Chapter 3 Cement

§3.3 Portland Cement With Mineral Materials Chapter 3 Cement §3.3 Portland Cement With Mineral Materials Mineral Admixture Ordinary Portland Cement (P.O) Portland granulated Blast-furnance-slag Cement (P.S) Portland-Pozzlana Cement (P.P) Portland fly-ash cement (P.F) Composite Portland Cement (P.C)

Mineral Admixture Definition Classification Active admixture Introduction Secondary Hydration Reaction Function of Active Admixture Inactive admixture

Mineral Admixture Definition Improving Property processed or raw mineral materials when grinding Adjusting Strength Grade Lowering Costs Mineral Admixture is the processed or raw with the purpose of improving cement property, adjusting cement grade and lowering costs.

Classification by performance active admixture (Pozzolan Admixture) and inactive admixture（filling admixture） Classification by performance Inactive admixture （filling admixture） Active admixture (Pozzolan Admixture)

Active Admixture Introduction It is not hardened after grinding and watering. But after mixed with lime and water A secondary hydration activity happens To form hydraulic cementing material activity Volcanic ash activity

Hydraulic cementing forms Secondary Hydration Reaction SiO2 +mH2O + xCa(OH)2 xCaO·SiO2·nH2O Hydraulic cementing forms Consumption Ca(OH)2 Active admixture Al2O3 +aH2O + yCa(OH)2 yCaO·Al2O3·bH2O

Active Admixture Although active admixture is not a compound of Portland cement. The replacement of a portion of cement with active admixture changes the properties of the various types of cement.

Secondary cementing reaction Hydration Reaction First reaction Portland cement hydrates Takes place when portland-pozzolan cement is used or when a pozzolan is added to concrete with portland cement Secondary cementing reaction

Characteristics of Secondary Hydration Reaction Sensitivity to temperature Low reaction speed at common temperature High reaction speed at high temperature Consumption Ca(OH)2 Improving the structure of pores

Consumption Ca(OH)2 When the calcium silicates hydrate, hydrated lime is one of the products of hydration This leaves a reactive soluble salt in the concrete mass and is responsible for the white encrustations and efflorescence which appears in hydraulic structures where the lime has leached to the surface and reacted with CO2.

Function of Active Admixture Improving products. Lower costs. Better the property of cement. Adjusting strength grade of cement. Expanding application range. Benefiting to prevention of environment. Making full use of industry rubbish. Protecting the environment.

Better the property of cement Reducing temperature rise Pozzolanic action occurs very slowly. Consequently the temperature rise is much smaller

Better the property of cement Reducing alkali-aggregate expansion A pozzolan is an active, amorphous silica. Reacting readily with any alkali in the presence of moisture. The pozzolan, as a very finely divided silica. Readily consuming the Na2O and K2O from the cement. Completely dispersing the expansive silica. Consequently, the alkalis are not available to react with reactive aggregates.

To Reduce Harmful Effects of C3A The harmful effects of tricalcium aluminates can be reduced by use of a pozzolan. If the pozzolan is used to replace 30 percent of the Portland cement, the percentage of tricalcium aluminates in the total cementing material will also be reduced by 30 percent.

Types of Active Admixture Fly ash Granulated blast furnace slag Other active admixture

Types of Active Admixture Fly ash is the flu dust that is precipitated in the smokestacks of coal-burning power plants Granulated blast furnace slag composed of the fine particles of shale in the coal which form tiny spheroids of glass when exposed to the hot flame of the furnace

Types of Active Admixture Other active admixture such as silica fume diatomite ground pumice other volcanic rocks

Inactive Admixture Characteristics It can’t form hydraulic cementing material with gelatification after grinding and mixing with lime in water. Quartz Clay Slow cooling slag