specification and site control of the permeability of the

Specification and site control of the permeability of the cover concrete:

The Swiss approach

E. Denarié, EPFL, LausanneF. Jacobs, TFB, WildeggA. Leemann, EMPA, DübendorfT. Teruzzi, SUPSI, LuganoR. Torrent, Quali-TI-Mat, Coldrerio

Switzerland

RILEM Workshop Durability, ETHZ, 17-18 April 2012

2

Content

Need to assess the penetrability of the covercrete onsite

Relevance of site measurement of air-permeability

Recommendations of the Swiss FHWA

Conclusions: foreseeable consequences of theSwiss approach for Concrete Construction

3

Content





4

Quality of Concrete in a Real Structure

Specimens, cast and cured under standard conditions, DO

NOT represent the quality of the vital “covercrete”

Due to:

• Segregation

• Compaction

• Curing

• Bleeding

• Finishing

• Microcracks

“Covercrete” ofPoorer Quality

CO2 Cl- SO42-, Abrasion,

Frost

Durability = f (penetrability, thickness)

5

Swiss Standard SIA 262:2003“Concrete Construction” (Swiss Concrete Code)

”With regard to durability, the quality of the cover concrete is of particular importance“

”The ‘impermeability’ of the cover concrete shall be checked, by means of permeability tests (e.g. air permeability measurements), on the structure or on cores taken from the structure“

6

Valve 1

Vacuum Pump

PressureRegulator

(Pe=Pi)

PiPe

i

i : Inner chamber

e : External chamber

2-Chamber

Vacuum cell

Computer

Touch-screen

Concrete

Soft rings

Valve 2

e

Air Permeability “in situ”: SIA 262/1-E:2003

PermeaTORR (M-A-S 2008)

Torrent Permeability Tester (Proceq 1995)

7

Evolution of Pi (simplified)

0

10

20

30

40

50

60

70

80

0 5 10 15 20 25 30

Pre

ssu

reP

i(m

bar)

60 720

Close V2

∆P=0

t =0Pi ~1000

Close V1

0 135tf

time (s) – square root scale

tmax

360

∆P~20 mbar

kT = 9.2 10 -16 m²

kT = 0.070 10-16

m²

807/05/2012 8

Pi = Pe Controlled unidirectional air-flow

i

e

Concrete

Unidirectional air flow

into the inner chamber

9

Calculation of kT

kT =A

ln

2 ε Pa

Vc2

2

µ

Pa + ∆Pi (tf)Pa - ∆Pi (tf)

√ tf - √ to

• kT: coefficient of air-permeability (m2)

• Vc : volume of inner cell system (m3)• A : cross-sectional area of inner cell (m2)• µ : viscosity of air (= 2.0 10-5 N.s/m2)• ε : estimated porosity of the covercrete (= 0.15)• Pa : atmospheric pressure (N/m2)• ∆Pi: pressure rise in the inner cell at end of test (N/m2)• tf : time (s) at the end of the test (2 to 6 or 12 min)• to : time (s) at the beginning of the test (= 60 s)

Derivation at www.m-a-s.com.ar

10

Content





11

Relation of kT with other Durability Indicators

0

5

10

15

20

25

0.001 0.01 0.1 1 10 100

kT (10-16

m²)

24

-h S

orp

tiv

ity

(g

/m²/

s½

)

Laboratory

Tunnel

Bridge

0

25

50

75

100

125

150

0.001 0.01 0.1 1 10

kT (10-16

m²)

Ma

x.

Pe

ne

tra

tio

n (

mm

) Water Penetration

under Pressure

(EN 12390-8)

100

1000

10000

100000

0.001 0.01 0.1 1 10 100

kT (10-16

m²)

Co

ulo

mb

s

Very

Low

Low

Moderate

High (+ Very High)ASTM C1202Water Sorptivity

0

5

10

15

20

25

0.001 0.01 0.1 1 10 100

28-d. kT (10-16

m²)

Carbonation

50

0-d

. C

arb

on

ati

on

(mm

)

12

Content





13

Involvement of ASTRA (Swiss FHWA)

(1993)

(2009)

14

Reproducibility of kT test

Specification of kT

Suitable age, temperature and moistureconditions

Sampling

Conformity Rules

Reporting

Recommendations for site kT quality control

Issued by the Swiss Federal Highway Administration end 2009

15

Reproducibility on Bridge and Tunnel Elements

0.001 0.01 0.1 1 10 100

Coeff. Air-Permeability kT (10-16

m²)

2

1

4

3

Very Low Low Moderate High

Lab

Bridge

low SD

N=15

Tunnel

high SD

N=6

5

Very High

2

1

4

3

16

Situation Swiss Standards

1010------------------DCl max(10-12 m²/s)

0.450.450.500.500.500.600.650.65w/cmax

320320300300300280280280Cmin (kg/m³)

30/37

30/37

25/30

25/30

30/37

25/30

25/30

25/30

StrengthClassmin

XD3XD2bXD2aXD1XC4XC3XC2XC1

0.50.52.02.02.0---------Site kTs(10-16 m²)

------101010---------qwmax (g/m²h)

ChloridesCarbonationExposure

Class

20

03

20

08

Ye

ar

20

13

?

kTs= "statistical maximum"; limits proposed in Recommendations

17

Testing Recommendations

Age of testing:Between 28 (60 for slow binders) and 90 days

Temperature

Concrete temperature should be ≥ 5°C.

Moisture (one of the following conditions should be fulfilled)

Absolute moisture, measured by contact impedance surface tester, ≤ 5.5 %

Electrical resistivity, measured by Wenner method, ≥10-20 kΩ.cm

Guidelines given on when the above conditions are likely to be fulfilled

18

Sampling

Elements made under nominally same conditions are grouped and listed chronologically

Surface Lots defined (500 m² or 3 concreting days)

Measurement points (6) selected at randomSurface LotH > 150 mm

H > 150 mm

D > 50 mm D > 50 mm

kT1

kT2

kT3

kT4 kT5

kT6

> 200 mm

19

Condition 1:Not more than 1 test (out of the 6) with kT > kTs

Condition 2:If 2 tests > kTs, 6 new points are selected at random from the same Lot

Not more than 1 (out of the new 6 tests) with kT >

kTs

Conformity Criterion

If none of the above Conditions is fulfilled, the Lot is considered as non-compliant with the specified kTs and consequences follow

20

O-C Curve of Adopted Conformity Criterion

This gives a probabilistic meaning to kTs

010

2030

4050

6070

8090

100

0 10 20 30 40 50 60 70 80

Percentage of Concrete with kT>kTs in Test Area

Pro

ba

bili

ty o

f Acc

ep

ting

Te

st A

rea

(%

)

Condition1

Condition 2

21

‘Covercrete’

Quality = K-1Execution:

• Placing• Compaction• Finishing• Curing

kT checked on

site

K = Penetrability

Concrete

Production

Standard “K”

Tests on cast

Specimens

New Situation

Performance specification of site concrete

DESIGN PRACTICE CONTROL

Specification

of

Kmax

on Delivered

and Site

Concrete

22

Content





23

1. Specifying the air-permeability of the covercrete, measured on site, aims at controlling the end product

Conclusions

2. By checking the end product, a performance-oriented mindset is created in all players, ensuring a fair competition for:

Contractors, who have to deliver the specified quality of the product to be tested

Concrete Producers, who have to efficiently design, produce and deliver mixes capable of achieving the required performance

Raw Materials Suppliers (cement, additions, admixtures) who have to design their products to achieve the best performance in concrete

24

3. Discourages all too common bad practices such as:

Accidental or deliberate transgressions of the specified w/cmax by concrete producers

Uncontrolled addition of water to the ready-mixed concrete trucks after leaving the batching point

Incorrect placing and compaction practices

Poor finishing techniques of floors and pavements

Insufficient or total absence of moist curing

Conclusions

25

SCC, creating a more compact and uniform covercrete

Permeable formwork liners

More efficient curing compounds and/or “self-curing”concretes

High Performance Concretes and Composites

Low or no Shrinkage Concretes (ShCC)

More sustainable systems, currently precluded by prescriptive standards

4. Incentives innovation by encouraging the use of:

Conclusions

26

Measurement of the coefficient of air-permeability kT

Measurement of cover depth

Application of models for carbonation-induced corrosion based on air-permeability kT (e.g. Parrott)

Application of models for chloride-induced corrosion based on air-permeability kT (e.g. EPFL) or through correlations of DCl and kT (e.g. EHE-08)

5. Allows estimating service life from measurements conducted on the structure

Conclusions

27

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References

specification and site control of the permeability of the

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