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

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

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

Advanced fatigue and rutting characterisation of Polish asphalt mixtures based on the VECD model and viscoplastic shift model

The advanced asphalt mixture performance-related specifications (AM-PRS) recently developed in USA can allow an optimisation of the design process of asphalt pavements thanks to the possibility to fully take into account the intrinsic material properties. In this study, four typical Polish mixtures, i.e. a Stone Mastic Asphalt (SMA) for wearing course, two mixtures for binder course with neat bitumen or Polymer modified Bitumen (PmB), and a mixture for asphalt base course with neat bitumen, were investigated by applying such advanced framework. The fatigue performance was studied through the simplified viscoelastic continuum damage (S-VECD) approach, whereas the rutting properties were assessed through the viscoplastic theory of the shift model. The findings were consistent with the composition of the studied mixtures, demonstrating the reliability and applicability of the AM-PRS even for typical Polish mixtures. Specifically, the high amount of soft PmB made the SMA mixture tough against fatigue cracking, but also more prone to rutting. The two binder mixtures exhibited good performance against both fatigue and rutting, and the polymer modification improved the toughness and increased the stiffness at high temperatures. The base mixture is expected to suffer fatigue cracking more than rutting, likely due to the low amount of bitumen and coarser aggregate gradation. These results can be used in the future for pavement performance predictions with FlexPAVE (TM) software programme to ultimately optimise the design of Polish pavements

Experimental investigation on the bond strength between sustainable road bio-binders and aggregate substrates

Interest is growing on the application of bio-binders in road pavements. However, currently there is a lack of data concerning the adhesion between bio-binders and aggregates, which is a crucial aspect to ensure adequate performance and durability of bituminous mixtures, especially in the presence of water. In this regard, the present investigation focuses on the evaluation of the binder bond strength (BBS) between bio-binders, characterized by different percentages of a renewable wood bio-oil and different aging levels, and aggregate substrates (limestone and porphyry), in dry and wet conditions. Preliminarily, the binders were subjected to viscosity tests to determine BBS application temperatures. The main results show that the bio-binders studied exhibit a good adhesion with limestone both in dry and wet conditions as well as with porphyry in dry conditions, resulting in cohesive failures. For porphyry substrate, after wet conditioning, a progressive transition from adhesive to cohesive failures is observed as the bio-oil content increases, indicating that the bio-oil might improve the adhesion between bitumen and siliceous aggregates. Based on previous findings on the chemical characteristics of the bio-binders, the contribution of the bio-oil to the adhesion may be attributed to its high content of esters. Overall, the results suggest that the use of bio-binders in road pavements could lead to significant benefits in terms of performance and resistance to moisture damage

State of the art of tribological tests for bituminous binders

Kinetic friction is a physical phenomenon which originates when two or more bodies are in contact and in relative motion, and causes energy consumption and wear. Lubricants are widely used in many fields to reduce kinetic friction and their behaviour is usually characterized through appropriate tribological tests. In fact, the science of tribology (from the Greek word “tribo” that means to rub and the Latin word “logia” that means study) investigates interactions between surfaces in relative motion. In the field of road materials, during asphalt mixing and compaction, bitumen acts similarly to lubricants, reducing friction between aggregates, and its lubricating properties significantly affect the energy required. According to recent studies, some Warm Mix Asphalt additives are able to reduce production and compaction temperatures (and therefore energy consumption) of asphalt mixtures by potentially improving the lubricating behaviour of the binder. Thus, tribological tests have recently been introduced in the investigation of bituminous binders to characterize their lubricating properties. This paper aims at providing the state of the art of tribological tests currently employed for the study of bituminous binders, as well as useful suggestions for improving these procedures. Since the introduction of such tests in the field of road materials is quite recent, an overview on tribology and tribological tests on common lubricants is presented, with the aim to highlight the main aspects to take into account when applying the tribological characterization of bituminous binders

Prediction of the Long-Term Performance of an Existing Warm Recycled Motorway Pavement

Warm mix asphalt (WMA) technologies allow the production, lay-down and compaction of asphalt mixtures at reduced temperatures and the use of higher amounts of reclaimed asphalt pavement (RAP) with respect to conventional hot mix asphalt (HMA), leading to significant environmental benefits and energy savings. However, limited data is available on the long-term performance of such pavements. The objective of this study was to predict the long-term performance of an existing warm recycled motorway pavement (made with WMA mixtures containing RAP) constructed in 2016 in central Italy, along with the corresponding hot recycled pavement (made with HMA mixtures containing RAP). For this purpose, cores were taken from the pavements in 2022 to investigate the binder and base courses through dynamic modulus and cyclic fatigue tests, according to the simplified viscoelastic continuum damage (S-VECD) testing approach. The results of the tests were used to predict the service life of the pavements using two pieces of software, KENPAVE and FlexPAVE, based respectively on the elastic design method and the viscoelastic design method in the presence of damage. The FlexPAVE results indicated that the expected service life of the WMA pavement is much longer than that of the HMA pavement, mainly because the WMA mixtures have better damage properties than the HMA mixtures. Conversely, the KENPAVE simulations predicted a similar service life for the two pavements, highlighting the impossibility of the elastic method to catch the actual contribution of high-performance non-standard materials. The promising outcomes of the FlexPAVE simulations further encourage the application of warm recycled pavements

Investigation of unaged and long-term aged bio-based asphalt mixtures containing lignin according to the VECD theory

In the near future, the world of civil and building engineering will be dominated by the advent of bio-materials. Even the road paving sector is involved in the transition towards more sustainable solutions, promoting at the same time environmental benefits and economic savings. Currently, one of the main goals is to ensure that bio-binders offer good performance, at least comparable with that offered by conventional materials. In the last decades, the exponential increase in traffic volumes has led to various types of asphalt pavement distresses, among which fatigue cracking is one of the most common. Within this context, this study presents the characterization of a bio-based asphalt mixture obtained by replacing 30% of bitumen with lignin, which was compared with a reference asphalt mixture containing a plain bitumen characterised by the same penetration grade. Laboratory produced and compacted specimens were subjected to complex modulus and cyclic fatigue tests with the Asphalt Mixture Performance Tester (AMPT). Both unaged and long-term aging conditions were investigated. The tests and the subsequent analyses were based on the simplified viscoelastic continuum damage (S-VECD) approach. Overall, the results showed that the presence of lignin led to a lower aging susceptibility, but also caused a slight reduction in fatigue life due to an increase in the material stiffness. Furthermore, the obtained results confirmed previous findings deriving from the study of the two binders and from the conventional characterization of the same asphalt mixtures as well