In the Netherlands, porous asphalt concrete (ZOAB) is used extensively as a wearing course on motorway networks, primarily for its noise-reducing capacity. However, its open structure exposes a large binder surface to moisture, oxygen, and temperature variations, which ages the binder and this makes the mixture prone to ravelling and progressive loss of aggregate from the surface. Previous studies have attributed this distress to, among other factors, the stiffness and relaxation capacity of the mastic, oxidative aging, and moisture resistance of the mixture. To improve the adhesion between the binder and aggregate, and thereby the moisture resistance of the mixture, the Dutch Standard RAW specifications require ZOAB to be produced with a middle filler containing at least 25% calcium hydroxide (Ca(OH)₂), the active component of Hydrated Lime. Literature on the effect of Hydrated Lime on the mastic stiffness, relaxation, aging and moisture strength of ZOAB is limited, even though these properties largely govern the ravelling susceptibility of the mixture. At the same time, ravelling remains the dominant damage type in ZOAB and an important cause of maintenance; therefore, material design choices that improve the resistance to it remain of great interest.
Three commercial limestone fillers containing 0%, 5.7%, and 25.6% Ca(OH)₂ by mass were combined with a single 70/100 penetration-grade bitumen at a filler-to-bitumen ratio of 1, with one aggregate source and one ZOAB 16 grading, so that the filler was the principal variable. Mastics were tested fresh, after aging the complete mastic using an extended pressure aging vessel protocol, and after blending the fillers into bitumen that had been aged before mixing. They were characterized by Dynamic Shear Rheometer through frequency sweeps and relaxation tests, and chemically by Infrared spectroscopy on the extracted binder using the carbonyl and sulfoxide indices. Fresh and oven-aged ZOAB 16 specimens were tested under indirect tension in dry and wet conditions.
In the fresh state, the Ca(OH)₂ content had no measurable effect on the stiffness and relaxation moduli of the mastics, as the differences between the three fillers did not exceed the spread between replicates. Once the binder was oxidized before mixing, the stiffness increased systematically with the Ca(OH)₂ content, by approximately 25% between the lowest and highest contents, which is small compared to the factor of approximately 27 by which the oxidation itself increased the stiffness. The residual relaxation modulus ratio increased from approximately 1% to approximately 10% with aging for all three filler types. The three mastics hardened to the same extent, but the phase angle aging index and carbonyl index were both lowest at 25.6% Ca(OH)₂, indicating a reduced aging effect. At the mixture scale, the dry strength was practically independent of the filler, whereas only the mixture with 25.6% Ca(OH)₂ met the 80% ITSR requirement in the fresh state, at 84% against 71% and 68%, respectively. After mixture aging, all three mixtures exceeded the requirement, indicating that the applied mixture aging protocol was not appropriate for assessing moisture susceptibility in the aged state of the mixtures.
Therefore, the durability-related responses of ZOAB 16 were governed by the oxidation of the bitumen, while the effect of Ca(OH)₂ content was of secondary importance at the mastic scale and appeared only at 25.6% Ca(OH)₂ content. At this content, which corresponds to the filler prescribed by the Dutch specifications, the aged mastics showed the least oxidative change, indicating a reduced oxidative change of the binder, although the age hardening itself, an approximately 27-fold increase in stiffness, was the same for all three fillers. For the moisture resistance of the fresh mixture, the effect of the Ca(OH)₂ content was dominant rather than secondary: only the filler with 25.6% Ca(OH)₂ produced a clear improvement and met the required strength ratio, whereas 5.7% Ca(OH)₂ and the limestone filler without hydrated lime showed no improvement. This dosage dependency supports the rationale for the requirement of at least 25% Ca(OH)₂ in the filler material.
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Re-refined Engine Oil Bottoms (REOB) are a waste product from the re-refining process of waste engine oil. There is a large incentive in the world to produce recycled engine oil and the production of REOB in this process is increasing. On the other hand refineries are going through transitions due to economic and regulatory reasons (i.e. IMO 2020) which has an impact on bitumen production process and its properties. As a result, harder grades bitumen are more readily available compared to the softer grades. Moreover, suppliers that are non-refiners are also part of the bitumen supply chain which has led to more variation in bitumen composition and properties. REOB, among other options of blending components, has posed a solution for this problem; making it possible to reach softer grade bitumen by blending the two. The pavement industry is however facing premature failures of pavements, less workable mixtures, earlier deterioration etc. and the question arises whether the diverse sources of blending components like REOB modification of the bitumen could be the cause of them. There exists no unique identification number (for example the CAS number used in the USA) for REOB as a material in Europe, which makes it untraceable when used in bitumen. While one is not obliged to notify contractors of the use of REOB, there also do not exist any guidelines for its use in asphalt mixtures; thus both the identification of REOB in bitumen as well as a clear evaluation of the bitumen properties and performance is wished for.
By using an extensive amount of chemical experimental tools like: Attenuated Total Reflectance Fourier-Transform Infrared Spectroscopy (ATR-FTIR), X-Ray Fluorescence (XRF), elemental analysis (CHNO+S), iatroscan chromatography (SARA fractioning), Gel Permeation Chromatography (GPC) and Differential Scanning Calorimetry (DSC) the characteristic properties of bitumen modified with REOB are mapped and identification and quantification of REOB in the bitumen is made possible. This is followed up by performing rheological experiments to map viscoelastic properties of the bitumen, using the Dynamic Shear Rheometer (DSR) and Bending Beam Rheometer (BBR). Mechanical performance of the bitumen and asphalt mixtures modified with REOB is evaluated by doing Dynamic Mechanical Analyser (DMA) tests on both cohesive/adhesive behaviour of stone-bitumen film and mastic column tests. Lastly, REOB modified asphalt mixtures are tested with Indirect Tensile (IDT) tests at dry and wet conditions and Cantabro Abrasion tests are done to evaluate impact resistance of the mixtures to simulate ravelling susceptibility.
Using the described approach, this study was able to present a methodology on how to analyse REOB modified bitumen to identify and quantify the presence of REOB and how to evaluate properties and performance of REOB modified bitumen and asphalt mixtures. ... Read more

Asphalt pavements play a crucial role in constructing durable and sustainable road infrastructure. In recent years, with the advancement of sustainability and circular economy goals, reclaimed asphalt (RA) has been widely used in road construction. While the use of RA effectively reduces resource consumption and environmental impact, research on the fatigue and healing performance of asphalt mixtures and binders with high RA content remains relatively limited. This study aims to evaluate the healing performance of binder components from three asphalt mixtures commonly used in the base layers of Dutch pavements, employing multiple healing test protocols and healing indices. Two of these binders contain a high proportion of RA bitumen.

To achieve the research objectives, fatigue and healing tests were conducted on three different asphalt binders: Binder 1, composed entirely of fresh bitumen; Binder 2, a blend of high RA content bitumen with softer fresh bitumen; and Binder 3, which includes high RA bitumen content, fresh bitumen, and the rejuvenator. Fatigue performance was evaluated using Time Sweep (TS) and Linear Amplitude Sweep (LAS) tests to determine the fatigue life of each binder. Additionally, healing performance was assessed through single-rest period and multiple-rest period Time Sweep Healing (TS-H) tests, as well as Linear Amplitude Sweep Healing (LAS-H) tests. To evaluate healing performance, two different indices were used: the Healing Shift Factor (SFh), based on fatigue life extension, and the Healing Index (HI), based on modulus recovery.

The differences between single and multiple rest periods TS-H tests highlight the limitations of single rest period tests in fully capturing material healing capacity, indicating that more complex loading patterns should be explored for more comprehensive assessments. The variations in healing potential results across different test protocols and indices suggest that the healing performance of binders is highly sensitive to test protocol and indices selection.

Based on the described approach, a better understanding of the healing performance of different asphalt binders is achieved. Conclusions and future recommendations for research in this field were provided at the end of this research. ... Read more

The widespread use of traditional bitumen, derived from finite crude oil resources, has led to growing concerns over its environmental impact, long-term availability, and cost. These challenges underscore the urgent need for sustainable, alternative binders in infrastructure applications such as road construction. Although previous research has explored bio-based and recycled waste materials as potential substitutes, these alternatives often fail to meet compatibility, durability, and performance standards.

To overcome these obstacles, this study employs a multifaceted methodology encompassing rheological, chemical, and mechanical analyses, along with environmental assessments. The objective is to develop an alternative binder synthesized from bio-based and waste materials that offers comparable or improved durability and performance. Our findings suggest that the alternative binder presents a viable replacement for traditional, petroleum-based bitumen. This innovation not only enhances the sustainability and circularity of road materials but also mitigates the construction industry's dependence on non-renewable oil resources. ... Read more

The Netherlands has one of the densest road networks with over 140,000 km of roadways. Fatigue cracking is an important distress in flexible pavements. This form of distress results from the application of repeated traffic loading which causes failure. Fatigue cracking assessment on various base layer asphalt mixtures including reclaimed asphalt pavement materials and recycling agents has been addressed in this research work. This research work aims to develop a method for quantifying and assessing this fatigue characterization including the self-healing mechanism of asphalt mixtures using Visco Elastic Continuum Damage Theory. The self-healing in asphalt mixtures was assessed by incorporating group-rest healing periods in a self-developed laboratory testing method. The reliable self-healing models for asphalt mixtures with recycled asphalt materials and recycling agents based on temperature, damage state, and rest periods were predicted using the damage characteristics curve (C-S). Bottom-up cracking in base layer asphalt mixtures was modeled and studied using finite element modeling software FlexPAVE based on the Visco-Elastic Continuum Damage theory. A vivid assessment of mixtures for fatigue and healing characterization is discussed in this research work.

This research work is interrelated with an ongoing project, which aims at developing a protocol to determine the shift factors for the fatigue life of asphalt mixtures to correct healing and aging. The project runs under the umbrella of Knowledge-based Pavement Engineering (KPE), a joint program among Rijkswaterstaat, TNO, and TU Delft. Dura Vermeer is contributing partner to this MSc graduation research work as well.
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This master's thesis addresses a critical gap in the field of road construction by focusing on the limitations of Styrene-Butadiene-Styrene modified bitumen (SBS-MB), a widely-used binder. While SBS-MB offers superior performance, its long-term efficacy is compromised due to various aging processes. Existing rejuvenators are insufficient for restoring the binder's original properties. To remedy this, our research introduces an innovative rejuvenator that provides a more comprehensive restoration of SBS-MB, especially in the reconstruction of the polymer network. The study employs a multifaceted evaluation approach, leading to an enhanced understanding of the rejuvenator's effectiveness and mechanisms of action. Furthermore, we validate the rejuvenator's efficacy using real-world, field-collected materials. The findings not only offer a more effective method for restoring aged SBS-MB but also hold promise for improving the recyclability of Reclaimed Asphalt Pavement (RAP), potentially leading to more sustainable road construction practices, particularly in the Netherlands. ... Read more

The Netherlands is a northwestern European country. The location makes the Netherlands an important entry for trade to the European continent resulting in high traffic intensities [1]. The Netherlands has one of the densest road networks in the world, having over 139.000km of roadways [2, 3]. The understanding of the link between the functional properties and the behavior of the road is crucial [4]. However, predicting such properties is still challenging, and expectations differ from the results found in the field [5, 4]. Data-driven approaches have been part of pavement engineering for decades and have shown to be a powerful tool for performance prediction [6]. This thesis aims to develop a machine learning framework for predicting stiffness, fatigue resistance, resistance to permanent deformation, and water sensitivity. Along with sensitivity analysis to understand the deviations from expectation. The objective is to develop a framework to understand the applicability of machine learning tools and the impacts of the composition parameters into the mix. The models developed applied three different machine learning tools for regression: Support Vector Machine, Random Forests, and Gradient Boosting. The models were compared to a statistical model to validate the work. The statistical approach was a Multiple Linear Regression. All developed models used the database from the NL-LAB project. The machine learning models were compared, and the best-performing proceeded to a sensitivity analysis. The sensitivity analysis used SHAP values, which derive from the Games Theory and have shown to be powerful tools for complex model interpretability [7]. The models had good accuracy prediction. For most properties, machine learning had a higher performance than the statistical model. Gradient Boosting performed the best from the machine learning tools and was selected to finalize the research. The sensitivity analysis had good results, confirming some of the expectations and setting a precedent for researching others. ... Read more

Because of the sustainability transition in the asphalt industry, it is increasingly popular to apply reclaimed asphalt pavement (RAP) instead of new asphalt. Then, less new material is needed and the amount of waste products is reduced. However, there are questions regarding the performance of asphalt mixtures with high RAP percentages, particularly in terms of potentially excessive high stiffness and a decrease in workability. In the Netherlands, a RAP content of 60% in combination with a softer binder is common practice, but an increase in RAP content means that rejuvenators are often required.

The research objective was to study the multi-scale material properties of hot mix asphalt mixtures with high reclaimed asphalt pavement percentages using micromechanics. At binder level, the DSR test was done and it was also used to select and reject the rejuvenators which are applied at mixture level. The chosen rejuvenators, Neomex HR and Cecabase RWI, were applied to the mixtures with 80% RAP. Besides that, a reference mixture was tested with 65% RAP and a reference mixture of 80% RAP. Further, the results were used to fit a modified micromechanical Hirsch model for RAP mixtures with rejuvenators.

Based on the material tests and comparing it with the reference (65% RAP mixture), it turned out that there is potential to implement 80% RAP mixtures. Both moisture sensitivity and the rutting resistance are improved when a higher RAP content is applied, while the total fracture toughness has remained the same. The stiffness of the 80% RAP mixture is substantially higher, but it is still applicable. The biggest concern is the fatigue resistance, because the fatigue resistance of the 80% RAP mixture without rejuvenator is worse for higher strains.

The application of the rejuvenating additives led to the properties of the 80% mixtures being more similar to the 65% RAP mixture and the workability is improved. However, it did appear that the dosage of the additives is on the high side. The stiffness is lower than the reference mixture, especially the mixture with Neomex HR. Also, the rutting resistance is lower than the reference mixture, especially the mixture with Cecabase RWI. Future research may optimize the dosage to improve results.

The micromechanical Hirsch model provided stiffness results with a reasonably accuracy, although this model used general model coefficients. The simplified Hirsch model with inclusion of the factor Pa could not be simply adopted when it is fit for other types of mixtures. The predicted stiffness for all three mixtures was much higher than it actually is. The adjustment of the fitting parameters, according to the laboratory results of the 80% RAP, led to accurate results making the simplified Hirsch model with inclusion of the factor Pa applicable to the mixtures with 80% RAP and a rejuvenating additive.
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Pavement structures are assessed based on its functional and structural capacity in order to evaluate the safety of its use. Structural pavement evaluation is often carried out by road authorities or consulting companies that use non-destructive testing (NDT) methods to assess the remaining life and structural capacity of a road structure at project or network level. In Western Europe and in most parts of the world, the most common equipment used as part of the NDT method is the use of the Falling Weight Deflectometer (FWD). The FWD is able to capture deflection values that can be used for the backcalculation of moduli and to determine remaining life of a structure by mechanistic-empirical equations.
In the Netherlands, like in many other countries, motorways have an increased number traffic flow based on high population densities accumulating in major cities. Due to this, pavement evaluation with stationary equipment such as the FWD can become relatively expensive due to the disruption of traffic. To solve this problem, research institutions and consulting companies have developed different versions of continuous evaluation equipment that are able to perform the structural analysis in a similar way to the FWD. In 2018, Dynatest® launched the Rapid Pavement Tester (RPT or RAPTOR) which aims to perform functional and structural evaluation of road networks at traffic speed. Continuous evaluation devices such as the RAPTOR are in constant development in order to achieve the quality and guaranty of use that equipment such as the FWD have in the pavement engineering industry. Currently this type of device uses technology that is less accurate than the sensors (Geophones) used in FWD equipment. This becomes a significant impediment in the evaluation of high stiffness pavement structures as the calculated deflections are in the lower end of the spectrum. This research aims to find a methodology that can be used in order to find limitation stiffness parameter values for which it is viable to use continuous evaluation equipment. Additionally, this research aims to find a method that can be used in the pavement engineering industry and research that is able to aid the data collection process of pavement layer information by means of machine learning tools. This was a problem faced during the elaboration of this research as the data collected to perform the analysis was incomplete in terms of layer thicknesses information. This process is carried by means of an artificial neural network (ANN) that is able to predict layer thicknesses and moduli based on deflection values and deflection parameters that obtained with the FWD.
The analysis of this research is carried by comparing deflection values in different road networks collected with the FWD and the RAPTOR under similar weather conditions, where the predicted layer information is used to assess the cut-off values and limitations that the current version of the RAPTOR has when compared to the FWD. From the presented results it was found that the asphalt layer modulus showed the highest correlation to the limitation values where the RAPTOR is able to present reliable results when compared to the FWD. Additionally, promising results were found in the use of ANN method to predict missing layer information which are assumed to improve with a specific build in the ANN architecture. ... Read more

The crumb rubber modified bitumen (CRMB) has been utilized in pavement industries to mainly reduce the environmental impacts of the wasted tires by turning unwanted scrap tires into new bituminous materials. However, the relatively high viscosity compared to the conventional asphalt is the major drawback of the CRMB. The higher mixing and working temperatures are thus required in order to achieve the desired workability of the CRMB. This results in more asphalt fume emission, higher energy consumption, and more harmful working environments for workers. Warm mix asphalt (WMA) technologies have been intentionally developed to lower the manufacturing and working temperatures of the asphalt by reducing the viscosity of the asphalt binder. Many studies suggested that coupling CRMB with WMA additives can promote better working conditions and minimize environmental issues of the CRMB.
In this study, experimental works were carried out to evaluate rheological and performance-based properties of the CRMB containing WMA additives in order to investigate the effect of the crumb rubber modifier (CRM) content and WMA additives (wax-based and chemical-base WMA additives) by using only one dynamic shear rheometer (DSR). The performance of the studied binder at high, intermediate, and low road service temperatures were investigated by performing Multiple Stress Creep and Recovery test, Linear Amplitude Sweep test, and 4-mm Dynamic shear rheometer test, respectively. Moreover, the Fourier Transform-Infrared Spectroscopy and the storage stability test were also performed to investigate the effects of the CRM dosage and the WMA additives on the aging susceptibility and the high-temperature storage stability of the binders. The results show that the incorporation of crumb rubber modifier can clearly improve the overall performance (rutting, fatigue damage, low-temperature thermal cracking resistances), and aging resistance of the asphalt binder in a bitumen-level. The high-temperature storage stability of the CRMB became more stable at the higher dosage of the CRM. Moreover, it was found that the wax-based WMA additive can only enhance the high-temperature rutting resistance but negatively impacted the fatigue and low-temperature damage resistances of both neat and CRM binders. The effect of the chemical-based additive on the neat and CRM binders are different as it improved the performance over the whole service temperature of the neat but lowered the damage resistances of CRMBs. Additionally, the addition of both WMA additives decreased the high-temperature storage stability of the CRMB. ... Read more

Skid resistance is an important parameter for road safety and therefore it is essential to monitor the skid resistance of pavements. In the Netherlands, skid resistance is measured with either the RWS Skid Resistance Tester -measuring the longitudinal friction coefficient- or the Seitenkraft-Messverfahren (SKM) -measuring the sideway friction coefficient. The latter is nowadays the preferred measurement device by Rijkswaterstaat. Skid resistance depends much on the vehicle speed: the higher the speed, the lower the skid resistance. Furthermore, the texture of the surface influences the speed dependency. Because it is not always possible to measure the skid resistance at target speeds set by Rijkswaterstaat, there is a demand for a speed conversion model for the skid resistance measured with the SKM. The objective of this research is therefore formulated as follows: the development of a speed conversion model for the wet skid resistance, measured with the SKM at different speeds, taking into account the macrotexture of the road surface. The used dataset consists of 718 sections of 100 metre, measured at the Dutch road network. Measurements were performed at 10 different roads with different pavement layers: porous asphalt, concrete pavements, dense pavements and stone mastic asphalt. The mean profile depth of the pavements varies between 0.21 and 1.80 mm. The performed measuring speeds were 40, 60 and 80 km/h, and for few sections 30 km/h. Three regression methods were performed. Firstly, a multiple linear regression was performed. The datapoints consisted of combinations of two measurements at different speeds on identical 100 metre sections. The second method estimated per 100 metre section a zero speed intercept which was used as a reference point. The third method used multilevel modelling and includes a hierarchical structure. Concluded was that the multiple linear regression on speed combinations is inappropriate for the objective of this research, because of two reasons: the datapoints are dependent on each other, and information is lost by splitting the 100 metre sections into datapoints with combinations of two measurements. In the second method, problems arise with estimating the zero speed intercept. The third method is most appropriate for this research and the three-level structure fits best on the dataset. The first level contains the individual measurements on the 100 metre sections, performed at different measuring speeds. The second level consists of the 100 metre sections and the third level consist of the roads on which the measurements took place. The standard error of the model on the training data is 0.032 whereas the average change in skid resistance for two datapoints is 0.053. This average change includes conversions over a speed difference from 10 to 40 km/h. From a sensitivity analysis of the macrotexture it was concluded that if no macrotexture can be measured, it is advised to use a different model in which no macrotexture is included. Recommendations for further research include among others registering more accurately the type and age of the measured pavements and extending the dataset with measurements performed at low measuring speeds and on curved sections. Furthermore, it is recommended to perform a more comprehensive outlier analysis and to optimise the hierarchical structure. ... Read more

Ageing of bitumen has been long-recognized as one of the major reasons responsible for the gradual deterioration of asphalt pavements. Age-hardening of the binder leads to the embrittlement of the overall asphalt mixture, which entails its increased susceptibility to traffic and environmental induced damage. As a result, high maintenance efforts as well as increased expenses are required to allow for an asphalt pavement to reach its expected service-life.
Past research efforts have established a solid background with respect to the implications of bitumen ageing on the overall response of an asphalt mixture as well as on the binder’s physico-chemical properties. In the same framework, studies have demonstrated that the ageing process of bitumen in the field is not solely a function of the bitumen type itself, but rather, added effects have been identified attributed to the mineral matter and the asphalt mixture design parameters.
This thesis attempts to provide a deeper understanding of the effect of mineral aggregates on the ageing of bitumen, and more specifically, the effect of a special fraction of the solid phase in asphalt mixtures, the mineral fillers. Six different mineral fillers were employed in this research, covering a wide range of physical and composition-related (i.e. elemental/mineralogical) properties. Bitumen-mineral filler blends were prepared, according to a single design protocol, and the resulting mastics along with neat bitumen were subjected to accelerated laboratory ageing by means of the Pressure Ageing Vessel.
The rheological (i.e. Dynamic Shear Rheometer) evaluation of the resulting materials and the derivation of ageing indices revealed the overall ability of the mineral fillers, regardless of their individual properties, to mitigate the ageing of bitumen incorporated in the mastics. The chemical (i.e. Fourier Transform-Infrared Spectroscopy) investigation of the materials showed that, in fact, the chemically active mineral fillers catalysed the oxidation of bitumen incorporated in the mastics. These results allowed for the identification of two mechanisms through which the effect of the mineral fillers on the ageing of bitumen occurs. The first one is related to the physical presence of the mineral matter in the mastics, whereas the second one to the developed physico-chemical interactions between the mineral fillers’ particles and the bitumen. Basic mineral fillers were found to be more efficient in reducing the age-hardening of mastics, compared to acidic ones, by allowing for more intensive interactions between the mastics’ constituent materials. Moreover, there are indications that the mineral fillers’ specific surface area also has a primary role to the developed interactions, and, by extension, to the ageing behavior of the mastics.
Finally, in addition to the aforementioned main findings, binders were extracted and recovered from the aged mastics, in an effort to derive further information on the effect of mineral fillers on ageing of bituminous mixtures by investigating the aged mastics’ constituent materials on their individual level. The rheological and chemical examination of the recovered materials did not lead to any further insight regarding the research questions of this study. Instead, features were revealed which manifest that the extraction and recovery of bitumen may not be a suitable approach for the investigation of the research problem addressed in this thesis.
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Recycled granular materials such as Recycled Concrete Aggregate (RCA) and Recycled Crushed Masonry (RCM) are widely used in The Netherlands as base layers in asphalt pavements. The lack of natural resources and the growing amounts of demolition waste made that the Dutch industries in the early 1980s started to explore the possibilities to use construction debris in road construction. Recently, the application of recycled materials in pavement structures has also found traction in South Africa. Due to differences in pavement design, however, the mechanical and environmental exposure of these materials will be more severe than in the Netherlands. This results in different challenges with respect to (long term) performance and material durability. Understanding the potential durability issues and the way durability affects pavement performance is crucial to successfully implement these materials in South African pavements.
This research, conducted at Stellenbosch University, South Africa, involves laboratory testing to investigate the performance and durability aspects of recycled aggregates. By means of triaxial testing before and after durability simulation, it is aimed to address the extent of potential material breakdown and the influence this has on performance. Tests are conducted on RCA, RCM, MG65 and MG30. The latter two refer to a mixture of RCA and RCM, with a mass percentage RCA of 65% and 35%, respectively. In addition to the recycled materials, a commonly used crushed rock of G2 quality is tested as well to serve as benchmark. Monotonic triaxial tests, to obtain the shear parameters, are performed on all materials except the pure RCM. Permanent deformation triaxial tests, to gain understanding of the long term response to cyclic loading, are performed on RCA and MG65. Specimens are tested under different confinement and deviator stress levels. For the durability simulation, the South African Durability Mill (DMI) is used. The DMI enables durability testing of the full grading under soaked and dry conditions. After the tests, the milled specimens are sieved out to obtain the change in grading.
The most important findings regarding granulate durability include that the breakdown in recycled materials is significant in comparison with the G2. Mainly the largest particle fractions are affected. Furthermore, for these particular resources of recycled granulates, the RCA suffers more breakdown than the RCM. The breakdown in the blends decreases with increasing masonry content, implying that the RCA is the most prone to mechanical damage. Considering the monotonic triaxial tests, substantial values of shear parameters are measured in all materials. The highest cohesion is measured in the MG30, while the highest internal angles of friction are measured in the pure RCA. The shear parameters in the recycled materials are in all cases higher than those for the G2. Differences in failure type (brittle versus plastic) are observed as well. Durability milling results in a small increase of the internal angle of friction and in a moderate decrease of cohesion. The latter is the most governing for the material’s compressive strength after milling, as this is decreased in all milled specimens. Still, the shear parameters of the milled specimens remain relatively high. In the permanent deformation triaxial tests, a decrease of performance can be observed in both the RCA and MG65. Delayed shear failure is observed in milled specimens tested at a deviator stress ratio (DSR) higher than 30%. Although the number of permanent deformation tests performed in this research is limited, 30% DSR seems the upper limit with respect to cyclic loading. This points out that monotonic triaxial testing alone is not sufficient for an adequate material characterization. A small linear elastic pavement analysis based on the tested materials, however, shows that the occuring DSR levels in a reference pavement caused by standard axles of 80 kN do not exceed 20% DSR, proving the potential of these materials for further studies. ... Read more

The increasing traffic load has led to the use of polymer modifiers in bituminous mixes in order to improve the performance and the durability of the pavement structures. Epoxy is a thermoset material which ensures enhanced fatigue performance and improved mechanical characteristics when used to modify bituminous materials. However, unlike conventional modification techniques, a series of experimental methods have to be conducted to evaluate the chemical- related phenomena occurring during the binder production and their effects on the performance of the epoxy modified bitumen. For this reason in this thesis, the utilization of epoxy modifiers was investigated at binder level.
Initially, the chemical hardening (curing) process of epoxy modified bitumens (EMBs) was investigated by means of Fourier Transform Infrared (FT-IR) spectrometer and Dynamic Shear Rheometer (DSR). Different combinations of hardening conditions for three epoxy modification levels were studied. Properties, such as modulus and viscosity, were utilized to determine the workability of EMB. At the same time, by using the FT-IR spectrometer, the functional groups of EMBs during the chemical reactions were identified for the understanding of polymerization in the epoxy components.
Additionally, the DSR device was utilized to determine the fatigue and tensile strength of EMBs. It was found that, with increasing the content of epoxy modifier, the fatigue life and tensile strength were increased significantly compared to an unmodified binder.
Finally, the age hardening (aging) of EMBs was evaluated at different time intervals. For the simulation of short-term aging on EMBs, a short-term oven aging method (STOA) was used. For long-term aging, simulations were performed in a pressure aging vessel (PAV) under constant pressure and temperature. The results of chemical characterization and rheological properties of the aged EMBs were obtained by using DSR and FT-IR and were compared to the unmodified bitumen.
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