Salvatore Mangiafico

Influence of reclaimed asphalt pavement content on complex modulus of asphalt binder blends and corresponding mixes: experimental results and modelling

The objective of the presented study is to determine linear viscoelastic (LVE) properties of corresponding binders and mixes and to check how they change with reclaimed asphalt pavement (RAP) content. The investigation is part of a wider on-going research project, in the framework of a PhD thesis, in collaboration between Université de Lyon/École Nationale Travaux Publics de l’État (ENTPE), EIFFAGE Travaux Publics and Beyond Petroleum. Dynamic shear rheometer and tension/compression (using a Métravib device) complex modulus tests were performed on nine different bitumens, produced as blends of two different base bitumens and RAP-extracted bitumen in various proportions. LVE properties of six asphalt mixes, produced with the same materials and proportions of certain bitumen blends among the nine tested ones, were measured in tension/compression mode. 2 Springs, 2 Parabolic Elements, 1 Dashpot model was used to fit experimental data both for binders and mixes. Shift-Homothety-Shift in time-Shift transformation (developed at ENTPE) was applied to verify the correspondence of LVE behaviours of related binders and mixes.

Quantification of biasing effects during fatigue tests on asphalt mixes: non-linearity, self-heating and thixotropy

Various phenomena other than fatigue (so-called “biasing effects”) occur during laboratory fatigue tests on asphalt mixes because of cyclic loading applications, thus altering experimental results and leading to misleading conclusions. The purpose of the study is to isolate and quantify biasing effects, therefore isolating real fatigue damage. In particular, non-linearity, self-heating and thixotropy (defined as a recoverable viscosity reduction after shear application) were evaluated. Six different mixes were produced using three distinct asphalt binders. Tests were performed in tension/compression mode on cylindrical samples. A particular test procedure was followed, consisting of two parts. In the first part, complex modulus measurements were performed at temperatures from 8°C to 14°C and strain amplitudes from 50 to 110 µm/m, at 10 Hz. Regression equations were fitted in order to evaluate variations of norm of complex modulus and phase angle caused by temperature and strain-level changes around common fatigue test conditions (10°C, 100 µm/m). In the second part of the test, five partial fatigue tests (each one consisting of 100,000 cycles at a 100 µm/m strain amplitude) were performed at 10°C, 10 Hz. After each fatigue lag, a 24 hour rest period was imposed. During rest periods, short complex modulus measurements were performed (10°C, 10 Hz) in order to monitor the recovery of mechanical properties. Surface and internal temperature of samples were constantly measured throughout the entire test, in order to monitor self-heating due to repeated loading. A significant temperature increase was observed during each fatigue lag, while, during rest periods, temperature rapidly decreased to the initial value. Self-heating was observed to be correlated to viscoelastic energy dissipation. The procedure used in the study allowed quantitatively estimating biasing effects. Therefore, unrecovered mechanical properties, due to damage accumulation, were obtained. Ninety per cent of total complex modulus and phase angle variations observed during each fatigue lag were found to be completely reversible. Non-linearity and thixotropy appear to influence mechanical properties variations more importantly than self-heating.

Complex modulus and fatigue performances of bituminous mixtures with reclaimed asphalt pavement and a recycling agent of vegetable origin

The paper focuses on the investigation of the effects of a recycling agent on mechanical performances of bituminous mixtures produced with reclaimed asphalt pavement (RAP). Twenty-one different bituminous mixtures were produced and tested, using three distinct virgin binders (15/25, 35/50 and 70/100 penetration grades), with RAP contents varying from 0% to 60%. Seven of the mixtures were produced by adding a recycling agent of vegetable origin (its content was fixed equal to 3.5% by weight of the RAP binder). One of the mixtures is a 100% RAP mixture, produced only with RAP-extracted binder and aggregates issued from RAP material. Another one is a “perfect” mixture, produced by perfectly blending 70/100 base binder with 60% RAP-extracted binder and using this blend to coat virgin and RAP aggregates. Material properties were investigated using classical tests commonly performed by the road paving industry in Europe, in order to assess the impact of the addition of the recycling agent according to the current standard procedures. In particular, complex modulus |E*| (at 15°C and 10 Hz) and fatigue parameters 6 and 1/b (at 10°C and 25 Hz) were determined by means of two-point bending tests on trapezoidal samples. The addition of the recycling agent was observed to generally lower |E*| and improve fatigue performances of mixtures with a RAP content equal or greater than 40%.

Statistical Analysis of Influence of Mix Design Parameters on Mechanical Properties of Mixes with Reclaimed Asphalt Pavement

The objective of this study was to evaluate statistically whether and how various mix design parameters influenced the complex modulus and fatigue resistance of asphalt mixes produced with reclaimed asphalt pavement material. Sixteen asphalt mixes were tested by following a 25-1 fractional factorial experimental design. Five mix design variables (considered as two-level factors) were selected: aggregate nature (limestone versus basalt), grading curve (continuous versus gap-graded), filler nature (limestone versus hydrated lime), binder content (4.35% versus 5.35%), and binder nature (35/50 versus 35/50 B). Analysis of variance was performed on experimental results obtained for three responses (used in the French pavement design guide): complex modulus |E*| (158C, 10 Hz) and fatigue parameters ∊6 and 1/b (10°C, 25 Hz). Main effects of all factors and their interactions with binder content were monitored. All factors appeared to have had a statistically significant influence on complex modulus |E*|. All factors except filler nature showed a significant effect on fatigue parameter ∊6. For both complex modulus |E*| and fatigue parameter ∊6, a significant interaction was observed between the effects of binder content and binder nature. For this reason, the influence of those two factors was mutually dependent, and they could not be evaluated separately. No conclusions could be drawn about the influence of mix design factors on fatigue parameter 1/b.

Biasing effects (non-linearity, self-heating, thixotropy) occurring during fatigue tests on bituminous mixtures

The study presented in the paper focuses on the evaluation of biasing effects occurring during laboratory fatigue tests on bituminous mixtures. The impact of biasing effects on complex modulus (norm and phase angle) values obtained during tests is estimated. Six mixtures were produced with three distinct base bitumens, including both modified and unmodified binders, and with varying contents of Reclaimed Asphalt Pavement (RAP), from 0% to 40%. Strain-controlled tension/compression tests were conducted on cylindrical samples according to a procedure specifically developed at the ENTPE, called ALFABET (Advanced Laboratory Fatigue And Biasing Effects Test). The test procedure is composed of an initial series of short complex modulus tests at varying temperatures and strain amplitudes, followed by five partial fatigue tests. After each fatigue period, a 24 hour rest period is observed, during which short complex modulus tests are performed in order to monitor recovery of mechanical properties. Surface and internal temperatures of samples are constantly monitored throughout the test. Biasing effects were isolated and quantitatively estimated. The influence of non-linearity, self-heating and thixotropy on norm of complex modulus and phase angle of bituminous mixtures was evaluated, both in absolute and relative terms, with respect to initial values obtained in undamaged conditions.

Bitumen fatigue performance evaluation - with or without RAP - a real challenge

Bitumen plays an important role in asphalt pavement fatigue. For normal paving grade bitumen fatigue performance generally improves with increasing penetration. However, this general rule does not hold for special binders like high stiffness binders, polymer modified bitumen and Multigrade bitumen. An estimation of the fatigue performance becomes even more difficult when part of the bitumen comes from reclaimed asphalt pavements (RAP). Evaluation of bitumen fatigue performance and the effect of RAP bitumen on bitumen fatigue performance are the main topics of this paper. The fatigue performance of 10 binders was investigated with a DSR time sweep test at constant strain amplitude. The binders were tested with and without bitumen that was recovered from RAP. Addition of up to 40 % RAP bitumen has various but little effect on the fatigue performance of standard paving grade bitumen but for the better performing bitumen products the shear strain amplitudes corresponding to a fatigue life of 10^6 cycles decreases significantly. When all 10 bitumen products with known significant differences in fatigue performance are considered, a good correlation with asphalt fatigue performance as measured with the 2-point bending test is observed. The DSR time sweep test method is not a practical tool to asses fatigue performance of bitumen as it takes a long time to complete the tests and reproducibility is poor. A number of binders have been tested according to the recently developed Linear Amplitude Sweep (LAS) test to investigate if this test has potential as practical test method to evaluate fatigue performance of bitumen. Some of the results presented in this paper are from a research project that has been carried out in collaboration between ENTPE in Lyon, EIFFAGE and BP. This research addressed the influence of asphalt mix design parameters on the mechanical response of bituminous mixtures produced with RAP. Scope and some of the main findings and conclusions of this work have already been presented at different international congresses and in a number of scientific publications.

Complex Modulus and Fatigue Resistance of Different Bituminous Binders and Corresponding Mixtures Containing Reclaimed Asphalt Pavement

The objective of the paper is to investigate the influence of bitumen nature on complex modulus and fatigue resistance of bituminous mixtures produced with reclaimed asphalt pavement (RAP). Eight distinct mixtures were produced with eight different modified and unmodified base binders. RAP content was fixed equal to 20% for all mixtures. For each mixture, the corresponding binder blend was produced by mixing the base binder with RAP-extracted binder, in the same proportions. A total of 16 binders (eight base binders and eight binder blends) were therefore used in the study. Both advanced and classical tests commonly used by road paving industry in Europe were performed. Complex modulus (at 15°C and 10 Hz) and fatigue (at 10°C and 25 Hz) DSR tests were carried out on all binders. Two-point bending complex modulus (at 15°C and 10 Hz) and fatigue (at 10°C and 25 Hz) tests were carried out on trapezoidal samples of mixtures. Complex modulus and fatigue resistance of mixtures appeared to vary significantly depending on the nature of the base binder. However, clear correspondences between values obtained for mixtures and corresponding binders could not be found.