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BM

VIDEO:Hydration of Cement

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BM Cement Hydration

• Water + Cement chemi cal reaction(Cement grains dissolve, di ffuse and precipitate)

• Reaction is exothermic (heat released)

• Heat signature can be important to characterize material development

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BM Heat of HydrationR

ate

of H

eat

Evol

utio

n

Time Stage I Rapid Heat Evolution (<15 mins)

Stage II Dormant Period Important for transportation (2-4 hrs)

Stage III Accelerating Stage Begins with initial set (4-8 hrs)

Stage IV Deceleration Stage No longer workable (12-24 hrs)

Stage V Steady State

I

II

III IV

Vnucleationdissolution

hydrolysisC3S reacts

diffusion control

Initial set

Final set

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BM

VicatVicat apparatusapparatus

Typical Setting Times for Portland Cements

(Gebhardt 1995 and PCA 1996).

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BM Conceptual View of Hydration

Portland Cement Grain (Unhydrated)Water Filled Capillary poresC-S-HNote: Calcium Hydroxide and Calcium Sulfoaluminates not shown

Initial During

Hydration w/c>0.32

100% Hydration w/c < 0.32

100% Hydration

• For complete hydration 1 g of PC requi res 0.32 - 0.36 g of water (i.e., equal volumes)

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BM Structure of Hydrated Cement Paste

Calcium Silicate Hydrate (C-S-H)

• 50-67% of solids volume (major product)

• C/S ranges f rom 1.5~2• Morphology - poorly

crystalline to reticular network

• Resembles tobermorite(naturally occurrin g mineral) Image is from Paul Stutzman, 2003

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BM Structure of Hydrated Cement Paste

Calcium Hydroxide - (CH, Portlandite)• 20-25% of solids volume• Known stoichiometry Ca(OH)2

• Morphology - hexagonal crystal plates• Adverse effect on durabilit y

C-S-H

CH

C3S

10 µm

Image is from Jennings, 2003

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BM Structure of Hydrated Cement Paste

Calcium Sulfoaluminates (ettringite)• 15-20% of solids volume• Minor role in structural behavior• Hexagonal plate crystal• Ettringite (Aft) formation

Unhydrated clinker grains• Cores of larger particles• Morphology - resembles clinker

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BM Relative Volume of Major Compounds in Hydrated Pastes

Function of Time Function of Degree of Hydration

Locher, Richartz, and Sprung 1976 Tennis and Jennings 2000

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BM Water In Hydrated Cement Past e

Interlayer water (X)- Associated with C-S-H structure- Lost on drying below 11 %

XXX

XX

XX

XX

XX

O OO

OO

XX

XX

XX

XO

OO

OO

OO

O

OO

XX

XX

XX

X

X

X

OOO

OO

OO

OO

O

OO

O

O

OO

O

O OO

OO

O

XX

XXX

X

XX

X

XX

XXX

XOO

OO

XX

X

X

X

XXX O O OO

OO

OOO

O

O OO

XX

XX

XX

X

X

OO

OO

Adsorbed water (O)- Held close to solid surface

- Up to approx imately 6 layers

•Capillary water- Large voids - Free water, pores > 50 nm- Capillary tension, pores 5-50 nm

Chemically combined water- Integral part that is not lost on heating**After Feldman and Serada 1970

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BM Voids in Hydrated Cement Past e

Interlayer space in C-S-H (gel void) à nm level• Small voids - probably 5-25Å

Capillary voids à µm level• Popularly called porosity

Air voids à mm level• Generally round• Entrapped air (as large as 3mm)• Entrained air (50 -200µm)

UnhydratedGrain

Hydration Products

Capillary Porosity

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BM Dimensions of Solids & Pores

0.001µm 0.01µm 0.1µm 1µm 10µm 100µm 1mm 10mm

Entrapped Air

Entrained Air

Max Air SpacingAggregation of C-S-H Particle

Capillary Void

Interparticle Spacing Between C-S-H Sheets

Hexagonal Ca(OH)2 Crystals

**After Monterio and Mehta Fig 2-7

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BM Volume of Products Effect of Time

Consider 100 cm3 of cement with w/c = 0.63 (by wt.)

( ) cc20063.0cc/g0.1

cc/g14.3cc100cwVV

Water

CementCementWater ==

ρρ

=

Tota

lVol

ume

of P

aste

(cc)

Initial

300

200

100

0

Day 7 50% hyd.

Day 28 75% hyd.

Day 365 100% hyd.

Capillary Pores

Hydration Product

Anhydrous Cement

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BM Volume of Products Effect of w/c Ratio

Consider 100 cm 3 of cement with 100% hydrationComplete Reaction = 200 cm 3

Conclusion: lower w/c has lower porosity, greater strength

Tota

l Vol

ume

of P

aste

(cc)

w/c

300

200

100

0

Vol.0.7320

37%

0.6288

30%

0.5257

22%

0.4225

11%

0.32200

0%

Capillary Pores

Hydration Product

Stre

ngth

w/c0.32

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BM Calculation of Volume Changes

Empirical equations deri ved by T.C. Powers from experimentsEvaporable Water - Lost at 105°C

Capillary and gel pores (interlayer pores)Non-Evaporable Water (wn) - Lost at 1000°C

Approximate measure of combined water

Unhydrated cement

Hydration products (gel)

Capillary pores

Gel pores

Increasing Hydration

Total ‘Solid Volume ’

Evaporable Water

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BM Calculation of Volume Changes

Assumption: 1 g of cement requires 0.36 g of w ater for complete hydration ( 1 g of cement = 0.32 cm 3)

Volume of gel: Vg = 0.68α cm3/g, where α = % hydrationCapillary Porosit y: VCP = w/c - 0.36α

= 0.63 - 0.36*1 = 0.27 cm 3/g(if w/c = 0.63 and α = 1) Volume of CP = CP*ρcement = 0.27*(100)*3.15 ≅ 85 cm3

Gel Space ratio = Volume of gel/Space ava ilable for gel= 0.68α/(w/c + 0.32α)

Note: because of space requirements minimum w /c = 0.42

(for 100 cc of cement)

Solid space = 1 - capillary porosity

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BM Porosity, Gel Space, Strength, and Permeability

1.0 0.9 0.8 0.7 0.6 0.5 0.4

Solid/Space Ratio (1-P)

Com

pres

sive

Stre

ngth

(x10

3ps

i)

30

20

10

0 Perm

eabi

lity

Coe

ffici

ent

(cm

/sec

x10

-12)120

80

40

0

Typical Capillary Porosity

0 0.1 0.2 0.3 0.4 0.5 0.6

Capillary Porosity, Vol. Fraction P

Wat

er/C

emen

t Rat

io

0.3

0.4

0.5

0.6

0.7

100% 75% 50% 25%

Typical Capillary PorosityHydration

0 0.3 0.45 0.6Capillary Porosity

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BM Ways to Measure Porosity

• Electrical Measurements• Image Analysis• Nuclear Magnetic Resonance (NMR)• Weight Loss• Computer Simulations (Virtual Cement and Concrete

Testing Laboratory-VCCTL)

• Mercury Intrusion Porosimetry

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BMMercury Intrusion Porosimetry

(MIP)

Hydration Pore Volume Pore Diameter

Pene

tratio

n Vo

lum

e (c

c/g) 0.5

0.4

0.3

0.2

0.1

0

Pore Diameter A5000 2000 1000 500 200 100

28 Days

90 Days365 Days

AGEINCREASING w/c

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BM Water and Shrinkage

Relative Humidity

Wat

er L

oss Chemically

Combined WaterAdsorbed and Interlayer Water

Free Water

100%

Note: Relationship between shrinkage and water loss is not unique, it depends on age and degree of hydration

Loss of WaterSh

rinka

ge

A

B

C

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C

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BM VIDEO:Microstructure of Concrete

0.45 w/c, 7 d 30 µm FW

0.45 w/c, 1 d, 50 µm FW

Clinker, HF-etch, 300 µm FW

Images from Paul Strutman, 2003

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BM Key Ideas

• How long are the stages of the hydrati on reaction?

• What is the relative sizes of C-S-H crystals, capillary voids, entrained air and entrapped air?

• What effect does w/c have on the microstructure … and other properti es?