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PC Cement Hydration. Introduction Portland Cement Concrete Continous binder phase: the cementitious matrix Binder effect on PCC behavior Affects permeability.

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Presentation on theme: "PC Cement Hydration. Introduction Portland Cement Concrete Continous binder phase: the cementitious matrix Binder effect on PCC behavior Affects permeability."— Presentation transcript:

1 PC Cement Hydration

2 Introduction Portland Cement Concrete Continous binder phase: the cementitious matrix Binder effect on PCC behavior Affects permeability Affects strength Dispersed particulate phase: the aggregates Coarse: #4 to 1½” Fine:#100 to #4 Aggregates have a major effect on PCC behavior Serve as a filler Increase concrete modulus of elasticity

3 Cementitious Phase Portland Cement Water Admixtures Liquid Mineral } Workability & Strength

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5 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)

6 Hydration process

7 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

8 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

9 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)

10 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

11 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

12 Reaction rate: C3A > C3S > C4AF > C2S

13 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

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

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21 Model of CSH

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

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27 IIIIIIIVV C3SC3S C2SC2S C3AC3A C 4 AF Fine

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30 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

31 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

32 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

33 Porosity and pore structure

34 Capillary pores Gel pores

35 Pore size distribution 2.5 nm

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38 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


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