Durability Design – The Indian Scenario

Manu SanthanamDepartment of Civil Engineering

IIT Madras

1-day Workshop on “Achieving Durable Concrete Construction Through Performance Testing

Durability of concrete

• Primary issues- Corrosion of rebars- Chemical attack- ASR / DEF

• Multiple transport mechanisms involved• Typically countered by choice of material and

mix design• Rarely checked in the specimens / structure

Conventional durability design

• Durability = fn (Compressive Strength)• Cement type, binder content and w/c

prescribed for durable concrete• Cover specified for service environment

(seldom actually checked on site!)

But research / field experience shows this does not necessarily work!

Example: Prescriptive requirements on materials in IS 456 : 2000

DURABILITY

THE CONCRETESYSTEM

AGGRESSIVENESSOF THE

ENVIRONMENT

MATERIALS PROCESS PHYSICAL CHEMICAL

•Binder type•Binder content•Aggregates•Admixture•Mix design

•Mixing•Transporting•Compaction•Curing•Temperature•Workmanship

•Abrasion•Erosion•Cavitation•Freeze-thaw

•Dissolution•Leaching•Expansion•Alteration

Specification issues! Ballim, 2008

Approaches for durability design

Prescriptive Approach Performance Approach

Avoidance of deterioration

• Use of non-reactive materials such as stainless steel or protection systems such as coatings

Based on performance

based tests and indicators

• Tests are generally accelerated

• Used to rank concrete qualities

Through modelling

• Design of service life of structure by means of analytical and numerical methods

• Needs test methods to verify the fulfillment of the characteristic values

• Models can be simple or complex

Deemed-to-satisfy Approach

• Prescriptive requirements on materials

• Followed by present codes

International developments on durability design

All-encompassing Prescriptive Approach

Cement content and w/c specified to achieve a particular strength was believed to be adequate for durability

The National Durability Grade Concept, U.K, 1980’s

Able to link durability and impermeability

The environmental exposure classification system (EN 206)

Deterioration Specific Prescriptive Approach

Durability is specified by putting limiting values of concrete composition

Durability design method and Performance Testing

Involves consideration of relevant deterioration mechanisms and estimation of expected service life of the structure

Considers the mechanisms leading to deterioration of concrete

(Richardson, 2002)

Indian codes and specifications for concrete design

– IS 456-2000 code of practice for concrete construction in India

– Indian Railway Standard IRS 1997– Code of practice for concrete road bridges IRC 112-2011– MOST or MoRTH (Ministry of Surface Transport or

Ministry of Road Transport and Highways) specification– Guidelines for the use of HPC in bridges – Metro rail specification of Chennai, Hyderabad and

Kolkata– Four laning and two laning projects of national highways

Dhanya and Santhanam, 2013

IS-456• 5 general exposure environments – Mild, Moderate, Severe, Very

Severe and Extreme• Limits on minimum cement content, maximum water cement ratio

and minimum grade of concrete for different exposures• Limits of chloride and sulphate content of concrete• Nominal cover to concrete based on exposure condition • Specific durability issues addressed : Abrasive action, freezing and

thawing, exposure to sulphate attack, ASR, presence of chlorides and sulphates, concreting in seawater and aggressive soils

• Inspection and testing: Compressive strength test • NDT to assess properties of concrete in structures: Ultrasonic Pulse

Velocity, Rebound hammer, Probe penetration, Pull out and Maturity tests

No mention of conducting durability tests to ascertain quality…Acceptance criteria also strength based

IRC-112• Same ‘deemed to satisfy’ approach, but exposure classes modified• Additional provision for specific mechanism of deterioration such as

corrosion of reinforcement, sulphate attack, alkali-silica reaction and frost attack

• Anticipated service life of 100 years is specified• For a design life of 50 years or less, the minimum cover can be reduced by

5 mm• Regarding the tests, the code says “there is no specified test method for

durability which can be completed within a reasonably short time”• For HPC, Rapid Chloride Permeability Test (ASTM C 1202) and Water

Permeability Test (DIN 1048 part 5) or Initial Surface Absorption Test (BS 1881 part 1) can be specified

• Upper limits for total charge passed in RCPT for the exposure conditions such as severe (1500 Coulombs), very severe (1200 Coulombs) and extreme (800 Coulombs) conditions are provided.

No basis provided for limiting values of RCPTRCPT may favour only mixes with silica fume / high quantities of fly ash / slag (which may not even be allowed in the project!)

Metro specifications

• Codes referred to : relevant IS Code / MOST/MORTH Specifications

• Automatic weigh batching or RMC• Mandatory Test - Cube compressive strength

test• Additional Test - Permeability test for Concrete as

per IS: 3085-1965, Section 1716.5 of MOST Specification and DIN 1048

• Limiting value of water penetration depth when tested as per DIN is less than 25 mm

Again, issue is with respect to the basis for providing certain limiting values – what is the link to actual performance?

• Clauses regarding durability in codes are varied and mostly unrelated to measurable durability parameters

• Specification - gives reference to different standards- do not provide information regarding age of testing and design life

- lack of clarity on limiting values of durability parameters

• Tests specified : Compressive strength test, Water permeability test (IS: 3085-1965, Section 1716.5 of MOST Specification and DIN 1048), Rapid chloride permeability test, Initial surface absorption test

• Present exposure classifications do not adequately address the relevant durability issues

Critical evaluation of clauses regarding durability in Indian codes and specifications

Dhanya and Santhanam, 2013

Lessons learnt

There is clearly a need to have guidelines and model specification for construction projects in India regarding concrete durability

Exposure classes need to be made more relevant – so that deterioration mechanisms may be identified, and suitable tests used

Exposure classes – international developments

• EN206-1:2000- first to link exposure conditions to deterioration mechanisms

• BS 8500-1:2006- prescriptions for 50 and 100 year design life

• ACI 318: 2008- prescriptive requirements, not as much depth as EN

• AS 3600: 2009- Good division of coastal environments, as well as above / below ground

Indian inputs: Kulkarni (2009) and IRC 112

Examples

EN 206-1 2000 BS 8500-2006 (50 years design life)

No risk of corrosion or attack: X0Corrosion induced by carbonation: XC1, XC2, XC3 and XC4Corrosion induced by chlorides other than from sea water: XD1, XD2 and XD3.Corrosion induced by chlorides from sea water: XS1, XS2 and XS3.Freeze / thaw attack with or without de-icing agents: XF1, XF2, XF3 and XF4.Chemical attack: XA1, XA2 and XA3.

No risk of corrosion or attack: X0Corrosion induced by carbonation: XC1, XC2, XC3 and XC4Corrosion induced by chlorides other than from sea water: XD1, XD2 and XD3.Corrosion induced by chlorides from sea water: XS1, XS2 and XS3.Freeze / thaw attack with or without de-icing agents: XF1, XF2, XF3 and XF4.Chemical attack: XA1, XA2 and XA3.

Proposal of a new classification system for India

• Work done by Saravanan (2011)• Basis:

- Review of international developments- Adoption of best practices in Indian specifications- Comparative evaluation of international proposals vis a vis live projects in India- Prescribe limiting values for different exposure classes

Air-borne chloride exposure class

Distance from coast

Exposure Classification

Min. grade of

concrete

Min. Cementitious

Content (kg/m3)

Max. w/cm

Min. clear cover (mm)

Remarks

Up to 10 km from

coastD1 M 40 360 0.40 50

Based on CPWD Specifications

(Distance up to 10 km to be treated

as coast) Beyond 10 km and up to 50 km

D2 M 30 320 0.45 40

Beyond 50 km

(Inland)D3 M 25 300 0.50 30

Based on AS3600 (Distance beyond

50 km to be treated as inland)

Sea water exposure class

Exposure classification

Min. grade of concrete

Min. Cementitious

Content (kg/m3)

Max.w/cm

Min. clear cover (mm)

SW1 M 40 360 0.40 50SW2 M 50 400 0.40 75

SW1: Concrete completely immersed in sea waterSW2: Concrete in spray / tidal zone

Sulphate exposure class

Exposure classification

Min. grade of concrete

Min. Cementitious

Content (kg/m3)

Max. w/cm

Min. clear cover (mm)

Type of cement

S0 M 25 300 0.50 30 OPC

S1 M 35 340 0.45 40SRC, PPC,

OPC with slag or silica fume.

S2 M 50 400 0.40 50SRC, PPC,

OPC with slag or silica fume.

S3 M 50 400 0.40 50 SRC, PPC

S0: No risk: SO3<0.2% (soil), <300 ppm (water)S1: Moderate risk: SO3: 0.2% to 1.0% (soil), 300 to 2500 ppm (water)S2: Severe risk: SO3>1% (soil), >2500 ppm (water)S3: Severe risk with magnesium sulphate SO3>1% (soil), >2500 ppm (water)

Carbonation class

CO: No risk of carbonation (i.e.) concrete which will remain dry during its service life or concrete permanently submerged in water.C1: Moderate to high humidity (i.e.) concrete inside buildings with moderate to high humidity, exposed concrete sheltered from rain.C2: Cyclic wet and dry (i.e.) concrete exposed to rain and not sheltered.

Exposure classification

Min. grade of concrete

Min. Cementitious

Content (kg/m3)

Max. w/cm Min. clear cover (mm)

C0 M 25 300 0.50 30C1 M 30 320 0.45 40C2 M 35 340 0.40 40

Note about presciptions

• Strength grade – minimum M25• Binder content inclusive of mineral admixtures• Cover may be modified: (a) for thin sections,

slabs, fins, (b) when higher grades of concrete are used, (c) min 50 mm to be maintained in foundation

• For the future – specify only strength, along with w/c: requirement on cementitious content must go!

Thank you…

Overview of research projects at IIT Madras

Study 1 – 2010-2011

Santhosh George CheriyanM Tech project

Result matrix – Study 1Replacement Level

(%)Compressive

Strength (MPa)RCPT Charge

Passed (Coulombs)

Chloride Conductivity

(mS/cm)

Sorptivity(mm/√hr)

Oxygen gas Permeability Index

Control Mix0 44 3210 1.9 11 10.09

Class F Fly ash Mixes15 37 2620 1.22 9.75 10.330 39 1725 1.19 8.42 10.550 24 1200 1.17 8.5 10.52

Class C Fly ash Mixes15 43 3400 1.81 10.33 10.1230 41 2650 0.8 8.2 10.3

Class C and Class F Fly ash Mix40 (20+20) 37 1700 1.08 8.51 10.42

Slag A Mixes15 44 3000 1.2 9.15 10.430 46 2580 0.96 8.5 10.6650 46 780 0.34 8.13 10.73

Slag A and Class F Fly ash Mix40 (20+20) 36 2090 0.65 9 10.44

Slag A and Class C Fly ash Mix40 (20+20) 47 1075 0.27 7.97 10.48

Slag B Mix11 46 3680 1.29 9.83 10.47

All mixes designed with 310 kg/m3

binder and 0.50 w/c; 60 : 40 coarse to fine aggregate ratio

As the replacement level increases, the charge passed in RCPT decreases.

For the Class F fly ash the drop in charge passed is significant even at lower dosages.

Class F fly ash mixes show low charge passed at all replacement levels.

RCPT

Chloride Conductivity

Slag A mixes have least chloride conductivity at all replacement levels.

All combination mixes performed well with Slag A and Class C fly ash mix having the lowest chloride conductivity.

This indicates that a Slag A and Class C fly ash may be a more economical and durable option in marine condition compared to the use of Slag A alone.

Oxygen Permeability

Class C and Class F combination mix would be the most economical and durable combination in chimneys were gaseous permeation is likely to occur.

Also, it will be suitable for regions were carbonation induced corrosion is prevalent.

Water Sorptivity

Sorptivity decreases as replacement level increases

No significant difference between the different mineral admixtures at 28th

day.

Fly ash F performs best at 90 days

How to choose the right blend?

• Ternary combinations not only make the mix economical but also more environment-friendly because fly ash is used

• 40 MPa concrete is more economical with 30% Class F fly ash rather than with Class C fly ash; further, it would also possess superior durability characteristics which will again decrease the cost by having longer service life.

• Evaluate the benefit to cost ratio!

Study 2 – 2011-2013

B S DhanyaPhD Scholar – Currently working

• 2 categories of mixtures

• Commonly used design mixes

– Four groups based on the total binder content and water binder ratio (280, 0.65; 340, 0.55; 310,0.5 and 310,0.6)

• Design mixes having limiting prescriptive values

– Concrete mixtures recommended in the IS 456:2000 for different exposure conditions

– Concrete mixtures recommended in the proposal by Saravanan and Santhanam (2012)

Sl. No. Mix ID w/b Binder content (kg/m3) Mineral Admixture content

1 LFM2 0.65 280 0

2 LFM9 0.65 280 30% slag A

3 LFM17 0.65 280 30% slag B

4 LFM29 0.65 280 30% Fly ash F

5 LFM4 0.55 340 0

6 LFM12 0.55 340 15% slag A

7 LFM21 0.55 340 15% slag B

8 LFM32 0.55 340 15% Fly ash F

9 LFM42 0.55 340 15% Fly ash C

10 LFM5 0.50 310 0

11 LFM13 0.50 310 15% slag A

12 LFM22 0.50 310 15% slag B

13 LFM23 0.50 310 30% slag B

14 LFM24 0.50 310 50% slag B

15 LFM28 0.50 310 20% slag B + 20% fly ash F

16 LFM33 0.50 310 15% Fly ash F

17 LFM34 0.50 310 30% Fly ash F

18 LFM35 0.50 310 50% Fly ash F

19 LFM39 0.50 310 20% slag B + 20% fly ash C

20 LFM40 0.50 310 20% fly ash F + 20% fly ash C

21 LFM43 0.50 310 15% fly ash C

22 LFM44 0.50 310 30% fly ash C

23 LFM46 0.6 310 0

24 LFM10 0.6 310 15% slag A

25 LFM19 0.6 310 15% slag B

26 LFM30 0.6 310 15% Fly ash F

27 LFM41 0.6 310 15% fly ash C

Category 1: Commonly used design mixes

Sl.No Mix ID w/b Cement content (kg/m3)

1 MA1 0.5 300

2 MA2 0.55 300

3 MA3 0.45 320

4 MA4 0.45 340

5 MA5 0.4 340

6 MA6 0.4 360

7 MA7 0.4 400

Category 2: Design mixes having limiting prescriptive values

• Mineral admixture mixes have higher resistivity than OPC mixes

• Slag with 50% replacement shows greatest resistivity

• Performance of Class C fly ash is close to OPC

Effect of mineral admixtures on concrete resistivity

Wenner resistivity test results on mixes with total binder content of 310 kg/m3

and w/b 0.5

OPC

15% sl

ag B

30% sl

ag B

50% sl

ag B

15% Fly a

sh F

30% Fly a

sh F

50% Fly a

sh F

15% Fly a

sh C

30% Fly a

sh C

Wen

ner r

esist

ivity

(kc

m)

0

10

20

30

40

50

60

70

80

90

100

110

12028 days90 days

Very poor

Poor

Normal

Good

OPC

15%sla

gA

15%sla

gB

30% sl

ag B

50%sla

gB

20%sla

gB+2

0%fly

ash F

15% Fly

ash F

30%Fly

ash F

50%Fly

ash F

20%sla

gB+2

0%fly

ash C

20%fly

ash F

+20%

fly as

h C

15% fly

ash C

30% fly

ash C

Enh

ance

men

t of W

enne

r res

istiv

ity fr

om 2

8 to

90

days

(kc

m)

0

10

20

30

40

50

60

• The enhancement of resistivity is more for mixes with mineral admixtures compared to OPC

• Mixes with Fly ash F shows better enhancement of resistivity as curing increases from 28 to 90 days, followed by ternary blends with fly ash

Effect of curing duration on concrete resistivity

Wenner resistivity test results on mixes with total binder content of 310 kg/m3

and w/b 0.5

• Mineral admixture mixes are showing low total charge passed than OPC mixes

• Slag with 50% replacement shows lowest charge passed, better chloride resistance

• Fly ash C perform similar to OPC at 28 days ; but improves at 90 days

RCPT results on mixes with total binder content of 310 kg/m3 and w/b 0.5

Effect of mineral admixtures on chloride ion penetrability

• Mineral admixture mixes are showing low total charge passed than OPC mixes

• Slag with 50% replacement shows lowest non-steady state migration coefficient

• Fly ash C perform similar to OPC at 28 days ; but improves at 90 days

ACMT results on mixes with total binder content of 310 kg/m3 and w/b 0.5

Effect of mineral admixtures on chloride ion migration

How to use this data?

• Explore correlations between tests• Use combinations of test parameters for

assessing concrete quality in a specific environment- e.g. Concrete submerged in seawater: (i) Resistivity and (ii) Chloride diffusion

• Strength grade classification – concrete with mineral admixtures can produce durable concrete even at low grades

Correlation between Wenner resistivity test and RCPT

Total charge passed (Coulombs)

0 1000 2000 3000 4000 5000

Wen

ner r

esis

tivity

(k

cm

)

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

28 days, no scm90 days, no scms28 days, class F90 days, class F

28 days, class C90 days, class C

28 days, slag90 days, slag

Similar correlation was seen between Resistivity and ACMT

ACMT Vs Wenner

Non steady state migration coefficient, m2/s

0.0 5.0e-12 1.0e-11 1.5e-11 2.0e-11 2.5e-11 3.0e-11 3.5e-11

wen

ner r

esis

tivity

, k o

hm c

m

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

28 days, no scms90 days, no scms28 days, class F90 days, class F 28 days, class C90 days, class C

28 days, slag90 days, slag

Correlation between Wenner resistivity test and ACMT

• Wenner indicator of surface resistivity, good indicator of the cover concrete quality, non-destructive test

• The results points to the fact that Wenner resistivity can be recommended as a good field test to check durability

Category

Resistivity[from Wenner

Resistivity test](kΩ.cm)

Total charge passed [from RCPT]

(Coulombs)

Non-steady state migration coefficient [from

ACMT](x 10 -12 m2/s)

Excellent > 50 <1000 <8Good 10-50 1000-2000 8-16

Moderate 10-50 2000-4000 16-24Poor <10 >4000 >24

Total charge passed, Coulombs

0 1000 2000 3000 4000 5000

wen

ner r

esis

tivity

, k o

hm c

m

0

20

40

60

80

100

120 28 days90 days

EXCELLENT

GOOD

MODERATE

POOR

Proposal for combined classification criteria

Strength class

Durability classbinder content and replacement

% ValuesConcrete resistivity

(kΩcm)

Risk of corrosion

20-30

<10 high 100%OPC 8.9

10-50moderate

30%slag, 30%flyashF, 50%fly ashF 18,32,10.1,4750-100 low>100 negligible

31-40

<10 high 100%OPC, 15%flyashC 9,11

10-50moderate 15%slag,15%flyashF, 30%flyashF,

30%flyashC 12, 16-12,23,1350-100 low 30%flyash F 69>100 negligible 50%fly ash F >100

41-50

<10 high 100%OPC, 15%flyashC 8-9,11,9

10-50moderate 15%slag, 30%slag, 15%flyashF,

15%flyashC15,21,20-26,33, 17,28-

37,11,17-1450-100 low 50%slag 85>100 negligible

51-60

<10 high

10-50 moderate 100%OPC, 30%slag 16,39

50-100 low

>100 negligible 50%slag >100

Durability matrix for Wenner Resistivity

Reliability of tests

Stage 1: Specimens stored in ideal lab conditions and tested

Stage 2: Specimens stored in site conditions and tested in the lab

Stage 3: Mock up beams / panels cast alongside structure on site; testing on panel, as well as on cores removed from panel

Stage 4: Tests on the actual site concrete!

Summary

• Durability design – a real necessity • Many challenges – what tests to use, how to

use them, what are the implications for service life

• How do mineral admixtures affect the results

• Long way to go, lot of scope for research!