Blast-furnace-slag binders by one-part (“just add water”)

alkali activation September 27th

Dr. Tero Luukkonen

University of Oulu

GEOBIZ B U S I N E S S F R O M G E O P O L Y M E R S

Tekes funded project, 2017 – 2018 Budget: 723 386 € Research partner: Fibre and Particle Engineering Research Unit, University of Oulu Industrial partners: Luja, Fescon Oy, Geberit Oy (IDO), Tulikivi Oyj, Matnur Oy, Reseptori Oy

Local industrial side streams (e.g. blast furnace slag, ceramic wastes, soap stone etc.)

Development of geopolymer technology according to industry in-puts

”JUST ADD WATER” GEOPOLYMERS DURABLE GEOPOLYMER CONCRETE SANITARY WEAR INTERIOR DESIGN ETC.

Potential applications

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Background

‒ The Paris agreement (2015): limit temperature increase to 1.5 °C compared to pre-industrial level

- Zero net anthropogenic green house gas emissions by 2030–2050 (?)

‒ Ordinary Portland cement (OPC) production results 1.45 ± 0.20 Gt CO2 = approx. 8% of total anthropogenic CO2 release (2016 numbers)

1. Process emissions from the calcination (decarbonation) of limestone: CaCO3 (s) CaO (s) + CO2 (g)

2. Energy-related emissions to produce 1400–1450 °C temperature.

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https://www.metoffice.gov.uk/news/releases/2017/a-pacific-flip-triggers-the-end-of-the-recent-slowdown

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Blast furnace slag & ordinary Portland cement

‒ Is already used as mineral admixture

‒ Can substitute up to 80% of OPC in mortar/concrete mixtures

‒ Decreases CO2 release up to 60–70% per 1 t mortar/concrete

- Energy use reduction - CO2 release reduction (from limestone decarbonation) - Primary material use reduction

‒ Replacing OPC by slag has several positive effects (e.g., improved workability, rheological properties, fast compressive strength development…)

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Blast furnace slag & alkali activation

‒ Not a new idea

‒ Conventional approach: blast furnace slag (with or without other aluminosilicates) is reacted with alkali activator solution (e.g., NaOH/Na silicate)

‒ Problem: alkali activator solutions are viscous, corrosive, occupational safety risks, and not economical to transport

‒ Can dry activator used instead followed by adding water (one-part approach)?

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Buildings made of alkali-activated blast furnace slag

1987–1989 Lipetsk, Russia

1960 Mariupol, Ukraine

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Solidaluminosilicate raw material

Solidalkali activator Calcination if necessary

~ 350–1500°C

Aggregates+ additionalalumina and/orsilica sources, additives, fibers

Water

One-partgeopolymer paste

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Current literature about one-part alkali-activation of BFS

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Aluminosilicate

precursor Solid activators Admixtures and fibers Aggregates L/S a

Curing 7 d UCS [MPa] 14 d UCS [MPa] 28 d UCS [MPa]

T [°C] RH [%]

BFS, fly ash Na2SiO3 PVA fibers - 0.35 23 n.r. n.r. n.r. 52.5

BFS, fly ash Na2SiO3 PE or PVA fibers - 0.35 23 n.r. n.r. n.r. 48.7

BFS, fly ash (Na2SiO2)nO Hydrophosphate - 0.28 n.r. n.r. 67.38 n.r. 80.13

BFS or fly ash (Na2SiO2)nO, NaOH - Sand 0.5 23 70 38.5 n.r. 49.6

BFS, fly ash Na2SiO3, NaOH, Ca(OH)2 PCE - 0.3 23 n.r. 33.9 n.r. 36.9

BFS or fly ash (Na2SiO2)nO - Sand 0.50 23 70 47.08 n.r. 51.28

BFS or fly ash (Na2SiO2)nO - Sand 0.3 23 70 64.5 n.r. 71.6

BFS NaOH, Na2CO3 - - 0.27 37 100 n.r. n.r. n.r.

BFS CaO or Ca(OH)2 - - 0.40 25 99 31 34 42

BFS (Na2SiO2)nO Polycarboxylic-based water

reducing admixture

Expanded clay

granule, sand 0.4 n.r. n.r. 49.3 n.r. 53.8

BFS, silica fume Na2CO3, slaked lime Sodium lignosulphonate Dolomite sand and

stone 0.35 25 > 90 n.r. n.r. ≈ 50

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Selected results from the GEOBIZ project

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Effect of BFS, NaOH, and Na2SiO3 amount on the 7 d compressive strength

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1. Minimizing NaOH increased strength - Probably too fast setting with NaOH - Too high alkali amount causes also efflorescence

(Na2O/Al2O3 should be near 1) - Heat generation evaporation of water, cracks

2. Increasing the sodium silicate amount

increased strength - The following molar ratios should be considered:

- SiO2/Al2O3 affects the structure of aluminosilicate framework (i.e., chains vs dimensional)

- Na2O/SiO2 should be high enough for depolymerization of raw materials

- CaO/SiO2 high value increases crystalline products over amorphous C-A-S-H gel

‒ Mixture consisting of 0.9 BFS and 0.1 Na2SiO3 of was selected for further experiments

1.

2.

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Effect of BFS particle size

Particle size increases

Compressive strength increases

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Reducing activator (Na2SiO3) amount

• Synthetic sodium silicate is expensive and thus its amount needs to be optimized

• Experiments were conducted to find minimized amount of activator to obtain acceptable mechanical properties

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0,00

10,00

20,00

30,00

40,00

50,00

60,00

70,00

0,04 0,05 0,06 0,07 0,08 0,09 0,1 0,11

Com

pres

sive

stre

ngth

[MPa

]

Na2SiO3 [fraction of binder]

7 d 14 d 28 d

6–10% Na2SiO3 results are approximately same

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Use of microsilica and rice husk ash

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• Aim is to replace synthethic Na2SiO3 by industrial by-products microsilica and rice husk ash

• Both are used by cement industry • Small amount of NaOH (5.7%) is required

to supplement Na and alkalinity

%, w/w Na2SiO3 Rice husk ash Silica fume

Al2O3 0,17 0,23 SiO2 46,2 88,461 94,254 CaO 0,753 0,784

Fe2O3 0,31 0,839 K2O 1,688 0,557 MgO 0,474 0,35 Na2O 50,5 0,217 0,178 P2O5 0,691 0,013 MnO 0,195 0,018 SO3 0,053 0,128

LOI (525°C) 1,69 8,88 LOI (950°C) 2,31 9,22

d50 = 199 μm

d50 = 172.33 μm

After milling:

Microsilica d50 = 23 μm

Rice husk ash d50 = 30 μm

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Conclusions ‒ For instance, workability and setting time need further experimental studies to achieve acceptable fresh-state properties

‒ The effects of using various admixtures are still poorly studied and needs further investigations

‒ Nevertheless, ”just add water” alkali activation appears a promising method to overcome some of the negative issues regarding conventional geopolymer such as safety issues

‒ Especially suitable for in situ casting

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Thank you for your attention!