Water week

Influence of Aggressivity of water on the long term sustainability of hydro power structures

Research Team Dr.Sameer Vyas Mrs.Beena Anand Dr Neetu Singh Dr.R.P.Parhak

NHPC P

India is endowed with rich hydropower potential to the tune of 148 GW (which would be able to meet a demand of 84 GW at 60% load factor) which makes it one of the most important potential sources to meet the energy security needs of the country.

30% of total electricity produced in India is through hydroelectric power through various large and middle scale dam

in 1947, there were 300 large dams in India. By the year 2000 the number had grown to over 4000, India ranks third in the world in dam building, after US and China. built primarily for flood control, water supply, and hydroelectric power generation, the primary purpose of most Indian dams (96 percent) remains irrigation.

In order to sustain these large dams structures for years, a good quality control practice is required at the time of construction and there after its monitoring .

The following safety measures at the time of construction is required to be taken care of

Quality of construction materials including cement, concrete, steel reinforcement etc..

Water quality to be used for mixing and curing of concrete.

Surrounding geology

DURABILITY OF CONCRETE IS DEFINED AS ITS ABILITY TO RESIST WEATHERING ACTION, CHEMICAL ATTACK, ABRASION, OR ANY OTHER PROCESS OF DETERIORATION.

DURABLE CONCRETE WILL RETAIN ITS ORIGINAL FORM, QUALITY, AND SERVICEABILITY WHEN EXPOSED TO ITS ENVIRONMENT

FOLLOWING CAUSES OF DETERIORATION NEED MOST ATTENTION * FROST ACTION IN COLD CLIMATES * CORROSION OF REINFORCING STEEL; * CHEMICAL EFFECTS ON HYDRATED CEMENT PASTE FROM EXTERNAL AGENTS. *WATER CONTAINING CARBON DIOXIDE SULPHATES OR CHLORIDES); *PHYSICAL-

CHEMICAL EFFECTS FROM INTERNAL PHENOMENON, SUCH AS ALKALIAGGREGATE REACTION AND SALT WEATHERING.

Temperatures Variations Soft water attack pH value below 3.5 TO 4.0 Temporary hardness Free lime in the set cement mortar / concrete paste is leached out

Concrete Deterioration symptoms Erosion Cracking Abrasion Diagonal Cavitation Hairline Joint-sealant failure Seepage Corrosion Random Discoloration or staining Efflorescence Disintegration Spalling Peeling Scaling Weathering

Causes of Distress and Deterioration of Concrete

Chemical Reactions Acid Attach Aggressive-water attach Alkali-carbonate rock reaction Alkali-silica reaction Miscellaneous chemical attach Sulfate attach Construction Errors Corrosion of Embedded Metals Fire Weathering

Peculiar problems like deterioration of concrete due to Poor water quality Problem of leaching of lime in seepage galleries High temperature of water springs inside head race tunnels etc. have been encountered at various projects.

In the present paper a case study on Nathapa Jhakri Hydroelectric power project, Himachal Pradesh, India, is going to discuss with particular reference to its post construction performance under aggressive

Water contributes an active part in imparting strength and durability to concrete.

The role of water is not The chemical reactions between cement and water enable the setting and hardening of cement, resulting in a binding medium for the aggregates and development of strength.

NJHPS THEP Figure 1 Location of THEP, NJHPS and KHEP

Case Studies : Nathpa Jhakri Powe Project, Himanchal Pradesh

• The 1500 MW hydro electric power project is situated in Kinnaur district, Himachal Pradesh.

• Stretched over 45 kms length on river Satluj • A civil engineering marvel.

• The Head Race Tunnel with 8.5 Mtr finished diameter and 27 kms long is longest in any Hydro Project in the country and probably in the whole of Asia.

THE PROJECT AT A GLANCE

The NJHEP project with an installed capacity of 1500 MW (6 X 250 MW), •A 62.50 m. high concrete Dam on Satluj river at Nathpa .

•An underground De-silting Complex, comprising four chambers which is one of the largest underground complex for the generation of hydro - power in the World.

•A 10.15 dia. and 27.394 km. long Head Race Tunnel,which is one of the longest hydro power tunnels in the World, terminating in a 21.60 m / 10.20 m dia and 301m deep Surge Shaft.

•An underground Power House having six Francis Turbine Units of 250 MW each, •6 nos. vertical axis Francis turbines Generating Units, each of 250 MW, with the total installed capacity as 1500 MW. •A 10.15 m dia and 982 m long Tail Race Tunnel to discharge the water back into the river Satluj.

• • • • •

Nature of Problem Hot water spring having temperature of 60-65oC Rock temperature 75oC Long term durability of concrete lining of HRT Reactive aggregate Hot water having temperature around 40-650C was found to seep through the inner face of the tunnel in a stretch of about 2500 m.

• To undertake concrete lining work under these adverse conditions, further investigation work was referred to CSMRS for long term effect of hot water on concrete.

• CSMRS undertook the water quality analysis along the whole length of HRT covering both hot and cold water seepage reaches.

The Naptha Jhakri Power Project

Brief Observations Average temperature of hot water

Varies from 26oC to 58o C

Calcium ion content in seepage water

Between 3.5 to 63.2 ppm

Average Chloride ion content

Varies between 5 to 25, and exceptionally high for two samples 254 ppm & 1296 ppm

Average sulphate content

Varies between 7.3 ppm to 208.06 ppm

Remedial Measures • Cementitious material.

75+25 blend of OPC+ Flyash or • 50+50 blend of OPC + Blast furnace slag conforming to IS: 455-1989 or • 15+85 blend of silica fume + OPC • Cementitious content • Maximum w/c ratio : • Minimum concrete cover : for reinforcement)

: 380 Kg/m3 0.45 50 mm

POST-CONSTRUCTION PERFORMANCE

The project presently is being managed by Satluj Jal Vidyut Nigam limited (SJVN), a joint venture of Government of India and Government of Himachal Pradesh.

Since its commissioning the project is functioning uninterrupted. Recently some leaching of materials was reported in some pockets of power house complex and dam foundation gallery.

Investigation for assessing the cause and degree of deterioration was carried out by Central Soil and Materials Research Station (CSMRS), New Delhi.

Results of insitu chemical analysis of water samples Lab. Sample Temp.

No. 0 C

Parameters pH

CaCO3 Saturated pH

Δ pH

Conductivity Ammonium μ mhos/ cm mg/l

Sulphide mg/l

12/893

15.1

12.02

12.17

-0.11

4460

0.0

0.0

12/894

19.2

7.89

8.95

-0.39

502

0.0

0.0

12/895

20.7

7.17

8.18

-0.34

468

0.0

0.0

12/896

23.2

7.97

8.48

-0.53

723

0.0

0.0

12/897

23.6

7.74

7.91

-0.28

661

0.0

0.0

12/898

24.1

7.35

7.77

-0.80

530

0.0

0.0

12/899

13.1

7.01

7.60

-1.35

386

0.0

0.0

12/900

14.5

7.57

8.12

-0.55

366

0.0

0.0

12/901

14.2

8.23

8.36

-0.13

331

0.0

0.0

Results of laboratory investigation of water samples Lab. Sample No.

Parameters Ca2+ mg/l

Mg2+ mg/l

K+ mg/l

Iron mg/l

Suspended Organic Solids, mg/l Solids, mg/l

Inorganic Solids, mg/l

Total Soluble Salts, mg/l

12/893

300.0

24.0

172.8

0.03

127.2

154.0

1115.0

1269.0

12/894

32.0

4.8

31.55

0.0

569.6

4.0

278.0

282.0

12/895

52.0

24.0

8.4

0.0

0.0

14.0

321.0

335.0

12/896

44.0

9.6

33.1

0.0

0.0

0.0

341.0

341.0

12/897

80.0

16.8

24.25

0.0

0.0

32.0

448.0

480.0

12/898

72.0

10.8

9.85

0.0

0.0

11.0

345.0

356.0

12/899

46.0

15.6

3.25

0.0

0.0

5.0

232.0

237.0

12/900

36.0

16.8

3.1

0.0

132.7

12.0

201.0

213.0

12/901

36.0

9.6

5.45

0.0

0.0

14.0

228.0

242.0

: Results of laboratory investigation of water samples Lab. Sample No.

Parameters CO32mg/l

HCO3mg/l

Cl mg/l

SO42mg/l

12/893

30.0

0.0

25.0

12/894

0.0

152.5

12/895

0.0

12/896

Alkalinity as CaCO3, mg/l

Acidity*

mg/l

Acidity as CaCO3, mg/l

Alakalinity**

21.14

459.0

0.0

1400.0

0.0

140.0

15.0

92.21

0.0

20.0

125.0

2.00

12.50

198.25

12.5

85.53

0.0

28.0

162.5

2.80

16.25

0.0

106.75

32.5

105.48

0.0

16.0

87.5

1.60

8.75

12/897

0.0

259.25

35.0

81.62

0.0

24.0

212.5

2.40

21.25

12/898

0.0

213.5

15.0

63.12

0.0

24.0

175.0

2.40

17.50

12/899

0.0

122.0

10.0

71.69

0.0

32.0

100.0

3.20

10.0

12/900

0.0

106.75

2.5

54.26

0.0

28.0

87.5

2.80

8.75

12/901

0.0

106.75

5.0

79.35

0.0

8.0

87.5`

0.80

8.75

Results of Mineralogical Analysis of Leachate Samples (Using X-ray Diffractometer) Lab. Sample No.

Mineralogical Analysis

12/902

The phase identification with ICDD database using Cement Materials and Minerals sub files indicates presence of Calcite and Calcium silicate hydrates in traces.

12/903

The phase identification with ICDD database using Cement Materials and Minerals sub files indicates presence of Calcite and Wolestonite in traces.

12/904

The phase identification with ICDD database using Cement Materials and Minerals sub files indicates presence of Calcite and Calcium silicate hydrates in traces.

12/905

The phase identification with ICDD database using Cement Materials and Minerals sub files indicates presence of Calcite.

12/906

The phase identification with ICDD database using Cement Materials and Minerals sub files indicates presence of Calcite.

12/907

The phase identification with ICDD database using Cement Materials and Minerals sub files indicates presence of Calcite and Aragonite.

12/908

The phase identification with ICDD database using Cement Materials and Minerals sub files indicates presence of Calcite.

12/909

The phase identification with ICDD database using Cement Materials and Minerals sub files indicates presence of Calcite.

Classification of Degree of Aggressiveness based on various prevailing standard practices

Lab. Sample No.

Degree of aggressiveness based on Langelier Index Values Langelier Index values

Aggressiveness

Indication

Degree of aggressiveness based on SO42-, Mg2+, NH4+ and pH values ( French National Standard, 1985)

12/893

5.73

Non aggressive

Deposition of Calcium

Non Aggressive (AO

12/894

-0.11

Non aggressive

-

Non Aggressive (AO)

12/895

-0.49

Slightly aggressive

-

Non Aggressive (AO)

12/896

0.03

Non aggressive

-

Non Aggressive (AO)

12/897

0.42

Non aggressive

-

Non Aggressive (AO)

12/898

-0.06

Slightly aggressive

-

Non Aggressive (AO)

12/899

-1.07

Moderately aggressive

-

Non Aggressive (AO)

12/900

-0.63

Moderately aggressive

-

Non Aggressive (AO)

12/901

0.01

Non aggressive

-

Non Aggressive (AO)

Interpretation of results for durability of concrete Lab. sample No.

Corrected Leaching Corrosion Index ( CLCI )

Corrected Spalling Corrosion Index ( CSCI )

Corrected Overall Corrosion Index ( COCI )

Degree of Aggressiveness Based on COCI value

Chloride Corrosion Subindex

Degree of Aggressiveness Based on Clconcentration

12/893

-189.76

5.22

-184.54

5.0

Mild

12/894

1077.12

9.77

1086.89

Not aggressive High

3.0

Mild

12/895

1138.50

13.82

1152.32

High

2.5

Mild

12/896

844.48

14.46

858.94

High

6.5

Mild

12/897

531.79

13.60

545.39

Fair

7.0

Mild

12/898

792.89

10.21

803.10

High

3.0

Mild

12/899

551.29

6.74

558.03

Fair

2.0

Mild

12/900

577.10

6.37

583.47

Fair

0.5

Mild

12/901

335.12

7.00

342.12

Mild to Fair

1.0

Mild

CONCLUSIONS Based on the studies carried out by CSMRS time to time leaching phenomenon was anticipated.

Current studies confirm the initiation of the same.

Although presently the leaching phenomenon is critical therefore vigil needs be kept on the locations where the leaching has already initiated or any new locations from where it might have initiated.

The mineralogy of the leached material samples indicates presence of Calcite as the main mineral. An in-depth study quantitative and qualitative behavior of seepage/leaching phenomenon and its effect on long term durability of the concrete needs to be carried out periodically.