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.

Fracture of rock particles is important inmany applications like mining, mineral comminution,unbound granular materials (UGMs) for railwayand road structures. The latter application is themain interest presently, as fracture of rock particles inUGMs affects the UGMs performance and may compromisestructural integrity of a pavement, potentiallyleading to premature road failures. Therefore, it isimportant to assess their resistance to aggregate fractureaccurately. In this study, a new statistical fracturemodel for particle fracture, based on the results ofsingle particle crushing tests, is introduced to investigateaggregate fracture. The proposed model istested for UGMs composed of three different aggregatetypes: brick, granite and a volcanic material andits results are compared with other widely used fractureforce models. The performance of the models isalso investigated by simulating uniaxial monotoniccompression tests on UGMs with different aggregatesize distributions using the Discrete Element Method(DEM) and comparing the results with experiments.Fracture at two different load levels for three differentparticle size distributions are investigated for eachmaterial. One particle size distribution at one loadlevel is used to identify the contact law parametersfor each material, and single particle breakage testare used to identify the fracture force model parameters.The DEM models with a new fracture forcemodel agrees well with the macro-mechanical behaviourobserved in experiments and exhibits the highestdegree of correlation to fracture results obtained fromexperiments.

Hot mix asphalt (HMA) has been widely used as a pavement material for decades because of its quick construction process and good engineering performance. However, its construction has to be performed at elevated temperature, causing significant energy consumption and hazardous emissions. Cold mix, which demands no heating in the construction process, is a cleaner and more environment-friendly paving technique. The cold mix binder, which bonds aggregates at ambient temperature, plays a key role in the environment-friendly cold mix pavement. However, in-depth understanding of the working mechanism and applications of cold mix binders is still lacking. To fill this gap, three different kinds of cold binders commonly used in pavement industry are extensively discussed, namely, the conventional bitumen emulsions, and the newly emerging epoxy resin and polyurethane. Bitumen emulsions are by far the most widely used cold binder in pavement construction for surface dressing, tack coat and cold mix. However, bitumen emulsions are inferior to HMA in terms of early strength and mechanical properties, which limited them from been used in structural layers. To improve the performance of bitumen emulsion, polymer latexes, such as SBR latex and waterborne epoxy resin, are commonly used as modifiers to prepare polymer modified bitumen emulsions. The incorporation of polymer latexes can significantly improve the performance of bitumen emulsion, including high- and low-temperature performance, adhesion with aggregate, and fatigue performance. Recently, polymer binders like epoxy resin and polyurethane have been introduced into the pavement industry. Epoxy resin and polyurethane are characterized as fast curing, remarkable mechanical strength, and strong adhesion with aggregate and substrates. However, there are still some shortcomings need to be addressed for the resin binders before they can be applied in large quantities, such as limited workability, insufficient resistance to weathering and high initial cost. This paper set out to provide a state-of-the-art review on the constitutions, properties, applications, and pros and cons of three cold binders, i.e., bitumen emulsion, epoxy resin and polyurethane, paving the way for future research and applications of these cleaner construction materials in pavement engineering.

Adequate aggregate resistance to crushing and abrasion is crucial for good performance of unbound road layers, in particular when incorporating marginal aggregates in road construction. In this study, aggregate crushing in unbound granular materials (UGMs) is investigated experimentally with uniaxial compression tests, and numerically with discrete element method (DEM). A DEM model of UGMs subjected to uniaxial monotonic compression is implemented in a commercial DEM software, incorporating granular mechanics-based particle-contact and breakage laws. Based on comparison with the experimental findings, it is shown that the implemented model captures the UGMs behavior well including aggregate breakage characteristics. The model is used furthermore to evaluate aggregate crushing in UGMs subjected to cyclic loading representative for unbound road layers of low-volume roads. The feasibility of using the developed DEM approach for evaluating the implications of using marginal UGMs in unbound road layers and for optimizing structural design of those layers is discussed.

Thermal contraction is a key factor in low-temperature cracking, contributing to internal stresses in the bitumen-aggregate composite. Most macromechanical models treat mastic as a continuous material, limiting an in-depth analysis of the component interactions, which is essential for improved material design. This study analyses the low-temperature behaviour of bitumen and mastic containing different basalt filler content using experimental testing and micromechanical finite element modelling (FEM). The model evaluates micromechanical interactions between bitumen and aggregates, with aggregates modelled as spherical particles in the bitumen. Thermal contraction coefficients are predicted via viscoelastic modelling and compared to experimental results. Findings show higher filler content lowers the thermal contraction coefficient while increasing stress concentrations due to the combined thermal properties of bitumen and filler. The micromechanical model aligns well with experimental data, confirming its reliability in predicting stress distribution and thermal behaviour. These insights enhance the understanding of bituminous materials in cold environments.

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.

Low-temperature cracking is one of the most common failures in asphalt pavements, especially in cold regions. Accordingly, considerable amount of research has been performed in order to understand the low-temperature cracking mechanisms and to propose test methods for characterizing and determining cracking performance of bitumen and asphalt mixtures under freezing conditions. The existing test methods, however, require expensive equipment and skilled technicians; they are thus not well suited for routine tests. As a contribution to mitigate this situation, this study intends to investigate experimentally and characterize numerically the low-temperature cracking behavior of bitumen and mastic materials using a refined thermal cracking test method. The proposed method, the annular restrained cold temperature induced cracking (ARCTIC) test, allows to determine the low-temperature cracking properties of the mastic and bitumen with a relatively simple setup. In this paper, finite element (FE) modeling is used for evaluating the effect of test parameters on the temperature, stress and strain gradients induced in the specimen during the test. The ARCTIC test is employed to measure cracking temperatures of two bitumen and two mastic materials. The measurements repeatability is examined and the effect of bitumen type on the thermal cracking potential of bitumen and mastic is evaluated. FE modeling is employed to examine the effect of thermomechanical parameters on thermal cracking performance of the materials and to back-calculate fracture stress and strain from measurements. The results highlight the potential of the proposed test and analysis method for evaluation of low-temperature cracking in bitumen and asphalt mastic.

Aggregate breakage in unbound pavement layers can lead to pavement distresses that affect their functionality and service life. Thus understanding the mechanics and clarifying the factors affecting materials breakage resistance are important for ensuring adequate performance of these layers. In this study, aggregate breakage in unbound granular materials (UGM) is investigated experimentally and numerically. Experimentally, aggregate breakage under uniaxial compression is examined for two UGMs prepared with the same aggregate type but different gradations. To capture the experimentally observed influence of gradation and load magnitude on aggregate breakage, a Discrete Element Method (DEM) model was developed, based on granular mechanics particle contact and failure laws. A simple procedure to identify the contact and failure law parameters from experiments is proposed. With those parameters, the model’s capability of capturing the effect of gradation and loading on the aggregate breakage in UGM is evaluated. Based on comparison with experimental findings, it is shown that the model can capture macro-scale properties of UGM, such as its deformation response under uniaxial compression, as well as the amount of aggregate breakage in the material.

Low-temperature cracking significantly affects durability of asphalt pavements. This research addresses the role of the mastic phase by experimentally evaluating the low-temperature cracking performance of selected bitumen and mastics with different filler types and contents. Their thermal contraction coefficient (αT), low temperature viscoelasticity, and strength properties are measured using standard tests like the dynamic shear rheometer (DSR) and fracture toughness tests (FTT). An enhanced laboratory technique, the annular restrained cold temperature induced cracking (ARCTIC) test, is employed to study combined thermal and mechanical effects on low-temperature cracking. The alignment of FTT with ARCTIC results highlights a good correlation between these methods for mastics with nearly the same αT. However, the insensitivity of FTT to αT raises concerns about its applicability to materials with significantly different αT, as it may not capture accurately their performance. The ARCTIC test is free of such a problem and even shows a higher sensitivity to the mastic composition. The findings demonstrate that the addition of filler significantly affects the resistance of mastic to low-temperature cracking by altering its αT. Additionally, the filler content, type, and gradation distinctly impact the thermal and mechanical characteristics of mastics, enhancing their ability to withstand lower temperatures more effectively than bitumen. In particular, adding 50 % by volume of different filler types reduces the αT of mastic by 45–60 % and results in 3–10 °C reduction in cracking temperature (Tcr) measured with the ARCTIC test.

Interlayers in asphalt pavements are potential structural damage initiators. In order to better understand the quantitative role of interlayer parameters, such as surface roughness, binder type, binder content and loading type on interlayer shear strength, this paper focuses on the effects of particle interlock and contact conditions on interlayer strength through experimental and numerical modelling. Experimentally, interlayer shear box strength tests on a model material consisting of stiff binder blended with steel balls are performed with and without normal force confinement. A Discrete Element method model of the test is developed using measurements of the model material for calibrating the contact law and for validating the model. It is shown that this model captures adequately the measured force-displacement response of the specimens. It is thus a feasible starting point for numerically and experimentally studying the role of binder and tack coat regarding interlayer shear strength of real asphalt layers.