Blast furnace slag in concrete, 100 years of durability? Clay + limestone –(heat)-> clinker …...
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Rob Polder, TNO/TUDelft Durable Structures, February 12, 2014, Oslo, Norwegian Public Roads Administration Blast furnace slag in concrete, 100 years of durability?
Transcript of Blast furnace slag in concrete, 100 years of durability? Clay + limestone –(heat)-> clinker …...
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!
