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Rheological Properties of Cement

P. Rheological Properties of Cement . Pastes Containing Admixtures . Rheology is derived from the Greek words rew ( flow) – logo s ( science). Rheology is defined as . the Science concerned with the laws of deformation and flow of materials under the influence of stresses.

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Rheological Properties of Cement

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  1. P

  2. Rheological Properties of Cement Pastes Containing Admixtures 

  3. Rheologyis derived from the Greek words rew ( flow) – logos (science)

  4. Rheologyis defined as the Science concerned with the laws of deformation and flow of materials under the influence of stresses

  5. What is the purpose of performing rheological measurement ? It gives a comprehensive characterization of cement It clarifies the interaction between different ingredients Rheological tests are used for quality control of raw materials, processing conditions and final products From the economic point of view, It helps in selection of the proper mix design for the desired workability pumbability and placement

  6. The principle of the coaxial-cylinders viscometer

  7. Flow Models Newtonian flow Non-Newtonian flow -time independent Non-Newtonian flow - time dependent

  8. Newtonian Flow  = .   : shear stress (Pa) : shear rate (1/s) : Newtonian viscosity (Pa.s)

  9. Flow curve Shear stress (Pa ) Viscosity curve Shear rate (s-1) Flow behavior of Newtonian liquid Viscosity Pa.s Shear rate (s-1) Newtonain Flow

  10. Non-Newtonian Flow, Time Independent • Shear thinning materials • Shear thickening materials • Materials with a yield value

  11. Non-Newtonian Flow Shear Stress =  n (Power law) : Apparent viscosity (Pa.s), : Shear rate (s-1), • n = 1Newtonian liquids • n < 1Shear thinning liquids • n > 1Shear thickening liquids

  12. Flow curve Shear stress (Pa ) Shear rate (s-1) Viscosity curve Shear rate (s-1) Flow behavior of shear thinning liquids Viscosity Pa.s Shear Thinning Liquids

  13. Dispersion with shear thinning behaviour at rest and high shear rate Dis-aggregation Orientation Stretching Deformation Materials at rest Materials at high shear rate

  14. Flow curve Viscosity curve Shear stress (Pa ) Viscosity Pa.s Shear rate (s-1) Shear rate (s-1) Flow behavior of shear thickening liquids Shear Thickening Liquids

  15. Materials With Yield Values • Materials having a yield value do not flow at rest • These materials tend to flow when the shear stress is exceeding a certain value, the so called yield point.

  16. Casson Model Herschel-Bulkely Model Bingham Model Shear Stress Pa Shear rate (s-1) Flow curves Flow Models For Materials Having Yield values

  17. Bingham Flow Model  = o +   o .  : Shear stress (Pa) o : Yield stress (Pa)  o : Shear rate (s -1)  : Plastic viscosity (Pa s)

  18. Casson Flow Model  1/2 = K1 + K2  1/2  : Shear stress (Pa)  : Shear rate (s-1) K1 and K2 are functions of yield stress and viscosity

  19. Herschel - BulkelyFlow Model  = y + Kh  1/m y , Khand mare equation Coefficients • If m = 1 andy= 0,the equation results in Newtonian model • If m = 1, the equation results in Bingham model • If y = 0, and 1/m= n the equation results in Newtonian model

  20. Non-Newtonian Liquids,Time Dependent Shear Stress (Pa) Shear Rate (s-1) • Thixotropic materials • Anti-thixotropic materials • Rheopectic materials

  21. (Pa) Shear rate (S-1) Area of hystresis(A) A=  . [Pa . S-1] A = Nm-2.S-1 = N.m.s-1.m-3 A = (work/shear time)/ volume A = energy/volume Shear Stress Thixotropic Material

  22. Thixotropy Shear rate Time Continually Changed Rate ShearStress Time

  23. Shear rate Time Thixotropy Break down Equilibrium Stepwise Changed Rate Shear stress Time

  24. Hattori-Izumi Theory Viscosity  = B . J2/3 (1) B: Friction coefficient J: Number contact points between particles in suspension per volume unit

  25. H-I Theory In suspension =ll+ ls+ ss(2) ll~ls<< ssSusp ss(3) ss = Bss . Jt2/3 (4)

  26. H-I Theory J=0 nt=16 ns =16 U=0 J=8 nt=8 ns =16 U=0.5 J=15 nt=1 ns =16 U=1 Degree of Coagulation

  27. Primary Particles Number. ns H-I Theory • From w/c, density of water (1)and the cement (2) Volume concentration of particles • From the fineness of the cement Average particle radius • Total number of particles (per unit volume)

  28. H-I Theory Shear Rate in Relation to Energy H-I Theory reported that shear rate is a function of energy and time t: time Em : mechanical energy K: Boltzman constant T: absolute temperature

  29. H - I Theory Diffused double layer The inverse of 1/k, the thickness of the diffused double is the estimated size of how far electrostatic stabilization reaches from the surface of the particles

  30. VT DLVO Theory Perikinetic coagulation rate VR Vmax + Total Interaction energy - VA VT = VR +VA Schematic illustration of the total interation energy VT

  31. DLVO Theory In the cement paste, the ions (electric charges) or dispersing agent adsorbed on the surface on the cement particles will creat repulsive forces (VR: Repulsive potential energy). Opposite of this, there are some attractive force, like Van der Vaal forces which try to pull the particles togather if they are close enough to each other (VA: Attractive potential energy

  32. DLVO Theory How the number of agglomerates of particles changes versus time k: Boltzman constant. T: Absolute temperature k: Debye Huckel parameter. K: Smoluchowski rapid coagulation constant. nt: Number of agglomerate at the time t. k: Boltzman constant. Vmax: maximum potential interaction energy.

  33. H - I Theory [P= 2. K.k.r.n3 &x = Vmax/Kt] Number of particles at time (t) Degree of coagulation at time t H-I Theory is partly based on the last equation. Number of junction at time (t) Jt = ns - nt

  34. Hattori-Izumi Theory Degree of coagulation at time t H: Coagulation rate constant

  35. Shear stress  = const. highshear rate  = 0 at rest Thixotropy

  36. Mathematical Explaination of Thixotrpy General viscosity in the H-I Theory Viscosity at equilibriun The increase in Viscosity at rest

  37. H O C H O H O 2 C C H C C 2 S O H O 3 Na- lignosulphonate

  38. H C 2 n S O Na 3 Na- naphthalene formaldehyde sulphonate

  39. N H C H O H N N H N H C 2 2 N N N H C H S O N a 2 3 Na-Melamine Formaldehyde Sulphonate

  40. R 1 R 1 C H 2 C C H 2 C n C O O R 2 C O O N a A typical polyacrylates admixture

  41. ( ) C H 2 C H C H 2 C H x C O O ( ) C H 2 C H 2 O H Polymer Backbone Side chain A typical polyacrylates admixture

  42. Individual Cement Compounds C3S andC2S together make up 75-80 % of OPC. Tricalclum silicate C3S Dicalcium silicate C2S Tricalcium aluminate C3A The Frrite phase C4AF Ettrengite and monosulphate are deposited on the surface of the gel-like CSH. Calcium ion, which rapidly adsorb on the hydrates cement grains giving a net positive charge.

  43. Tricalcium Silicate C3S 2 [3CaO*SiO2]+7 H2O 3CaO*2SiO2*4H2O +3Ca(OH)2

  44. Dicalcium Silicate C2S 2[3CaO*SiO2l]+ 5 H2O 3CaO*2SiO2*4H20+Ca(OH)2

  45. Tricalcium Aluminate C2A C3A + 3CSH2 + 26H C3A*3CSH32 C3A*3CSH32 + C3A + 4H 3[C3A*CSH12]

  46. Tetracalcium Aluminoferate C2S C4AF+ 3CSH2 + 16H C4(A,F)Hl3 +(AF)H3 C3AF+ 12CSH2+110H 4[C6(A,F)SH32]+2(AF)H3

  47. Interfacial electric double layer

  48. Schematic description of the hydration and structure Development in cement paste.

  49. Effect of SNF on zeta potential in a cement paste

  50. Zeta potential vs admixture concentration of different molecular weight in a cement paste

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