Appraisal of a Cementitious Cementitious Material Material - - PowerPoint PPT Presentation

Australian Nuclear Science & Technology Organisation Australian Nuclear Science & Technology Organisation

Appraisal of a Appraisal of a Cementitious Cementitious Material Material for Waste Disposal: Neutron Imaging for Waste Disposal: Neutron Imaging Studies of Pore Structure and Studies of Pore Structure and Sorptivity Sorptivity

Peter McGlinn Peter McGlinn, , Frikkie de Beer Frikkie de Beer, , Laurence Aldridge Laurence Aldridge, , Mabuti Mabuti Radebe Radebe, , Robert Nshimirimana Robert Nshimirimana, , Daniel Brew Daniel Brew, , Timothy Timothy Payne Payne, , Kylie Kylie Olufson Olufson

ANSTO NECSA

Aim Aim

To characterise and to evaluate the durability, To characterise and to evaluate the durability, structural properties and structural properties and sorptivity sorptivity of a candidate

• f a candidate

wasteform wasteform for ILW and gain an understanding of for ILW and gain an understanding of the factors that control water movement through the factors that control water movement through the matrix and the matrix and the resultant the resultant degradation process. degradation process.

Background Background

• Australia has a small amount of low and intermediate

Australia has a small amount of low and intermediate level radioactive waste from medicine, research and level radioactive waste from medicine, research and industry. industry.

• In addition, ILW from reprocessing of spent fuel will

In addition, ILW from reprocessing of spent fuel will be returned from be returned from Dounreay Dounreay as cement. as cement.

• In 2004, the Australian Government announced

In 2004, the Australian Government announced a a plan plan to establish a nuclear waste facility by 2011. to establish a nuclear waste facility by 2011.

• ANSTO has established a project to undertake

ANSTO has established a project to undertake research relevant to the safety case for the facility. research relevant to the safety case for the facility.

Material Material

• The samples tested simulated the Materials Testing

The samples tested simulated the Materials Testing Reactor (MTR) Reactor (MTR) wasteform wasteform (AEA Technology in UK). (AEA Technology in UK).

• Formulation of 9:1 ground granulated blast furnace slag

Formulation of 9:1 ground granulated blast furnace slag to Ordinary Portland Cement (OPC). to Ordinary Portland Cement (OPC).

• Waste liquor contained detectable amounts of some

Waste liquor contained detectable amounts of some simulant fission products, although in much lower simulant fission products, although in much lower concentrations than normally encountered in typical concentrations than normally encountered in typical MTR cement. MTR cement.

Methodology Methodology

• Characterisation

Characterisation of un

• f un-
• leached and leached cement

leached and leached cement – – bulk solids composition; mineralogy; bulk solids composition; mineralogy; microstructure microstructure

• Durability

Durability testing of cement: testing of cement:

• previous studies

previous studies → → long long-

• term non

term non-

• replacement

replacement tests tests

• current studies

current studies → → replacement tests (ANS 16.1) replacement tests (ANS 16.1)

• Neutron imaging

Neutron imaging (radiography and tomography): (radiography and tomography):

• residual water

residual water

• sorptivity

sorptivity (comparison with ASTM gravimetry (comparison with ASTM gravimetry-

• based

based protocol) protocol)

• pore size, volume and distribution

pore size, volume and distribution

Methodology Methodology

Characterisation (before and after leaching) Characterisation (before and after leaching)

• Mineralogy

Mineralogy – – XRD XRD

• Bulk solids elemental analysis

Bulk solids elemental analysis – – XRF XRF

• LOI

LOI -

• TGA

TGA

• Microstructural and compositional changes of cement

Microstructural and compositional changes of cement matrix (primary phase for waste encapsulation) matrix (primary phase for waste encapsulation) -

• SEM/

SEM/ EDS EDS

Methodology Methodology

Durability testing Durability testing

• Previous studies

Previous studies -

• non

non-

• replacement

replacement in deionised water in deionised water for 1, 3, 6 for 1, 3, 6 mths mths (40 (40° °C) and 92 months (first 12 months C) and 92 months (first 12 months at 40 at 40° °C, thereafter RT); SA/V = 0.03 mm C, thereafter RT); SA/V = 0.03 mm-

• 1

1; whole

; whole specimens specimens

• Current studies

Current studies – – ANS 16.1 ANS 16.1 -

• leachate

leachate replacement replacement (deionised water at RT) (deionised water at RT) – – 2 h to 90 d 2 h to 90 d; ; SA/V = 0.01mm SA/V = 0.01mm-

• 1

1 ;

; sections of interior matrix and surface layer sections of interior matrix and surface layer

• Leachate

Leachate analysis analysis – – ICP ICP-

• MS and ICP

MS and ICP-

• AES for Na, Mg,

AES for Na, Mg, Al, Al, Si Si, S, K, Ca, Ti, , S, K, Ca, Ti, Mn Mn, Fe, , Fe, Sr Sr, , Zr Zr and and Ba Ba

Current durability studies Current durability studies (ANS 16.1) Previous durability studies Previous durability studies (ANS 16.1)

1.5 cm 1.5 cm 2 c m

Interior Interior Surface Surface NB: Same SA:V ratio (0.01 mm-1) for interior and surface samples

Epoxy resin Epoxy resin

8 cm 4 cm

Methodology Methodology

Sorptivity Sorptivity testing testing

• Samples enclosed in Al tape with only the base

Samples enclosed in Al tape with only the base exposed, facilitating water transport in one direction exposed, facilitating water transport in one direction

• nly (upwards).
• nly (upwards).
• Base continuously immersed in water

Base continuously immersed in water -

• adsorption

adsorption measured over periods of 1, 2, 4, 6, 9, 12, 16, 20 and measured over periods of 1, 2, 4, 6, 9, 12, 16, 20 and 25 minutes (up to a month where possible). 25 minutes (up to a month where possible).

• At the end of each time interval the samples were

At the end of each time interval the samples were removed from the water, removed from the water, weighed weighed and then and then transferred to the transferred to the Nrad Nrad facility to collect facility to collect 2 2-

• D

D radiographic data radiographic data and chart water ingress. and chart water ingress.

• Water contents were computed from the image.

Water contents were computed from the image.

• At the end of the final acquisition period a 3

At the end of the final acquisition period a 3-

• D

D tomography was carried out on the specimens to tomography was carried out on the specimens to construct macro construct macro-

• pore distributions.

pore distributions.

2 cm 2 cm

Methodology Methodology

Sorptivity Sorptivity testing testing

• Samples enclosed in Al tape with only the base

Samples enclosed in Al tape with only the base exposed, facilitating water transport in one direction exposed, facilitating water transport in one direction

• nly (upwards).
• nly (upwards).
• Base continuously immersed in water

Base continuously immersed in water -

• adsorption

adsorption measured over periods of 1, 2, 4, 6, 9, 12, 16, 20 and measured over periods of 1, 2, 4, 6, 9, 12, 16, 20 and 25 minutes (up to a month where possible). 25 minutes (up to a month where possible).

• At the end of each time interval the samples were

At the end of each time interval the samples were removed from the water, removed from the water, weighed weighed and then and then transferred to the transferred to the Nrad Nrad facility to collect facility to collect 2 2-

• D

D radiographic data radiographic data and chart water ingress. and chart water ingress.

• Water contents were computed from the

Water contents were computed from the images. images.

• At the end of the final acquisition period a 3

At the end of the final acquisition period a 3-

• D

D tomography was carried out on the specimens to tomography was carried out on the specimens to construct macro construct macro-

• pore distributions.

pore distributions.

2 cm 2 cm

Water

Methodology Methodology

Neutron Imaging Neutron Imaging

• Penetrating; complementary to X

Penetrating; complementary to X-

• ray and gamma

ray and gamma radiography. radiography.

• Require strong, stationary, n sources for good beam

Require strong, stationary, n sources for good beam collimation and for a high spatial resolution collimation and for a high spatial resolution ⇒

⇒ reactor

reactor

• r accelerator based.
• r accelerator based.
• For

For Ntom Ntom, require fixed beam line, stationary detector, , require fixed beam line, stationary detector, and rotating turntable for sample. and rotating turntable for sample.

• Advantage over X

Advantage over X-

• rays is their high interaction

rays is their high interaction probability with H and lower attenuation in several probability with H and lower attenuation in several heavy elements. heavy elements.

SANDSTONE FROM LIVERINGA GROUP SANDSTONE FROM LIVERINGA GROUP

Principle of Conventional Radiography Principle of Conventional Radiography

Source Source Collimator Collimator Detector Detector

I I0

∫Σ

− dx x

e I

) (

~ ~ I I0

0 –

– primary beam

primary beam

Σ Σ(x) (x) – – attenuation coefficient

attenuation coefficient

x x x x – – propagation direction

propagation direction

Object Object

Beam line 2 : Beam line 2 : Neutron Radiography Neutron Radiography

SAFARI SAFARI-

• 1

1 reactor wall reactor wall Shielding Shielding Beam stop/ Beam stop/ door door

Methodology Methodology

Application of Application of Nrad Nrad/ / Ntom Ntom

• Neutrons

Neutrons -

• transmit thick layers of material samples

transmit thick layers of material samples such as cements/ concretes. such as cements/ concretes.

• Can neutron radiography be used to interpret

Can neutron radiography be used to interpret sorptivity sorptivity in cement? in cement?

• How do the data compare with the traditional ASTM

How do the data compare with the traditional ASTM procedure? procedure?

• Where can neutron radiography and tomography be

Where can neutron radiography and tomography be applied that offer advantages over other cement applied that offer advantages over other cement characterisation techniques? characterisation techniques?

» » Water loss determination Water loss determination » » Pore distribution Pore distribution » » Sorptivity Sorptivity determination determination

Results Results

XRF XRF -

• average bulk solids elemental concentrations (wt%)

average bulk solids elemental concentrations (wt%)

• f whole, interior and surface (on pressed powders)
• f whole, interior and surface (on pressed powders)

Element Element Na Na Mg Mg Al Al Si Si S S K K Ca Ca Ti Ti Fe Fe Sr Sr Whole Whole 4.0 4.0 2.4 2.4 5.1 5.1 9.9 9.9 0.6 0.6 0.3 0.3 22.1 22.1 0.3 0.3 0.4 0.4 0.04 0.04 Interior Interior 3.6 3.6 2.5 2.5 5.1 5.1 10.0 10.0 0.6 0.6 0.3 0.3 22.2 22.2 0.3 0.3 0.4 0.4 0.04 0.04 Surface Surface 5.6 5.6 2.3 2.3 5.1 5.1 9.6 9.6 0.3 0.3 0.4 0.4 20.3 20.3 0.3 0.3 0.4 0.4 0.04 0.04

Unleached Unleached

2 cm 2 cm

After 92 months After 92 months

NB: These samples used in the neutron imaging and NB: These samples used in the neutron imaging and sorptivity sorptivity studies studies

SEM/ EDS SEM/ EDS

Unleached Unleached Leached for 92 months Leached for 92 months

50 50 u um m 50 50 u um m

500 1000 1500 2000 2500 3000 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Interior K Na S Surface K Na S

Fraction leached

time

1/2 (sec)

500 1000 1500 2000 2500 3000 0.00 0.01 0.02 0.03 0.04 0.05

Interior Ca Sr Surface Ca Sr

Fraction leached

time

1/2 (sec)

500 1000 1500 2000 2500 3000 0.000 0.004 0.008 0.012 0.016 0.020

Interior Al Fe Si Surface Al Fe Si

Fraction leached

time

1/2 (sec)

500 1000 1500 2000 2500 3000 0.00000 0.00003 0.00006 0.00009 0.00012 0.00015

Interior Mg Ti Surface Mg Ti

Fraction leached

time

1/2 (sec)

Leach results Leach results – – current studies (replacement current studies (replacement leachate) leachate)

Summary of durability tests Summary of durability tests

• Fractional releases of K, Na, S and Fe similar for interior

Fractional releases of K, Na, S and Fe similar for interior and surface samples over total 90 day leach period. and surface samples over total 90 day leach period.

• Al, Mg and Ti within a factor of 3 higher, and Si within a

Al, Mg and Ti within a factor of 3 higher, and Si within a factor of 3 lower, from the interior samples. factor of 3 lower, from the interior samples.

• Ca and

Ca and Sr Sr -

• factor of 12 lower from the surface samples

factor of 12 lower from the surface samples than from the interior. than from the interior.

• Materials in the surface samples that bind Ca and

Materials in the surface samples that bind Ca and Sr Sr not not present in the interior sample? present in the interior sample?

• Investigated further by

Investigated further by Nrad Nrad in attempt to determine any in attempt to determine any structural or water transmission differences between structural or water transmission differences between surface layer and underlying matrix. surface layer and underlying matrix.

Results Results -

• Neutron imaging

Neutron imaging

• Residual water determination

Residual water determination

• Sorptivity

Sorptivity: :

» » Gravimetry (ASTM C1585 Gravimetry (ASTM C1585-

• 04)

04) » » Nrad Nrad » » Comparison with OPC Comparison with OPC

• 2D imaging (

2D imaging (Nrad Nrad): ):

» » Water front progression Water front progression

• 3D imaging (

3D imaging (Ntom Ntom): ):

» » Macro Macro-

• pore distribution

pore distribution » » Constructed tomograms Constructed tomograms

2 4 6 8 10 10 20 30 40 50 Drying time (days) Cumulative mass loss (%)

Gravimetry Nrad

• Un

Un-

• leached cement as determined by gravimetry and

leached cement as determined by gravimetry and Nrad Nrad

• Specimens dried at 50

Specimens dried at 50° °C to constant weight C to constant weight

• Difference between gravimetry and

Difference between gravimetry and Nrad Nrad due to multiple neutron scattering due to multiple neutron scattering effect by water ( effect by water (Hassanein Hassanein et al et al – – correction factor 2 to 2.5) correction factor 2 to 2.5)

Residual water determinations Residual water determinations

Sorptivity Sorptivity – – Gravimetry (ASTM) and Gravimetry (ASTM) and Nrad Nrad

2 4 6 8 10 12 14 16 18 20 20 40 60 80 100 120 140 160 Time1/2 (sec) I (mm) Leached Un-leached

10 20 30 40 50 20 40 60 80 100 120 140 160 Tim e1/2 (sec) L (mm) Un-leached; cracked Un-leached Leached

Gravimetry Gravimetry Nrad Nrad

• I and L labels to distinguish between derived values obtained directly (ASTM

procedure) and those calculated from a pixel intensity using Nrad.

• Nrad a factor >3 for the un-leached cement than gravimetric calculated value,

and a factor >2 for the leached cement than gravimetric measurement.

• Gravimetric determinations of water movement appear to underestimate the

true value.

Sorptivity Sorptivity – – MTR and OPC ( MTR and OPC (Nrad Nrad vs vs Gravimetry) Gravimetry)

10 20 30 40 50 60 20 40 60 80 100 120 140 160 Time1/2 (sec) L (mm) MTR (un-leached) P42 P80 5 10 15 20 25 30 20 40 60 80 100 120 140 160 Time1/2 (sec) I (mm) MTR (un-leached) P42 P80

Gravimetry Gravimetry Nrad Nrad

• MTR cement has a higher rate of sorptivity than both the OPC samples,

although is similar to the OPC with a w/c of 0.8 after about 4 hours.

• Short-term sorptivity rate higher for MTR.
• Gravimetric values typically lower ⇒ NRad measures actual position and

ASTM method calculates the value of water movement.

Water front movement ( Water front movement (Nrad Nrad) )

13 sec 20 sec 3 min 2 hrs 5 hrs 7 hrs 2 sec 1 min 12 min 90 min 5 hrs 6 hrs

Leached (92 months) Un-leached

Water front movement Water front movement (Nrad (Nrad) ) -

• Summary

Summary

• Analyses of the un

Analyses of the un-

• leached and leached cement verify

leached and leached cement verify the the sorptivity sorptivity calculations calculations ⇒

⇒ un

un-

• leached cement visually

leached cement visually has a greater has a greater sorptivity sorptivity rate than leached sample. rate than leached sample.

• Nrad

Nrad results could not highlight any significant results could not highlight any significant differences in the rate of water movement between the differences in the rate of water movement between the surface layer and the interior of the sample. surface layer and the interior of the sample.

• Resolving any differential in

Resolving any differential in sorptivity sorptivity between the thin between the thin surface layer and the underlying matrix difficult due to surface layer and the underlying matrix difficult due to the fine scale (<1 mm) and the relatively rapid water the fine scale (<1 mm) and the relatively rapid water movement through the cement. movement through the cement.

3D Imaging 3D Imaging – – Neutron Tomography Neutron Tomography

Macro Macro-

• pore volume distribution as a function of depth within

pore volume distribution as a function of depth within the the un un-

• leached

leached cement sample cement sample

Macro Macro-

• pore volume distribution as a function of depth within

pore volume distribution as a function of depth within the the leached leached cement sample cement sample

3D Macro 3D Macro-

• pore

pore analysis analysis -

• Summary

Summary

• Macro

Macro-

• pore size distribution in both the un

pore size distribution in both the un-

• leached and

leached and leached cement samples between 0.01 and 1 mm leached cement samples between 0.01 and 1 mm3

3.

.

• Un

Un-

• leached sample

leached sample -

• 88% of pores have a volume < 0.1

88% of pores have a volume < 0.1 mm mm3

3, whilst for the leached sample 95% of the pores

, whilst for the leached sample 95% of the pores have a volume < 0.1 mm have a volume < 0.1 mm3

3.

.

• The leached cement has a higher density of smaller

The leached cement has a higher density of smaller pores throughout its entire length. pores throughout its entire length.

• Macro

Macro-

• pore distribution is reasonably even in both

pore distribution is reasonably even in both samples showing that matrix segregation not significant. samples showing that matrix segregation not significant.

• Ntom

Ntom -

• useful information on the position and density of

useful information on the position and density of the pores showing that they may contribute to water the pores showing that they may contribute to water transmission. transmission.

Neutron Tomograms Neutron Tomograms – – Un Un-

• leached and Leached Cement

leached and Leached Cement

Un-leached cement which (as tested for sorptivity with water using Nrad) Leached cement which (as tested for sorptivity with water using Nrad)

Neutron Tomography Neutron Tomography – – pore structure pore structure

3D Neutron Tomography 3D Neutron Tomography -

• Summary

Summary

• Provides

Provides detailed reconstruction of the pore and crack detailed reconstruction of the pore and crack microstructure in the sample. microstructure in the sample.

• Visualisations correlate well with the respective

Visualisations correlate well with the respective sorptivity sorptivity rates for the un rates for the un-

• leached and leached cements.

leached and leached cements.

• Apparent greater void volume and connectivity of the

Apparent greater void volume and connectivity of the pores and cracks in the un pores and cracks in the un-

• leached sample reflected in

leached sample reflected in its higher its higher sorptivity sorptivity rate. rate.

Conclusions Conclusions

• Different rates of leaching Ca and

Different rates of leaching Ca and Sr Sr from the surface from the surface layer and the bulk interior of the layer and the bulk interior of the wasteform wasteform controlled by controlled by undetermined binding mechanism. undetermined binding mechanism.

• Correlate

Correlate sorptivity sorptivity rates determined by rates determined by Nrad Nrad with pore with pore size and connectivity, and crack density, exhibited by size and connectivity, and crack density, exhibited by Ntom Ntom analysis. analysis.

• Water penetration

Water penetration rate compared rate compared to those on other to those on other cement types e.g. OPC. cement types e.g. OPC.

• Advantage of visualising and measuring,

Advantage of visualising and measuring, non non-

• destructively

destructively, material distribution within macroscopic , material distribution within macroscopic samples and to describe their inherent processes. samples and to describe their inherent processes.

• Useful in tracking movement of water through the

Useful in tracking movement of water through the cements due to the strongly attenuating properties of cements due to the strongly attenuating properties of hydrogen. hydrogen.