Sandra Erkens

A Note on Fatigue Bending Tests Using a Haversine Loading

ABSTRACT Four point bending fatigue tests under haversine and pure sinusoidal loading is discussed from a theoretical point of view. In this discussion the material is considered to be visco-elastic rather than linear elastic. The differences between the two types of loading in force control are easily understood, but for deformation controlled tests the effect of different signals is less obvious. Tests that were performed to verify the theoretical considerations seem to indicate that the effect is different for different mixtures. The implication is that the results of fatigue tests under different loading signals cannot readily be compared.

Study of Asphalt Binder Fatigue with a New Dynamic Shear Rheometer Geometry

With the effort to precisely predict the lifetime of asphalt binders and subsequently optimize their utilization in a more economical way, the objective of this study was to introduce a new methodology to improve the fatigue characterization of asphalt binders through a new dynamic shear rheometer (DSR) sample testing geometry. Initially, numerical analyses were performed to study the geometry-related issues of a standard DSR sample on time sweep tests, and to assist in the effort to increase understanding of the DSR damage phenomena of asphalt samples. On the basis of these numerical analyses, a new testing geometry, the parallel hollow plate, was developed and its test results compared with the standard sample testing geometry. A single type of asphalt binder was assessed using amplitude sweep tests. The obtained results demonstrated a significant difference between the fatigue of the two sets of DSR sample geometries. On the basis of these, time sweep tests were conducted for the same sample geometries and the results demonstrated that the new testing geometry yields material response consistency under different loading conditions. The lifetime prediction of the standard parallel plates showed a significant difference with the newly developed DSR sample testing geometry by overestimating the total number of cycles until asphalt binder failure. The new testing geometry allowed the isolation of the damaged area of asphalt binder by localizing the shear stresses in the samples’ periphery.

The influence of boundary conditions on the healing of bitumen

Damage in pavements is known to reduce over time when the material is left to rest, this phenomenon is identified as healing. It has been shown that healing has a large influence on pavement performance. However, as the healing mechanism is not fully understood, there is currently no accepted method available to assess the healing performance of an asphalt binder. Healing of cracks can be seen as the sum of two processes, cracked surfaces coming into contact (wetting) and strength gain of the contact area (intrinsic healing). This paper aims to increase the understanding of the process of two surfaces coming into contact. Healing of bitumen is assessed using a novel test method, which allows for controlled variation of the stress state during healing. This method consists of bringing two pieces of bitumen together and allowing them to heal under controlled conditions. The extent of healing is then assessed by testing the healed specimens in direct tension. The results, presented in this paper, show that the stress state at assembly and during healing has a significant impact on the extent of healing.

Infrastructure for Automated and Connected Driving: State of the Art and Future Research Directions

The integration of automated and connected vehicles on our existing road network is expected to impact traffic efficiency and safety. This upcoming new reality causes road operators, researchers, and policy makers to raise critical questions on the requirements and implications of automated and connected vehicles on the road infrastructure. We present a state of the art on this topic while considering both the digital and the physical infrastructure. A considerable research effort exists with respect to the digital infrastructure, while for the physical infrastructure it is scarce. Based on the state of the art, and a brainstorming workshop involving experts from different disciplines in the Netherlands, a detailed mind map is presented and recommendations for future research directions are suggested.

Ageing Effect on Chemo-Mechanics of Bitumen

Ageing has a significant impact on the chemical and mechanical behavior of bituminous materials. In this study, Fourier Transform Infrared (FTIR) spectrometer and Dynamic Shear Rheometer (DSR) tests were utilized to investigate the effect of ageing on the chemical and mechanical properties of bitumen. Bitumen films with thickness of 2 mm were exposed to laboratory ageing at various conditions. Specifically, different combinations of ageing time, temperature and pressure were applied on the materials. The FTIR results were used to quantify the changes in the chemical functional groups and to calculate the combined ageing index (summation of carbonyl and sulfoxide indices) of bitumen. In addition, the DSR test results were analyzed to determine the evolution of the crossover frequency and crossover modulus with ageing. A linear relationship was found between the combined ageing index and the distance in the crossover map, providing thus a chemo-mechanics framework to describe bitumen ageing.

Mechanisms in Healing of Bitumen and the Impact of Normal Force

Damage in pavements is known to reduce over time when the material is left to rest, this phenomenon is known as healing. It has been shown that healing is an important influence factor in pavement performance. However, an accepted method to assess the healing capability of a pavement is currently not available. Healing of cracks is assumed to be the sum of two processes, cracked surfaces coming into contact (wetting) and strength gain of surfaces in contact (intrinsic healing). The paper describes influencing parameters of these two processes. The healing potential of bitumen is assessed using a novel test method. In this method two pieces of bitumen are brought together and left to heal under controlled conditions. After healing the amount of healing is assessed by testing the specimens using a direct tensile test. From the results it can be seen that normal force has a significant impact on the observed healing, indicating that the process of two surfaces coming into contact (wetting) has a significant impact on healing behavior of the bitumen.

American and European Mix Design Approaches Combined: Use of NCHRP Performance Indicators to Analyze Comité Européen de Normalisation Test Results

This paper describes a project that is part of NL-LAB, a larger, long-term program at Delft University of Technology, Netherlands, which aims to establish the predictive capacity of the current European functional tests for Dutch asphalt concrete (AC) mixtures. In this NL-LAB program, the functional characteristics of resistance to rutting (EN 12697–25), fatigue (EN 12679-24), stiffness (EN 12697–26), and moisture sensitivity (EN 12697-12 and EN 12697–23) are determined for specimens that are (a) mixed and compacted in the lab, (b) mixed in the plant and compacted in the lab, and (c) mixed in the plant and compacted in the road. Eventually, these tests will provide insight into the effect of mixing and compaction on the functional characteristics. The project described in this paper focused on the indirect tensile strength (ITS) and the triaxial cyclic compression test for two AC mixes. The properties found for all three stages of preparation were analyzed with the use of formalistic expressions from the NCHRP Design Guide 1–37A, Level 2, for the estimation of performance indicators. This project aimed to see if these relations remained valid for the Comité Européen de Normalisation tests, especially for mixes with high recycled asphalt pavement content. In the Netherlands, 50% reclaimed asphalt pavement is standard. It was found that the NCHRP Design Guide 1–37A expressions fit the Comité Européen de Normalisation test data quite well for the reclaimed asphalt pavement that contained mixes, especially for the ITS. Currently, another two construction projects are being sampled, and the results will be used to validate and improve the relations.