1 / 38

PC Cement Hydration

PC Cement Hydration. 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

quade
Download Presentation

PC Cement Hydration

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

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

  4. 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)

  5. Hydration process

  6. 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

  7. Hydration - Exothermic Reaction • 2C3S + 11H C3S2H8 + 3CH H = -500 J/g • 2C2S + 9H C3S2H8 + CH H = -250 J/g • Calcium silicates (C3S or C2S) + water • Calcium silicates hydrate (C-S-H) + calcium hydroxide • Amount of CH depends on proportion of C3S and C2S • CSH - amorphous in nature, is an inexact composition, • and is extremely fine (Colloidal).

  8. Tricalcium Aluminate (C3A) C3A + H2O  reacts very fast C3A + H2O + CSH2 (Gypsum)  reacts much slower C3A + 3CSH2 + 26H  C6AS3H32 H = -1350 J/g Tricalcium Aluminate + Gypsum + Water  Ettringite (product #3) Once CSH2 is depleted: C6AS3H32 + 2C3A + 4H  3C4ASH12 Ettringite + Tricalcium Aluminate + Water  Monosulfoaluminate (product #4)

  9. Ferrite Phase: C4AF • Forms same reaction as C3A but to a lesser degree • Uses small amount of gypsum • C4AF + 2CH + 14H  C4(A,F)H13 + (A,F)H3 • Ferrite + Calcium Hydroxide + Water •  Tetracalcium Hydrate + Ferric Aluminum Hydroxide • (product #5) (product #6) • like monosulfoaluminate amorphous

  10. 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

  11. Reaction rate: C3A > C3S > C4AF > C2S

  12. 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

  13. Heat of hydration (Cal/g)

  14. Model of CSH

  15. ASTM Types of Portland Cements I II III IV V C3S 50 45 60 25 40 C2S 25 30 15 50 40 C3A 12 7 10 5 4 C4AF 8 12 8 12 10 Gypsum 5 5 5 4 4 Fineness 350 350 450 300 350 (m2/kg) CCS (psi) 1000 900 2000 450 900 Heat of 330 250 500 210 250 Hydration (J/g)

  16. 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

  17. Pozzolans • 2S + 3CH + 7H  C3S2H8 • First used by Romans • CSH is of lower CaO content • Low heat and slow strength gain • Similar to increase in C2S • 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

  18. Blast Furnace Slag • Rapidly cooled slags - to prevent crystallization • (CSA)glass + H  C3(SiA)2H8 (self - reacting) • Forms alumin substituted CSH • Presence of CH accelerated reaction • Mixed with cement

  19. Porosity and pore structure

  20. Capillary pores Gel pores

  21. Pore size distribution 2.5 nm

  22. 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

More Related