Hugo Manuel Ribeiro Dias da Silva

Changes in Rubber Due to its Interaction with Bitumen when Producing Asphalt Rubber

ABSTRACT The negative impact of the used tires residues can be reduced by reusing their rubber as a constituent of asphalt rubber (AR) mixtures, thus contributing for a sustainable development of road infrastructures. However, the increasing demands on the durability of pavements require a deeper knowledge about the physicochemical changes of the AR binders. The main objective of this research is to characterize the influence of bitumen in the rubber morphology and the changes in the density of bitumen, rubber and AR during its production. Four base bitumens interacted with crumb rubber in order to produce AR binders, which were then separated by using a modified “basket drainage method”. The changes in rubber were studied through microscopy, swelling and depolymerization tests. It was concluded that i) the rubber particles swelled 250% their weight, but only increased 2.5% their equivalent diameter; ii) rubber particles can swell till saturation after interacting with softer bitumens; iii) re-vulcanization and re-polymerization among the rubber particles can eventually occur.

Rheological changes in the bitumen caused by heating and interaction with rubber during asphalt-rubber production

The demand for more safe and durable roads, combined with the need to preserve the environment, led to the production and application of asphalt–rubber (AR) on roads. Nevertheless, this complex material needs further study in order to better distinguish among the phenomena that take place during AR production, as they impact on the final product characteristics. Here, we effectively quantify the rheological changes related to bitumen aging due to diffusion of small molecules of bitumen into the rubber particles and to the release of fillers from rubber into the bitumen during AR production. “A sphere AR production simulator” was developed to assess AR aging independently. The comparison of the characteristic relaxation times of both AR and simulated AR shows that the aging alone cannot explain the rheological changes during AR production. The extent of the changes related to the combined effects of aging and filler release increases as the bitumen used to produce AR is softer.

Asphalt surface mixtures with improved performance using waste polymers via dry and wet processes

AbstractThe mechanical performance of a typical surface course mixture, modified with two different plastic wastes, both via the wet and dry processes, was evaluated in this study. Water sensitivit...

Comparison between tensile, stiffness and fatigue life tests results

A laboratory mechanical test is being implemented in the University of Minho to evaluate the asphalt/interaction. This test measures the tensile properties of the bituminous mixture in the interface between the asphalt and the aggregates. By using the tensile test it is intended to observe how the asphalt-aggregate interaction influences the mechanical properties of the bituminous mixtures, namely, stiffness modulus and fatigue life. The tensile test results must have a good correlation to the ones of the stiffness and fatigue life tests in order to assure that the tensile test can be used to investigate the influence of the asphalt-aggregate interaction in the mechanical behaviour of the bituminous mixtures. Thus, this paper presents the comparison between the tensile strength results and the fatigue life and stiffness modulus results of the corresponding mixtures. For the covering abstract see ITRD E117423.

Mechanical, surface and environmental evaluation of stone mastic asphalt mixtures with advanced asphalt binders using waste materials

The reuse of waste materials in asphalt mixtures has been recently investigated, in order to develop new sustainable solutions for the road-paving industry. Such materials should improve the mechanical performance and provide safe/comfortable pavement surface courses for road users, without compromising their environmental performance. Thus, the aim of this study is to evaluate the mechanical, surface and environmental properties of stone mastic asphalt (SMA) mixtures produced with forward-looking asphalt binders incorporating waste materials. These binders were designed to maximise the waste material content using motor oil, high-density polyethylene, styrene–butadiene–styrene and crumb rubber, while performing so well as a commercial modified bitumen. Finally, the overall performance of the SMA mixtures produced with the selected binders was evaluated. It was concluded that these mixtures improve the water sensitivity, fatigue cracking and permanent deformation performance. The requirements for macrotexture, skid resistance and presence of heavy metals in leachates of these mixtures were similarly fulfilled. Thus, this work shows that new asphalt mixtures with waste materials can be used in road-paving works to improve the performance without compromising human and environmental safety.

Development of a laboratory test for characterization of asphalt – aggregate adhesion

The mechanical properties of bituminous mixtures depend on the adhesion between mastic and aggregate, as well as on the cohesion within the mastic. These properties vary as a function of the composition of the bituminous mixture, of the chemical and physical features of the aggregate and bitumen and of the condition under which the mixing is carried out. It is thus fundamental to develop an adhesion test, which is of easy execution and, at the same time, represents correctly the bituminous mixture and its mechanical behaviour, essentially the aggregate-mastic adhesion. The test described here simulates the behaviour of a small representative specimen of the bituminous material subject to increasing tension or shear force, inducing rupture of the aggregate-mastic bond. The specimens have a prismatic shape and comprise a single large piece of aggregate between two layers of mastic. The efficiency of the aggregate-mastic bond will be evaluated by the necessary force to rupture the specimen and by the form of rupture. The results obtained from this test will not only allow the features which most influence the adhesion of mastic to aggregate to be established, but also reveal the best aggregate-fines-binder combinations as a function of the type of aggregate and bituminous mixture. For the covering abstract see ITRD E117840.