The present study aims at experimentally and numerically investigating the effect of an encapsulated healing agent on the mechanical characteristics of a stone mastic asphalt (SMA-15) after cyclic loading. As healing agents a thiol-containing urethane AR-polymer (ARP) and a sunflower oil (SfO) are used. The comparison of self-healing results in asphalts show that the use of encapsulated ARP allows to restore strength and stiffness up to 93% of whereas encapsulated SfO restores up to 90%. Without capsules, the self-healing effect is 81%. After self-healing, the structure of asphalt concrete with encapsulated ARP is capable of withstanding 15% and 22% more loads than original SMA-15 and SMA-15 with encapsulated SfO, respectively. To gain numerical insight into the mechanical behavior of the capsules in SMA-15, micromechanical finite element modeling is employed. The model is used to evaluate the effect of damage formation with respect to stresses and strains in the capsules and their propensity to breakage.

Due to economic and land use constraints, the low-volume roads tend to be narrow and with steep side-slope angles, resulting in traffic loads applied close to the pavement edge and in compromised confinement of unbound granular layers (UGLs). Field evidence suggests that both edge loads and steep side slopes accelerate pavement deterioration, but the mechanics remain unclear. This paper presents a computational approach to evaluate the impact of load position and side-slope angle on pavement deterioration. A 3D finite element (FE) model of low-volume pavement is developed, incorporating novel material models to account for stress-dependent behaviour and permanent deformation in unbound layers, along with a method to evaluate the impact of side-slope material on road performance. The numerical results concerning reduced bearing capacity and accelerated deterioration due to increased slope angles and edge-proximal loads are in agreement with field and full-scale test data. Thus, the proposed approach serves as a viable tool to quantify the impact of shoulder width and side slope on pavement performance.

Semi-flexible pavement (SFP) material is a composite comprising cement, coarse aggregates and asphalt mortar, which has complex mechanical properties. Traditional experimental methods struggle to accurately quantify the effect of each phase and their interfaces on the SFP's mechanical properties. Micromechanical modelling based on finite element method offers a promising solution. In this study, a new micromechanical model for SFP is proposed, idealizing the material by representative volume elements. SFP mesostructure is represented as a simplified five element composite consisting of cement, asphalt mortar, aggregate, pore and cement-asphalt mortar interface. Periodic boundary conditions are used to simulate an infinite repetitive structure within a finite computational domain. The resulting model allows evaluating the stiffness and damage resistance of SFP in a computationally efficient manner. This model is utilized to explore the mechanical properties of SFPs and the results are compared with the experimental findings. The results show that the model captures the uniaxial compressive strength and stiffness for all materials examined. The model is further used to evaluate the effect of properties of individual elements of SFP on its stiffness and strength. The feasibility of using the proposed modelling approach to optimize the material design of SFP is discussed.

The stiffness and failure properties of cement-asphalt mastic-aggregate (C-AM-A) interface are among the most important factors affecting the performance of pouring semi-flexible pavement materials (SFP). Therefore, determining the characteristics of C-AM-A interface are essential for guiding the design of SFP from the perspective of interface enhancement. In this study, the failure characteristics of C-AM-A interfaces are examined experimentally and numerically. Firstly, the effects of temperature and the proportion of cement substituting limestone filler on the bonding strength of C-AM-A interface are analyzed via pull-off tests. Then, an innovative test method based on a three-point bending test of C-AM-A beam is proposed to investigate the influence of test temperature and asphalt mastic type on the fracture characteristics of the C-AM-A interface. Finally, based on the cohesive surface techniques, numerical modeling of C-AM-A beam under three-point bending was applied to study the effect of cohesive parameters on the interfacial fracture characteristics. The results show that the interface bonding strength decreased significantly with the increase of temperature. Using cement as a filler improves the bonding strength, fracture strength, stiffness and fracture energy of C-AM-A interface as compared to the case when limestone filler is used. As the temperature increases from -10 degrees C to 20 degrees C, the failure mode of the C-AM-A interface first alters from adhesive failure to mixed failure mode, and then to cohesive failure. It suggests that enhancing the adhesion of C-AM-A interface is more advantageous for improving the fracture resistance at low temperatures, while increasing the interface cohesion is more important at relatively high temperatures. The laboratory test methods, the numerical model and methodology developed in this study are useful to study the failure behavior of C-AM-A interface and optimize the performance of SFP from the perspective of interface enhancement.

Aggregate contacts significantly affect the mechanical behavior of asphalt concrete. However, there still lacks an effective way to account for them in numerical modeling. Therefore, to address this concern, a new virtual-specimen-based modeling approach was developed in this study by simplifying aggregate particles in asphalt concrete as spheres and incorporating aggregate contacts through Contact Region (CR) elements. The complex moduli of both gap-graded and dense-graded mixtures were predicted using this approach and compared with those predicted using the conventional image-based modeling approach and laboratory-measured values. The virtual-specimen modeling revealed that the CR in the gap-graded mixture with a higher proportion of large aggregates can better transmit load among aggregates than in the dense-graded mixture. Both modeling approaches were found to provide good prediction accuracy, but the stress distributions in the virtual-specimen models were more uniform and continuous, leading to better computational convergence and the possibility of nonlinear analysis of asphalt concrete.

The present study aims at experimentally and numerically investigating the effect an encapsulated healing agent on the mechanical characteristics of a stone mastic asphalt (SMA). As a healing agent a thiol-containing urethane AR-polymer is used in this study. In order to gain a numerical insight into mechanical behavior of the capsules in SMA, a micromechanical finite element modeling is employed. The developed model allows capturing the stresses induced in the capsules at different load cases applied to the SMA on macro-scale. Particular attention is paid presently to the numerical evaluation of the local stress state that arises around capsules during compaction, operation, and also during crack initiation. SMA mixtures with various volumetric contents of healing capsules were manufactured and the capsules survival during mixture production was evaluated based on X-Ray Computed Tomography measurements. The effect of capsules on the self-healing properties of asphalt mixtures has furthermore been examined with repeated compressive strength tests. The obtained experimental results indicate that the absolute majority of capsules survive mixture production, and that their addition increases the SMA strength recovery during the healing period. The experimental and numerical results concerning capsules breakage are found to be in reasonable agreement. The developed micromechanical model may thus potentially provide a useful tool for optimization of capsules mechanical properties in order to improve their survival during mixture production as well as their timely activation.

The performance of asphalt mixtures is significantly affected by the viscoelastic properties of their mastic phase. The analytical approaches used to predict the mastic’s properties from its composition and constituents are limited in their accuracy as well as potential to handle non-linear material behaviour. An alternative micromechanical finite element modelling approach to calculate the mastic’s master curve from the binder and filler phase properties is presented in this paper. In the model, the mastic’s representative volume element is generated and it consists of a linear viscoelastic bitumen matrix and elastic spherical filler particles. In order to validate the model, shear relaxation moduli of bitumen and bitumen-filler mastics are measured at temperatures between −10 to 80 °C. For the two mastic materials characterized experimentally, micromechanical models are set-up and their capability to capture the measured response is evaluated and compared with the existing analytical solutions. The obtained results indicate that the proposed finite element modelling approach is advantageous as compared to the analytical solutions, as it both allows predicting mastic’s properties over wider temperature, frequency and material range as well as results in a better agreement with the measurements.

The performance of asphalt mixtures is significantly affected by the viscoelastic properties of their mastic phase. The analytical approaches used to predict the properties of mastics from their constituents’ properties are limited in their accuracy and potential to handle non-linear material behaviour. An alternative micromechanical finite element modelling approach to calculate the master curves of mastics from the binder and filler phase properties is presented, where the representative volume elements of mastics consist of linear-viscoelastic bitumen matrices and elastic spherical filler particles. For validation, shear relaxation moduli of bitumen and bitumen-filler mastics are measured at (Formula presented.) °C (Formula presented.) °C. Additionally, the model is evaluated and compared with the existing analytical solutions. The results indicate that the proposed approach is advantageous as compared to the analytical solutions, as it allows predicting the mastics’ properties over wider temperature, frequency and material ranges at better agreement with the measurements while giving insight into the micromechanical behaviour.

The indentation test is a promising technique for the viscoelastic characterisation of asphalt concrete (AC). Indentation measurements are primarily influenced by the material properties in the direct vicinity of the indenter-specimen contact point. Accordingly, it may become a useful alternative for the characterisation of thin asphalt layers as well as for a quasi-non-destructive AC characterisation in the field. In this study, the spherical indentation test is used to measure the linear viscoelastic properties of AC mixtures extracted from a road test section. The measured complex moduli are compared to those obtained by the shear box test and are found to exhibit a linear correlation. The measurements are further analysed using the Gaussian mixture model to assign each indentation test to either aggregate-dominated or mastic-dominated response. The measurements attributed to mastic-dominated response are found to be more sensitive to the temperature and AC's binder properties as compared to the average measurements. Accordingly, the proposed test method may provide a promising tool to measure AC viscoelastic properties and monitor the changes in AC binder phase in a non-destructive manner. A finite element micromechanical model is used to identify a representative scale for the response measured in mastic-dominated tests as well as to quantify the effect of measured properties on the AC damage propensity.

The viscoelastic properties of asphalt  mixtures  strongly  influence the  performance of flexible pavements  with respect to  their resistance to several common distress modes. Therefore, accurate measurement of these properties and their change during the service life is an important area of ongoing research. Despite considerable progress in this field, certain questions are still not fully resolved. In particular, commonly used experimental methods cannot be applied for the viscoelastic characterisation  of  thin asphalt layers and asphalt overlays.  Moreover,  measuring the  viscoelastic properties of the  downscaled sub-phases of asphalt mixtures, such as mastic or mortar, in the field remains a challenge. Understanding the viscoelastic properties of those sub-phases  is crucial  for gaining fundamental insight  into  the mixture performance. In this context, advanced and computationally efficient micromechanical models are also needed in order to establish the quantitative link between the viscoelastic properties of asphalt mixtures and of their sub-phases. This thesis aims to contribute to this important area through  the  development of new experimental and modelling  tools for  the  multiscale characterisation of asphalt mixtures. 

In this thesis, a new micromechanical modelling approach for bitumen-aggregate composites is proposed and used to investigate the mechanical behaviour of mastic, mortar and asphalt mixtures.  To achieve  computational efficiency, the proposed approach is based on a simplified, computer-generated representation of materials internal structure and utilises periodic boundary conditions to reduce the representative volume element size. Based on the Dynamic Shear Rheometer (DSR) measurements,  it is shown that the proposed model can capture the measured viscoelastic behaviour of mastics for the range of loading, temperature and material parameters examined.  For  the  modelling of mortar and asphalt mixtures, the multiscale approach is applied in order to improve computational efficiency. Obtained computational results indicate that the developed approach is capable of capturing the mixtures’ macro-scale viscoelastic properties with reasonable accuracy. 

An instrumented indentation test for the viscoelastic characterisation of bitumen and bitumen-aggregate composites, such as mastic, mortar and asphalt mixtures is proposed in this thesis as a new alternative to existing techniques. A new methodology for the indentation testing of linear viscoelastic materials is developed, allowing their characterisation at arbitrary non-decreasing loading.  In order to extend the developed method to the multiscale characterisation of bitumen-aggregate composites, the spherical indentation on different types of asphalt mixtures, such as asphalt mortar, mastic asphalt (MA) and asphalt concrete (AC), has been investigated experimentally and through micromechanical modelling. The effect of the indentation test parameters on the measured apparent viscoelastic properties of bitumen-aggregate composites has been evaluated. A particular emphasis  is put on  the  identification of test parameters corresponding to  the characterisation of binder-aggregate composites on the macroscale as well as on the individual component scale. The experimental results demonstrate that the developed indentation test can capture the macroscale properties of materials reasonably  well, and the obtained results  correlate linearly with the properties measured with established test methods. Furthermore, in order to gain better insight into mastic phase properties from the indentation tests performed on MA and AC, a new statistical analysis procedure has been developed for the evaluation of a series of indentation tests. The developed procedure allows identifying clusters of measurements capturing the mastic-  and aggregate-dominated responses of the asphalt mixture.  The  indentation  measurements attributed to mastic-dominated response are found to be more sensitive to the temperature and mastic properties as compared to the mean measurements of the indentation test series. 

The obtained results  indicate that  the  developed  indentation  test  is a  viable alternative to existing viscoelastic characterisation methods, in particular as the test is quasi-non-destructive and can be used to characterise thin asphalt layers. Furthermore, combined with the developed statistical analysis procedure, indentation testing is a promising tool to monitor the changes in the mastic phase of the materials due to ageing, moisture damage or fatigue from the measurements on asphalt mixtures  without extracting the binder.  The developed micromechanical model can also be used to quantify the effect of  changing mastic properties on the asphalt mixture performance. This is particularly true for the strain localisations in the mastic phase and thus the mixture’s damage resistance. 

Asfaltsblandningars viskoelastiska egenskaper har en stor påverkan på uppträdandet av asfaltsvägar på grund av deras resistens mot flera vanliga skadeorsaker. Precisa mätningar av dessa egenskaper och deras förändringar under deras livslängd är därför ett viktigt område för pågående forskning. Trots omfattande framsteg inom området så har vissa frågor fortfarande inte besvarats helt. I synnerhet kan inte de existerande experimentella metoderna appliceras för viskoelastisk karakterisering av tunna asfaltslager och asfaltslagningar. Dessutom finns inga tillgängliga metoder för mätning av subfaserna av asfaltsblandningar på en mindre skala, såsom mastix, i.e. en blanding av bitumen och partiklar mindre än 64 mikrometer, och asfaltbruk, i.e. en blandning mellan bitumen och stenpartiklar mindre än 2 mm. Förståelse av de viskoelastiska egenskaperna är av största vikt för att få en grundläggande föståelse i blandningens uppträdande. För detta behövs även avancerade och beräkningseffektiva mikromekaniska modeller för att etablera en kvantitativ länk mellan de viskoelastiska egenskaperna hos asfaltsblandningar och deras subfaser. Denna avhandling strävar mot att bidra till detta viktiga område genom utvecklingen av nya experimentella verktyg och modelleringsverktyg för multiskalekarakterisering av asfaltsblandningar.  

I denna avhandling föreslås ett nytt tillvägagångssätt för mikromekanisk modellering som används för att undersöka det mekaniska beteendet av mastix, asfaltbruk och asfaltsblandningar. För att uppnå beräkningseffektivitet baseras det föreslagna tillvägagångssättet på en förenklad, datorgenererad representation av materialens interna struktur och utnyttjar periodiska randvillkor för att reducera storleken på det representativa volymelementet. Med hjälp av mätningar i Dynamisk Skjuvreometer (DSR) visas det att den föreslagna modellen kan fånga det uppmätta viskoelastiska beteendet av mastix för de belastningar, temperaturer och materialparametrar som undersökts. För modelleringen av asfaltbruk och asfaltsblandningar appliceras multiskaletillvägagångssättet för att förbättra beräkningseffektiviteten. De erhållna beräknade resultaten indikerar att det utvecklade tillvägagångssättet är kapabelt att fånga de viskoelastiska egenskaperna på blandningens makronivå med rimlig noggrannhet.  

Ett instrumenterat intrycksprov för viskoelastisk karakterisering av bitumen och kompositer bestående av bitumen och stenmaterial, såsom mastix, asfaltbruk och asfaltsblandningar, föreslås i denna avhandling som ett nytt alternativ till existerande tekniker. En ny metodologi för intrycksprovning av linjära viskoelastiska material har utvecklats, vilket tillåter karakteriseringen av dem vid en godtycklig icke-minskande belastning. För att bredda användningsområdet för den utvecklade metoden till multiskalekarakterisering av bitumen-stenkompositer har den sfäriska intryckningen på olika typer av asfaltsblandningar undersökts experimentellt och genom mikromekanisk modellering. Effekten av de olika parametrarna i intrycksprovet på de mätta viskoelastiska egenskaperna av bitumen-stenkompositerna har utvärderats. Ett särskilt fokus har lagts på identifieringen av provningsparametrar som korresponderar till karakteriseringen av kompositerna på makronivå samt på den individuella komponentnivån. De experimentella resultaten demonstrerar att det utvecklade intrycksprovet kan fånga de testade materialens egenskaper på makronivå på en rimlig nivå och de erhållna resultaten korrelerar linjärt med egenskaperna som mätts med etablerade provningsmetoder. För att få en bättre insikt i mastixfasens egenskaper från intrycksprovningen utförd på asfaltsblandningar, har dessutom en ny statistisk analysprocedur föreslagits för utvärderingen av en serie intrycksprover. Den föreslagna proceduren möjliggör identifiering av kluster av mätningar som fångar asfaltsblandningars mastix-  och stendominerande respons. Intrycksmätningarna som tillskrivs den mastixdominerande responsen konstaterades vara mer känslig för temperatur och mastixens egenskaper jämfört med de genomsnittliga mätningarna.  

De erhållna resultaten indikerar att det utvecklade intrycksprovet är ett lovande alternativ till existerande viskoelastiska karakteriseringsmetoder, särskilt eftersom metoden är kvasi-icke-förstörande och kan användas för att karakterisera tunna asfaltslager. Dessutom är intrycksprovning, i kombination med den utvecklade statistiska analysproceduren, ett lovande verktyg för att övervaka förändringar i mastixfasen i material på grund av åldring, fukt eller utmattning från mätningar på asfaltsblandningar utan att extrahera bindemedlet. Den utvecklade mikromekaniska modellen kan också användas för att kvantifiera effekten av mätta förändringar i mastixens egenskaper på asfaltsblandningens uppträdande med avseende på till exempel töjningslokaliseringarna i mastixfasen och därmed blandningens resistens mot skada.