Production Of Asphalt Mixtures Research Articles

Emission of Volatile Organic Compounds in Crumb Rubber Modified Bitumen and Its Inhibition by Using Montmorillonite Nanoclay

Bitumen emits a large amount of volatile organic compounds (VOCs) during the production and construction of asphalt mixture, which can cause both environmental hazards and health risks. In this study, a setup was designed to collect the VOCs released by base and crumb rubber-modified bitumen (CRMB) binders and their composition was characterized by thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS). Next, organic montmorillonite (Mt) nanoclay was added into CRMB binder and its inhibiting effect on the VOCs emission of the binder was investigated. Finally, the VOCs emission models for the CRMB and Mt-modified CRMB (Mt-CRMB) binders were established according to reasonable assumptions. The results indicated that the VOCs emission of CRMB binder was 3.2 times larger than that of the base binder. Due to its intercalated structure, the nanoclay can reduce the VOCs emission of CRMB binder by 30.6%. Especially, its inhibition effects on alkanes, olefins, and aromatic hydrocarbons were more significant. After finite element verification, the established model based on the Fick's second law can describe the emission behavior of CRMB and Mt-CRMB binders well. Overall, the Mt nanoclay can be used as an effective modifier to inhibit the VOCs emission of CRMB binder.

Restoration of physical properties on an aged crumb rubber modified bitumen adding a bio-based recycling agent

Reclaimed asphalt pavement (RAP) is a popular practice in the pavement industry due to environmental and economic benefits. But, RAP must be processed and treated before being reused in new pavements for preventing premature failures. A widely adopted strategy consists of adding recycling agents, and specifically rejuvenators, to mitigate the aging of the RAP binder. From the circular economy perspective, also crumb rubber (CR) from end-of-life tyres have been used to prepare binders with enhanced properties. The actual possibility of using the RAP derived from removed and/or reprocessed pavements containing CR particles (CR-RAP) for the formulation of new suitable mixtures is still a little-explored topic. Moreover, the available rejuvenators tailored on RAP have not yet evidence of effectiveness in producing asphalt mixtures containing CR-RAP. For this purpose, unaged, aged and rejuvenated blends with and without CR were studied through a rheological characterisation to evaluate the potential restoration of their physical properties when a bio-based recycling agent is added. The results of viscosity, frequency sweep, creep-recovery and multiple stress creep recovery (MSCR) tests have highlighted on the one hand the significant contribution of CR in reducing the accelerated aging effects of the binder, on the hand the effectiveness of the rejuvenator in restoring, more clearly at low temperatures, the rheological behaviour of the binders (above all for CRMB) similar to the unaged condition.

Bitumen binders modified with chemically-crosslinked chitosan

Nowadays, the observed trend in road materials technology covers the study of environmentally-friendly modifiers. Therefore, the possibility of modifying bitumen with chitosan and its mixtures with epichlorohydrin was evaluated. The studies were carried out for four different percentages of biopolymer (1.0%, 2.5%, 4.0% and 5.5%) and two percentages (1% and 2%) of crosslinking agents and included the assessment of their influence on the basic binder properties, surface free energy parameters and chemical structure. The results indicate that the appropriately selected quantitative chitosan/epichlorohydrin ratio leads to their crosslinking inside the bitumen causing a softening effect. The study also shows the possible benefits of using biopolymer-modified binders in the production of asphalt mixtures by the enhancement of surface-free energy parameters and reduction of the dynamic viscosity. Chitosan is an environmentally-friendly biodegradable biopolymer, and its chemical crosslinking has a positive effect on the properties of modified bitumen.

Effects of the addition of fatty acid from soybean oil sludge in recycled asphalt mixtures.

Recycling agents provide better additions of reclaimed asphalt pavement (RAP) in the production of new asphalt mixtures. Alternative and residual materials that have the potential as asphalt binder viscosity reducers have gained visibility in the field of paving due to the perspective of circular economy in recycled mixtures. Soybean oil sludge fatty acid is a material produced from soybean oil sludge, a waste generated in the soybean oil refining step. Thus, this paper investigated the physical, chemical, and rheological effects of the asphalt binder PG 64-XX modified by the fatty acid of soybean oil sludge in the contents of 6% and 7% by weight of the binder. The modified binder samples were submitted to penetration tests, softening point, rotational viscosity, performance grade (PG), before and after short-term aging (RTFO), and multiple stress creep and recovery (MSCR). A control asphalt mixture and recycled asphalt mixtures produced with 40% RAP and fatty acid-modified binders were subjected to tensile strength, induced moisture damage, resilient modulus, and fatigue life. A Student's t statistical test verified the significance of the data, as well as the estimation of production costs of these asphalt mixtures. The use of the fatty acid significantly reduced the stiffness and viscosity of the control asphalt binder, decreasing the mixing temperatures at 14°C and 17°C to 6% and 7%, respectively. Using higher fatty acid contents from soybean oil sludge significantly improved the performance of recycled mixtures in tensile strength, moisture damage, and fatigue life. The production cost of recycled asphalt mixtures was lower than that of the control mixture.

Interlayer bonding properties of warm recycled asphalt pavements

The need for sustainable road infrastructures has led to great interest in Warm Mix Asphalt (WMA) technologies, which allow the production, lay-down and compaction of asphalt mixtures at reduced temperatures, about 40°C lower than traditional Hot Mix Asphalt (HMA). The use of WMA ensures lower emissions and is also beneficial in the recycling of Reclaimed Asphalt (RA) deriving from the milling of end-of-life pavements. One of the main concerns regarding WMA is the possible poor adhesion between the pavement layers that could be caused by the reduced working temperatures during the paving operations. However, almost no data are currently available in literature on this aspect, which thus could represent a deterrent to the wide application of WMA by road agencies. In this regard, this paper focuses on the investigation of the interlayer bonding properties of warm recycled asphalt pavements constructed along various Italian motorways and national roads using different WMA chemical additives. The Interlayer Shear Strength (ISS) was measured at different pavement interfaces (wearing-binder, binder-base) and time intervals by testing extracted cores with ASTRA and Leutner equipment. The results show that the interlayer bonding properties of WMA pavements are comparable to HMA pavements and are not affected by the WMA additive type. Moreover, ISS depends on the properties of the tack coat applied between the layers and increases over time due to aging effects, especially when the interface is below an open-graded friction course (OGFC). These findings further encourage the use of WMA as environmentally sustainable technologies for the construction and maintenance of asphalt pavements.

Optimizing the Dose of Warm-Mix Asphalt Additives by Maximizing the Asphalt-Aggregate Adhesion Measured via Surface-Free Energy

Warm-mix asphalt (WMA) is a group of technologies focused on reducing the viscosity of the asphalt binder (or binder) to produce asphalt mixtures at a reduced temperature compared with that specified for conventional hot-mix asphalt mixtures. The WMA technologies include two main groups: foaming and additives. The additives can be classified as synthetic-chemical or natural-based. This study aims at assessing the feasibility of optimizing the WMA additives dose by maximizing the adhesion between the asphalt binder and the aggregate at their interface in WMA mixtures. Adhesion is quantified using energy parameters derived from surface-free energy measurements (SFE), including three WMA additives (Carnauba wax, a natural-based warm-mix additive, Sasobit, and Evotherm). Accomplishing this objective required measurements of SFE for four different asphalt binders, and corresponding WMA-modified asphalt binders were performed. The results suggest the possibility of identifying a WMA-additive dose that maximizes adhesion at the binder–aggregate interface in terms of resistance to fracture (i.e., adhesive failure) and moisture damage, and the wettability of the binder. In addition, the results showed that the inclusion of Carnauba wax as a warm-mix additive yielded equivalent adhesion at the binder–aggregate interface compared with the response of the other commercially available WMA additives evaluated (i.e., Sasobit and Evotherm). Additional studies at the mixture level are recommended to validate further the conclusions obtained in this study.

Sustainable asphalt mixtures: enhancing environmental impact by partial fine aggregate substitution with rubber powder and bitumen modification using Nano-SiO2

ABSTRACT The costs of producing asphalt mixtures are increasing day by day, and with the expansion of roads, the use of natural resources of aggregates has also increased. On the other hand, several factors, such as the increase in traffic load and the number of vehicles, intensify the stress in the pavement layers, reduce the service life of asphalt pavements, and increase the cost of maintenance of road pavements. For this reason, researchers are striving to reduce the costs of asphalt mixture production and the need for natural aggregates by taking advantage of rubberised asphalt in this field. However, when using rubber powder as aggregate, some weaknesses are observed in this mixture, which this study strives to solve by modifying bitumen and improving its performance. The objective of this study is to evaluate the effect of bitumen modified with Nano-SiO2 on the mechanical properties of rubberised asphalt mixture. The percentages of Nano-SiO2 are 0, 0.3, 0.6, 0.9, and 1.2% by weight of bitumen, and used rubber powder has been replaced with fine aggregates with different percentages of 0, 1, 3, and 5%. The characteristics investigated in this study are rutting and fatigue, evaluated in various laboratory conditions. Considering all three target criteria of this study (i.e. environmental, economic and technical), an asphalt mixture containing 3% rubber powder and 1.2% Nano-SiO2 can be considered the best combination to deal with rutting and fatigue. A combination by replacing 3% of aggregates with rubber powder, needs less to extract natural aggregates resources, and also the use of a waste material whose depot in nature is known as an environmental problem in the construction of new asphalt mixture. In addition to environmental aspects, This sample fatigue resistance is about 5%, and the rutting resistance is about 17% more than the control specimen (without additives).

Volumetric Properties and Stiffness Modulus of Asphalt Concrete Mixtures Made with Selected Quarry Fillers: Experimental Investigation and Machine Learning Prediction.

In recent years, the attention of many researchers in the field of pavement engineering has focused on the search for alternative fillers that could replace Portland cement and traditional limestone in the production of asphalt mixtures. In addition, from a Czech perspective, there was the need to determine the quality of asphalt mixtures prepared with selected fillers provided by different local quarries and suppliers. This paper discusses an experimental investigation and a machine learning modeling carried out by a decision tree CatBoost approach, based on experimentally determined volumetric and mechanical properties of fine-grained asphalt concretes prepared with selected quarry fillers used as an alternative to traditional limestone and Portland cement. Air voids content and stiffness modulus at 15 °C were predicted on the basis of seven input variables, including bulk density, a categorical variable distinguishing the aggregates' quarry of origin, and five main filler-oxide contents determined by means of X-ray fluorescence spectrometry. All mixtures were prepared by fixing the filler content at 10% by mass, with a bitumen content of 6% (PG 160/220), and with roughly the same grading curve. Model predictive performance was evaluated in terms of six different evaluation metrics with Pearson correlation and coefficient of determination always higher than 0.96 and 0.92, respectively. Based on the results obtained, this study could represent a forward feasibility study on the mathematical prediction of the asphalt mixtures' mechanical behavior on the basis of its filler mineralogical composition.

Prediction of the Long-Term Performance of an Existing Warm Recycled Motorway Pavement.

Warm mix asphalt (WMA) technologies allow the production, lay-down and compaction of asphalt mixtures at reduced temperatures and the use of higher amounts of reclaimed asphalt pavement (RAP) with respect to conventional hot mix asphalt (HMA), leading to significant environmental benefits and energy savings. However, limited data is available on the long-term performance of such pavements. The objective of this study was to predict the long-term performance of an existing warm recycled motorway pavement (made with WMA mixtures containing RAP) constructed in 2016 in central Italy, along with the corresponding hot recycled pavement (made with HMA mixtures containing RAP). For this purpose, cores were taken from the pavements in 2022 to investigate the binder and base courses through dynamic modulus and cyclic fatigue tests, according to the simplified viscoelastic continuum damage (S-VECD) testing approach. The results of the tests were used to predict the service life of the pavements using two pieces of software, KENPAVE and FlexPAVE, based respectively on the elastic design method and the viscoelastic design method in the presence of damage. The FlexPAVE results indicated that the expected service life of the WMA pavement is much longer than that of the HMA pavement, mainly because the WMA mixtures have better damage properties than the HMA mixtures. Conversely, the KENPAVE simulations predicted a similar service life for the two pavements, highlighting the impossibility of the elastic method to catch the actual contribution of high-performance non-standard materials. The promising outcomes of the FlexPAVE simulations further encourage the application of warm recycled pavements.

Effects of recycling agents and methods on the fracture and moisture resistance of asphalt mixtures with high RAP contents

The design guidelines for recycled asphalt mixtures recommend rejuvenating the oxidized binder by adding recycling agents, which are viscosity and, consequently, temperature-reducing additives. As it is a component of recent use in pavement and its variety, there has yet to be a consensus on the determination of the recycling agent content or the ideal moment of its addition in the recycled asphalt mixture production process. This study aimed to analyze the fracture and moisture performance of asphalt mixtures with the addition of high contents of RAP (25%, 50%, 75%, and 100%) and two recycling agents (ADCAP WM and residual engine oil) in stages distinct from the production of recycled asphalt mixture (directly to the RAP and directly to the virgin asphalt binder). The recycling agents were added at 12%, 15%, and 18% residual engine oil by mass of RAP and 2%, 2.5%, and 3% of ADCAP WM by the total mass of asphalt binder. The asphalt mixtures were submitted to mechanical tests of tensile strength, resilient modulus, ice and thaw cycles, bending fracture, and fatigue life. The results showed that adding residual engine oil in the asphalt binder enables using up to 75% of RAP. In the case of ADCAP WM additions, identical additions of RAP can be performed. Mixtures with ADCAP WM showed higher consumption of fracture energy, while blends with residual engine oil showed a lower slope of the post-peak curve. Conditioning by the freeze–thaw (F-T) cycle method increased the susceptibility of mixtures to the deleterious effect of water. Statistical analyzes showed that the parameters RAP content, recycling agent, and time of addition of the recycling agent presented adequate significance for the analyzed tests. The maximum RAP content to be applied should be 75%, and adding ADCAP WM directly to the binder showed slightly better results than the other combination.

Volumetric view on asphalt mixture

An asphalt layer consists of stone aggregates, binder and air voids. The content of air voids (Vmin and Vmax), the voids filled with bitumen (VFBmin and VFBmax), the content of air voids in stone aggregates (VMAmin and VMAmax) and volume content of bitumen (VBmin) should be determined for each type of asphalt mixture. The volumetric properties of asphalt layer listed above are important parameters for assessing the properties of asphalt and are usually first presented in the requirements for produced asphalt mixtures and built in asphalt layers. Visualization of volumetric properties is important for understanding the composition of the produced asphalt mixture. The most appropriate is a triangular representation of the volumetric requirements for three main components of asphalt layer (stone, bitumen and air).

Moisture susceptibility of waste ceramic tiles modified asphalt mixtures

Waste ceramic tiles have been recognized as viable in producing asphalt mixtures. However, the primary concern is the assurance of its durability, especially in terms of moisture damage. Therefore, this research aims to investigate the moisture susceptibility of asphalt mixtures incorporating waste ceramic tiles (WCT). The coarse aggregates of 25 mm size were partially replaced with WCT at 0%-50% proportions. The Marshall Method of mix design was used to calculate the optimum bitumen content (OBC) at various levels of WCT replacement. Utilizing the retained strength index (RSI) and tensile strength ratio (TSR) tests, the moisture susceptibility of the mixes compacted at OBC was assessed. The results indicate that the continuous increase of WCT leads to decreased TSR and RSI values. The RSI ranges from 91.10%-81.90%, 74.91%-61.07% and 47.89%-41.05% at 1, 3, and 7-day curing, respectively. The TSR ranges from 89.27-74.73%, 71.48-63.81% and 58.02-46.79% at 1, 3, and 7-day curing, respectively. Nevertheless, it was determined that the WCT-modified asphalt mixtures met the TSR and RSI standards for asphalt mixtures with satisfactory moisture resistivity performance at 1 and 3 days of curing. For satisfying performance of WCT-modified asphalt mixtures, the study recommends an optimum proportion of 30% WCT.

Investigating changes in the stiffness of asphalt mixtures caused by laboratory ageing and varying asphalt binder content

The research focuses on evaluating the changes in stiffness of the AC11 50/70 asphalt mixtures with different bitumen content. These changes are induced by the action of thermo-oxidative ageing in both short and long term process. The short-term aging simulates the process of asphalt mixture production, transport and laying. Long-term aging simulates the serviceability process that pavement must withstand during 10 to 15 years of service life. Asphalt mix stiffness measurements were made using the IT-CY method according to EN 12697-26 for 3 different temperatures of 10, 20 and 30°C. To investigate the effect of asphalt binder content on stiffness, measurements were performed on 3 types of mixes with 4.9, 5.4 and 5.9% asphalt binder in the mix. Research in this area has revealed that both the binder content and the thickness of the asphalt film have a relatively significant effect on the change in the stiffness of the asphalt mixture. The changes in stiffness for the asphalt mixture with a binder content of 4.9% were only minimal in terms of the degree of aging. At 10°C, even a minor decrease in stiffness was observed for this mix. The asphalt mixture with 5.9% binder had a very significant increase in stiffness in terms of the degree of ageing.

Use of Recycled Asphalt and Waste Materials in Production of High-Performance Asphalt Mixtures

The research has been conducted to test the asphalt produced in Latvia using local mineral materials and local recycled modifiers (fiberglass, crumb rubber), as well as the recycled asphalt used in the production of high-modulus asphalt mix, which will meet the local Latvian road construction specifications and will be economically, environmentally and technically more attractive. In the theoretical part, the available sources were studied to establish a theoretical framework, assess possibilities for using recycled materials, define the concept of fiberglass, and consider its performance in asphalt mixes. During the experimental stage of the research, different asphalt mix formulas with glass fiber, crushed rubber, RAP, and other additives used to stabilize asphalt mixtures for surface and base layers were designed in the laboratory; they were compared to the reference mixes using performance tests. Then the mixtures with the best results were used in the test section of a high-intensity local road. The samples of the asphalt layers of the paved test section were tested as well. Two asphalt mixes were designed according to local Latvian road-building specifications, using fiberglass reinforcement 0.15% + 30% RAP for the base layer and crushed rubber 15% and RAP 30%+EVOFLEX CA© variable for the surface layer. The aim of the research is to offer solutions for reducing new asphalt pavement production allowing for the use of recycled asphalt mixes in local road building. The performance tests of the test asphalt mixes showed that recycled asphalt pavement fully meets the requirements of the local Latvian road-building specifications.

Effect of low dosage crumbed rubber on the mechanical properties of a dense graded asphalt mixture

The benefits of crumb rubber modification of bituminous binder for asphalt mixture production is well established. Although most research has used high (20–30% by mass of the bitumen) crumb rubber dosages, there is now interest in low (5–15%) dosages for use in local road surfacing, where mechanical properties are less important. This paper quantifies the effects of low-dosage crumb rubber on the mechanical properties of a typical dense graded local road surface mixture. It was concluded that 5–10% crumb rubber dosage significantly increased the deformation (rutting) resistance and crack (fatigue) resistance of the asphalt. The effect of crumb rubber on mixture stiffness (modulus), moisture damage (stripping) resistance and workability (compactability) was mixed but was unlikely to present any practically important benefit or detriment. Consequently, 5–10% was concluded to be the preferred range of crumb rubber dosage for dense graded asphalt for local road surfacing.

Numerical Approach Regarding the Effect of the Flight Shape on the Performance of Rotary Dryers from Asphalt Plants

Thedistribution of aggregates in the cross-section of the drum, in the case of equipment used for the production of asphalt mixtures, essentially influences the performance of rotary dryers. In the research carried out in this article, the optimization of the distribution of particles in the active region of the drum was pursued by modifying the geometric shape of the flights, taking into account at the same time the influence of the technological parameters of operation such as drum rotation speed and drum filling degree. The studies were performed using the discrete element method (DEM), and the obtained results revealedthat flight geometry strongly influences drying efficiency. The efficiency of rectangular double-angled type flights is strongly influenced by the drum rotation speed, especially at high levels of filling degree (20%), with the mass of aggregates exposed to drying increasing by 41.11% when drum rotation speed increases from 10 rpm to 15 rpm. Similarly, hook-type flights show a minimum efficiency at 15% filling degree and 15 rpm. The comparative analysis of the flight shape is not only carried out in order to establish the variant that ensures maximum drying efficiency but also from the point of view of execution technology. (Original flights can be obtained by deep drawing, but they have a complex geometric configuration; cup flights can be obtained very easily from tubular material cut on the generators; hook flights by deep drawing or welding the cut tubular material on a straight plate, and the L type by deep drawing). Taking into account that semi-finished products can be very thick, it is possible that, in some cases, hot embossing is necessary, so making them out of tubular material eliminates these inconveniences. All the presented results highlight that the rectangular, double-angled and hook-type flights are the most appropriate shapes that can be used regardless of the drum filling degree and rotation speed.

Comparative environmental performance of pavement structures considering recycled materials and regional differences

The construction of pavements incorporating reclaimed asphalt pavement (RAP) is taking place around the world, implying the necessity to quantify their net environmental impacts. Life cycle assessment (LCA) is a popular method to analyze the environmental impacts of a product along the whole value chain, providing guidance to practices and technologies from environmental perspectives. However, the LCA research of RAP-modified pavement is seldom performed in Brazil. In addition, as an important source of uncertainties, there is also need of discussion regarding the geographical and technological characteristics in the LCA of pavements. For these motivations, this paper performs a cradle-to-gate LCA to compare the environmental performance of asphalt pavement in Brazil and Switzerland, using the practical rates of RAP use. The functional unit was defined based on the same traffic volume and service life of asphalt pavements, where the mix design and pavement structures follow the standards of the two countries. The results showed that RAP recycling can improve the environmental performance of hot asphalt mixtures in both countries. Binder amount has a high environmental burden and its reduced use by adding RAP has a positive environmental effect. Type of fuel also plays an important role in LCA. In Brazil, it is not recommended to use heavy oils as fuel during the mixing process if other options such as methane gas is available. The results show that the Swiss production of asphalt mixture had lower environmental impact. Nevertheless, a strategic location of material suppliers and mixing plants could lower the transportation distances, improving its environmental performance.

Rubberised stone mastic asphalt mixtures: a performance-related evaluation

ABSTRACT The binder content of rubberised asphalt mixtures is usually increased compared to that used in conventional asphalt. This increase is deemed important to compensate for the reduction in the actual bitumen due to the existence of rubber particles. This study presents the results of performance evaluation conducted on different rubberised Stone Mastic Asphalt (SMA) mixtures produced using different types and contents of rubberised bitumen. The energy ratio (ER) computed from Superpave Indirect Tensile (IDT) tests was used to evaluate the cracking resistance of asphalt mixtures while the rutting behaviour was evaluated using the Repeated Load Axial Test (RLAT). The indirect tensile stiffness and strength were used to evaluate the moisture susceptibility. Using the same binder content for rubberised SMA mixtures as used in the conventional mixtures can still give superior performance properties. Adding crumb rubber to softer base bitumen can produce asphalt mixtures with superior cracking and rutting resistance.

ДОСЛІДЖЕННЯ СТРУКТУРУВАЛЬНОЇ ЗДАТНОСТІ МІНЕРАЛЬНОГО ПОРОШКУ РІЗНОГО ПОХОДЖЕННЯ

Introduction. Mineral filler is an important component of asphalt mixture which plays an important role in ensuring the quality of asphalt mixtures. The specific surface of mineral filler is about 90 % of the specific surface of aggregates in asphalt mixture. Being a part of asphalt mixture, mineral filler performs two roles: it fills the pores between fine grained and coarse-grained aggregate and structurizes bitumen. Recently, a significant amount of works has been devoted to the study of industrial waste as a raw material for the production of mineral filler. First of all, these studies are related to the evaluation of the direct effect of mineral filler mainly on the volumetric properties of asphalt concrete or on its strength properties. Since one of the purposes of mineral filler is structurizing of bitumen, it is reasonable to pay considerable attention when studying the alternative raw materials, to the structurizing ability of the obtained mineral filler, as insufficient structurizing ability of mineral filler can cause plastic deformations, and too high structurizing ability causes the decreasing of its low-temperature crack resistance. Problem statement. In order to evaluate the structurizing ability of the mineral filler, the «ring and ball method» is preferably used, in which the structurizing ability is evaluated by ane increase in the softening point of bitumen after mixing with the mineral filler. However, this method characterizes only the effect of mineral filler on the properties of bitumen at high operating temperatures, but it does not consider the possible change in the properties of bitumen at low operating temperatures and at process temperatures. Objective. This study explores the evaluation of the effect of mineral filler of different origin on the structuring of bitumen at low and high operating temperatures, as well as at process temperatures for the production of asphalt mixtures. Materials and methods. Mineral filler of limestone, granite, quartzite, fly ash, mechanically activated fly ash, the ash from hydraulic waste disposal, blast furnace slag and cement had been used for research. Results. The results of researches showed a significant effect of the mineral filler origin on its structurizing capacity. The structurizing capacity of mineral filler increases with growing temperature; so at low operating temperature mineral filler has almost no effect on the properties of bitumen, and with the increase of temperature to the values of high operating temperature and process temperatures of asphalt mixtures production, the effect of mineral filler on bitumen properties becomes much more significant. Conclusions. Studies of the structurizing capacity of mineral filler of different origins by changing the softening point had shown the possibility of using the raw materials of different origins for the production of mineral filler namely: raw materials from rock (sedimentary, erupted and metamorphic), raw materials from industrial by-products (fly ash, ash from hydraulic waste disposal, blast furnace slag), and also practically finished construction product (cement). For evaluation of the effectiveness of mineral filler, it is possible to study its structurizing capacity by changing the brittleness temperature, as during determination of this indicator, it is possible to evaluate the effect of structuring, which consists in maintaining the homogeneity of asphalt binder during the preparation of plates.

Regulating asphalt pavement temperature using microencapsulated phase change materials (PCMs)

The use of phase change materials (PCMs) to regulate pavement temperatures has been previously studied, with the most successful studies using porous aggregates to stabilize the PCMs. However, this technique can lead to issues with PCM leakage and low PCM content. A less studied method is the use of PCM microcapsules, which also presents challenges since most microcapsules are not strong nor stable enough to survive the high temperatures and compressive forces experienced during asphalt mixture production and placement. This work presents a study of the properties of a new commercial microcapsule type with robust walls and high thermal stability, that are expected to overcome the aforementioned issues. Results from differential scanning calorimetry and thermogravimetric analysis confirmed the microcapsules exhibited high latent heats (200 J/g) and are thermally stable below 400 °C. Additionally, approximately 90% of the capsules remained unbroken after being milled at 140 °C for 20 min, suggesting they are capable of withstanding the mixing and compaction stages of asphalt pavement construction. When PCM microcapsules were added to HMA, thermal cycling experiments showed that specimens containing 10 and 20 vol% PCM exhibited temperature lags of 5 to 10 °C from the control mixture, as they approached the PCM melting/freezing temperature. These results confirm the ability of microencapsulated PCMs to regulate asphalt pavement temperature. However, results from measurements conducted at 40 °C and 1 Hz showed a 75% reduction of the dynamic modulus in specimens containing PCM microcapsules, which could indicate that the addition of these materials also affect asphalt mixture stiffness.