly with time. (This is the reactive barrier effect.)

SewperCoatrMis farbetterthan othermixes with an almost inconsequential increase in the time.

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Due to this mineralogy, SewperCoatTM hinders the progress and production of the bacterium activity. SewperCoatTM concrete and mortar for structures or linings are exceptionally effective and low-price solutions which are able to give the demanded longevity in sewer corrosive environments.

LAFARGE solutions shown both in 40 years of field experience and in the laboratoty test rooms, show excellent resistance to extreme conditions, and durability that end-users require.

Microscopic picture view of the superficial protective reactive barrier. The external layer shows the concentrated activity of bacteria and the Reactive Barrier on the top of the picture.

IV. USAGES Lining New Pipes - Concrete, Ductile Iron, Steel, or Precast Sections Chambers, Treatment Plants, Lift Networks, Pipe Relining,. . .

Repair - Manholes, Connection

Stations,. . .

Rehabilitation - Waste Water

ADDITIONAL FEATURES OFFERED IN SEWER ENVIRONMENTS:

High temperature resistance. (SewperCoatTM: 21 00°F)

High resistance to freeze-thaw/Hot and cold temperatures

High early strength

Note: Refer to technical spec-data sheets for installation guidelines.

LAFARGE THE WORLDWIDE LEADER

LAFARGE FONDU INTERNATIONAL around the world

FRANCE Head Office: LAFARGE FONDU INTERNATIONAL

157, Avenue Charles-de-Gaulle - 92521 NEUILLY-SUR-SEINE CEDEX Tel. (33 1) 47 38 04 04 - Telex 620 742F - Fax (33 1) 47 47 00 53 - 47 22 23 90

NORTH AMERICA - Lafarge Calcium Aluminates - Tel. (1 804) 543 88 32 AUSTRALIA - Lafarge Fondu Australia - Tel. (61) 2 437 49 66

JAPAN - Lafarge Japan - Tel. (81 3) 3230 15 21 SINGAPORE - Lafarge Coppee PTE (Ltd) - Tel. (65) 733 28 09

GERMANY - Lafarge Tonerdezement GMBH - Tel. (49 203) 31 11 03 BELGIUM, HOLLAND, LUXEMBOURG - Lafarge Fondu Benelux - Tel. (32 2) 647 32 76

GREAT BRITAIN - Lafarge Special Cements - Tel. (44 708) 86 33 33 ITALY - Lafarge Alluminoso ltalia - Tel. (39 2) 33 61 05 26

BRAZIL - Lafarge Aluminoso do Brazil - Tel. (55 21) 701 01 01 SWEDEN - iaiarge Nordiska Kaicium Aiuminater AB - Tei. (46 i60) 88U20

I Corporate Headquarters: P.O. Box 5806, Chesapeake, Virginia 23324

LAFAFGE CALCIUM ALUMINATES

(804) 543-8832, (800) 524-8463, FAX (804) 545-8933