2 Cement Hydration

Hydration of Pure Cement Compounds

Hydration - reaction with water

Reaction products formed hydration products

Calcium silicates

100 + 21 99 22

Note: Difference in mass of water for hydration, products C-S-H and CH

100 + 24 75 49

Tricalcium Aluminate (C3A)

Primary initial reaction

(AFt)

Ettringite (Aft) is a stable hydration product only while

there is an ample supply of sulfate

(Intergrind gypsum with clinker to avoid flash set)

(No measured expansion after 2 days max. SO3)

(Unstable at temperatures > 70OC potential DEF)

If the sulfate is consumed before C3A has completely hydrated

monosulphoaluminate

(Afm)

HSCAC 323 3

HSCAC 123

Hydration of Pure Compounds

Ferrite Phase C4AF

Forms similar hydration products to C3A, but less reactive

Reactions are slower and involves less heat

Changes in the composition of ferrite phase affect the rate of hydration

Fe , hydration becomes slower

Reactions

Hydration Products

Precipitation of CH and ettringite

at early time

after ~2 hrs, CSH formed

6 hrs 1 day, rapid increase of

CH, CSH, and

ettringite

After ~2 days, ettringite

monosulpho-

aluminate

(Locher & Richartz 1976)

Hydration Rate

Example of relative rate

of hydration of main

potential compounds

C3A fast early hydration

(within 1st minute) but

small amount of hydrates

High heat generation over

next few days (< 100 h)

Hydration of C3S

generates Ca(OH)2

(potential for pozzolanic

reaction with SCMs, e.g. fly ash, ggbs, silica fume)

Hewlett , Ed., 1998

Notes

Gypsum is important to avoid flash set; but if it is too much, affect setting and hardening, also affect long-

term volume stability as ettringite has high volume that

can cause expansion and cracking if formed at later

age.

The amount required increases with C3A content.

Limit: specified in standards, e.g. SS EN 197-1, Table 3

C3A is undesirable as it contributes little to strength except at early

stage; but it is useful to reduce

production temperature of cement

clinker.

(Mindess et al 2003)

Hydration of Portland Cement

Assumption: the cement compounds hydrate independently

Compound interactions

C3A & C4AF both compete for sulfate ions

It is suggested that gypsum accelerates C3S hydration

Increasing SO3 may reduce rate of heat evolution and total hear evolved at early age, but not after 28 days

(Lawrence in Hewlett, 1998)

Kinetics

The rate of hydration during the first few days

C3A > C3S > C4AF > C2S

Rate of heat evolution

(Mindess et al. 2003)

Stage 1 dissolution Stage 2 induction (dormant)

Stage 3 Acceleration Stage 4 Deceleration

Stage 5 - Steady

Determine

initial setting

Determine final setting

& initial hardening

Hydration Heat Evolution

Stage 6 onwards hydration rate depends diffusion rate of

water and ions of hydration product (solid state diffusion)

Hewlett, Ed., 1998

Heat of Hydration

Heat of hydration in J/g of a typical cement

H 3 days = 240 C3S + 50 C2S + 880 C3A + 290 C4AF

H 1 year = 490 C3S + 225 C2S + 1160 C3A + 375 C4AF

Quantities of C3S, C2S, and so on are expressed as weight fraction

of the cement (potential compounds)

C3S (502 J/g), C2S (260 J/g), C3A (1160 J/g), C4AF (420 J/g)

Temperature rise due to heat of hydration under adiabatic condition is ~12-14 oC per 100 kg of OPC

T = (Mc . H) / (Mc . Sc + Ma . Sa + Mw . Sw)

Where

H = heat of hydration (increases with degree of hydration -time)

M = mass ( c-cement, a-aggregate, w-water)

S = specific heat (c = 0.88 J/goC, a = 0.75 J/goC, w = 4.18 J/goC)

Concrete: c = 300-500, w = 140-180 , aggregate = 1600-1800 (kg/m3)

Heat of Hydration

ASTM Type l = CEM l (strength class 42.5)

ASTM Type III CEM l (strength class 52.5)

ASTM Type IV CEM l (strength class 32.5)

Peak temperature in thick sections , e.g. Pile caps and

raft foundations with least dimension 2 m occurs at around 3 days (one dimension heat lost)

Neville, 1995, Ref. 1.30, Lerch & Ford, 1948)

(Note: Temperature Effect)

C-S-H

Compositional variation C/S = 1.5 - 2.0, depends on age of the paste, curing

temperature, w/c, impurities

Varying water content, water in C-S-H exists in several different states

Physical behavior Amorphous, poor crystalline materials

Extremely small irregular particles in the size range of colloidal matter (< 1m)

High surface area ~400 m2/g

Develop at the surface of calcium silicate, forms a coating covering the grain, thickness of the hydrate layer increases and forms a barrier further hydration is controlled by diffusion of water in and ions out through the barrier

Model of C S - H structure

Layered structure

C-S-H

bread calcium silicate sheets

filling Ca++, H2O

- Sheets are distorted

and randomly arranged.

- Space between the

calcium silicate sheets

is the intrinsic porosity:

I interlayer pores

M- micro pores

P isolated capillary pores

Clay C-S-H

(Mindess 2003)

Model of C S - H structure

Source: Young et al, 1998

Estimated Properties & Influence of C-S-H

Source: Young et al, 1998

C-S-H Model of CS-H structure and water held in C-S-H

In capillary pores (P), menisci are created as the pores are filled or emptied (high mass loss, low shrinkage)

In micropores (M), the adjoining surfaces are so close together that water cannot form menisci, and

consequently has different behavior from bulk water.

Water in M acts to keep the layers apart by exerting disjoining pressure.

The disjoining pressure depends on RH and disappear below 50% RH (high shrinkage)

In interlayer pores (I), water are structurally associated with solid

Hydroxyl water in solid lattice

No sharp distinction between different forms of water

As water is removed from C-S-H, rearrangement of particles is possible.

Calcium Hydroxide (CH)

Well crystallized material with definite stoichiometry

In voids or cracks: Hexagonal tabular morphology

Strong alkaline, in solution gives a pH>12, responsible for the protection of steel from corrosion in reinforced concrete

Calcium Sulphoaluminates

Ettringite

Hexagonal crystals in the form of needles, typically 10x0.5 m

Often found in voids or cracks in mature concrete

Monosulphoaluminate

Clusters or rosettes of irregular plates when first formed

Grow into well-developed, but very thin, hexagonal plates

Degree of crystallinity is decreased to some extent due to impurities

monosulphoaluminate

CH (striated)

ettringite

(Mindess 2003)

Note: For Information ONLY

Properties of the Hydration Products (Mindess 2003)

Microstructure of Hydrated Cement Paste

(a) Water separates

cement grains

(b-d) solid hydration

products form a

continuous matrix

and bind the

residual cement

grains together.

This happens

because the

hydration products

occupy a greater

volume than the

original cement

compounds due to

their lower specific

gravity (~2.0 vs 3.2)

CH

(Mindess 2003)


C-S-H

Occupy > 50% volume of hydrated paste

Two forms of C-S-H

Early product C-S-H (groundmass & undesignated product)

Grows out from the particle surface into the surrounding water-filled space in the form of low density arrangement of

thin sheets (outer product from surface of cement grain)

Higher micro porosity

Contains a high level of impurities (Al, SO4, K, Na)

Later product C-S-H (inner product)

Denser coating around the hydrating cement grains

The coating forms diffusion barrier during later hydration, thicken with time, growing inwards & outwards

The coating maintains the shape of original grains

Less impurities, more resistant to physical change on drying

The proportion as hydration or the w/c

Fractured surface

< 3 days

Polished surface

28-day old paste

High degree of complexity

Unhydrated

cement particle

Later CSH

product

Early CSH

product

(Darwin 1994)

Ettringite needles

Interface between early & later CSH

indicate cement grain boundary


Calcium hydroxide

Occupy ~20-25% of the pastes solid volume

In Stage 3 of C3S hydration, many CH crystals nucleate and grow within the capillary pore space

CH will only grow where free space is available

Morphology vary, particularly affected by admixtures and by temperature of hydration

Calcium sulphoaluminates

Occupy only ~10-15% by solid volume

Play a minor role in the microstructure (although not necessarily in properties)

Both ettringite and monosulphoaluminate are well dispersed throughout the paste


Unhydrated residue of cement grains

may persist even in well hydrated cements

Porosity

Classification (Mindess 2003)

Enormous range of pore sizes

Water that occupies the pores plays many different roles


Mehta & Monteiro, 1997

Note: Fine aggregates (> 150 m and < 4 mm)

Coarse aggregates (> 4 mm and < 150 mm)


Porosity - Classification

Capillary pores remnants of water filled space that exists between the partially hydrated cement grains

Gel pores regarded as an intrinsic part of the C-S-H (cannot be resolved by SEM), (include small capillary pores)

Capillary pore system is the interconnected network of pores through which bulk water flow & ion diffusion occur easily

Porosity - Measurements

Mercury intrusion porosimetry

Forcing mercury into pore system by applying external pressure, pressure required is inversely proportional to

the pore radius

Give better appreciation of capillary pore system

Physical adsorption of gases

Pores are filled by a condensed vapor (gas) through capillary condensation

Give better measure of gel-pore system

(Medium capillary pores)

(small capillary pores)

Capillary

pores

Gel pores

Mindess ,2003

Note: Shrinkage and creep both lead to change in surface energy of CSH,

fundamentally related to thermodynamics of gel water

Microstructure of Hydrated Cement Paste (HCP)

Pore solution

Fluid contained in capillary pores is not pure water, but an ionic solution that is in equilibrium with hydrated paste

inde

In low alkali cement, pH ~ 13

In high alkali cements, pH > 13.5

(S. Diamond, Figure 4.11,

Mindess et al, 2003 )

Note: Role of alkalis in ASR & corrosion passivation in concrete

Note:

Time (> 3 days) for

sufficient amount

of CH to activate

pozzolans

Interfacial Transition Zone

Microstructure of HCP is highly modified in the vicinity of embedded materials: aggregates, fibers, and reinforcing steel

The modified volume is called interfacial transition zone (ITZ)

Common features of ITZ

Increased porosity

Reduction of unhydrated cement

Higher w/c due to the wall effect and localized bleeding

Within the free space close to the surface, crystals of CH or ettringite can readily form, CH predominates and often highly

oriented

Thickness of ITZ: ~20-40 m

vary depends on the size, shape, and volume of aggregate, w/c, mixing and placing procedures

due to wall effect

Interfacial transition zone

ITZ plays an important role in mechanical properties

and permeability

Recent views:

Potential weakness for crack initiation in concrete

May be modified by pozzolanic

reaction products and/or nano

particles

Difficulties in determining ITZ properties due to its small

thickness and changing with

distance from particle surface

Mindess et al. 2003

Volume changes during hydration

All cement hydration products have lower specific

gravities than the cement compounds

Hydration reaction is accompanied by an increase in

solid volume and decrease in porosity.

Expansive reactions

CH grows around solid particles or stops growing when it

meets obstacles. The same is true of C-S-H. Thus, the

hydration of calcium silicates is not accompanied by increase

in the total volume of paste. If original water occupied space is

filled, hydration will cease.

Bulk expansion occurs when ettringite is formed after cement

paste is hardened. If space is limited, ettringite crystals may

develop crystal growth pressures.

Early age, plenty space for ettringite to grow, no problem

Calculation of volume change

Equations are empirical, derived from experimental data

The hydrated cement includes all hydration products, CH, C-S-H, and sulphoaluminates

Evaporable water lost under D-drying or oven drying condition (include water in capillary and gel pores, and water in sulphaluminates)

Non-evaporable water - lost from D-drying to 1000oC (measures water chemically combined in hydration products)

Non-evaporable water

, = degree of hydration

Evaporable water associated with hydration products

wg : gel water (C-S-H) + water

in in calcium sulphoaluminates

Total volume of hydration products

Gel porosity

constant for all normally

hydrated cements

Calculation of volume change

Capillary pore volume

Volume occupied by unhydrated cement

c specific volume of cement, (1/specific gravity) = 0.32

Original volume of the paste

Capillary porosity

Gel/space ratio

Volume relationships among constituents of hydrated cement pastes

w/c = 0.5

= 1.0

Mindess et al. 2003

Full Hydration

POSSIBLE in practice?

Calculation of Volume Change

Minimum w/c ratio

At low w/c ratios, there is insufficient space for the hydration products to form so that complete hydration is

not possible. The minimum w/c that can be used and still

ensure complete hydration can be determined from

Set Vc = 0, and =1, the minimum w/c = 0.36

However, the hydration products must be formed with the gel pores saturated. Thus, water required for

complete hydration is

For complete hydration (=1), the w/c should not be

Volume Relationship

For example 100 g of cement at = 1 (fully hydrated)

Vhc = 100/3.15 = 32 cm3 (density 1 g/cm3 = 1000 kg/m3)

wn = 0.24 g/g of cement, Vwn = 24 cm3

wg = 0.18 g/g of cement, Vwg = 18 cm3

Vhp = 0.68 cm3/g of cement = 68 cm3

Vhc + Vwn < Vhp < Vhc + Vwn + Vwg

32 + 24 68 32 + 24 + 18

(56) (74)

[vol. of reactants]< [vol. of product] < [vol. of components]

Note: Vhc, space for inner product. Outer product in space

provided by water (w/c 0.42 for full hydration)

Volume Relationship

For example 100 g of cement at = 1 (fully hydrated)

Vhc = 100/3.15 = 32 cm3 (density 1 g/cm3 = 1000 kg/m3)

wn = 0.24 g/g of cement, Vwn = 24 cm3

wg = 0.18 g/g of cement, Vwg = 18 cm3

Vhp = 0.68 cm3/g of cement = 68 cm3

Vhc + Vwn < Vhp < Vhc + Vwn + Vwg

32 + 24 68 32 + 24 + 18

(56) < (74)

[vol. of reactants]< [vol. of product] < [vol. of components]

Note: Vhp < volume of components , difference in volume to

be filled from ingress of external water (curing) otherwise by

some capillary water forms vapour (vapour pressure < 1, RH

< 100%) e.g. sealed specimen or external RH < 100%

Volume Relationship Non-evaporable water

Evaporable water in hydrated products

Volume of hydrated products

Capillary porosity

Gel/space ratio

Except for X, all are linearly proportional to degree of hydration,

Consider the cases at = 0.5 (50% hydration) for w/c of 0.36, 0.42 and 0.50

Factors Leading to Cessation of Hydration

Environmental factors:

Temperature lower than ( 10 OC) freezing of pore fluid

Lack of water for hydration, e.g. w/c < 0.42, < 1.0

Lowing vapour pressure in capillary pores, e.g. sealed

specimen, no ingress of water (curing)

Vapour pressure < 0.8: hydration rate is low

Vapour pressure < 0.3: hydration rate is negligible [Powers, 1947 Ref. 7.36 in Neville, 1995, Fig. 7.1]

Physical factors:

Lack of space for hydration products, e.g. w/c < 0.36

Large grain size cement particles (> 40 m in diameter)

In practice, common curing period is 7 days, < 0.6 to 0.7

w/c 0.2 to 0.3 for high strength concrete [What value is ?]

Environmental Factor

Hydration rate highest when capillary

pores are saturated, i.e. vapour

pressure of 1.0 (RH 100%)

Below vapour pressure of 0.8 (RH 80%)

hydration is low

Below vapour pressure of 0.3 (RH 30%)

hydration is negligible

Note: Tropical hot wet climate, range of ambient RH between 60% (afternoon)

and over 80% (night)

Air-conditioning may bring RH to 30%

Source: Properties of Concrete, A.M. Neville, 4th Ed. 1995, Pitman

Powers, T.C., A discussion of cement hydration in relation to curing of concrete, Proc. Highw. Res. Bd, 27, 1947

Fig. 7.1

Schematic Representation of Single Cement Grain

Modified from Williamson, 1970

Comparison of ASTM and BS-EN Standards ASTM BS-EN

Portland

cement

C 150 Spec for Portland cements

197-1: 2000 (SS EN 197-1: 2008)

CEM I Portland cement

[197-1: 2011]

Blended

cements

C 595 Spec for blended hydraulic cements

197-1: 2000 (SS EN 197-1: 2008)

CEM II Portland comp. cem

CEM III blastfurnace cem

CEM IV pozzolanic cem

CEM V composite cem

C 1157 Performance Spec for blended hydraulic

cements

Mineral

admixtures

C 618 Spec for coal fly ash and raw or calcined natural

pozzolans for use in concrete

450-1: 2005

Fly ash for concrete Definition, spec, and conformity criteria

C 989 Spec for GGBFS for use in concrete and mortars

15167-1: 2006 (SS EN 15167: 2008)

Ground granulated blast furnace

slag for use in concrete, mortars,

and grouts

C 1240 Spec for silica fume used in cementitious

mixtures

13263-1: 2005

Silica fume for concrete

Portland cement

CEM I K = 95 to 100%, MAC = 0 to 5%

Portland-fly ash cement (MAC = 0 to 5%)

CEM II/A-V: K = 80 to 94%, V = 6 to 20%

CEM II/B-V: K = 65 to 79%, V = 21 to 35%

Portland-silica fume (MAC = 0 to 5%)

CEM II/A-D: K = 90 to 94%, D = 6 to 10%

Clinker: K, Blastfurnace slag: S

Silica fume: D, Fly ash: V (siliceous)

Blastfurnace cement (MAC = 0 to 5%)

CEM III/A: K = 35 to 64%, S = 36 to 65%

CEM III/B: K = 20 to 34%, S = 66 to 80%

CEM III/C: K = 5 to 19%, S = 81 to 90%

No change in Table 1 of BS EN 197-1: 2011

Specification for Constituent Materials Cement

Revision of BS EN 197-1: 2011

Combining EN 197-1 and EN 197-4 and addition of sulfate resisting

classes of cement (superseding EN 197-1 and EN 197-4)

SS EN 197-1: 2008 to be revised as per BS EN 197-1: 2011

Sulfate resisting cements 3 main groups:

Sulfate resisting Portland cement

CEM I-SR 0, sulfate resisting Portland cement (C3A content of clinker = 0%)

CEM I-SR 3, sulfate resisting Portland cement (C3A content of clinker 3%)

CEM I-SR 5, sulfate resisting Portland cement (C3A content of clinker 5%)

Sulfate resisting blast furnace cement (no requirement on C3A content of clinker)

CEM III/B-SR, sulfate resisting blast furnace cement

CEM III/C-SR, sulfate resisting blast furnace cement

Sulfate resisting pozzolanic cement (C3A content of clinker 9%)

CEM IV/B-SR, sulfate resisting blast furnace cement

CEM IV/C-SR, sulfate resisting blast furnace cement



Table 2 Seven products in sulfate resisting common cements

Main types

Notation of the seven

products

(types of common

sulfate resisting

cements)

Composition (percentage by mass)

Main constituents Minor

additional

constituents Clinker

K

Blast

furnace

slag

S

Pozzolana

natural

P

Siliceous

fly ash

V

CEM

I

Sulfate

resisting

Portland

cement

CEM I-SR 0

CEM I-SR 3

CEM I-SR 5 95 - 100 - - - 0 - 5

CEM

III

Sulfate

resisting

blast

furnace

cement

CEM III/B

- SR 20 - 34 66 - 80 - - 0 - 5

CEM III/C

- SR 5 -19 81 - 95 - - 0 - 5

CEM

IV

Sulfate

resisting

pozzolanic

cement*

CEM IV/A

- SR 65 - 79 21 - 35 0 - 5

CEM IV/B

- SR 45 -64 36 - 65 0 - 5

* Main constituents other than clinker shall be declared by designation of cement (P or V)



Table 3 Mechanical and physical properties as characteristic values

Strength

class

Compressive strength (MPa) Initial setting

time

Soundness

(expansion Early strength Standard strength

2 days 7 days 28 days min mm

32,5 La - 12

32,5 52,5 75

10

32,5 N - 16

32,5 R 10 -

42,5 La - 16

42,5 62,5 60 42,5 N 10

42,5 R 20

52,5 La 10

52,5 - 45 52,5 N 20

52,5 R 30

a Strength only defined for CEM III cements

NOTE: CEM III cements are distinct low early strength blastfurnace cements

VICAT APPARATUS EN 196-3: 2005

Standard Consistence:

Water content for 500 kg cement when

distance between plunger (Figure 1 c)

and base-plate is (6 2) mm (to the

nearest 0,5%)

Initial Setting Time:

The elapsed time, measured from zero to

time at which distance between needle

(Figure 1 d) and the base-plate is (6 3)

mm (to the nearest 5 min.)

Final Setting Time:

The elapsed time, measured from zero to

that at which the needle (Figure 1 e) first

penetrates only 0,5 mm into the

specimen (to the nearest 15 min.)

Note: No requirement in BS EN 197-1

Chemical Requirements (BS-EN 197-1: 2000)

Note:

SO3 limit for

different

strength class

Note:

Higher limit

for CEM II/B-T

& CEM lll/C

Identical with

Table 4 of BS

EN 197-1:

2010

Compressive Strength Determination

Cartoon on Concrete

Source: IEM Bulleting

2 Cement Hydration

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