Blast-furnace-slag binders by one-part ( just add water ) alkali activation. September 27 th Dr. Tero Luukkonen

Transcription

1 Blast-furnace-slag binders by one-part ( just add water ) alkali activation September 27 th Dr. Tero Luukkonen

2 GEOBIZ BUSINESS FROM GEOPOLYMERS Potential applications JUST ADD WATER GEOPOLYMERS DURABLE GEOPOLYMER CONCRETE SANITARY WEAR Local industrial side streams (e.g. blast furnace slag, ceramic wastes, soap stone etc.) Development of geopolymer technology according to industry in-puts INTERIOR DESIGN ETC. Tekes funded project, Budget: Research partner: Fibre and Particle Engineering Research Unit, Industrial partners: Luja, Fescon Oy, Geberit Oy (IDO), Tulikivi Oyj, Matnur Oy, Reseptori Oy

3 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 (?) Ordinary Portland cement (OPC) production results 1.45 ± 0.20 Gt CO 2 = approx. 8% of total anthropogenic CO 2 release (2016 numbers) 1. Process emissions from the calcination (decarbonation) of limestone: CaCO 3 (s) CaO (s) + CO 2 (g) /10/ Energy-related emissions to produce C temperature.

4 Blast furnace slag & ordinary Portland cement Is already used as mineral admixture Can substitute up to 80% of OPC in mortar/concrete mixtures Decreases CO 2 release up to 60 70% per 1 t mortar/concrete - Energy use reduction - CO 2 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 ) 4 10/10/2017

5 Blast furnace slag & alkali activation Buildings made of alkali-activated blast furnace slag 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)? Lipetsk, Russia 1960 Mariupol, Ukraine 5 10/10/2017

6 Solid aluminosilicate raw material Aggregates+ additional alumina and/or silica sources, additives, fibers Water Solid alkali activator Calcination if necessary ~ C One-part geopolymer paste 6 10/10/2017 Replace footertext if needed

7 Current literature about one-part alkali-activation of BFS Aluminosilicate precursor Solid activators Admixtures and fibers Aggregates L/S a Curing T [ C] RH [%] 7 d UCS [MPa] 14 d UCS [MPa] 28 d UCS [MPa] BFS, fly ash Na 2 SiO 3 PVA fibers n.r. n.r. n.r BFS, fly ash Na 2 SiO 3 PE or PVA fibers n.r. n.r. n.r BFS, fly ash (Na 2 SiO 2 ) n O Hydrophosphate n.r. n.r n.r BFS or fly ash (Na 2 SiO 2 ) n O, NaOH - Sand n.r BFS, fly ash Na 2 SiO 3, NaOH, Ca(OH) 2 PCE n.r n.r BFS or fly ash (Na 2 SiO 2 ) n O - Sand n.r BFS or fly ash (Na 2 SiO 2 ) n O - Sand n.r BFS NaOH, Na 2 CO n.r. n.r. n.r. BFS CaO or Ca(OH) BFS (Na 2 SiO 2 ) n O Polycarboxylic-based water reducing admixture Expanded clay granule, sand 0.4 n.r. n.r n.r BFS, silica fume Na 2 CO 3, slaked lime Sodium lignosulphonate Dolomite sand and stone > 90 n.r. n.r. 50

8 Selected results from the GEOBIZ project 8 10/10/2017 Replace footertext if needed

9 Effect of BFS, NaOH, and Na 2 SiO 3 amount on the 7 d compressive strength Minimizing NaOH increased strength - Probably too fast setting with NaOH - Too high alkali amount causes also efflorescence (Na 2 O/Al 2 O 3 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: - SiO 2 /Al 2 O 3 affects the structure of aluminosilicate framework (i.e., chains vs dimensional) - Na 2 O/SiO 2 should be high enough for depolymerization of raw materials - CaO/SiO 2 high value increases crystalline products over amorphous C-A-S-H gel 2. Mixture consisting of 0.9 BFS and 0.1 Na 2 SiO 3 of was selected for further experiments 9 10/10/2017 Replace footertext if needed

10 Effect of BFS particle size Compressive strength increases Particle size increases 10

11 Reducing activator (Na 2 SiO 3 ) 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 70,00 Compressive strength [MPa] 60,00 50,00 40,00 30,00 20,00 10, % Na 2 SiO 3 results are approximately same 0,00 0,04 0,05 0,06 0,07 0,08 0,09 0,1 0,11 Na 2 SiO 3 [fraction of binder] d 14 d 28 d

12 Use of microsilica and rice husk ash d 50 = 199 μm d 50 = μm %, w/w Rice Na 2 SiO 3 Silica fume husk ash Al 2 O 3 0,17 0,23 SiO 2 46,2 88,461 94,254 CaO 0,753 0,784 Fe 2 O 3 0,31 0,839 K 2 O 1,688 0,557 MgO 0,474 0,35 Na 2 O 50,5 0,217 0,178 P 2 O 5 0,691 0,013 MnO 0,195 0,018 SO 3 0,053 0,128 LOI (525 C) 1,69 8,88 LOI (950 C) 2,31 9,22 Aim is to replace synthethic Na 2 SiO 3 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 After milling: Microsilica d 50 = 23 μm Rice husk ash d 50 = 30 μm

13 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 13 10/10/2017 Replace footertext if needed

14 Thank you for your attention! 14