Towards a Performance Evaluation Method for Durable and Sustainable Thin Surfacings

Yue Xiao. Towards a Performance Evaluation Method for Durable and Sustainable Thin Surfacings. PhD dissertation, Delft University of Technology, the Netherlands, 2013. ISBN: 978-94-6186-186-3.

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Summary:

Thin surfacings are widely used as surface layers to provide additional functions and to extend the service life of existing pavements. They can protect the treated road surfaces from external aggressive substances, the degeneration process of weather and the ageing caused by Ultraviolet light and oxygen.

Antiskid surfacing is one type of thin surfacings. It refers to road surface treatment which includes high-friction aggregates and an adhesive binder to bond the aggregates to the road surface. Antiskid surfacing is designed to provide skid resistance, which means excellent adhesion property is then necessary for binding the aggregates together on the surface. So binders with high adhesion strength with aggregates are strongly required.

In the Netherlands, most of the airfield runways used tar-containing binders for the antiskid surfacings. Unlike bitumen based materials, tar-containing surface layers, because of the unique chemical and molecular structure of refined tar, are inherently resistant to chemicals and can provide better adhesive property. However, tar-containing binder is toxic and carcinogenic because of its high Polycyclic Aromatic Hydrocarbons (PAHs) content. It cannot meet the Dutch environmental standards and hence will not be allowed for antiskid surfacing on the runways. Therefore, alternatives to tar-containing binders are urgently required. Research on this topic has been being under investigation for a number of years.

This research mainly focuses on the definition of requirements for the alternatives, together with a design approach on thin surfacings. Firstly, specimens with tar-containing antiskid layers on the surface were collected from six airfields’ runways. Fourier Transform Infrared, surface characteristics, tensile adhesion and shear adhesion at the interface were investigated. The tar-containing antiskid layers have a minimum 1.26 mm of texture depth and can keep this texture depth for a long service life. The improved pull test and shear test methods are suitable for evaluating the adhesive properties between thin antiskid surface layer and underlying asphalt mixture layer. The shear strength at the interface between tar-containing antiskid layer and underlying asphalt mixture layer is higher than the value at the interface between asphalt mixture layers. The conclusions from these test results are used as benchmarks for alternative antiskid surfacings.

Secondly, newly designed binders, which are considered as potential binders for antiskid surfacings, were researched. Copolymer modified bitumen emulsion (MBE), 2-component Modified Epoxy Resin (MER) and 2-component Epoxy Modified Bitumen (EMB) were included. The curing behavior, direct tensile strength, high temperature resistance, weather resistance and low temperature relaxation properties were studied by means of Direct Tensile Test, oven ageing and weatherometer ageing, Dynamic Shear Rheometer test, Dynamic Mechanic Thermal Analysis and Relaxation test. Test results indicate that the investigated 2-component epoxy modified bitumen can be designed as a suitable binder for antiskid surfacing, with good high temperature resistance, qualified relaxation behavior, sufficient tensile strength and enough failure strain.

Thirdly, one of the researched 2-component epoxy modified bitumen was then used to design antiskid surfacing in the lab. The surface characteristics, resistance to tensile stress and shear stress were then investigated. Noise-reducing thin surface layers were also included in this research. The results show that EMB based antiskid layer can provide better adhesion at the interface than tar-containing antiskid layer and polymer modified bitumen based antiskid layers.

Fourthly, the Finite Element Models of antiskid surfacing were developed to simulate the loading condition in the antiskid surface layers. The viscoelastic properties of EMB and MBE were used as input. The calculation shows that the antiskid structure has huge influence on the resulting binder behaviors. The stresses generated in the EMB binder are slightly higher than in the MBE binder, while the MBE is subjected to much higher maximum principal strain and shear strain levels. Furthermore, the EMB binder has better ability to recover after loading. The aggregate skeleton has a higher influence on the stresses and strains in the soft MBE binder than on the stresses and strains in the EMB binder.

At the end, some recommendations are given for further research. Trial sections in the field and fuel resistance are suggested. Fatigue property and failure mechanics are also recommended to investigate the damage mechanisms with FEM model.

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