Cement Chemistry for Engineers, Cape Town 31st January 2013

Lecture 3: Hydration Mechanisms

Physical structure

Mechanism – Induction period and beyond

Pore structure

Kinetics are key, but underlying mechanisms not well understood

~10 h

Accele

rati

on

peri

od

~3 h

Ind

ucti

on

peri

od

Decele

rati

on

peri

od

~24 h

He

at e

vo

lutio

n

Why does the initial

rapid reaction slow down? What limits this

phase of reaction?

0

1

2

3

4

0 3 6 9 12 15 18 21 24

He

at F

low

(m

W/g

)

Age of Specimen (Hours)

sta

ge

1

sta

ge

2

sta

ge

3

sta

ge

4

Alite reaction

3

A) PROTECTIVE MEMBRANE LAYER

1. Anhydrous grain 2. Formation of a

protective layer

around the grain

preventing

further dissolution

3.a) Disruption of the protective

layer by osmotic pressure due to

the difference of ion concentration

between the inner solution and

the pore solution creating an osmotic

pressure.

3.b) Disruption of the protective

layer due to the nucleation and

growth of more stable hydrates

in the protective membrane

[Stein & Stevels, 1964], [de Jong, 1967], [Kondo & Daimon, 1968], [Brown et al. 1985]

[Stein & Stevels, 1964]

[Gartner & Jennings, 1987]

[Powers], [Double et al., 1980]

No direct evidence

Different theories about the induction period

100 nm

Image from Luc Nicoleau of BASF.

Portland cement observed in the cryo SEM

AFM wet cell

Thesis Helène di Murro U. Bourgogne

B) NUCLEATION THEORY

Formation of nuclei on surface

controls early reaction.

Growth of the nuclei is the rate

limiting factor.

[Fierens and Verhaegen, 1976],[Odler and Dorr, 1979],[Gauffinet et al., 1998]

[Garrault et al., 2007]

What explains initial slow down?

Different theories about the induction period

Study of theories of dissolution from Geochemistry dissolution as negative growth

Albite dissolution at 80°C and pH 8.8

[Burch et al., 1993] Dove et al., 2007

Does this apply to alite?

Fresh alite

Alite 2 minutes in pure water

Multiple etch pits

2 minutes in saturated lime sol.

Smooth surface

Juilland et al 2009

0 6 12 18 24 30

0.0

0.5

1.0

1.5

2.0

Ra

te o

f h

ea

t [m

W/g

]

Time [h]

Alite, 82 m: reference

Alite, 82 m: 650°C during 6h

Alite, 38 m: reference

Alite, 38 m: 650°C during 6h

w/c = 0.4

Hand mixing for 2 min

Effect of annealing

Juilland 2009

Critical role of defects in reactivity:

Cannot be explained by protective membrane theory

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

-140 -120 -100 -80 -60 -40 -20 0

lnP

r (µ

M/s

/g)

G*first pit/RT

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

-140 -120 -100 -80 -60 -40 -20 0

lnP

r (µ

M/s

/g)

G*first pit/RT

Evolution of the rate of dissolution

Juilland et al 2009

From theory Nicoleau et al 2011

From experiment

Rate of Dissolution: modelling

Rate = kdiss

· aSSA

(SIm a x

– SIalite

) + aSSA

. cstep_ retreat

SIalite

= IAP/Ksp

of alite

SImax

= Critical undersaturation of alite

aSSA

= Specific surface area

kdiss

, SImax

and c

step_retreat are calibrated from model systems

12

Fast dissolution regime

Step-retreat regime

Kumar and Scrivener 2011

Kumar et al 2012

Induction period, summary

No evidence for protective layer,

cannot explain many experimental results

Dissolution as a function of undersaturation:

Based on solid theoretical foundation from geochemistry;

Excellent agreement between, theory, experimental measurement

of dissolution and modelling fit to calorimetry curves;

Can explain all experimental observations.

13

Kinetics are key, but underlying mechanisms not well understood

~10 h

Accele

rati

on

peri

od

~3 h

Ind

ucti

on

peri

od

Decele

rati

on

peri

od

~24 h

He

at e

vo

lutio

n

Why does the initial

rapid reaction slow down? What limits this

phase of reaction?

2 hrs

End of induction period growth of C-S-H (& CH)

5 hrs

10 hrs 15 hrs

16

Need model to handle complexity µic: vector model covering wide range of PSDs

Bishnoi 2008

• Not digitised – no lower resolution micron to nanometre

• Products in pore space and around grains

• Integrated kinetics

• Fast and flexible

2 hours for 20,000,000 particles

down to <0.1 µm size

Fully flexible microstructural development

x% on reacting particle

y% in pores

z% on filler particles

or

Deposit in proportion to area available

on reactive and filler particles

Variants

?

Bishnoi 2008

17

classic, compact product

Bishnoi 2008

Modelling Nucleation and growth

Classic Boundary Nucleation and Growth

Deceleration not captured

Bishnoi 2008

Bishnoi 2008 : Post-peak “Diffusion”

Good fits were obtained but diffusion coefficient varied by 10x

Layer at peak

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

5.5

0 0.2 0.4 0.6 0.8 1 1.2

e (C-S-H thickness), microns

Rate

of

Hyd

rati

on

, %

PSD-6microns PSD-18microns PSD-38microns PSD-82microns

Costoya 2008

• Same C-S-H for different particle sizes, why should diffusion coefficient

vary by 10X

• Success of maturity approaches: same activation energy throughout

main hydration peak

• Bond breaking / making processes typically have Ea > 40 kJ/mol

• Transport controlled processes have Ea <~20 kJ/mol

• Low density region inside “shell”

does not fill in until much later

Evidence that diffusion control does not occur at peak maximum

In fact C-S-H hydrates do not grow in uniform compact manner

Richardson 1999

Richardson 1999

Mechanism of rapid outward growth in diffuse manner (low packing density) then densification

Bishnoi 2008

Diffuse nucleation and growth

Studying nucleation and gowth of C-S-H using µic - Shashank Bishnoi, Karen L. Scrivener

Cement and Concrete Research, 39, (10), October 2009, 849-860

Bishnoi 2008 :

Insights on C-S-H from 1H NMR

Solid echo pulse sequence: Water in Portlandite

CPMG pulse sequence: interlayer water, C-S-H gel, capillary pore water

[ P. J. McDonald]

1H Nuclear Magnetic Resonance

-0.5

1.5

3.5

5.5

7.5

9.5

1.000E-06 1.000E-05 1.000E-04 1.000E-03 1.000E-02 1.000E-01

Sig

na

l In

ten

sit

y (

a.u

)

T2 Relaxation time

2 d.

6 d.

7 d.

14 d.

62 d.

24 h.

12 h.

6 h.

28 m.

10 µs 100 µs 1 ms 10 ms 0.1 s

Interlayer water (1 nm) Gel water (3-4 nm)

Water in Ca(OH)2

1.05

9.53

9.87

8.72

5.45

8.67

7.02

4.22

Capillary

water

Evolution of pore structures with hydration

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.0 0.1 1.0 10.0 100.0

Sig

na

l fr

ac

tio

n

Age (days)

Water in Portlandite

Interlayer water

Gel water

Capillary water

TRANSCEND ITN: project 7 Arnaud Muller, EPFL with Peter McDonald and Agata Gajewicz, U Surrey, UK

White Cement paste W/C = 0.40

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.0 0.1 1.0 10.0 100.0

Sig

na

l fr

ac

tio

n

Age (days)

Water in Portlandite

Interlayer water

Gel water

Capillary water

3 nm

White Cement paste W/C = 0.40

TRANSCEND ITN: project 7 Arnaud Muller, EPFL with Peter McDonald and Agata Gajewicz, U Surrey, UK

Evolution of pore structures with hydration

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0.00 0.20 0.40 0.60 0.80 1.00

Cu

mm

ula

tive

vo

lum

e (

cc

) / g

of

an

hyd

rou

s c

em

en

t

Degree of Hydration

C1.69-S-H1.77

ρ = 2.44 ± 0.07

Voids

Ca(OH)2 Cement

Gel water

Inter-

hydrate Cap. water

TRANSCEND ITN: project / Arnaud Muller, EPFL with Peter McDonald and Agata Gajewicz, U Surrey, UK

C-S-H “density”

33

Nanocrystalline “solid”

“bulk” including gel pores

Substantial experimental evidence for “densification”

However current mathematical representation of densifying

growth does not fit all evidence

Little evidence to support conventional views of diffusion

control.

34

PHYSICAL STRUCTURE: Pore structure

35

Conventional categories of pores structure

10-10

10-9 10

-8 10

-7 10

-6 10

-5 10

-4 10

-3 10

-2

nm m mm

gel

pores

Air voids

and compaction voids capillary pores

HRLn

1cosT2

RT

MR lpK

0.1 µm

99 % RH

Filled pores as a function of RH: Kelvin Laplace equation

Problems of characterising pore structure

Conventional methods require prior drying

Mercury Intrusion porosity most widely used, but much maligned

New results from proton NMR show what is happening in undried

materials

Turns out MIP is not too bad if you understand what is happening

Mercury porosimetry

Intrusion of non-wetting fluid: mercury

Rp

Increasing presssure

Pr

2 cos

Problems

Size of sample - representitivity

Need for pre-drying

“Ink bottle” effect

Increasing presssure

1 pixel =

1nm

512x512

Hardened cement paste,HCP

R.A. Cook, K.C Hover : CCR 1999

Poro

sity %

0,7

0,6

50

40

30

20

10

0

100 100 1 0,1 0,01 0,001

Size of equivalent pore (µm)

0,5

0,4

0,3

50

40

30

20

10

0

100 100 1 0,1 0,01 0,001

Size of equivalent pore(µm)

Po

rosity %

1

3

7

14

28

56

Age

(days) w/c Breakthrough

diameter

Total porosity

Given the process of MIP,

it makes NO SENSE to differentiate the curves

MIP experiment and MIP simulation results of pore-structure

0

0.1

0.2

0.3

0.4

0.5

0.001 0.01 0.1 1

Radius (micron)

Vo

lum

e f

ra

cti

on

(%

)

8% (6hours) DoH experiment 23% (12hours) DoH experiment 60% (3 days) DoH experiment

8% DoH, Simulation (C-S-H den=0.9) 23% DoH, Simulation (C-S-H den=1.5) 60% DoH, Simulation (C-S-H den=1.9)

Comparison of MIP and model output

Need to assume changing density of C-S-H

C-S-H “density”

44

Nanocrystalline “solid”

“bulk” including gel pores

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.0 0.1 1.0 10.0 100.0

Sig

na

l fr

ac

tio

n

Age (days)

Water in Portlandite

Interlayer water

Gel water

Capillary water

3 nm

White Cement paste W/C = 0.40

TRANSCEND ITN: project 7 Arnaud Muller, EPFL with Peter McDonald and Agata Gajewicz, U Surrey, UK

Evolution of pore structures with hydration

MIP experiment and MIP simulation results of pore-structure

0

0.1

0.2

0.3

0.4

0.5

0.001 0.01 0.1 1

Radius (micron)

Vo

lum

e f

ra

cti

on

(%

)

8% (6hours) DoH experiment 23% (12hours) DoH experiment 60% (3 days) DoH experiment

8% DoH, Simulation (C-S-H den=0.9) 23% DoH, Simulation (C-S-H den=1.5) 60% DoH, Simulation (C-S-H den=1.9)

Comparison of MIP and model output

Wide discrepancy in breakthrough diameter

Is this really surprising when we see how C-S-H is growing.

No currently available

microstructural model can

capture this complexity

Alite paste 25 hours

Slag blend w/c =0.45 at 5 years.

5 year old white cement paste w/c=0.4

Summary

Induction period is governed by the undersaturation of the solution –

there is no protective layer. The theoretical support for this

mechanism is well established and allows the effects of many

experimental parameters to be explained and modelled.

The mechanisms governing the main heat evolution peak still need

clarification. However space filling almost certainly plays and

important role – we will come back to this when we talk about SCMs

The new findings on the space filling of C-S-H have important

implications . Powers model needs to be refined to take into account

that the capillary and gel porosity are not linear functions of the

degree of hydration.

There are also profound implications for durability. Beam bending

experiments to measure permeability in pastes show very low values-

Practical measurements on concrete are almost certainly dominated

by (micro)cracks.

Cement Chemistry for Engineers, Cape Town 31st January 2013

End Lecture 3