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.
Role du traitement thermique sur la determination par DSC des caracteristiques thermiques des bitumes routiers
Le comportement thermique de onze bitumes a ete etudie par analyse calorimetrique differentielle (DSC). L'influence des vitesses de chauffe et de refroidissement sur les valeurs des parametres thermiques, tels que la temperature de transition vitreuse Tg et la teneur en fractions cristallisees FC, a ete etudiee dans le domaine de temperature - 100 degres C/120 degres C. L'etat physique initial du bitume, diphasique a temperature ambiante ou monophasique a 120 degres C a egalement ete aborde. La dependance de Tg et de FC avec la vitesse de refroidissement utilisee a ete mise en evidence. En revanche, la vitesse de chauffe et l'etat physique du bitume n'ont que peu d'incidences sur les determinations des parametres thermiques. A partir de ces resultats, un nouveau protocole experimental a ete propose pour la caracterisation thermique des bitumes par DSC. Une etude comparative des resultats obtenus selon l'ancien et le nouveau protocole a ete realisee sur les onze bitumes de l'etude. (A). (Titres en anglais et allemand : Role of heat treatment in the DSC-based determination of the thermal characteristics of road bitumens - ; Einfluss der thermischen Behandlung auf die Bestimmung der therminschen Eigenschaften von Stassenbaubitumen durch DTA).