KING SAUD UNIVERSITY COLLEGE OF ENGINEERING CIVIL ENGINEERING DEPARTMENT Students Names: Abdulrahman Albedah Ali Al-theeb CE-477 Supplementary Cementitious Materials

Types 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 SCMs Industrial by-products (waste utilization) Typically cheaper than cement (except for silica fume and metakaolin) Environmentally conscious No CO 2 emission during processing Less landfill waste

Influence 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) 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 Composition

Basic Cement Hydration 2C 3 S + 6H  C-S-H + 3CH 2C 2 S + 4H  C-S-H + CH Cement Chemistry Notation: C = CaO; S = SiO 2 ; H = H 2 O 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 Reactions C 3 S + H C-S-H + CH C 2 S + H C-S-H + CH FAST SCMs + CH + HC-S-H SLOW

Fly 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 Ash Pozzolanic reaction  slower rate of reaction than Class C fly ash Typical composition: 50% SiO 2 Pozzolanic and hydraulic reactions  typically faster rate of reaction than Class F fly ash Chemical composition: >20% CaO, 30-50% SiO 2 Class C Fly Ash

Physical Characteristics of Fly Ash Mainly solid sphere with some cenospeheres (hollow) or plerospheres (containing smaller spheres) Particle size ~ 5-20 μm Surface area ~ m 2 /kg Color ranges from off- white to light gray

Silica Fume

Highly reactive pozzolan due to high SiO 2 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 Properties Physical Particle size ~ μm Surface area ~15,000-25,000 m 2 /kg Generally, black in color Chemical % SiO 2 SiO 2 content dependent upon alloy

Shape of Silica Fume Silica fume is almost always spherical in shape

Slag

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 Properties Chemical % CaO % SiO % Al 2 O % MgO Physical Particle size < 45μm Surface area ~ m 2 /kg Angular particle shape Generally, white to off-white color

Metakaolin

Calcined ( ° C) clay Typical cement replacement amounts of <10% (similar to silica fume) More expensive than portland cement

Metakaolin Al 2 Si 2 O 5 (OH) °C Al 2 Si 2 O 7 De-hydroxylation +

Metakaolin Average particle size: 1-2 µm Chemical composition: 45-55% SiO % Al 2 O 3 Average surface area: 10,000-25,000 m 2 /kg

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 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 SCMs

Heat of Hydration Most SCMs reduce overall heat of hydration and rate of heat liberation. Eliminated need for ASTM Type IV cement.

Setting Time Slag and Class C Fly Ash: ↑ setting time (15-60 minutes for initial, 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 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.

Workability 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.

Bleeding 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)

Total 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.