Supplementary Cementitious Materials Design and Control of Concrete Mixtures – Chapter 4

Overview Fly ash Slag cement Silica fume Natural pozzolans Reactions Effects on concrete Proportioning

Supplementary Cementitious Materials

SCM Properties

Fly Ash

ASTM C618 Class F  Pozzolanic  SiO 2 + Al 2 O 3 + Fe 2 O 3 ≥ 70% Class C  Pozzolanic with some hydraulic behavior  SiO 2 + Al 2 O 3 + Fe 2 O 3 ≥ 50%

Fly Ash – Physical Properties

Slag Cement

ASTM C989 Grade 80 Grade 100 Grade 120

Slag Cement

Silica Fume

ASTM C1240 As-produced Slurry Densified Up to 99% silica content

Silica Fume

Natural Pozzolans ASTM C618, Class N Calcined shale Calcined clay Volcanic ash

Natural Pozzolans

Metakaolin

Pozzolanic Reactions Pozzolan + CH = C-S-H Different from portland cement C-S-H Contribute to strength Reduces permeability

Hydraulic Reactions Slag cement and some pozzolans with high calcium contents No calcium hydroxide byproduct; may consume calcium hydroxide from system Reactivity dependant on fineness and composition of slag cement, temperature, and alkali content of portland cement

Effects on Freshly Mixed Concrete

Water Demand

Workability Increases Fly ash Slag cement Calcined shale and clay Decreases Silica fume Metakaolin

Bleeding and Segregation

Setting Time

Air Content SCMs generally require more air-entraining admixture Effect of fly ash dependent on carbon content, fineness, alkali content Effect of slag cement is minimal; caused by fineness Effect of silica fume is significant due to fineness

Heat of Hydration

Effects on Hardened Concrete

Strength (Whiting 1989).

Strength (Detwiler 2000).

Impact and Abrasion Resistance (Gebler and Klieger 1986)

Permeability and Absorption SCMs generally reduce permeability and absorption Silica fume and metakaolin significantly reduce permeability and absorption Increased corrosion resistance

Alkali-Silica Reactivity (Detwiler 2002)

Alkali-Silica Reactivity (Lerch 1950).

Alkali-Silica Reactivity (Thomas 2007).

Sulfate Resistance SCMs improve sulfate resistance Fly ash: Class F better than Class C Calcined clay: better than Type V portland cement

Deicer-Scaling Resistance

(After Whiting 1989).

Deicer-Scaling Resistance (Whiting 1989).

Deicer-Scaling Resistance

Concrete Mixture Proportions Optimums determined by testing Ternary/Quaternary systems Synergy between SCMS  Fly ash offsets silica fume workability issues  Silica fume compensates for low early-strength of fly ash

Summary Fly ash Slag cement Silica fume Natural pozzolans Reactions Effects on concrete Proportioning

Questions