Reference Concrete Sidney Mindess J. Francis Young Prentice-Hall, Inc Chapters 3 and 4

Portland Cement Manufacture Quarrying – Raw materials Crushing Grinding Mixing Calcinated (1100  C) Burned (1450  C) Clinker is produced (10 mm size) Inter-ground with 5% gypsum (1-100  m) - most reactive ( <50  m)

Schematic Outline of Cement Production Limestone Quarry Crush Storage Grind Blend Other raw materials Clay/shale Quarry Crush Storage Grind Blend Storage and final blending

Schematic Outline of Cement Production PreheatersBurning (kiln) Gypsum Finish grinding Storage Distribution to markets

Schematic Outline of Conditions and Reactions in a Typical Cement Rotary Kiln Gas temp. Feed temp Free water Clay decomposes Limestone decomposes Formation of products DehydrationCalcination Clinkering Clinker out Degrees C Cooling

Hydration process

Setting – Solidification of the plastic cement paste Initial set – beginning of solidification – Paste become unworkable – loss in consistency - not < 45 min. Final set – Time taken to solidify completely – Not > 375min. Hardening – Strength gain with time – after final set

2C 3 S + 11H C 3 S 2 H 8 + 3CH  H = -500 J/g 2C 2 S + 9H C 3 S 2 H 8 + CH  H = -250 J/g Calcium silicates (C 3 S or C 2 S) + water Calcium silicates hydrate (C-S-H) + calcium hydroxide Amount of CH depends on proportion of C 3 S and C 2 S CSH - amorphous in nature, is an inexact composition, and is extremely fine (Colloidal). Hydration - Exothermic Reaction

Tricalcium Aluminate (C 3 A) C 3 A + H 2 O  reacts very fast C 3 A + H 2 O + CSH 2 (Gypsum)  reacts much slower C 3 A + 3CSH H  C 6 AS 3 H 32  H = J/g Tricalcium Aluminate + Gypsum + Water  Ettringite (product #3) Once CSH 2 is depleted: C 6 AS 3 H C 3 A + 4H  3C 4 ASH 12 Ettringite + Tricalcium Aluminate + Water  Monosulfoaluminate (product #4)

Ferrite Phase: C 4 AF Forms same reaction as C 3 A but to a lesser degree Uses small amount of gypsum C 4 AF + 2CH + 14H  C 4 (A,F)H 13 + (A,F)H 3 Ferrite + Calcium Hydroxide + Water  Tetracalcium Hydrate + Ferric Aluminum Hydroxide (product #5)(product #6) like monosulfoaluminateamorphous

Hydration of Portland cement  Sequence of overlapping chemical reactions  Hydration reactions of individual clinker mineral proceed simultaneously at differing rates and influence each other  A complex dissolution and precipitation process  Leading to continuous cement paste stiffening and hardening

Reaction rate: C3A > C3S > C4AF > C2S

Hydration of Portland cement Reactivity Crystal size – Heating rate, burning temp. Crystal defects vs. impurities polymorphic form – rate of cooling Fineness e.g. C3S and C2S with impurities hydrate faster than their pure forms

Heat of hydration (Cal/g) Compound3 days90 days13 years C3SC3S C2SC2S C3AC3A C 4 AF

Model of CSH

ASTM Types of Portland Cements IIIIIIIVV C3S C2S C3A C4AF Gypsum Fineness (m2/kg) CCS (psi) Heat of Hydration (J/g)

IIIIIIIVV C3SC3S C2SC2S C3AC3A C 4 AF Fine

Blended Cements 20 to 70% of total binding material Total = Cement & supplementary cementitious material Most mineral admixtures are industrial by products Use is economical, ecological, or technical in nature Fly ash: coal fired power plants Blast furnace slag: steel production lower heat, improved durability Fine pore structure and lower permeability with same w/c Improve workability

Pozzolans 2S + 3CH + 7H  C 3 S 2 H 8 First used by Romans CSH is of lower CaO content Low heat and slow strength gain Similar to increase in C 2 S Reactivity based on surface area (silica fume) Some contain alumina (can present durability problems) Crystalline compounds (quartz); acts to dilutents Unburned carbon may affect air entrainment Can have a wide range of composition and reactivity

Blast Furnace Slag Rapidly cooled slags - to prevent crystallization (CSA) glass + H  C 3 (SiA) 2 H 8 (self - reacting) Forms alumin substituted CSH Presence of CH accelerated reaction Mixed with cement

Porosity and pore structure

Capillary pores Gel pores

Pore size distribution 2.5 nm

High strength and low permeability concrete Low W/C ratio  Proper mixture proportioning  Use of superplasticizers  Use of pozzolans High degree of hydration  Good curing