[PPT] - CRACKS AND PORES -THEIR ROLES IN THE TRANSMISSION OF WATER L.P. PowerPoint Presentation

SLIDE 1

CRACKS AND PORES -THEIR ROLES IN THE TRANSMISSION OF WATER

L.P. Aldridge1 H.N. Bordallo2

K. Fernando1 & W.K. Bertram1

1ANSTO, Private Mail Bag 1, Menai 2234 NSW, Australia 2Helmholtz-Zentrum Berlin für Materialien und Energie–

Berlin - D-14109, Germany

SLIDE 2

Water Transmission in cement paste

The aim of this work is to differentiate the rate of

water transmission through

– Cracks – Pores

Capillary Pores (Diameter > 100 Å)
Gel pores (Diameter < 100 Å)
Using the techniques of

– Permeability – Quasi Elastic Neutron Scattering

SLIDE 3

Why this study

Cementitious materials are used as barriers to

radioactive wastes

– Rate of transmission of radionuclides depends on rate of water transmission

Durability of concrete related inversely to its

ability to transmit fluids.

– Hence an ability to predict future water transmission gives information on likely service life of concrete structures

The service life of a low level repository is

expected to be greater than 300 years

– Tools to demonstrate that this is a likely outcome are desirable.

SLIDE 4

Definitions

Concrete - cementitious materials & aggregate &

sand & water

Mortar - cementitious materials & sand & water
Paste - cementitious materials & water
OPC Ordinary - Portland Cement manufactured

by Blue Circle Southern.

GGBFS - Ground Granulated Blast Furnace Slag
Marine Cement –OPC with 60% replaced with

inter-ground GGBFS

SLIDE 5

Experimental I Low & medium water pastes & mortars had similar flow.

Paste

– Low Water

W/C 0.32

– Medium Water

W/C 0.42

– High Water

W/C 0.6 & 0.8
Mortar

– Low Water

W/C 0.32
Binder/Sand 1.2

– Medium Water

W/C 0.46
Binder/Sand 1.0

SLIDE 6

Experimental II Shear Mixed and cured 28 days sealed

OPC & Marine

– Mortars Pastes

Mixed in Wearing Blender
Cured 28 days Sealed
Low Medium similar flow

0.42 0.43 0.44 0.45 0.46 20 40 60 80 100

Flow before shear mixing Flow (Seconds) Water to Cement ratio

SLIDE 7

Ludirinia's apparatus for permeability measurement

A’(m2) - the cross section
f the pipette,
A(m2) area of specimen
h(m) the water head

– ho is the initial level – hl the final level

L(m) the thickness
t(s) the time
Note can only measure

when K’ > 1*10-12m/s

K K’ ’= (A = (A’ ’ L)/(A t) ln(h L)/(A t) ln(h0

0/h

/hl

l)

)

SLIDE 8

Effect of Crack Width on Water Transmission

l l Length Crack Length Crack w w Width Width

f crack
f crack

d d Depth Cylinder Depth Cylinder From the From the Navier Navier-

Stokes equation

Stokes equation It can be shown that It can be shown that w w3

3= 3

= 3πμ πμd d2

2 K

K’ ’ / ( / (ρ ρl) l) Where w is the width of the crack Where w is the width of the crack L is the crack length L is the crack length d is the depth of the cylinder d is the depth of the cylinder μ μ is the viscosity of water at 20 degrees is the viscosity of water at 20 degrees ρ ρ is the density of water is the density of water K K’ ’ is the permeability of the sample is the permeability of the sample

SLIDE 9

Relationship between crack width and measured Permeability

100 200 300

1E-12 1E-11 1E-10 1E-9 1E-8 1E-7 1E-6 1E-5

Permeability (m/s) Crack Width (μm) Cracks <50 Cracks <50μ μm m => => Permeability >10 Permeability >10-

8

8m/s

m/s

SLIDE 10

For pastes (uncracked) it will be the capillary pores that carry the majority of water

The capillary pores are the space remaining after

hydration takes place

Thus they are highest at the start of hydration
Paste made up

– Un-hydrated cement – Hydrated cement – gel – Gel – pores – Capillary pores – Pores due to chemical shrinkage (capillary pores)

Volume at a time depends on the extent of the

paste hydration (α) which varies between 0 and 1

SLIDE 11

Powers Brownyard Model – Volume of components depends on α

Define p the initial porosity of the paste

– depends on density of cement water and w/c

Vol( chemical shrinkage) = 0.20(1-p) α
Vol( capillary pores) = p-1.32(1-p) α
Vol( gel pores) = 0.62 (1-p) α
Vol( gel) = 1.52 (1-p) α
Vol( un-hydrated cement) = (1-p) (1-α)
Relationship depends on assumptions

– e.g that chemically bound water (non-evaporable water) 0.23 g binds per gram of cement hydrated – Gel water 0.19g binds per gram of cement hydrated

SLIDE 12

0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0

W/C = 0.80

unhydrated cement gel solids gel water

capillary pores

chemical shrinkage pores

Volume Fraction

α

So these approximations show that capillary pore volume decreases with hydration

SLIDE 13

Even low w/c pastes have large capillary pore volumes

when uncured.

0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0

W/C = 0.32

chemical shrinkage pores capillary pores gel water gel solids unhydrated cement

Volume Fraction

α

SLIDE 14

From work by Powers and his co-workers we also find that capillary pore space is related to the permeability

Powers plotted permeability

for pastes at different w/c ratios

Pastes were almost fully

saturated

Pastes with continuous

capillary pores had greater permeability than indicated by line.

After at low pore volume the

capillary pores became discontinuous and results followed the line

The point of imitation of the

discontinuous pores is indicated.

0.0 0.1 0.2 0.3 0.4 0.5 1E-16 1E-14 1E-12

Discontinous Capillary Pores Continous Capillary Pores

Permeability (m/sec) fractional volume of capillary pores

SLIDE 15

Further work by Powers and co-workers indicated the relationship between curing time and w/c ratio

Pastes cured longer

were less permeable.

Pastes made with

greater W/C had dramatic differences in permeability

10 20 30 0.01 1E-3 1E-4 1E-5 1E-6 1E-7 1E-8 1E-9 1E-10 1E-11 1E-12 1E-13

Permeability m/s Days Curing (Paste W/C =0.7)

0.2 0.3 0.4 0.5 0.6 0.7 1E-14 1E-13 1E-12

Permeability m/s W/C

SLIDE 16

Powers work indicated that with proper curing at w/c 0.42 the pores should be discontinuous.

At 7 days the paste with w/c
f 0.45 should have an

approximate degree of hydration 0.60 and have acquired a discontinuous pore structure.

However this does assume

– Proper Mixing – Proper Compaction – Proper Curing

Furthermore these are

theoretical estimates

assuming ALL

cements hydrate in the same manner.

0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0

unhydrated cement gel solids gel water capillary pores chemical shrinkage pores

W/C = 0.42

Volume Fraction

α

SLIDE 17

0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0

unhydrated cement gel solids gel water capillary pores chemical shrinkage pores

W/C = 0.42

Volume Fraction

α (degree of hydration)

(degree of hydration) ~28day ~28day 1year 1year

SLIDE 18

Pore Water Ratios in 1g of Fully Hydrated Pastes (1 year old α~0.95) for w/c=0.42

Mobile water is in both gel and Mobile water is in both gel and capillary pores capillary pores C C3

3S

S CH CH

Cap Pore Cap Pore > 100 > 100Å Å water water ∼ 2% ∼ 2%

Gel pores < 100 Gel pores < 100Å Å Amount of water ~ 43% Amount of water ~ 43%

~52% of initial water ~52% of initial water Bound CH & C Bound CH & C-

S

S-

H

H

SLIDE 19

Pore Water Ratios in 1g of Fully Hydrated Pastes (28 day cure α~0.75) for w/c=0.42

Mobile water is in the smaller pores Mobile water is in the smaller pores C C3

3S

S CH CH

Cap Pore Cap Pore > 100 > 100Å Å water water ∼ 25% ∼ 25%

Gel pores < 100 Gel pores < 100Å Å Amount of water ~ 34% Amount of water ~ 34%

~41% of initial water ~41% of initial water Bound CH & C Bound CH & C-

S

S-

H

H

SLIDE 20

Water Diffusivity can be measured by QENS

Bulk water 25*10-10 m2 /s
OPC Paste 12*10-10 m2 /s at ΔE = 98 μeV
OPC Paste 6*10-10 m2 /s at ΔE = 30 μeV

QENS Results from QENS Results from

1. 1. Bordallo, H.N., Aldridge, L.P., and Bordallo, H.N., Aldridge, L.P., and Desmedt Desmedt, A. (2006) , A. (2006) Water Dynamics in Hardened Ordinary Portland Cement Water Dynamics in Hardened Ordinary Portland Cement Paste or Concrete: From Paste or Concrete: From Quasielastic Quasielastic Neutron Scattering. Neutron Scattering.

J. Phys. Chem. C, 110(36), 17966
J. Phys. Chem. C, 110(36), 17966-
6.

6. 2. 2. Bordallo, H.N., Aldridge, L.P., Churchman, G.J., Gates, W.P., Bordallo, H.N., Aldridge, L.P., Churchman, G.J., Gates, W.P., Telling, M.T.F., Kiefer, K., Telling, M.T.F., Kiefer, K., Fouquet Fouquet, P., , P., Seydel Seydel, T., and , T., and Kimber Kimber, S.A.J. (2008) Quasi , S.A.J. (2008) Quasi-

Elastic Neutron Scattering Studies on Clay

Elastic Neutron Scattering Studies on Clay Interlayer Interlayer-

Space Highlighting the Effect of the

Space Highlighting the Effect of the Cation Cation in Confined in Confined Water Dynamics. J. Phys. Chem. C, 112(36), 13982 Water Dynamics. J. Phys. Chem. C, 112(36), 13982 -

13991.

13991. 3. 3. Aldridge, L.P., Bordallo, H.N., and Aldridge, L.P., Bordallo, H.N., and Desmedt Desmedt, A. (2004) , A. (2004) Water dynamics in cement pastes. Water dynamics in cement pastes. Physicia Physicia B, 350, e565 B, 350, e565-

e568.

e568.

SLIDE 21

QENS – Quasi-Elastic Neutron Scattering

The signal from H dominates the spectra:

We can “see water”, and the signal from the rest is very small

By using the elastic fixed window approach

that is similar to Debye-Waller evolution

btained from X-rays, we can determine

the temperature where the water starts to move

SLIDE 22

Elastic Windows on SPHERES (ns time scale) define when the water motion is unlocked!!!

50 100 150 200 250 300 0.0 0.2 0.4 0.6 0.8 1.0

~220K ~210K 240K

Paste w/c=0.42 Paste,dried after re-hydration at RH=50% Dried sample at 105C

SNormalised(Q,0) T(K)

SLIDE 23

QENS – Quasi-Elastic Neutron Scattering

The signal from H dominates the spectra:

We can “see water”

QENS allows measurements in different

time and length scales – ΔE (Δt)

We can differentiate between bound water

and “free” water – because they move differently

SLIDE 24

NEAT - ToF Spectrometer at BENSC

Q: 0.4 Å-1 < Q < 2.1 Å-1 resolution at elastic

peak: ΔE ~ 98 or 30μeV

time scale: picosecond

multidetector radial collimator double-trumpet: converging/diverging neutron guide sections straight neutron guide multidetector chamber sample monitor chopper housing with two choppers diaphragm system 2 diaphragm system 1 388 single detectors

SLIDE 25

Dynamics Model

) , ( ) , ( e ) , (

3 /

2 2

ω ω ω Q R Q T Q S

Q u

⊗ =

−

Jump Translational Isotropic Rotation Oscillation High Frequency: Stretching

<u2>½ Debye-Waller

τr Rotational Correlation Time rg Radius of Gyration Dt Translational Diffusion τt Residence Time L Mean Jump Distance

SLIDE 26

1.5
1
0.5

0.5 1 1.5 Q=0.665Å-1 0.001 0.01 0.1 1 10

S(Q,ω) (arbitrary units) Energy Transfer (meV)

1.5
1
0.5

0.5 1 1.5 Q=2.11 Å-1 0.001 0.01 0.1 1 10

S(Q,ω) (arbitrary units) Energy Transfer (meV)

QENS results from NEAT

1 2 3 4 5 0.01 0.02 0.03 0.04 0.05 0.06

Γ(Q)=(Dt Q

2)/(1+Dt Q 2τ0)

& Dt= L

2/(tτ0)

Γ(meV) Q

2 (Å

2)

SLIDE 27

QENS results from NEAT

1.5 2.0 2.5 3.0 3.5 4.0 4.5 1 10 100 Dt *10

10 m

2/s

τ0 ps L (Å) 5 10 15 20 25 30 OPC0.4 GGBFS0.6 OPC RT Cure OPC 40

Cure

H2O

SLIDE 28

Chemically “bound” water

Heating pastes at 105°C

– removes both glassy and unbound water. Only chemically bound water remains. – No QE broadening after heating – Dynamics of chemically “bound” water molecules

ccurs on a timescale