selected contributions to the rilem sib2015 symposium

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experimental characterization of the 3d linear viscoelastic behavior of cold recycled bitumen emulsion mixtures

Cold mixtures with bitumen emulsion are produced at ambient temperature, leading to substantial reductions of energy consumption and atmospheric emissions. In cold recycling applications, cement is normally used to improve the mixture performance. Thus, the rheological behavior of cold recycled mixtures is different from that of conventional hot mixtures because it is due to the interaction of fresh bitumen, aged bitumen and cementitious bonds. In this study, we investigated the three-dimensional (3D) linear viscoelastic (LVE) behavior of a cement-bitumen treated material (CBTM) mixture fabricated using bitumen emulsion and cement. For comparison, we also investigated the 3D LVE behavior of hot-mix asphalt containing 25% of reclaimed asphalt and fabricated using polymer-modified binder. Sinusoidal axial tests on cylindrical specimens, were carried out at various temperatures (from 0 °C to 50 °C) and frequencies (from 0.1 to 12 Hz). The complex Young's modulus E∗ and the complex Poisson's ratio v∗ were determined through the measurement of axial and transverse strain. We show that when considering E∗, CBTM mixtures may be considered thermo-rheologically simple and the Huet-Sayegh model can be used to simulate the frequency–temperature dependence. On the other hand, when considering v∗ the behavior of CBTM mixtures is very different from that of hot mix asphalt. In particular, its absolute value is almost constant and very close to 0.15. Keywords: Bitumen emulsion, Cold recycling, Complex modulus, Complex Poisson's ratio, Huet-Sayegh mode

Influence of rejuvenators on bitumen ageing in hot recycled asphalt mixtures

The use of reclaimed asphalt pavement (RAP) in new hot mix asphalt (HMA) by means of hot recycling techniques generates the advantage linked to the exploitation of both lytic and bituminous component, consequently leading to the decrease of both virgin aggregates and bitumen supplying. However, many agencies and public administration authorise RAP percentages ranges from 10% to 30% in hot recycling. The main reason for such a low amount of allowable RAP content is related to the aged bitumen contained in the RAP materials, which is more brittle than a virgin bitumen leading to a final mixture more susceptible to fatigue, thermal and reflection cracking. The use of rejuvenators has the potential to restore rheology and chemical components of aged RAP bitumen, thus allowing a significant increase in the amount of RAP to be properly implemented in HMA.The experimental investigation is described in this paper and carried out through a dynamic shear rheometer (DSR) which provides the rheological characterisation of a paving grade bitumen during its overall service life including its reuse in hot recycling by adopting different rejuvenators.Results show that rejuvenators modify bitumen chemistry and consequently rheology by enhancing the viscous response. Moreover, it was observed that oxidation is less harmful, in terms of stiffness increase, on the 50/50 aged bitumen - virgin bitumen blends (rejuvenated or not) than on the virgin bitumen. Moreover, the addition of a rejuvenator in a bituminous blend containing 50% of bitumen reactivated from RAP could lead to a corresponding composite bituminous phase less subjected to ageing phenomena and even less stiff at the end of service life than the associated virgin bitumen alone. Keywords: Rejuvenator, Reclaimed asphalt pavement, Bitumen, Ageing, Dynamic shear rheometer (DSR

Effect of geocomposite reinforcement on the performance of thin asphalt pavements: accelerated pavement testing and laboratory analysis

Abstract The objective of this study is to assess the effect of geocomposite reinforcement on fatigue cracking, reflective cracking and permanent deformation accumulation of thin asphalt pavements. For this purpose, a full-scale trial section was constructed with different interfaces: unreinforced (reference) and reinforced with three types of geocomposites, formed by the combination of a bituminous membrane with a fabric or grid. The experimental program included accelerated pavement testing (APT) carried out by means of Fast Falling Weight Deflectometer (FastFWD) and laboratory tests (three point bending tests) on samples taken from the trial section. After APT, significant permanent deflections were observed, likely due to the plastic yielding of the unbound layers. Nevertheless, all the geocomposites improved the permanent deformation resistance as compared to the unreinforced pavement by reducing the vertical strain at the top of the subgrade. Moreover, the geocomposites increased the energy necessary for the crack propagation by three to eight times with respect to the unreinforced pavement. Overall, these findings indicate that the use of geocomposites can extend the service life of thin asphalt pavements in terms of both cracking and permanent deformation accumulation

Effect of temperature and chemical additives on the short-term ageing of polymer modified bitumen for WMA

Nowadays warm mix asphalt (WMA) is recognized as a very competitive alternative to hot mix asphalt (HMA). This technology allows to obtain an excellent and environmentally-friendly material for road construction. This paper focuses on the effect of a reduced short-term ageing temperature on the binder behaviour and on the effect of WMA chemical additives on the performance of short-term aged binders. Three asphalt binders (one polymer modified bitumen combined with two WMA chemical additives) were aged through the rolling thin film oven test (RTFOT) at different temperatures (120, 130 and 163 °C). Conventional, rheological and chemical tests were used for characterising the binders. Lower ageing temperatures provided reduced oxidation, implying lower oxidative hardening but also reduced permanent deformation resistance. A general reduction of ageing effects is observed in the WMA binders, with both positive (moderate deceleration of the ageing process) and negative (more noticeable reductions in the permanent deformation resistance) outcomes. The microscopic analysis showed that the chemical additive likely alters the structural interactions of bitumen and polymer. A comparison between WMA binders short-term aged in laboratory and in field, indicates that the RTFOT performed at reduced temperature could properly simulate the field ageing when WMA production temperatures are considered. Keywords: WMA, RTFOT, Polymer modified bitumen, Chemical additive, FTIR, DS

Mix design validation through performance-related analysis of in plant asphalt mixtures containing high RAP content

Producing new asphalt mixtures with high content of Reclaimed Asphalt Pavement (RAP) is a major challenge in road construction for economic and environmental reasons. Although many laboratory studies addressed this issue, concerns related to the number of variables involved in the plant production process still limit hot recycling, especially when Styrene–Butadiene–Styrene (SBS) modified bitumens are used. In this sense, plant produced mixtures should be directly investigated to obtain reliable performance evaluations.Given this background, the paper proposes the mechanical characterization of dense-graded mixtures with 40% RAP produced at the asphalt plant as part of rehabilitation activities of an in-service motorway. The Bailey Method was applied to optimize the mix design. Mixtures were prepared by using two polymer modified bitumens (with high and low SBS polymer content) and selected RAP fractions composed only of asphalt layers including SBS modified bitumen itself. An additional mixture prepared according to the current practice for binder layers of motorway pavements was produced for comparison purposes.Advanced laboratory tests allowed the determination of the main material properties (i.e. compactability, cracking and rutting aptitude, indirect tensile strength, fatigue and self-healing). Results showed that mixtures with 40% RAP had performance comparable or even enhanced than the reference mixture especially when prepared with low modified bitumens. Consequently, this study shows that an accurate mix design and the selection of adequate bitumens overcome the potential drawbacks related to the use of high RAP percentage given the possibility to produce suitable recycled mixtures. Keywords: Hot recycling, Compactability, Polymer modified bitumen, SBS, RAP, Mechanical propertie

Top-down cracking in Italian motorway pavements: A case study

Abstract Top-down cracking (TDC) is a distress affecting asphalt pavements and consists of longitudinal cracks that initiate on the pavement surface and propagate downwards. In general, TDC is more critical in the case of thick pavements with open-graded friction course (OGFC), which are the typical characteristics of Italian motorway pavements. Recent surveys showed the presence of many longitudinal cracks potentially ascribable to TDC on Italian motorways. Within this context, this study has two main objectives: 1) to define reliable identification criteria allowing to distinguish between TDC and the other types of longitudinal cracks observed and 2) based on the developed criteria, to quantify TDC in Italian motorway pavements. In this regard, a 200 km long trial network (400 km considering both directions) was studied, taking into account the effect of several variables (e.g. geometric characteristics, traffic level, wearing layer type and climate). For this purpose, images of the trial network acquired during pavement monitoring were visually analysed and some control cores were taken. Specific criteria (which can be used in a pavement management system, PMS) were developed to distinguish between the main types of longitudinal cracks observed on the trial network, i.e. TDC, cracks due to heavy vehicles tire blowout and construction joints, based on their geometric features on the pavement surface. It was found that TDC can affect up to 20–30 % of the slow traffic lane. Specifically, the highest TDC concentrations were observed for high traffic levels and OGFC, whereas TDC was absent in the case of a dense-graded wearing layer. Finally, surprisingly the concentration of tire blowout cracks was even higher than TDC. This study provides evidence on the fact that, for thick pavements with OGFC, TDC has to be considered a priority problem to be addressed in both pavement design and maintenance

Chemical, morphological and rheological characterization of bitumen partially replaced with wood bio-oil: Towards more sustainable materials in road pavements

Nowadays, sustainability and circular economy are two principles to be pursued in all fields. In road pavement engineering, they can be put into practice through the partial substitution of bitumen with industrial residues and by-products deriving from renewable materials. Within this framework, this paper presents an extensive investigation of the chemical, morphological and rheological properties of bio-binders obtained by mixing a conventional 50/70 bitumen with different percentages by weight (0, 5%, 10% and 15%) of a renewable bio-oil, generated as a residue in the processing of wood into pulp and paper. Results show that overall the bio-oil provides a softening effect, which, in terms of performance, leads to an improvement of the low-temperature behaviour and fatigue resistance with respect to the control bitumen, in spite of an increased tendency to permanent deformation. Although no chemical reaction appears to occur after blending, the peculiarities of the bio-oil affect the chemistry of the resulting bio-binders, whereas no phase separation is observed from the microscopic analysis. In addition, a Newtonian behaviour, an unchanged temperature susceptibility and a good fitting of 1S2P1D model to the rheological data are found, regardless of the bio-oil percentage considered. These promising outcomes suggest that such bio-binders can be favourably employed for several applications in road pavements. Keywords: Road materials, Bio-binders, FTIR, SARA, 1S2P1D, Sustainabilit