Lecture Asphalt -2024 part 2.pdf

2024-03-20 CIVI321 ENGINEERING MATERIALS Asphalt Cement Grading of Asphalt Cement Asphalt cements are classified based on their rheological and physical properties at temperatures that are representative of their preparation and field conditions. Asphalt cement have traditionally been graded accordi...

2024-03-20 CIVI321 ENGINEERING MATERIALS Asphalt Cement Grading of Asphalt Cement Asphalt cements are classified based on their rheological and physical properties at temperatures that are representative of their preparation and field conditions. Asphalt cement have traditionally been graded according to:  Penetration (PEN) (i.e. Asphalt cement Stiffness)  Viscosity  Performance Grading 1 2024-03-20 1-Penetration (PEN) Test A mass of 100 g is applied to a standard needle at temperature of 25°C and the penetration of the needle in the asphalt cement sample is measured. Penetration is given in units of 0.1 mm and reported in penetration units (e.g. needle penetrates 9 mm, penetration = 90) Needle Sample 2 2024-03-20 Penetration is given in units of 0.1 mm and reported in penetration units (e.g. needle penetrates 9 mm, penetration = 90) The higher the penetration number, the lower the viscosity 3 2024-03-20 Example Penetration test was conducted on two asphalt cement samples. The needle penetrated 8 mm in the first and 28 mm in the second samples. What are their grades, and which one has a higher viscosity? a) 8 mm b) 28 mm 2- Viscosity Grades Are the most widely used (ASTM D-3381). Viscosity is measured at high temperatures 60-135°C  Viscosity on asphalt cement (AC) Based on measurements of absolute viscosity of asphalt tested at 60°C.  Viscosity on aged residue (AR) Based on measurements of absolute viscosity of asphalt tested at 60°C after being aged in rolling thin-film oven 4 2024-03-20 The viscosity of asphalt cements is measured by various techniques:  Capillary flow under gravity (ASTM D2170)  Capillary flow under vacuum (ASTM D2171)  Rotational coaxial-cylinder viscometers (ASTM-D4402)  Dynamic shear rheometers (AASHTO TP5) High temperature range Dynamic shear rheometer. The higher the number of poises, the higher the viscosity 5 2024-03-20 A General Comparison There is a general relationship between stiffness and viscosity. Higher penetration numbers correspond with lower viscosities New 3-Performance-Based Grading System Performance grading (PG) is based on the idea that any asphalt cement properties should be related to the surrounding conditions. 6 2024-03-20 3-Performance-Based Grading System The selection concept is not new :  Same logic to penetration or viscosity graded asphalt binders  But the relationships between asphalt binder properties and conditions of use are more complete and more precise with the PG system. 3-Performance-Based Grading System PG XX YY XX = 7-day maximum pavement temperature, 52 to 70°C YY = minimum expected pavement temperature, -16 to -40°C PG 64-16 Average 7-day maximum pavement temperature in summer near 64°C, and minimum pavement temperature in winter near -16°C. 7 2024-03-20 3-Performance-Based Grading System PG 73-34 Rolling Thin-Film Oven (RTFO) Test Rotational Viscometer Performance Grading Asphalt Binder Tests Pressure Aging Vessel (PAV) Bending Beam Rheometer (BBR) 8 2024-03-20 Asphalt cement Stiffness The deformational behaviour of asphalt cements depends substantially on: Temperature Loading Rate Loading Duration Low temperature and/or short duration: Elastic behaviour High temperature and/or long duration: Viscous behaviour Asphalt cement Stiffness In the practical range of field conditions, the behaviour of asphalt cement lies between these two extremes and can be described in terms of the stiffness or (stiffness modulus): 𝑺𝒕, 𝑻   t,T where: St,T: stiffness or (stiffness modulus) at time t and temperature T. σ : stress at time t and temperature T. ε : strain at time t and temperature T. 9 2024-03-20 Elastic Behaviour S=E Stiffness modulus Viscous-elastic behaviour Viscous behaviour (Newtonian fluid) S=3η/t Time Very long loading time: a viscous Newtonian fluid, stiffness approaches Short loading time: curve horizontal, indicates stiffness ≈ elastic modulus. Intermediate loading time: elastic + viscous, stiffness decreases nonlinearly with loading time. Very long loading time: approaches a viscous Newtonian fluid, stiffness approaches 3 𝑡 10 2024-03-20 At very low temperatures, the asphalt cement is too stiff for its deformation to be tested using the rheological methods. The bending beam rheometer (BBR) method The variation of the deflection versus time is used to determine the stiffness. Mold Sample 11 2024-03-20 12 2024-03-20 13