RILEM interlaboratory study on the mechanical properties of asphalt mixtures modified with polyethylene waste

Acknowledgments The Swiss company Innoplastics is acknowledged for providing the waste plastics. Empais participation is supported by Swiss National Science Foundation grant SNF 205121_178991/1 for the project titled “Urban Mining for Low Noise Urban Roads and Optimized Design of Street Canyons”. The participation of University of Belgrade, Faculty of Civil Engineering, is supported by the Ministry of Education, Science, and Technological Development of the Republic of Serbia under research project No. 2000092.This research aims to determine if the observed improvements using polyethylene (PE) waste in asphalt binder translate into better performance at the asphalt mixture scale in the laboratory environment while overcoming the stability and homogeneity issues experienced at the binder level. This is accomplished through a round-robin multinational experimental program covering four continents, with the active participation of eleven laboratories within the RILEM TC 279-WMR. PE modified AC16 mixtures were prepared employing the dry process using local materials with the PE waste provided by one source. Various mechanical tests were performed to investigate the compactability, strength, moisture sensitivity, stiffness and permanent deformation. Compared to the control mixtures, the following observations were made for PE modified mixtures: easier to compact, lower time dependence of stiffness, higher elastic behavior, lower creep rate, and higher creep modulus. Furthermore, cyclic compression test results showed that the resistance to permanent deformation is improved when using PE in asphalt mixtures, whereas the wheel tracking tests showed relatively similar or better results when 1.5% PE was added to the control mixture. The wheel tracking test results in water showed an increase in deformation with increasing PE content. The interlaboratory investigation showed that the use of PE as a performance-enhancing additive in asphalt pavements is a viable, environmentally friendly option for recycling waste plastic and could potentially reduce the use of polymer additives in asphalt.Swiss National Science Foundation grant SNF 205121_178991/1Ministry of Education, Science, and Technological Development of the Republic of Serbia under research project No. 200009

Urban mining for asphalt pavements: A review

The increasing consumption of natural resources for road construction and generation of urban waste materials are two global ecological problems. Urban mining aims to convert waste materials into raw materials for industrial production, and as a result, address both problems simultaneously. This study explores the potential of urban mining for asphalt pavement surface courses. In the first part, as each country/region has its unique challenge with waste materials, a screening method taking the EU and Switzerland as case studies is employed to select waste materials that potentially qualify for asphalt surface courses. The second part presents a review of laboratory studies regarding the performance of asphalt mixtures with selected waste materials. Based on the industrial experience, the third part dis- cusses the technology, specifications and cost considerations of asphalt surface courses with waste materials. Furthermore, the technical maturities for using waste materials are estimated in terms of technology readiness level (TRL). Overall, the paper demonstrates that various categories of waste ma- terials can be potentially used in asphalt surface courses, revealing urban mining opportunities. The selected waste materials may improve the performance of asphalt mixtures with optimization of several factors, such as the fraction size and amounts of waste materials for addition or replacement. The TRL results showed that using crumb rubber (wet process) and steel slag are currently more mature than using other waste materials in asphalt surface course

Effect of waste PET and CR as sand replacement on the durability and acoustical properties of semi dense asphalt (SDA) mixtures

Construction materials research is consistently striving to improve sustainability, in the reduction of virgin materials by use of otherwise landfilled materials of the same purpose. Crumb rubber (CR) from end-of-life tires and polyethylene terephthalate (PET) from post-consumer liquid containers are two of the most commonly circulating forms of waste in the urban environment. This study investigated the replacement of semi-dense asphalt (SDA) sand by untreated mechanically shredded CR and PET, at 2.5 and 5.1% respectively by total mass of aggregates. The mixtures were evaluated by compactability, indirect tensile strength (ITS), fracture energy (FE), water sensitivity by ITS ratio (ITSR%), surface texture and acoustic absorption tests. After compaction, the CR and PET samples experienced an elastic rebound effect, which resulted in the air voids being higher than expected. Also, the PET samples required more compaction energy. The ITS, FE and ITSR% were significantly reduced with CR replacement, while the PET mixture performed similar to the control, especially in FE. The sound absorption was related more to the air voids than the material type, although the absorption coefficients of the SDA was not found to be significant. The CR reduced the texture level of the pavement significantly in comparison to the control, while texture level remained the same for the PET mixture, despite a difference in the porosity. Further studies were performed using a mixture replacing PET by aggregate volume at 5.1%, comparing it to the control SDA in terms of low temperature cracking and permanent deformation at 50 °C. While the compactability of the PET mixture was now similar to that of the control, the resistance to cracking and permanent deformation was lower. Although the PET mixture had some interesting ductility properties, the replacement of sand by CR and PET is not recommended, and the more common use as asphalt mixture modifiers with fairly low addition contents of around 1% is more sound

A cluster-based pore network model of drying with corner liquid films with application to a macroporous material

A pore network model (PNM) of drying in a gravity-dominated macroporous material has been developed. The pore network geometry used for the simulations is extracted from microcomputed tomography scans of porous asphalt (PA), a macroporous, hydrophobic material. The drying of liquid water in PA is modeled using a cluster-based approach with a two-step drying process i.e. elements go first from being fully saturated to having liquid only in pore and throat corners, and then to becoming completely dry. The PNM simulations are validated with gravimetric experiments performed under controlled conditions and the simulations show good agreement with experiments for most of the drying period. From experiments, it is seen that drying in PA completely skips the constant drying rate period (CDRP) and instead begins with the decreasing drying rate period (DDRP) due to the poor hydraulic connectivity in PA as a result of its large and hydrophobic pore space. The PNM simulations exhibit CDRP initially and then transitions to DDRP after a third of the total drying time. The CDRP at the beginning of the PNM simulations is due to the simplified liquid configuration assumed in the network, and its duration can be minimized to an extent by increasing the number of hydrophobic pores in the network that does not retain any liquid after drainage. Although promising, the first results call for a more accurate representation of both the complex pore space of PA and the physics involved in drying of a macroporous material

Investigation of Water Uptake in Porous Asphalt Concrete Using Neutron Radiography

Porous asphalt (PA), a highly porous hydrophobic composite material, is subjected to water uptake and the process is documented with neutron radiography (NR). While the un-aged laboratory-prepared PA specimens do not show any water uptake, we observe uptake in aged PA even though the bitumen binder is a hydrophobic material. The moisture content distribution plots derived from the NR images clearly identify regions in the aged specimens where water uptake is active. Two-dimensional degree of saturation (DoS) distribution images, which are obtained by combining micro-computer tomography and NR images, identify those pores where saturated flow is certainly active. However, to clearly distinguish between saturated and unsaturated flows in the remaining wet pores, the DoS distribution images are read together with the three-dimensional PA microstructure obtained by micro-CT. It is observed that uptake begins mainly as unsaturated film/corner flow at large well-defined pores. As this uptaken water travels further into the material, the flow transforms into a combination of saturated flow and unsaturated film/corner flow. Saturated flow is seen to be mostly active in the small pores within the mastic. From the observed succession of unsaturated and saturated flows in an aged PA specimen, it can be concluded that years of environmental and mechanical loading has resulted in the stripping of binder from the aggregate surfaces and has consequently exposed patches of hydrophilic aggregate to water, which enables the capillary uptake of water. We also simulate an absolute permeability experiment and observe that relatively less tortuous and more connected paths play an important role in determining the preferential path of the uptaken water

Laboratory investigation of bitumen based on round robin DSC and AFM tests

In the past years a wide discussion has been held among asphalt researchers regarding the existence and interpretation of observed microstructures on bitumen surfaces. To investigate this, the RILEM technical committee on nano bituminous materials 231-NBM has conducted a round robin study combining differential scanning calorimetry (DSC) and Atomic Force Microscopy (AFM). From this, methods for performing DSC and AFM tests on bitumen samples and determination of the influence of wax on the observed phases, taking into account thermal history, sample preparation and annealing procedure, are presented and critically discussed. DSC is used to measure various properties and phenomena that indicate physical changes such as glass transition temperature (T g) and phase transition such as melting and crystallization. In the case of existence of wax, either natural or synthetic, it can further indicate the melting point of wax, that could be used to determine wax content. The results from seven laboratories show that T g temperatures obtained from the heating scans are more repeatable and easier to obtain in comparison to the cooling scans. No significant difference was noted for T g's obtained from the first and second heating scans. AFM is an imaging tool used to characterize the microstructures on a bituminous surface. Using AFM three phases in the materials with wax could be distinguished. The changes in the phases observed with AFM for increases in temperature were correlated with the DSC curve, and it could be established that the so called "Bee” structure disappeared around the melting peak in the DSC curve. Thus, this research has confirmed the relation between the microstructures on a bitumen surface and the wax content

Review of advanced road materials, structures, equipment, and detection technologies

As a vital and integral component of transportation infrastructure, pavement has a direct and tangible impact on socio-economic sustainability. In recent years, an influx of groundbreaking and state-of-the-art materials, structures, equipment, and detection technologies related to road engineering have continually and progressively emerged, reshaping the landscape of pavement systems. There is a pressing and growing need for a timely summarization of the current research status and a clear identification of future research directions in these advanced and evolving technologies. Therefore, Journal of Road Engineering has undertaken the significant initiative of introducing a comprehensive review paper with the overarching theme of “advanced road materials, structures, equipment, and detection technologies”. This extensive and insightful review meticulously gathers and synthesizes research findings from 39 distinguished scholars, all of whom are affiliated with 19 renowned universities or research institutions specializing in the diverse and multidimensional field of highway engineering. It covers the current state and anticipates future development directions in the four major and interconnected domains of road engineering: advanced road materials, advanced road structures and performance evaluation, advanced road construction equipment and technology, and advanced road detection and assessment technologies

Ice adhesion behavior of heterogeneous bituminous surfaces

The phenomenon of icing, and the derived processes for its mitigation, are of great importance in many applications, ranging from transportation and energy to food and refrigeration. This phenomenon has been studied mostly with respect to its manifestation on rigid, homogeneous surfaces, with soft materials being the topic of more recent investigations. Although, icing often occurs on substrates that are chemically and mechanically heterogeneous, e.g., widely used asphalt concrete, which consists of rigid aggregates embedded in soft bitumen, to date, ice adhesion behavior on such substrates needs to be better understood. Here, we study ice adhesion stresses—the stresses necessary to remove ice—of ice blocks on heterogeneous materials, juxtaposing the behavior of the two main constituents of asphalt concrete, the rigid aggregates (modeled by Macor®) and bitumen, to the behavior of bitumen-Macor® composites. We show that the ice adhesion shear stress on Macor® is almost twice as large as that on bitumen, whereas the ice adhesion normal stress and the normal and shear components of composite stress are in a similar range. We synthesize composite substrates that consist of bitumen stripes on Macor® and find that increasing bitumen width leads to lower ice adhesion stress, while the stripe direction with respect to the applied force direction has a minor effect. Based on our findings, we then coat the most ice-adhesive component (Macor®) with a thin superhydrophobic coating and show that this can reduce ice adhesion stress on the heterogeneous substrates. We also find that for ice formed half on bitumen and half on Macor®, if Macor® is first and bitumen second with respect to the applied force direction (material order), then the measured ice adhesion stress is less compared to the reverse case in material order.ISSN:0165-232XISSN:1872-744