A 5 EE-157 MEASURING THE RHEOLOGICAL PROPERTIES OF BITUMINOUS BINDERS FINAL RESULTS FROM THE ROUND ROBIN TEST OF THE BNPÉ / P 04 / GE 1 WORKING GROUP ( FRANCE )
In a previous paper presented at the 2008 E&E Congress, the French mirror group (BNPé/P04/GE1) of the CEN/TC336 – WG1 committee (bituminous binder) has reported the results of a round robin test on DSR complex modulus measurements involving two paving grade bitumen (10/20 and 50/70 classes) and three modified binders (plastomer, elastomer and cross-linked elastomer). This paper presents the outcome of the follow-up studies which had been decided at the time. In a first step, a number of dedicated investigations have been made to identify the potential contribution of different factors to the variation in measurement results. In particular, the impact of waiting time after test sample preparation, gap setting procedure, bonding temperature, conditioning times and temperature sweep procedure have been investigated. How to establish the limits of the linear domain of visco-elasticity is another issue which has been dealt with. This has allowed to define more stringent operating conditions which have then been followed by the participating laboratories for a final round robin limited to a pure bitumen (50/70) and the “most difficult” PmB (high level of plastomer modified product). In comparison to the first round robin, reproducibility was indeed improved, even for the modified product. The BNPé/P04/GE1 work does thus further open the way for the definition of binder performance indicators based on DSR measurements. This will however only be possible (especially for modified binders) if operating conditions are strictly defined and followed.
RHEOLOGICAL ANALYSIS OF BITUMENS BY DYNAMIC SHEAR RHEOMETER: EFFECT OF THE THERMAL HISTORY ON THE RESULTS
In order to prevent binder-related pavement failures, it is very important to be able to characterize the performances of bituminous binders that play an essential role in the construction and reinforcement of pavements. However, because of its specific and complex composition, bitumen is a visco-elastic material whose intrinsic rheological properties depend upon the temperature and the loading time. One way to characterize this particular behaviour is to measure the response of the material under dynamic loading conditions, for instance in shear mode. The visco-elastic nature at high and intermediate pavement temperatures can then be described by Dynamic Oscillatory Shear Rheometer (DSR) measurements. But, the applicability of the preparation of test samples usually carried out on neat bitumens is now questioned when analyzing, in particular, modified binders: test standardisation becomes more and more necessary with a wide agreement on the required specifications. This paper points out the effect of the test sample preparation on the rheological results obtained by DSR measurements. In this study, two different sample preparations were used to explore the thermal effect: loading the binder into moulds, 24 hours prior to testing in the rheometer, or loading of the sample directly into the plates gap. In order to cover a variety of sampling procedures, a 70/100 penetration grade bitumen was chosen and two Polymer modified Bitumens were manufactured by adding 3% of saturated plastomer (Ethylene/Vinyl Acetate) or 3% of unsaturated elastomer (Styrene/Butadiene/Styrene) to this base bitumen. These three binders were then tested before and after ageing. Moreover, the effect of temperature rising up or going down during testing in the rheometer was determined on a 6% saturated plastomer modified bitumen. Because of this high degree of modification (phase inversion), the temperature effect was exalted. This effect was then studied against both sample preparations previously analysed. In conclusion, the determination of the complex modulus and the phase angle using a Dynamic Shear Rheometer appears to be sensitive to the sample preparation and especially to the thermal history of the binders. Consequently, in order to make relative comparison between samples, it seems very important to have the same sample thermal history. This one appears to be more critical in the case of plastomer modified bitumen. For the covering abstract see ITRD E121480.
Neutron Residual Stress Measurements on Rail Sections for Different Production Conditions
Rail sectioning with subsequent neutron diffraction experiments has been used to assess residual stresses in the rails. In this study we present the results of neutron stress measurements performed at the NIST Center for Neutron Research (NCNR) on rail sections from rails that were produced under various conditions. Specifically, these are air-cooled, air-cooled and roller-straightened, head-hardened and head-hardened and roller-straightened. More significantly, a head-hardened and roller-straightened rail was also studied after service to elucidate evolution of the service-induced residual stresses. In the latter case both a transverse-cut slice and the central region of a 0.53 m long piece were studied. Measurements on this piece are the first in which triaxial stresses have been determined for an intact rail. Neutron strain measurements with 3×3×3 mm3 spatial resolution were successfully employed for transversally cut slices to verify the difference in the stress state depending on the production process. Although examination of slices allows determination of only two-dimensional stresses in the plane of the slice, additional measurements on obliquely-cut slices, which were also carried out, and utilization of FEM gives the possibility of reconstructing the full triaxial stress distribution. Together, these approaches provide a better understanding of rail fabrication and the possibility of improving the durability and safety of rails in the future.Copyright © 2004 by ASME