METHOD FOR DETERMINING THE SENSITIVITY TO OXIDATION OF A BITUMINOUS BINDER BY ELECTRON SPIN RESONANCE

Abstract

This invention concerns a method for analysing the ageing stability of a bituminous binder, in particular by reference to its susceptibility to oxidation, by analysing a sample of the bituminous binder by means of electron spin resonance and measuring the integral of the signal of the carbon-centred stable radicals; accelerated ageing of the bituminous binder, comprising: i) heating the bituminous binder, followed by ii) heating the bituminous binder resulting from step i) under pressure; analysing a sample of the aged bituminous binder obtained from step b) by means of electron spin resonance and measuring the integral of the signal of the carbon-centred stable radicals; and comparing the integral of the signal of the carbon-centred stable radicals of the bituminous binder obtained from the first step and that obtained from the previous step.

Claims

1. A method for analysing the ageing stability of a bituminous binder, in particular by reference to its susceptibility to oxidation, comprising: analysing a sample of the bituminous binder by means of electron spin resonance and measuring the integral of the signal of the carbon-centred stable radicals; accelerated ageing of the bituminous binder, comprising: i) heating the bituminous binder, followed by ii) heating the bituminous binder resulting from step i) under pressure; analysing a sample of the aged bituminous binder obtained from the accelerated ageing step by means of electron spin resonance and measuring the integral of the signal of the carbon-centred stable radicals; and comparing the integral of the signal of the carbon-centred stable radicals of the bituminous binder obtained from the analysing step and that obtained from the analyzing the aged sample step.

2. The method according to claim 1, wherein step i) of accelerated ageing of the bituminous binder takes place between 100 and 200° C. for a duration of between 5 and 200 min.

3. The method according to claim 1, wherein step ii) of accelerated ageing of the bituminous binder occurs between 50 and 150° C., at a pressure ranging from 0.5-5 MPa, over a duration of between 1 and 100 h.

4. The method according to claim 1, wherein step i) of accelerated ageing of the bituminous binder corresponds to a Rolling Thin Film Over Test.

5. The method according to claim 1, wherein step ii) of accelerated ageing of the bituminous binder corresponds to a long-term accelerated ageing test in a pressure ageing vessel.

6. A method for classifying a bituminous binder as a function of its ageing stability, in particular as a function of its susceptibility to oxidation, comprising: analysing a sample of the bituminous binder by means of electron spin resonance and measuring the integral of the signal of the carbon-centred stable radicals; accelerated ageing of the bituminous binder; analysing a sample of the aged bituminous binder obtained from step 2) by means of electron spin resonance and measuring the integral of the signal of the carbon-centred stable radicals; determining the percent increase in the number of carbon-centred stable radicals in the bituminous binder by comparing the integral of the signal of the carbon-centred stable radicals of the bituminous binder obtained in the analysing step and that obtained in the analysing the aged sample step; and determining the level of susceptibility of the bituminous binder: low in the case of an increase in the number of stable radicals of less than 60%; medium in the case of an increase in the number of stable radicals of 60-80%, or high in the case of an increase in the number of stable radicals of more than 80%.

7. The method according to claim 6, wherein the accelerated ageing of the bituminous binder comprises: i) heating the bituminous binder, followed by ii) heating the bituminous binder resulting from step i) under pressure.

8. The method according to claim 6, wherein the level of susceptibility of the bituminous binder is: extremely low in the case of an increase in the number of stable radicals of less than 40%; very low in the case of an increase in the number of stable radicals of 40-50%, low in the case of an increase in the number of stable radicals of 50-60%, medium in the case of an increase in the number of stable radicals of 60-70%, medium-high in the case of an increase in the number of stable radicals of 70-80%, high in the case of an increase in the number of stable radicals in the number of stable radicals of 80-90%, or very high in the case of an increase in the number of stable radicals of more than 90%.

9. A method for continuous monitoring of the production of a bituminous binder, wherein the method is used on a production line in a refinery, wherein the continuously produced bituminous binder is regularly analysed according to the classification method according to claim 6.

10. A method for quality control of a bituminous binder, wherein the bituminous binder is analysed at the end of the production process by the classification method according to claim 6.

11. The method according to claim 7, wherein step i) of accelerated ageing of the bituminous binder takes place between 100 and 200° C. for a duration of between 5 and 200 min.

12. The method according to claim 7, wherein step ii) of accelerated ageing of the bituminous binder occurs between 50 and 150° C., at a pressure ranging from 0.5-5 MPa, over a duration of between 1 and 100 h.

13. The method according to claim 7, wherein step i) of accelerated ageing of the bituminous binder corresponds to a Rolling Thin Film Over Test.

14. The method according to claim 7, wherein step ii) of accelerated ageing of the bituminous binder corresponds to a long-term accelerated ageing test in a pressure ageing vessel.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0060] FIG. 1 shows an ESR spectrum of a bituminous binder.

[0061] FIG. 2 shows the development of the percentage of carbon-centered stable radicals following RTFOT or RTFOT+PAV, normalized relative to the non-aged sample.

DETAILED DESCRIPTION

[0062] The invention will now be described by reference to the following non-limiting examples.

Ageing of Bituminous Binders

[0063] First, the bituminous binder undergoes an RTFOT test, in which a thin film of 80 g of bituminous binder is continuously rotated around the inner surface of a glass bottle at a temperature of 163±0.5° C. The test lasts 75 min, during which hot air is injected every 3-4 s.

[0064] This test is considered a realistic simulation of the conditions experienced by a bituminous binder during use, and is governed by European standard EN 12607-1.

[0065] The bituminous binder then undergoes a second test, the PAV test, in which 50 g of binder that has undergone the RTFOT test is heated at 100° C. for 20 h at a pressure of 2.1 MPa.

[0066] This test allows for a simulation of the ageing of a bituminous binder over a period of 7-10 years of use, and is governed by standard EN 14769.

Preparation of Samples for ESR Analysis

[0067] Prior to the ESR analysis, the aged and non-aged bituminous binders are stored at −20° C. in aluminum receptacles. A sample is taken at a depth of approximately 3 mm using a sharp blade and hand-modelled to obtain a sample of approximately 30 mg, shaped like a grain of rice, 1 cm in length and 3 mm in diameter. The sample is analyzed at 25° C.

ESR Analysis of Samples

[0068] The analyses were conducted in CW (Continuous Wave) mode on a Bruker ELEXSYS-E500 spectrometer. The ESR parameters used are listed in Table 1.

TABLE-US-00001 TABLE 1 Microwave frequency 9.3 ± 0.1 GHz Microwave power 0.25 mW Centre of field 3500 G Field amplitude 150.0 G Amplitude modulation 2 G Modulation frequency 100 KHz Time constant 40.96 ms Acquisition time 60 s

[0069] Table 1. ESR parameters used to analyze the bituminous binder samples.

[0070] A typical ESR spectrum of a bituminous binder sample is shown in FIG. 1. The majority signal corresponds to the carbon-centered stable radicals, and the minority signals on either side of the majority signal correspond to vanadyl ions.

Results

[0071] Nine samples of bituminous binder were analyzed by the method according to the invention.

[0072] The bituminous binders were of various geographic origins (the crudes are Iranian, Venezuelan, Ural, light and heavy Arabian, etc.), all originating from oil refinement, but obtained by different refinement methods: [0073] Y0820-18: 35/50 bitumen from the Feyzin refinery—classic refinement method; [0074] X0490-06: 35/50 bitumen from the Feyzin refinery—classic refinement method; [0075] Y0625-05: 35/50 bitumen from the Donges refinery—classic refinement method; [0076] 16-00-756-10: 35/50 bitumen from the Feyzin refinery—classic refinement method; [0077] X1029-03, X1030-05, and X1031-02: 30/45, bitumens of Cuban origin, refinement method unknown; [0078] 35/50: corresponds to 35/50 bitumen from the Feyzin refinery, classical method; [0079] 70/100 : corresponds to 70/100 bitumen from the Feyzin refinery, obtained by the classical method.

[0080] The ESR spectra of these samples were recorded prior to ageing, following the RTFOT test (step i according to the invention), and then following the RTFOT+PAV tests (steps i) and ii) according to the invention). FIG. 2 shows the development of the percentage of carbon-centered stable radicals following each ageing step, normalized relative to the non-aged sample.

[0081] The RTFOT and RTFOT+PAV tests both result in an increase in the number of carbon-centered stable radicals. Given that, the greater this increase, the greater the susceptibility of the bituminous binder to oxidation, and thus to ageing, it is possible to establish a classification of the 9 bituminous binders tested based on their ageing resistance. However, this classification differs depending on whether the bituminous binder has undergone the RTFOT test only or the RTFOT+PAV test.

[0082] The RTFOT test simulates the conditions experienced by a bituminous binder during initial use, whilst the PAV test allows for a simulation of ageing of a bituminous binder over a period of 7-10 years of use.

[0083] Thus, the results obtained on the bitumens that underwent the RTFOT+PAV test allow for a reliable analysis of the long-term ageing stability of a bituminous binder, whilst an ageing method that only involves heating the bituminous binder for a certain amount of time (e.g., the RTFOT test) does not allow for a rapid, reliable analysis of the ageing stability of a bituminous binder.