Rob Polder, TNO/TUDelft

Durable Structures, February 12, 2014, Oslo,

Norwegian Public Roads Administration

Blast furnace slag in concrete,

100 years of durability?

contents

General introduction

NPRA-TNO collaboration

STAR "slag in concrete"

Cement & concrete

History of slag use

Durability with slag

Overview and conclusions

General introduction

Reinforced concrete:

Mechanical

Physical

Chemical

= Excellent cooperation!

Passivation = no corrosion

“temporary” condition … 100 .. >1000 years

critical: chloride penetration, (carbonation)!

DEpassivation = corrosion (starts)

Cement and Concrete

Cement + water + aggregate –(hydration)->

concrete

Clay + limestone –(heat)-> clinker … Portland

cement, OPC, CEM I

Blended cements: SLAG (fly ash, silica fume)

SLAG clinker

clinker clinker

strength pores pores

fast fast

fast

slower

[Bertolini 2013 after Bakker]

pore structure

early –(hydration) -> later

coarse (Portland) fine (slag)

[from De Rooij 2010]

History of slag use Ground granulated blast furnace slag, GGBS; SLAG

Specific (by)product from steel production

Early 1900s: experiments; Germany OK in 1917

NL regulations 1918: forbidden

1920s experiments IJmuiden locks

1931 joint steel & cement company: designed &

controlled slag properties

! Microscopically identical 1931 – present

Subsequent regulations more tolerant

1986 recommended for marine environment

Since 1970 >50% market share (10 M m3/year)

= now CEM III/B LH SR 42.5 @ 70-72% slag

sold as cement, equal strength at 28 d, 42.5

RWS (NL vegvesen) in XD/XS > 50% slag (or

>25% fly ash)

also prevents damage due to ASR

NL < 50% clinker, green!

Durability with slag

experience, research, focus on NL!

1980 Wiebenga, 50 marine structures up to 40

years age: corrosion is rare

1996 Polder & Larbi prisms 16 year submerged

in North Sea, chloride penetration much lower

than OPC, higher resistivity

2005 Polder & De Rooij 6 marine structures,

chloride profiles, cover depth!

5 slag OK

1 slag corrosion (low cover, low quality) &

Portland corrosion (low cover, high qual)

effect on chloride transport & corrosion initiation

Cs chloride surface content:

driving force

DCl resistance against

transport (penetration rate)

Ccrit threshold for corrosion

(resistivity: corrosion rate

after depassivation)

DCl

Cs

Ccrit

# effective DCl after n years * 10-12 m2/s

ref age year,

type

CEM I # CEM

III/B #

Cs %

cement

Polder &

Larbi 1996

16, subm.

prism tests

1 - 3

~w/c

0.3 2.5 – 5

Polder &

De Rooij

2005

structures

splash

zone

40, pier

low cover:

corrosion

0.14/0.28

sheltered

(high spl.)

0.33 ~ 3

20-33,

3 quays

- 0.12-

0.19

3-4

40, barrier - 0.12 2.8

20, barrier - 0.24 2.2 (..5)

Research: Cl transport (& Resistivity)

1998 Salt 1 day/dry 6 day, 26 weeks; CEM, w/b

DCl, Cs, @ 26 weeks

27% fly ash [Polder & Peelen 2002]

2000s: new test method (Tang et al.)

accelerated transport potential field

rapid chloride migration, RCM, NT Build 492

10-60 V; 1- 4 days, split/AgNO3, calculate DRCM

analysis 500+ results

cement, w/b, 28d – 3 year

slag 50-75% is one group

• slag >50%: more tolerant for w/b variation

28 days

critical chloride content..

literature: no effect of cement type (effect w/b!)

experiment: 26 weeks salt/dry cycles, 4 CEM

Corrosion Potential, then chloride profile

probability of corrosion: f (w/b), not f(CEM)

p

robabili

ty o

f corr

osio

n (

%)

Cl at steel depth (% cem)

0.55

all CEM

0.40

slag

0.45 all

0.40 CEM I, II

other durability aspects of slag cement

carbonation: higher in accelerated lab tests,

similar & low in field (climate, NLNO)

lab: freeze-thaw/salt scaling: more sensitive

field: damage small & no difference CEM I

both: proper curing important!

ASR >50% slag: no deleterious reaction

few hundred cases, none with >50% slag

low heat: less cracking..

100 year life?

model DuraCrete, CUR 1, (semi-)probabilistic 10% probability of corrosion initiation @ 100 y marine environment, similar "North Western Europe" guesstimate from correlation D(RCM) ~ w/b

min. cover depth (mm)

CEM III >50% slag

XS3 splash & tidal

max.

D(RCM,28 d)

* 10-12 m2/s

approx.

w/b

57 5.3 0.55

55 4.7 0.50

52 4.0 0.45

50 3.4 0.40

45 2.8 0.35

overview and conclusions

Experience: 80 year slag cement

>50 y 70% slag

Cs same as Portland

DCl lower, n(time), resistivity higher

Ccrit same

chloride, corrosion: slag cement better performance

than OPC! and prevents ASR

100 year life: possible at reasonable cover depths

DCl

Cs

Ccrit

resistivity 1998 - 2010 (outside)

measure for ionic transport!

CEM III/B > CEM II/B-V > CEM I

slag reacts faster than fly ash!

R

• Chloride penetration: slower with time

due to pore refinement (hydration)

DRCM(t) = D0 * (t0/t)n n slope of log-log plot

0.1

1

10

100

1000

1 10 100 1000 10000

RC

M (

10

^-1

2 m

2/s

)

age (day)

CEM I

CEM III/B

CEM I n~ 0.25

>50% slag n~ 0.4

Dslag<Dopc for

> 7 days

[Caballero 2012]

References

M.R. de Rooij, 2010, Cementsteen, basis voor beton, Hardened cement paste, basis for concrete, in Dutch, Betoniek, Aeneas, Boxtel, ISBN 978-90-75365-99-3 others: See SVV 270!