Material Solutions for Challenges in Underground Construction

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1 Material Solutions for Challenges in Underground Construction Dr.-Ing. Edgar Bohner VTT beyond the obvious 1

2 VTT impact from excellence VTT Technical Research Centre of Finland Ltd is one of the leading research, development and innovation organizations in Europe. We help our customers and society to grow and renew through applied research. The business sector and the entire society get the best benefit from VTT when we solve challenges that require world-class know-how together and translate them into business opportunities. Our vision A brighter future is created through science-based innovations. Established in M Net turnover and other operating income (VTT Group 2017) 2,368 Total of personnel (VTT Group ) Our mission Customers and society grow and renew through applied research. Strategy Impact through scientific and technological excellence VTT 2018 Owned by Ministry of Economic Affairs and Employment 36% from abroad (VTT Group 2017) 27% Doctorates and Licentiates (VTT Group 2017) 2

3 Outline Low ph concrete for geological waste disposal Concrete for sealing of deep boreholes Geopolymers for waste solutions Concrete admixtures for various applications 3

4 Concrete for final disposal of nuclear spent fuel in Finland Spent fuel repository, Posiva s ONKALO (Eurajoki-Olkiluoto) -425 m Slide courtesy of Tiina Jalonen, Posiva Oy 4

5 Concrete development for special applications Low ph concrete High durability meets requirements for long service-life High workability Low emissions to groundwater suitable for applications in groundwater sensitive areas 5

6 Low ph concrete Normal concrete has ph 12,5-13 Releasing high amout of hydroxide to groundwater harmfull in some applications Special concrete for tunnel end plugs Low heat, minimal shrinkage, highly flowable (SCC) Target ph leachate < 11 High durability, 100 years design service life Long term behaviour years 6

7 Low ph concrete recipe developments Two mix design options developed and finalised Binary mix (60% cement + 40% silica fume) Ternary mix (38% cement + 32% silica + 30% fly ash) Successful upscaling: laboratory studies field trials demonstration in real structure Ternary mix design Binary mix design CEM I 42,5 MH/SR/LA 105 kg/m kg/m 3 Silica 91 kg/m 3 80 kg/m 3 Fly ash 84 kg/m 3 - Quartz filler 114 kg/m kg/m 3 Local aggregate 1840 kg/m kg/m 3 VTT laboratory aggregates Effective water content 126 kg/m kg/m 3 Water/binder ratio 0,45 0,60 7

8 Low ph concrete conclusions Two new concrete recipes were developed for challenging environmental and construction demands Challenging balance to achieve both early age (workability, stability) and long-term (shrinkage, permeability) requirements Results are used to demonstrate to Nuclear Regulator Authorities the readiness for operation Reliable watertight and structurally-sound design that can be repeated Unique repository tunnel end plug yields material designs that can have applicability for other harsh environments, where low emissions to groundwater, high durability and very long service life is expected 8

9 Concrete development for special applications Concrete for sealing of deep boreholes Extremely high workability High durability extremely long service life required 9

10 Concrete for deep boreholes Posiva Oy has tens of deep cored holes of varying diameter (typically 56 or 76 mm) and lengths from 200 up to 1000 meters bentonite Example conceptual design of borehole sealing, with 10 meter layers of bentonite (yellow) and remains filled with concrete High flowability, placeability, pumpability, durability (design service life years), low ph Low cement content (Finnish sulphate resistant, CEM I 42,5 N); use of alternative binders to lower ph VTT beyond the obvious Dr. Edgar Bohner Material Solutions for Challenges in Underground Construction

11 Concrete for deep boreholes Laboratory mix development Optimal aggregate and filler gradation achieved using packing calculations High workability and low segregation; compressive strength at 7 and 28 days was 37 MPa and 64.5 MPa, respectively Field trials Mix can be produced in real plant with same properties Demonstration Complete sealing of two boreholes: 558 m vertical hole and 302 m hole with 45 inclination; diameters 56 and 76 mm 11

12 Concrete for deep boreholes conclusions Materials developed for sealing of deep boreholes proved to be successful; high workability and stability of material was achieved and hardened material fulfilled the performance requirements Hundreds of meters deep narrow holes (56-76 mm) could be casted with developed concrete Work was done in close cooperation of VTT, Posiva, ADC, Saanio & Riekkola and Rudus Results are being used by Posiva to demonstrate that the boreholes can be safely sealed, to maintain the environmental protection of the biosphere and prevent radionuclide release from the repository VTT beyond the obvious Dr. Edgar Bohner Material Solutions for Challenges in Underground Construction

13 Geopolymers for waste solutions Geopolymer-based materials are studied and developed at VTT for nuclear waste management and other toxic waste applications (Nuclear) waste immobilisation and encapsulation For these applications, geopolymers possess superior properties compared to currently used cementitious materials High radionuclide binding/isolation capacity Stable after leaching of alkalies Studies on mix designs, mechanical performance, durability, application testing 13

14 Concrete admixtures for various applications Used admixtures must not endanger the concrete performance in northern climate VTT is a research partner for infrastructure owners and contractors to study and verify concrete performance with various admixtures 14

15 Concrete admixtures for various applications Air entrainment studies Air-void systems Effects on workability and durability Interaction of admixtures and effect on air entrainment Shrinkage reducing admixtures (SRA) and air entrainment agents Some SRAs destroy the air-void system, others retain it, but frost resistance is poor Prototype of VTT s digital air meter 15

16 Concrete admixtures for various applications VTT studies continuously new ways to valorize bio-based materials: Lignin, cellulose, nano-cellulose etc. Construction chemicals and admixtures are an interesting market due to large volumes 16

17 EU project in H

18 Dr. Edgar Bohner Material Solutions for Challenges in Underground Construction 18

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20 Kiitos Thank you Dankeschön Contact Dr-Ing. Edgar Bohner phone VTT beyond the obvious 20