Stopping distance is considered to be an important factor for providing a safe roadway network to the road users. Stopping distance is defined as the distance that the vehicle travels before it comes to a complete halt by considering both, the braking distance and the brake reaction/perception distance. With the emergence of Autonomous Vehicles (AVs), new challenges regarding stopping distance are currently posed to the engineering community. Depending on their total computational power, AVs can have a quicker perception as compared to human beings which can be standardized. AVs need a well-defined process to estimate the braking distance as they significantly lack the experience of human drivers. Current AI technology utilized by AVs incorporates a constant coefficient of friction (µ) for estimating braking distance and applies various factors of safety for unfavourable driving conditions. Such practices can overestimate the braking distance or sometimes underestimate it. Either estimates are not good for a smooth travel of the autonomous vehicle. This is because the stopping distance depends on the fundamental friction relationship between tire and pavement. A research study considering input of realistic tire-pavement friction, signified by the variable coefficient of friction into AVs AI toolkits has never been performed. The absence of research with respect to realistic coefficient of friction for AVs can be attributed to the fact that tire-pavement contact is a complex interaction to investigate and model.
The goal of this MSc graduation thesis is to develop a methodology for investigating the variable coefficient of friction between tire-tread rubber blocks and aggregate blocks utilizing a Tribometer. A Finite Element Model (FEM) of the interaction between tire-tread rubber blocks and aggregate blocks is developed to upscale the empirical findings from Tribometer tests to a large range of variables. The data obtained from the scientific methodologies is suggested to be incorporated into intelligent stopping distance algorithms in AVs AI toolkit to improve road safety. Such research involving Tribometer to study the coefficient of friction between tire-tread rubber and aggregates has never being performed. The study also investigated the hysteretic friction in tire-tread rubber which has never been performed previously. Key aspects of the thesis project included studying the effect of varying rubber temperature and frequency on the sliding friction between tire-tread rubber blocks and aggregate blocks. The research studied the varying effect of rubber temperature and frequency on the coefficient of friction for two surface conditions, dry/wet and three types of aggregates: Bestone, Scottish granite, cement concrete. The FEM results offered a preliminary insight on the investigated variable coefficient of friction. The scientific findings from the model and empirical results show a dependence of thermomechanical properties of the rubber material and surface conditions on the coefficient of friction between tire-tread rubber blocks and aggregate blocks. The findings indicate that the coefficient of friction decreases with increase in rubber temperature, interaction frequency and lubrication at the contact.

This study investigates the impacts of rejuvenator type/dosage and the aging degree of bitumen on the chemical and rheological properties of rejuvenated bitumen, and propose critical chemo-rheological indicators for evaluating rejuvenation efficiency. Moreover, the potential connections between essential chemical and rheological indices of rejuvenator-aged bitumen blends are explored. Results indicate that chemical indices show linear relationships with rejuvenator dosage and vary depending on the rejuvenator type and aging level of bitumen. All rejuvenators can regenerate certain rheological parameters of aged bitumen to varying degrees, but cannot restore the crossover modulus (Gc). Various rheological indices exhibit different correlations with rejuvenator dosage and sensitivity degrees to the discrepancy in rejuvenator type and aging degree of bitumen. Critical chemical and rheological indicators are proposed based on their sensitivity levels to influence factors, with the aromaticity index (AI), carbonyl index (CI), and sulfoxide index (SI) as effective chemical indices and the complex modulus (G*), crossover frequency (fc), and high-temperature master curve area (AMH) as critical rheological indices for rejuvenation efficiency evaluation. The study finds that the magnitude of rejuvenation efficiency for four rejuvenators is Bio-oil > Engine-oil > Naphthenic-oil > Aromatic-oil, and the linear correlations between the critical chemical and rheological indices, together with their rejuvenation percentages, are significantly affected by the rejuvenator type and aging level of bitumen.@en

Membranes of sufficient bonding characteristics could improve the integrity of the multi-layer structures on orthotropic steel deck bridges (OSBDs), enhancing thus the structural response of these systems and, ultimately, their service life. In this research, full-scale experiments were performed at the LINTRACK accelerated pavement testing facility of the Delft University of Technology to evaluate the performance of two surfacing systems commonly used in the Netherlands, giving emphasis on assessing the interface response of membranes with the surrounding materials. Results indicated that the tensile strains remain almost uniform at the top of porous asphalt, in both transverse and longitudinal directions, as no appreciable loss in stress-carrying capabilities was seen even at the end of the testing program. The sections exhibited similar behaviour in terms of strains, with some differences in strains indicating the impacts of membranes at interfaces. The importance of membranes of the desired bonding characteristics was also reflected by the relative displacement measurements. The relative interlayer slip had been higher in the transverse direction than the longitudinal one, with slightly higher displacements in one of the test sections. Overall, no cracking was observed on either section, and the current findings support the use of membranes between surfacing layers on OSBDs.

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