KING SAUD UNIVERSITYCOLLEGE OF ENGINEERING

CIVIL ENGINEERING DEPARTMENT

Students Names:

Abdulrahman Albedah. 423102910Ali Al-theeb. 423103457

CE-477Supplementary Cementitious

Materials

Types of SCMsTypes of SCMs

• Natural (ASTM C 618 Class N)• Produced from natural mineral deposits

(e.g., volcanic ash)• May require heat treatment (e.g.,

metakaolin)

• Processed / Manufactured• Silica fume (ASTM C 1240)• Slag (ASTM C 989)• Fly Ash (ASTM C 215)

Benefits of SCMsBenefits of SCMs

• Industrial by-products (waste utilization)• Typically cheaper than cement (except for

silica fume and metakaolin)• Environmentally conscious

• No CO2 emission during processing

• Less landfill waste

Influence of SCMsInfluence of SCMs

• Concrete Fresh State• Heat of Hydration• Water demand• Workability• Bleeding• Setting time

• Concrete Hardened State• Mechanical properties• Durability

Hydraulic vs. Pozzolanic Reaction (1)Hydraulic vs. Pozzolanic Reaction (1)

• Latent Hydraulic Reactions:

Chemical reaction with water that leads to setting and hardening of the material.

• Pozzolanic Reactions:

Chemical reaction with calcium hydroxide (lime) and water that leads to the formation of cementitious products.

SCM Chemical CompositionSCM Chemical Composition

Basic Cement HydrationBasic Cement Hydration

2C3S + 6H C-S-H + 3CH

2C2S + 4H C-S-H + CH

Cement Chemistry Notation:C = CaO; S = SiO2; H = H2O

C-S-H; molar ratios can vary; strength-giving phase

No cementitious properties (does not contribute to strength); easily leached; prone to chemical attack

SCM ReactionsSCM Reactions

C3S + H C-S-H + CH

C2S + H C-S-H + CH

FAST

FAST

SCMs + CH + H C-S-HSLOW

Fly AshFly Ash

Fly AshFly Ash

• The most widely used SCM.

• Inorganic by-product of powdered coal after burning in power plants.

• Approximately ½ the cost of cement

• 10 % to 30 % limit on cement replacement.

Class F Fly AshClass F Fly Ash

• Pozzolanic reaction slower rate of reaction than Class C fly ash

• Typical composition: <10% CaO, >50% SiO2

• Pozzolanic and hydraulic reactions typically faster rate of reaction than Class F fly ash

• Chemical composition: >20% CaO, 30-50% SiO2

Class C Fly AshClass C Fly Ash

Physical Characteristics of Fly AshPhysical Characteristics of Fly Ash

• Mainly solid sphere with some cenospeheres (hollow) or plerospheres (containing smaller spheres)

• Particle size ~ 5-20 μm

• Surface area ~ 300-500 m2/kg

• Color ranges from off-white to light gray

Silica FumeSilica Fume

Silica FumeSilica Fume

• Highly reactive pozzolan due to high SiO2 content and extremely small particle size (i.e., large surface area).

• Typical cement replacement values of <10%

• Approximately 5X cost of portland cement

Silica Fume PropertiesSilica Fume Properties

• Physical• Particle size ~0.1-0.3 μm

• Surface area ~15,000-25,000 m2/kg

• Generally, black in color

• Chemical• 85 - 98% SiO2

• SiO2 content dependent upon alloy

Shape of Silica Fume Shape of Silica Fume

Silica fume is almost always spherical in shape

SlagSlag

SlagSlag• Also known as ground granulated blast furnace slag.

• Typical cement replacement values <70%. May have pure slag (alkali-activated) matrix.

• Cost is slightly lower than portland cement (was significantly less).

Slag PropertiesSlag Properties

• Chemical• 35 - 45% CaO• 32 - 38% SiO2

• 8 - 16% Al2O3

• 5 - 15% MgO

• Physical• Particle size < 45μm

• Surface area ~ 400-600 m2/kg

• Angular particle shape

• Generally, white to off-white color

MetakaolinMetakaolin

MetakaolinMetakaolin

• Calcined (700-900° C) clay

• Typical cement replacement amounts of <10% (similar to silica fume)

• More expensive than portland cement

MetakaolinMetakaolin

Al2Si2O5(OH)4 700-900 °C

AlAl22SiSi22OO77

De-hydroxylation+

MetakaolinMetakaolin

Average particle size: •1-2 µm

Chemical composition: •45-55% SiO2

•40-45% Al2O3

Average surface area:

•10,000-25,000 m2/kg

Effect of SCMs on Cement &

Concrete Properties

Effect of SCMs on Cement &

Concrete Properties

Many of the beneficial effects of using SCM are related to

the effect they have on the pore structure by:

Micro-filler effect:Increased packing of cementitious particles.

Increased C-S-H: Replacing porous CH with C-S-H.

Wall effect: Densifying the ITZ (interfacial transition zone) at the cement-aggregate interface.

Benefits of SCMsBenefits of SCMs

Pore blocking:which occurs because of a combination of these factors.

•These effects refine the pore structure and reduce the permeabilty of concrete thereby making it more resistant to the penetration of deleterious agents.

Benefits of SCMsBenefits of SCMs

Heat of HydrationHeat of Hydration

• Most SCMs reduce overall heat of hydration and rate of heat liberation.

• Eliminated need for ASTM Type IV cement.

Setting TimeSetting Time

• Slag and Class C Fly Ash:

↑ setting time (15-60 minutes for initial, 30-120 minutes for final).

• Class F Fly Ash:

↑ setting time (more than Class C); dependent upon chemical composition

• Silica Fume and Metakaolin:

↓ setting time due to high reactivity.

Water DemandWater Demand

Fly Ash:

• ↓ water demand due to “ball bearing” effect of spherical particles

• For every 10% FA, ~2-3% reduction in water demand

Silica Fume:

• ↑ water demand due to increasing surface area.

Slag:

• ↓ water demand.

WorkabilityWorkability

• Silica fume containing concretes tend to be “sticky” and more difficult to finish, leading to decreased workability or the need for high-range water reducer.

• Slag and fly ash improve workability.

BleedingBleeding

• Fly ash: ↓ bleeding

• Slag: ↕ bleeding; depends upon fineness of slag particles (fine particles decrease bleeding and vice versa for coarse particles)

• Silica fume: ↓ bleeding and may eliminate it altogether, thus making finishing difficult

Rate of Strength Gain (1)Rate of Strength Gain (1)

Total Strength GainTotal Strength Gain

Percentage Of Silica Fume Effect

Using smaller particle sizes than cement, SCMs improve “particle packing,” leading to decreased transition zone porosity and increased overall strength gain.