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A simple rational approach for temperature correction of deflection basins

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A simple rational approach for temperature correction of deflection basins

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    1. A simple rational approach for temperature correction of deflection basins Denis St-Laurent Transports Québec

    2. Contents Objective Background Approach Verification of the approach Conclusion I will define the objective, Briefly talk about the backgroud concerning this problem Explain the approach with all the necessary details (everybody will be able to apply it after that) Show some validation exercise of the approach (including field verification and sensitivity analysis) And concludeI will define the objective, Briefly talk about the backgroud concerning this problem Explain the approach with all the necessary details (everybody will be able to apply it after that) Show some validation exercise of the approach (including field verification and sensitivity analysis) And conclude

    3. Objective Remove temperature effects on measured deflection basins.

    4. Background Surface deflections depends from Loading conditions Distance from load application Pavement properties Layer ticknesses Effective modulus of each layers Type of material and rheology Condition of the material Stress-strain level Temperature environment conditions, etc. Every body knows that ...Every body knows that ...

    5. Background Temperature effects on surface deflections mainly due to temperature effect on the Asphalt modulus other, less important, factors also exists effects on underlying layers ex: change in the granular modulus due to a different asphalt modulus (stress-dependency)

    6. History of the presented approach First developped in 1993-94, home made computer program for DOS

    7. Why a customized approach ? Deflection correction formula in the litterature usually apply only to the center deflection « do » AASHTO design guide (1986-93) Kim and al. (1994)...

    8. Definition Correction factors Asphalt modulus CFE = EAC (at Tref) EAC (at Tmeasured) Deflections CFD = D (at Tref) D (at Tmeasured) A similar ratio is applied (a ratio of modulus or a ration of deflectionsA similar ratio is applied (a ratio of modulus or a ration of deflections

    9. Reasoning of the approach Temperature-DEFLECTION relations more complex than Temperature-MODULUS relations

    10. Reasoning of the approach Theoretical solutions exist to predict deflections from layer moduli (and other parameters)

    11. Procedure for Deflection Correction Factor (CFD)

    12. E1: Asphalt modulus equation

    13. E2: Boussinesq approach

    14. G. Swift ’s (1972) « empirical equation »: Layered model (2 layers)

    15. Model parameters Deflection basin : Def ? E2 H1 Temperature (measure & reference) AC modulus-temperature relation: A, B, etc...

    16. Verification Field verification (4 sections in 1996) Sensitivity analysis and comparison with LTPP data: ? Report FHWA-RD-98-085 from Lukanen, Stubstad and Briggs (2000)

    17. Field verification (Road 269, H1=83mm) Thin asphalt => Only the 2 first sensors are affected by temperatureThin asphalt => Only the 2 first sensors are affected by temperature

    18. Field verification (Road 269, H1=83mm)

    19. Field verification (Road 269, H1=50+150 mm) Thicker asphalt: The temperature effect is visible at at larger distance from loadThicker asphalt: The temperature effect is visible at at larger distance from load

    20. Field verification (Road 269, H1=50+150 mm)

    21. Pay attention to the direction of the arrow: Knowing that we have the neutral line where CFD=1 (no correction at 20°C), here we are going toward this line when we increase the sensor distance. Inverselly, this means that the more your are close from the load; bigger is the need for a temperature correctionPay attention to the direction of the arrow: Knowing that we have the neutral line where CFD=1 (no correction at 20°C), here we are going toward this line when we increase the sensor distance. Inverselly, this means that the more your are close from the load; bigger is the need for a temperature correction

    22. Effect of pavement thickness Here we have the inverse phenomenon when looking at the pavement thickness. We are going away from the neutral line: The thicker is the asphalt, the bigger is the need for a correction factorHere we have the inverse phenomenon when looking at the pavement thickness. We are going away from the neutral line: The thicker is the asphalt, the bigger is the need for a correction factor

    23. Effect of bitumen viscosity

    24. Effect of subgrade stiffness

    25. Conclusion Simple version seems to gives reasonable precision accurate temperature measurement is needed Simplicity of programmation Low computation time Allow Sensitivity analysis

    26. Conclusion Flexibility Sensor positioning Loading conditions Stiffness of subgrade Asphalt thickness and behaviour Evolutivity Allow replacement of mathematical equations May add layers or add stress sensitivity

    27. LIMITATION Small errors on deflection values may lead to large errors in a set of backcalculated modulus NEVER BACKCALCULATE LAYER MODULUS FROM A CORRECTED DEFL. BASIN… Corrected basins are intended for direct interpretation of deflection basins (DMD, SCI, AREA, etc.)

    28. Example of chart for direct interpretation of corrected deflection data

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