Ionic Liquid Incorporation for Self Healing Purposes: New Measuring Methods for Bitumen Binder, Applications to Asphalt Concrete and Understanding of Chemical Interactions

Asphalt concrete is the most commonly used material in pavement industry. It is prepared by mixing bitumen, which is the bottom product of crude oil distillation, and aggregates at temperatures around 180 ⁰C. Asphalt concrete, once paved in the roads, experiences traffic loading along with changes in the ambient temperature throughout its service life. Thereby, failures in asphalt pavement such as fatigue cracking, rutting and thermal cracking, occur due to these continuous loading and climatic conditions. The mentioned failures in the roads give rise to building of new roads or maintaining the damaged roads. Building new roads or maintaining the already built ones requires preparation of asphalt mixtures, which consume large amounts of hydrocarbons, bitumen, together with excess energy due to high mixing temperatures. In addition to the large resource and energy consumptions, heating the mixture to high temperatures results in emission of greenhouse gases and bitumen fumes into the air. Therefore, extending the service life of asphalt pavements is very important both from an economic and environmental point of view. Such an improvement would also mean more efficient usage of the fossil resources.

Bitumen, which is the binder of asphalt concretes, is known to have intrinsic self- healing properties. It has the ability to restore its mechanical strength by closing the cracks at high temperatures or during long rest periods. However, during its service life, the asphalt pavement may not always have enough resting periods or the high temperatures which are needed to heal itself. Therefore, improving the self- healing capabilities of bitumen/asphalt is a necessity to minimize the mentioned environmental and economic problems.

In this study, the effects of ionic liquids, which are also known as green solvents, on the self- healing properties of bitumen is studied. 50/70 penetration grade bitumen from Tupras İzmit Refinery is used in the studies. As part of the ionic liquid characterization, Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry and Fourier Transform Infrared Spectroscopy are carried out. The bitumen is characterized by means of TGA, FTIR, DSC, Elemental Analysis and Saturate- Aromatic- Resin- Asphalthene (SARA) fractionation. Two new test methods are developed in order to measure the self- healing capability of bitumen. One of these methods is developed to see the effects of rest periods when intermittent loading is applied on the sample at high temperatures. The other method is developed to investigate the effects of long rest periods on the self- healing capability of bitumen at low temperatures. Measurements are carried out both on unmodified and ionic liquid modified bitumen to investigate the effects of ionic liquids with different side chain lengths on the self- healing properties of the bitumen. In addition to the measurements by the newly-developed techniques, stripping tests are carried out to find out about the effects of different ionic liquids on bitumen- aggregate interactions. Zeta potential measurements are done to quantify the electrostatic interactions between bitumen and aggregates. The asphalt performance of the modified bitumen is measured by Universal Testing Machine with Fatigue test, in which a loading- rest period cycle is applied to the sample until the sample is cracked, and Stiffness tests, which measures the hardness of the asphalt sample.

The results indicated that different ionic liquids have different effects on the bitumen/asphalt properties. With the addition of ionic liquids into bitumen, a 25% improvement in stripping properties, 30% improvement in high temperature self-healing performance, 200% improvement in low temperature performance and 120% improvement in asphalt fatigue life is obtained, meaning that different modification recipes can be used in road pavements depending on the climatic conditions and traffic density.