Fatigue Characterization of Bituminous Binders Containing Crumb Rubber from End-of-Life Tires

This paper presents the outcomes of an experimental investigation which focused on the fatigue behavior of bituminous binder for paving applications prepared by combining a single reference neat bitumen with different types of crumb rubber products derived from the processing of end-of-life tires. In the laboratory preparation of the blends, crumb rubber dosage was conveniently limited in order to obtain binders characterized by viscosity values compatible with standard operating conditions normally adopted in the production and compaction of bituminous mixtures. Results obtained from time sweep tests carried out in equi-stiffness conditions showed that fatigue performance is enhanced by the use of the considered crumb rubber modifiers with a dosage-dependent improvement of both fatigue life and crack propagation amplitude. Given that the considered crumb rubber products were quite similar, no significant effects were associated to changes of crumb rubber type

Investigating cohesive healing of asphalt binders by means of a dissipated energy approach

The paper reports the results of an experimental investigation in which the cohesive healing properties of different types of asphalt binder were evaluated by means of the dissipated energy ratio approach. A specifically designed testing methodology was proposed which involves comparing the response of binders subjected to continuous oscillatory shear loading carried out without rest periods and with single rest periods introduced at predefined levels of damage A rheological parameter (Healing Ratio) was introduced to quantify the magnitude of healing occurring during rest time and to rank the consequent healing potential of binders. Obtained results indicate that the investigated binders did not completely recover their original fatigue resistance after rest time, confirming the existence of some intrinsic irreversible damage, the amount of which depends on the total damage experienced before load removal. Experimental results also indicate that healing performance of binders can be significantly enhanced by polymer modification. Keywords: Healing, Fatigue, Dissipated energy ratio, Asphalt binder, Polymer modificatio

Evaluation of the anti-rutting potential of polymer-modified binders by means of creep-recovery shear tests

In the experimental study reported in this paper a creep-recovery shear test method was used to evaluate the anti-rutting potential of different polymer-modified bituminous binders. The effects of several factors related to modification were investigated, such as polymer type (SBS, Styrene-Butadiene-Styrene vs. EVA, Ethylene-Vinyl-Acetate), composition (styrene content), structure (linear vs. radial SBS) and dosage (3-6% by weight of the base bitumen). The effect of short-term aging was also considered by comparing binder response before and after treatment with the Rolling Thin-Film Oven Test (RTFOT). Following previous work on the development of the test protocol, experimental results were analyzed by referring to shear modulus curves G(t) and to permanent compliance (JP), obtained by dividing residual strain at the end of the unloading phase by the stress applied during creep loading. Results indicated the effectiveness of the proposed method in discriminating between the behavior of the different polymer-modified binders and in capturing the effects caused by the factors considered in the investigation. Reliable rankings of the binders were established and were explained by referring to the specific behavior of employed modifiers

Fatigue and healing properties of bituminous mastics reinforced with nano-sized additives

The research work described in the paper focused on fatigue and healing properties of bituminous mastics reinforced with nano-sized additives. Commercially available multiwall carbon nanotubes (CNTs) and montmorillonite nanoclay (NC) were combined with a single base bitumen and a standard mineral filler to produce bituminous mastics. These blends were prepared in the laboratory by making use of a technique consisting in simple shear mixing followed by sonication. Fatigue behaviour of mastics under repeated loading was investigated by means of time sweeps performed in the strain-controlled mode at various amplitudes. Healing potential was assessed by adopting a testing protocol specifically conceived to discriminate between recovery of damage induced by fatigue loading and other artefact phenomena which may affect material response. All rheological measurements were carried out with a dynamic shear rheometer in the parallel plates geometry. Outcomes of the experimental investigation were found to be highly dependent on the nature of additive type, as a result of the key role played by interaction mechanisms that nano-particles can establish within the bituminous mastic

Effect of sonication on high temperature properties of bituminous binders reinforced with nano-additives

The study focused on the effect of sonication on high temperature properties of bituminous binders containing carbon nanotubes and nanoclays. Blends at various dosages were prepared in the laboratory according to two techniques, based on sonication and/or shear mixing. Rheological behaviour of binders was investigated, in the unaged and short-term aged state, by means of oscillatory and creep–recovery tests. Experimental results were found to be coherent with interaction phenomena occurring at the nano-scale and indicate that effects caused by sonication on nano-modified blends are not univocal, but are highly dependent on additive type

Life Cycle Assessment of a Sustainable and Innovative Solution for Unpaved Rural Roads

The use of recycled aggregates, including waste materials and by-products, has attracted increasing interest in the last decades as a sustainable and cost-effective solution for the construction and maintenance of road pavements, due to the reduction of excavation operations and depletion of natural resources. Life cycle assessment (LCA) represents a valuable methodology for the evaluation of the environmental sustainability of technologies involving the use of such materials. This paper deals with the LCA of an innovative emulsion-based cold recycled mixture specifically conceived to be used as a sustainable solution for the surface finishing of unpaved rural roads. Two scenarios entailing the employment of recycled or virgin materials were analyzed with the assessment of global warming potential (GWP), energy requirement, and water consumption. Results obtained confirmed that the scenario entailing the use of recycled materials represents the most sustainable and environmentally friendly solution

A novel methodology for the evaluation of low temperature failure properties of asphalt binders

This paper presents the results of an experimental investigation that focused on the failure properties of asphalt binders at low temperatures. A novel test method was developed, based on the use of the dynamic shear rheometer equipped with 4 mm parallel plates. The method entails the application of constant shear strain rates at various temperatures until failure. Test data are modelled by means of the elasticviscoelastic correspondence principle and by thereafter referring to the shear stress at failure, to a purposely defined brittleness index and to a critical brittleness temperature. Results discussed in the paper, which refer to a preliminary set of experimental data, indicate that the proposed methodology may be very effective in evaluating and comparing low temperature failure properties of asphalt binders of various types and origins

Ageing effects on the linear and nonlinear viscoelasticity of bituminous binders

The paper investigates the effects of ageing on the linear and nonlinear viscoelastic properties of bituminous binders for paving applications. Four neat binders were analysed in their unaged state and after long-term ageing, which was simulated in the laboratory with the Rolling Thin Film Oven (RTFO) and the Pressure Ageing Vessel (PAV). Amplitude sweep tests and frequency sweep tests were performed to explore the response in the linear domain. Repeated strain sweep tests were carried out to isolate nonlinearity from other mechanisms related to damage. The time–temperature superposition principle and the generalised Maxwell model with a Prony series discretization were used to describe the overall viscoelastic response of binders, introducing strain-dependent shift factors to account for nonlinearity. Results indicate that the adopted experimental and modelling approach allows a proper assessment of the effects of ageing on viscoelasticity

Fatigue properties of nano-reinforced bituminous mixtures: A viscoelastic continuum damage approach

The experimental investigation described in this paper focused on the effects of nanoclays on the fatigue behaviour of bituminous mixtures. Damage characteristics of a bituminous mixture produced by making use of a nano-reinforced binder were compared to those of a reference mixture obtained by employing the same neat bitumen used as a base in the preparation of the nanoclay–bitumen blend. Dynamic modulus tests and direct tension cyclic fatigue tests were carried out to determine the linear viscoelastic properties and the damage evolution characteristics of materials. Corresponding results were modelled by means of a viscoelastic continuum damage approach and by making use of a more empirical evaluation based on the classical Wöhler representation. It was found that the use of nanoclays produced a reinforcement of bituminous mixtures, the benefits of which were observed both in the progression of damage and in the occurrence of ultimate failure condition

Engineering models for the design of long-lasting, sustainable, cost-efficient and climate-responsive pavements for Ashghal road projects in the State of Qatar

The planning, design, construction and management of modern transportation infrastructures is based on the use of continuously updated methodologies that consider, among others, the concept of sustainability. In such a context, for the specific case of road pavements, it is of crucial importance to carry out quantitative analyses based on the use of optimized engineering models. These models explicitly consider environment-pavement interactions, environmental impacts generated by all the components involved in the supply chain, and financial flows associated to pavement construction and maintenance. Such an approach is being adopted by the Public Works Authority (Ashghal) of the State of Qatar, that is developing and implementing models tailored for its infrastructure projects and local environmental conditions. This paper provides an overview of some of the employed models and methodologies that are based on the physics of pavement structures and on the assessment of environmental and economic indicators. It is shown that such an approach leads to significant improvements to current practice and to the enhanced use of recycled materials, while still guaranteeing required pavement performance