Hydration of cement

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Hydration of cement

  1. 1. 1
  2. 2. HYDRATION OF CEMENT Presented To: Dr. M. Irfan Ahmad KhokharPresented By:• M. Rizwan Riaz 2011-MS-CES-01 (rizwansamor@gmail.com)• Muhammad Safdar 2011-MS-CES-11• Fatima Mehvish 2011-MS-CES-30 2
  3. 3. CONTENTSThe discussion is divided into the following sections :• Introduction• Hydration Process• Heat of Hydration• Factors Affecting Hydration• Measurement of Cement Hydration• Approaches to Control Hydration• References 3
  4. 4. Hydration• Series of irreversible exothermic chemical reactions between cement and water• Cement-water paste sets and hardens, “gluing” the aggregate together in a solid massFormation of hydration products over time leads to:• Stiffening (loss of workability)• Setting (Solidification)• Hardening (Strength gain) 4
  5. 5. Why is it Important?Understanding the basics of hydration is important to• Ensure the strength and durability of concrete• Recognize and mitigate the stresses to prevent cracking• Appreciate the importance of good curing and construction practices 5
  6. 6. Composition of Cement ClinkerConsists primarily of calcium aluminates and calcium silicates Calcium aluminates – Tricalcium aluminate (C3A) – Ferrite (C4AF) Calcium silicates: – Alite (C3S) – Belite (C2S) Gypsum is added to avoid the uncontrolled setting resulting from C3A reaction with water. 6
  7. 7. Cement ComponentsAlite or 3CaO•SiO2 or C3S −Hydrates & hardens quickly −High early strength −Higher heat of hydration (setting)Belite or 2CaO• SiO2 or C2S −Hydrates & hardens slower than Alite −Gives off less heat −High late strength (> 7 days) 7
  8. 8. Cement ComponentsAluminate or 3CaO• Al2O3 or C3A −Very high heat of hydration −Some contribution to early strength −Low C3A for sulfate resistanceFerrite or 4CaO• Al2O3 • Fe2O3 or C4AF −Little contribution to strength −Lowers clinkering temperature −Controls the color of cement 8
  9. 9. Hydration ProcessThere are two types of reaction underlying the hydration process:• Through-solution hydration• Solid-state hydration or Topochemical hydration 9
  10. 10. Hydration Process 10
  11. 11. Stage 1: Mixing/ Dissolution Stage (< 15 minutes)Sulfate reacts with aluminate and water to form C-A-S-H, a precursor toEttringite.The gel limits water’s access to aluminateReactions slow. Heat dropsToo little sulfate: flash setToo much sulfate: false set 11
  12. 12. Stage 2: Dormant/ Induction Period (2–4 hours)During this dormant period, the silicates (alite and belite) slowlydissolve, releasing calcium ions in solutionDuring dormancy; before initialset; the mix can betransported, placed, finished, and textured. 12
  13. 13. Stage 3: Hardening/ Acceleration Stage (2–4 hours)C-S-H, fiber-like particles & CH forms and give concrete its strengthHeat is generated causing thermal expansionInitial and Final Set occurThe gel-like C-A-S-H transforms into a needle-like solid(ettringite) that contributessomewhat to early strength.Curing necessary right afterfinishing 13
  14. 14. Stage 4: Cooling/ Deceleration Stage (several hours)After final set, the buildup of C-S-H and CH begins to limit access ofwater to undisclosed cementSilicate reactions slow.Heat peaks and begins to dropConcrete cools and contractsCracking can occur 14
  15. 15. Stage 5: Densification/ Steady Stage (can continue for years)Start of belite reactions and they can continue for yearsBelite reactions also produce C-S-H and CH, forming a solid massLonger length of this stage gives:•Greater concrete’s strength•Lower permeability•Greater durabilityTo promote continuedhydration, moisture must beretained in the slab as long aspossible. 15
  16. 16. 5 Stages of Hydration 16
  17. 17. Hydration Reactions 17
  18. 18. Characteristics of hydration cement compound 18
  19. 19. Heat of hydration• Heat liberated when cement comes in contact with water as a result of the exothermic chemical reaction between cement and water.Significance:• Can result in thermal cracking which can reduce concrete durability.• Significantly influences lift thickness which impacts economic savings and construction period. 19
  20. 20. Cement Hydration Mapped on a Heat vs. Time Curve 20
  21. 21. Effect of member thickness on temperature of concrete 21
  22. 22. Mechanism of heat generationReaction of calcium silicates:• 2C3S + 7H → C3S2H8 + 3CH ΔH=-500J/g• 2C2S + 7H → C3S2H8 + CH ΔH=-250J/gReaction of tri-Calcium Aluminate• C3A + 3CŠH2 + 26H → C6AŠ3H32 ΔH=-1350J/g 22
  23. 23. Measurement of Heat of HydrationStandards: ASTM C 186we measure the heat of solution of; Dry cement. Partially hydrated cement. 23
  24. 24. Use & Significance• Cement specification.• For research purposes at any age.• Helpful for calculating temperature rise in mass concrete 24
  25. 25. Apparatus• Calorimetric apparatus. 25
  26. 26. Cont… 26
  27. 27. Cont… 27
  28. 28. Cont..• Mixer• Storage• Mortar• Drying oven• Weighing bottles• Stop watch• Sieves• weights 28
  29. 29. Cont…Plastic vials Muffle furnace 29
  30. 30. Cont…crucibles Analytical balance 30
  31. 31. Reagents &Materials• HF• HNO3• WAX• ZnO 31
  32. 32. Determination of heat capacity of apparatus• Take total weight of the solution to 425g• Assemble calorimeter• Start stirring motor (20 mint)• Allow system to become uniform• Introduce ZnO• Read the temperature OF;solution periodrating period 32
  33. 33. Cont..• Calculate the corrected temperature rise as follows: 33
  34. 34. Cont..• Calculate the heat capacity of the calorimeter and contents as follows: 34
  35. 35. Sampling & Test Specimens• Preparation of Cement Paste• Preparation of Partially Hydrated Sample for Heat of Solution Test 35
  36. 36. Procedure:• Calorimetric ProcedureDetermine the heat of solution of the dry cement sample.Determine the heat of partially hydrated sample.• Determine loss on Ignition• 36
  37. 37. Calculations.• Heat of Solution of Dry Cement 37
  38. 38. • Heat of Solution of Partially Hydrated Sample 38
  39. 39. • Heat of Hydration 39
  40. 40. Approaches to control heat of hydration• Control of Cement Amount• Use of low-heat Cement• Use of Pozzolans• pre-cooling• post-cooling 40
  41. 41. Factors Affecting HydrationMajor factors:• Chemical Composition of Cement• Cement Type• Sulfate Content• Fineness• Water/Cement Ratio• Curing Temperature• Effects of SCMs and Admixtures 41
  42. 42. Chemical Composition of Cement 42
  43. 43. Cement Type 43
  44. 44. Cement Type 44
  45. 45. Sulfate Content 45
  46. 46. Fineness of Cement 46
  47. 47. Water/Cement Ratio 47
  48. 48. Curing Temperature 48
  49. 49. Supplementary Cementitious MaterialsHow they work• SCMs convert CH (a somewhat less desirable product of hydration) into C-S-H (which gives concrete its strength).How SCMs may affect hydration• Often slow hydration, extending working time and delaying set, strength gain.• Reduce heat peak.• Extend heat generation. 49
  50. 50. Fly Ash Replacement Effect 50
  51. 51. Water ReducersHow they work• Disperse cement clusters, freeing trapped water which can then react (hydrate) with cement.• How they affect hydration• More of the mix cement is hydrated, resulting in a greater volume of hydration products. 51
  52. 52. Water ReducersHow they work• Coats cement particles so they dissolve more slowly.How they affect hydration• Slow hydration.• Reduce heat peak and extend hydration and heat generation (similar to water reducers). 52
  53. 53. Set AcceleratorsHow they work• Reduce time required for super saturation of calcium ions.How they affect hydration• Earlier initial and final sets.• Increased heat generation; higher maximum peak on the hydration curve. 53
  54. 54. References• Technical summary 4-a, National concrete pavement technology center, IOWA State University, August 2007.• Wolfgang B., Concrete an example for complex porosity, Institute of building materials research (IBAC), RWTH Achen university, Germany.• Dr. K. Kurtis, Cement and Hydration, School of civil engineering, Georgia Institute of technology, Atlanta, Georgia.• Feng Lin, Modelling of hydration kinetics and shrinkage of Portland cement paste, Coloumbia University, 2006.• S. G. kim, Effect of heat of hydration on mass concrete placement, IOWA state university, 2010.• A.S.M abdul Awal & M. Warid Husain, Effect of palm oil fuel ash in controlling heat of hydration of concrete, University of technology, Johor Malaysia.• P. Juilland et al., Effects of mixing on early hydration of alite and OPC system, Cement and Concrete Research, 2012. 54
  55. 55. References• Concrete technology today, Vol. 18, Portland Cement Association, July 1997.• A.K Schindler & K. J. Folliard, Heat of hydration Model for cementitious materials, ACI Material Journal.• L. E. Copeland et al. Chemistry of hydration of Portland Cement, Search Department, Bulletin 153.• Jochen Stark, Recent Advances in field of cement hydration and microstructure analysis, cement and Concrete Research, 2011.• J. W. Bullard et al., Mechanism of Cement Hydration, Cement Concrete Research, 2011.• H. F. W. Taylor, Cement Chemistry, Academic Press London, 1990.• Mindess et al., Properties of hydrated Cement Compounds, 2004.• Standard Test Method for Measurement of Heat of Hydration (ASTM C 186)• Class Notes 55
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