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Senior/Graduate HMA Course. General Rheology. Rheology. Rheology: the study of flow and deformation Constitutive relations fundamental relationships between force and deformation. Rheometers. Equipment used to measure rheology Shear rheometers Drag flow Pressure driven flows
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Senior/Graduate HMA Course General Rheology General Rheology
Rheology • Rheology: • the study of flow and deformation • Constitutive relations • fundamental relationships between force and deformation General Rheology
Rheometers • Equipment used to measure rheology • Shear rheometers • Drag flow • Pressure driven flows • Rheometers for measuring stiffness and strength • Bending beam • Direct tension General Rheology
Shear Rheometers General Rheology
Drag Flow Rheometers • Sliding plate General Rheology
Schematic of Sliding Plate Viscometer Chart Recorder (not to scale) General Rheology
Assumptions • Steady, laminar flow, isothermal flow • No radial or vertical flow • Negligible gravity and end effects General Rheology
Mi t Rq = 2 p Ri2 L q R g = Ro - Ri Narrow gaps: Ri / Ro > 0.99 Drag Flow Rheometers • Concentric Cylinder General Rheology
Drag Flow Rheometers • Cone and Plate Similar triangles for shear flow Homogeneous flow General Rheology
Drag Flow Rheometers • Parallel Plate Shear flow varies with gap height and radius Non-homogeneous flow General Rheology
Assumptions • Steady, laminar, isothermal flow • Negligible body forces • Cylindrical edge General Rheology
Oscillating Plate B C A Fixed Plate B Test operates at 10 rad/sec or 1.59 Hz 360o = 2 p radians per circle 1 rad = 57.3o Time A A C 1 cycle General Rheology
Elastic Viscous B Strain Time A A C Strain out-of-phase d = 90o Strain in-phase d = 0o General Rheology
Complex Modulus, G* Viscous Modulus, G” d Storage Modulus, G’ Complex Modulus is the vector sum of the storage and viscous modulus General Rheology
Master Curves • DSR testing can be used to develop master curves • Need range of temps and frequencies at each temperature • Information • Affect of loading time on asphalt binder stiffness • Estimate of thermal coefficient of expansion General Rheology
Equipment Example General Rheology
Equipment Examples General Rheology
Equipment Example 25 mm Plate with Sample General Rheology
Pressure Driven Rheometers • Vacuum Viscometer Shear Stress Profile Velocity Profile General Rheology
Viscometer Tube • Asphalt Institute Tube General Rheology
Stiffness and Strength Rheometers General Rheology
Bending Beam Rheometer Computer Deflection Transducer Air Bearing Load Cell Fluid Bath General Rheology
Bending Beam Rheometer • S(t) = P L3 4 b h3d (t) Where: S(t) = creep stiffness (M Pa) at time, t P = applied constant load, N L = distance between beam supports (102 mm) b = beam width, 12.5 mm h = beam thickness, 6.25 mm d(t) = deflection (mm) at time, t General Rheology
Bending Beam Rheometer • Evaluates low temperature stiffness properties • Creep stiffness • Slope of response (called m-value) Log Creep Stiffness, S(t) 8 15 30 60 120 240 Log Loading Time, t (sec) General Rheology
Load Direct Tension Test Stress = s = P / A sf DL DLe ef Strain General Rheology
Equipment Example Fluid Bath Loading Ram Cooling System General Rheology
Direct Tension Test General Rheology
QUESTIONS? General Rheology