Betong med alkali-aktiverad slagg och nano-impregnerat kolfibernät

2021-04-29
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Concrete with Alkali-Activated Slag and
Nano-Impregnated Carbon fibre Mesh
Tang Luping
Full professor of Building Materials
Department of Architecture and Civil Engineering
Chalmers University of Technology
Gothenburg, Sweden
2021-04-29
This presentation try to address
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 What is alkali-activated slag (AAS) concrete? Which factors
affect the strength and shrinkage of AAS concrete?
 What is the general durability of AAS concrete? How is the acid
resistance and temperature stability of the concrete affected
when using AAS?
 What potential structures can AAS concrete be suitable for?
 What are the obstacles to the application of AAS concrete in
ordinary structures?
 How to improve adhesion between carbon fiber mesh and
concrete?
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Background
•What is alkali-activated slag (AAS) concrete?
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Problem in Portland Cement Production
4
600
400
200
800
1000
1200
1400
5 20 25 30 35
10 min
˚C
Mass
portions
CO2
Pre-Heating
Burning
Calcining Transiting
1200-1500 C
CaCO3 → CaO + CO2
Calcining process
Molecular weight 56 44
+ CO2 release from fuel
 0.9 kg CO2 per kg cement
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History of Alkali-Activated Materials (AAM)
5
Year Researcher Country Main work
1930 Kuhl Germany Setting of slags + caustic potash
1937 Chassevent unknown Reactivity of slags + caustic potash and soda solution
1940 Purdon Belgium Clinker-free cement: slag + caustic soda or alkalis
produced by a base and an alkaline salt
1957 Glukhovsky USSR Soil cement: hydrous or anhydrous aluminosilicates
(glassy rocks, clays metallurgical slags, etc.) + alkalis,
proposed cementing system M2O-MeO-Me2O3-SiO2-H2O
1982 Davidovites France Geopolymer: alkalis + a burnt mixture of kaolinite,
limestone and dolomite
1990 Tomas Kutti Sweden Alkali Activated Slag Mortar – Mechanical strengths,
shrinkage and structure, Chalmers PhD thesis P-90:6
(M: alkali metal; Me: alkaline earth metal)
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A Hot Topic since 2000
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2006 2014
2014
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Some Example Buildings Made of AAM
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A 24-storey buildig built with AAS on
Berezinsa street 2, City of Lipetsk, Russia
Residential building in Mariupol, Ukraine,
constructed from AAS precast blocks
(exterior clad in plaster)
6-storey office and retail building built with AAS in
Anyang City, Henan Province, China
2021-04-29
Groups of Alkali-activator
8
1. Caustic alkali: MOH (e.g. NaOH, KOH)
2. Non-silicate weak acid salts: M2CO3, M2SO3, M2PO4, MF, etc.
(e.g. Na2CO3, K2CO3)
3. Silicates: M2OnSiO2 (e.g. Na2OnSiO2, K2OnSiO2)
4. Aluminates: M2On Al2O3
5. Aluminosilicates: M2OAl2O3 (2-6) SiO2
6. Non-silicate strong acid salts: M2SO4 (e.g. Na2SO4 )
(Glukhovsky et al., 1980)
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Two Big Problems in AAS
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• Low CaO/SiO2 (only about 1) resulting in high
shrinkage
• Variable setting time (sometimes it is advantage but
sometimes it is too quick to complete casting)
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Vinnova research project
10
Green Cement Based on Ground Granulated Blast furnace Slag (GGBS)
(2018 – 2021)
Merox
Aim of the project:
Develop fiber reinforced sustainable, competitive and advanced
cementitious materials for industrial applications ranging from
construction to transportation
Mainly based on alkali-activated GGBS (AAS)
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Important Parameters in Proportioning AAS
Concrete
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• Alkali content (Na2O by wt% of slag)
• Silica content (SiO2 by wt% of slag)
• Gypsum content (CaSO42H2O by wt% of slag)
(Which factors affect the strength and shrinkage of AAS concrete?)
2021-04-29
Results from Compressive Strength Test
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Alkali-activated slag with different additions of alkali and silica
OPC
3d
OPC
7d
OPC
28d
OPC
3d
OPC
7d
OPC
28d
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Effect of Combined Additions
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CA = Na2O% + 0.3SiO2% - 0.3Gypsum%
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CA = Na2O% + 0.3SiO2% - 0.3Gypsum%
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Results from Shrinkage Test
15
-5
-4.5
-4
-3.5
-3
-2.5
-2
-1.5
-1
-0.5
0
1 10 100 1000
Length
change
(vertical),
permil
Drying duration, day
100%SL+0%C+0%G+6%N+7%S
100%SL+0%C+1.5%G+5.9%N+6.9%S
2.5%G+5.9%N+6.8%S
3.5%G+5.8%N+6.7%S
0%G+2.4%N+2.8%S
1.5%G+2.4%N+2.8%S
3.5%G+2.3%N+2.7%S
2.5%G+3.1%N+3.6%S
0%G+4.8%N+5.6%S
2.5%G+4.7%N+5.5%S
0%G+5.2%N+6%S
2.5%G+5.1%N+5.9%S
2.5%G+4.7%N+6.8%S
3.5%G+4.7%N+5.4%S
5%G+4.7%N+5.5%S
5%G+5.1%N+8.4%S
5%G+5.1%N+7.4%S
5%G+4.7%N+8.2%S
5%G+5.1%N+8.2%S
0%SL+100%C+0%G+0%N+0%S
100%SL+0%C+5%G+4.8%N+5.5%S
94.3%SL+5.7%C+5%G+4.8%N+5.5%S
89.3%SL+10.7%C+5%G+4.8%N+5.5%S
1.4%G+5.2%N+6.1%S
0%G+5.1%N+6.6%S
OPC
Low activator
(low strength)
100% slag, 0-2.5% gypsum
100% slag, 3.5% gypsum
100% slag, 5% gypsum
6% OPC, 5% gypsum
11%OPC, 5% gypsum
20%OPC, 5% gypsum
2021-04-29
Effect of Combined Additions for Shrinkage
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CA = Na2O% + ·SiO2% + ·Gypsum%
y = -14.312x - 0.2562
R² = 0.9495
-4.5
-4
-3.5
-3
-2.5
-2
-1.5
-1
-0.5
0
5% 10% 15% 20% 25% 30%
Lenght
change
(‰)
Combined Additions
Vertical
measurement
80% GGBS & 20% OPC
Dried for 1 year
y = -20.005x + 0.7712
R² = 0.9636
-4
-3.5
-3
-2.5
-2
-1.5
-1
-0.5
0
5% 10% 15% 20% 25% 30%
Lenght
change
(‰)
Combined Additions
Vertical
measurement
80% GGBS & 20% OPC
Dried for 3 months
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Effect of Combined Additions for Shrinkage
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Shrinkage (‰) = a1·Na2O% + a2 · SiO2% + a3 ·Gypsum% + b
-50
-40
-30
-20
-10
0
10
20
0 100 200 300 400
Drying duration, days
a1
a2
a3
SiO2
Na2O
Gypsum Expansion
Shrinkage
2021-04-29
Exemple of Alkali-Activated Binder
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80% Slag
Water
(w/b 0.4-0.6)
20%
Cement
Na2O (4-6% of binder)
SiO2 (4-8% of binder)
Gypsum (2-5% of slag)
waterglass
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Durability of AAS Concrete
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• General durability (frost attack, chloride ingress,
carbonation)
• Acid resistance
• High temperature stability
(What is the general durability of AAS concrete? How is the acid
resistance and temperature stability of the concrete affected when
using AAS?)
2021-04-29
Resistance to Frost Scaling
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0
0.5
1
1.5
2
2.5
0 10 20 30 40 50
Scaling
[kg/m
2
]
Freeze-Thaw cycles
0
1
2
3
4
5
6
Scaling
after
28
FT
cycles
[kg/m
2
]
w/b 0.40 w/b 0.50
w/b 0.45
• Similar level of concretes with 5% silica and 30% GGBS,
• Better than those with commercial cement CEM I and CEM II/A.
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Resistance to Chloride Ingress
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• Significantly better than that of concrete with Portland cement,
even blended with GGBS.
0
5
10
15
20
25
AAS555 PC PCSL20 PCSL30 PCSL40 PCSL60 PCFA20
Chloride
migration
coefficient
[x12
m
2
/s]
28 days
2021-04-29
Resistance to Carbonation
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• Higher than the plain
Portland cement
• Similar as those blended
with mineral additions
(due to the lack of
portlandite as a buffer for
carbonation)
Tested under the accelerated
and relatively dry condition!
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Acid Resistance
23
pH-stat
Samples
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Acid Resistance of AAS Mortar
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Sample Ref
Alkali-activated sample
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Acid Resistance of AAS Mortar
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Acid Resistance of AAS Concrete
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-3%
-2%
-1%
0%
1%
0 5 10 15 20
Weight
change
Immersion duration [weeks]
PC High
AAS555
pH 2.5
pH 2.0
pH 1.0
0
10
20
30
40
50
60
70
80
AAS555 PC High PC Low
Compressive
strength
[MPa]
in water pH 2.5/1m+2.0/1m
pH 2.5/1m+2.0/1m+1.0/2w pH 2.5/1m+2.0/1m+1.0/4w
pH 2.5/1m+2.0/1m+1.0/8w pH >1.0/2m
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High Temperature Stability of AAS
Mortar
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High Temperature Stability of AAS
Concrete
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0
100
200
300
400
500
600
0 60 120 180 240
Temp/°C
Time/min
OVEN
R1
L2
L1
initial mass=1970g
mass loss= 14%
init. mass=1280g
mass loss= 39%
R = AAS concrete
L = AAS lightweight
concrete (with
vermiculite)
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Potential Applications
• Sewage pipes, blocks and elements for infrastructures of wastewater purification;
29
(What potential structures can AAS concrete be suitable for?)
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• Composite concrete beams or walls for potential use in modular fireproof safes
and vaults
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• Improved aggregate from recycled concrete or waste mineral tailings.
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Mortar with Fine Recycled Concrete
Aggregate and Bottom Ash
0
10
20
30
40
50
60
Compressive
strength
[MPa]
2 days
7 days
28 days
EnergiForsk project 2019-118
”Bottom Ash for Green Aggregate”
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Obstacles to Application of AAS
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(What are the obstacles to the application of AAS concrete in
ordinary structures?)
• Relatively larger drying shrinkage (about 3 times as much as OPC concrete);
• Relatively poor resistance to carbonation (similar to the other SCMs);
• Uncertain air-entraining for resistance to frost scaling; and
• Uncertain superplasticizers for adjusting workability of fresh concrete
Technical obstacles:
• National regulations or standardization!!!
Non-technical obstacles:
USSR Industry standard OST 67-11-84: “Slag Alkaline Binders. Technical Specifi cations” (1984)
Ukrainian Technical Specifications TU 10.20 UkrSSR 169-91: “A slag alkaline binder on sulfate-containing
compounds of alkali metals” (1991)
BSI PAS 8820: “Construction Materials -Alkali Activated Cementitious Materials – Specification” (2016)
Chinese standard JGJ/T439 “Technical standard for application of alkali-activated slag concrete” (2018)
2021-04-29
Carbon fiber mesh from China
4 mm, 12k 10 mm
3 mm, 6k
8 mm
(How to improve adhesion between carbon fiber mesh
and concrete?)
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Pull-out Test of a Single Bundle
Specimen on the frame
Pull-out test
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Fibers after the pull-out test
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0
100
200
300
400
500
600
700
800
900
1000
0 1 2 3 4 5 6 7 8
Force,
N
Displacement,mm
Ref
Epoxi-sized
CF6
CF8
CF12
CF14
CF18
CF20
Results from Pull-out Test
SBR-impregnated
Nano-CSH
impregnated
carbon fiber
bundle
2021-04-29
Pull-out Forces (average of two samples)
0
100
200
300
400
500
600
700
800
900
1000
Ref Epoxi-sized CF6 CF8 CF12 CF14 CF18 CF20
Pull-out
force,
N
Specimens
SBR-
impregn.
Nano-CSH impregnated carbon fiber bundle
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Nano Impregated Carbon Fiber Mesh
Large plate 900x200x20 mm
Prism 160x40x40 mm
5 mm
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Cracks after 1st Bending Test (OPC)
Crack wideness 0.12 mm
Ref: No fiber mesh
N0: Original fiber mesh
N1: Nano-CS treated fiber mesh
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Results from Prisms with OPC
• Dramatically increase the bonding between
fibers and cementitious materials
• Significantly increase the flexural strength
• Significantly increase the ductility
Broken after 3rd bending
Broken after 11th bending
Ref: No fiber mesh
N0: Original fiber mesh
N1: Nano-CS treated fiber mesh
2021-04-29
Five Different Types of Fiber Meshs
Resin-
impregnated
basalt fiber
SBR impregnated
carbon fiber
Original
carbon fiber
from China
Geopolymer
impregnated
carbon fiber
Nano-CSH
impregnated
carbon fiber
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Casting Fiber Mesh Prisms
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3-Point Bending Tests
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Industrial meshs after 1st & 4th bending
2021-04-29
Impregnated Meshs after n-th Bending
after 1st loading after 4th loading
after 15th loading
after 10th loading Ncsh-1
Non-impregnated
Geopolymer-impregnated
Nano-CSH-impregnated
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Strength-Strain Curves
Non-impregnated
Geopolymer-impregnated
Nano-CSH-impregnated
2021-04-29
Locations of Mesh in ASS Prisms
N3 N5 N6
5 mm
40
mm
40 mm
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After n-th Loading
After 15th loading (max. loading)
After 20th loading
After 3rd loading
N3
N5
N6
2021-04-29
Strength-Crack Curves after n-th Bending
0
2
4
6
8
10
12
14
16
0 0.5 1 1.5 2 2.5 3 3.5
Flexural
strength
[MPa]
Crack wideness [mm]
Ref 28d N3-28d
N5-28d N6-28d
Shear cracking
Manually max load
N3
N5
N6
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Large Plate under 4-P Bending Test
DIC (Digital Image Correlation)
2021-04-29
Deformation of Large Plate under
Bending
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Results form 4-Point Bending Test
53
0
200
400
600
800
1000
1200
1400
1600
0 10 20 30 40 50 60
Force
[N]
Mid-span deflection [mm]
2021-04-29
Concluding Remarks
on AAS Concrete
54
• The main contributor to the strength of alkali-activated slag (AAS) materials is
alkali (Na2O in this study), whilst the addition of molecular silica contributes to
the strength by 30% of that of alkali;
• Addition of gypsum negatively contribute to the strength but positively
contribute to the reduction of shrinkage;
• Partial addition of ordinary Portland cement (OPC) and/or gypsum can
markedly reduce drying shrinkage of AAS materials;
• A combination of 20% OPC and 5% gypsum can reduce the drying shrinkage
of AAS at the early age (about 10 days) to a level similar to hardened OPC;
• AAS showed a better resistances to chloride ingress and acid attack, as well
as better stability under high temperatures.
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Concluding Remarks
on Nano-Impregnated Carbon Fiber
55
• Increased bonding with concrete by a factor of 2-3;
• Concrete reinforced by nano-impregnated carbon fiber mesh revealed
good loading capacity with shear failure, similar as over-sized steel
reinforcement.
• It is possible to produce bendable concrete plate with nano-impregnated
carbon fiber mesh.
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Betong med alkali-aktiverad slagg och nano-impregnerat kolfibernät

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Betong med alkali-aktiverad slagg och nano-impregnerat kolfibernät