Browsing by Author "Hoffmann, Olivier"

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    Development of Simple Asphalt Test for Determination of RAP Blending Charts
    (2004-06-01) Zofka, Adam; Marasteanu, Mihai O; Clyne, Timothy R; Li, Xinjun; Hoffmann, Olivier
    There are two main reasons why the use of RAP (reclaimed asphalt pavement) as a construction material is profitable. First, the use of RAP is economical and can reduce material and disposal problems. Second, using RAP conserves natural resources. According to Federal Highway Administration (FHWA) nearly 30 million tons of RAP are recycled into Hot Mix Asphalt (HMA) pavements every year and thus RAP is the most recycled material in the United States. The purpose of this study was to investigate the possibility of developing a simple test that could be used to obtain asphalt binder properties that are required in developing blending charts to select the appropriate percentage of RAP. Based on the laboratory testing and data analysis it was found that Bending Beam Rheometer (BBR) tests performed on thin beams of asphalt mixture can be successfully applied into derivation of the creep compliance (and stiffness) of asphalt mixtures. It was shown that recently proposed Hirsch model can be then used to back-calculate the binder stiffness. The detailed procedure that leads to constructing blending charts and obtaining the critical temperatures was proposed. It was concluded that additional research is needed to further investigate Hirsch model and refine it to obtain reasonable stiffness values and binder m-values. It is recommended to employ the proposed procedure only in low temperature grading since the addition of RAP affects mostly the low temperature PG limit.
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    Enhancements and Verification Tests for Portable Deflectometers
    (2002-02-01) Hoffmann, Olivier; Guzina, Bojan; Drescher, Andrew
    In this study, the accuracy of the stiffness estimate from portable deflectometer devices is investigated, based upon the example of a particular device, the Portable Falling Weight Deflectometer PRIMA 100. A laboratory calibration setup, assembly comporting a simply supported steel beam of variable span, is designed to verify the calibration of the device (sensors and data interpretation method). Associated with the tester apparatus, an enhanced setup for the portable device is examined. From verification of the stiffness estimated from the portable device against the known stiffness of the beam the inconsistency of the data interpretation method using peak values of load and displacement time histories is pointed out. An alternative method using Frequency Response Functions, spectral average, Single Degree of Freedom System analog, zero frequency estimates and curve fitting is proposed to extract the static stiffness from PRIMA measurements. Test results show the good agreement between estimates stemming from the modified analysis and true beam stiffness. Baseline for the application of both the alternative method and the enhanced device setup to quality control field measurements is proposed.