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!