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Asphalt pavements inevitably deteriorate over time, requiring frequent maintenance work to ensure the proper serviceability of the road network. Small interventions, such as resurfacing for pavement preservation, are preferable to reconstruction at the end of roads’ in-service lives as they limit environmental- and economic-related impacts. Thin asphalt overlay (TAO) mixture represents a suitable maintenance solution to restore the functional properties of road surfaces. Due to the increasing awareness of the depletion of non-renewable resources and the importance of promoting the circular economy, this study evaluated the possibility of using fully recycled TAO mixes by investigating their volumetric and mechanical properties. Two eco-friendly TAO mixes were designed using recycled aggregates from reclaimed asphalt pavements, a municipal solid waste incinerator, and steel slags in order to meet EN 13108-2 requirements. The TAO mixes differed in regard to the type of bituminous binder (neat/SBS-modified bitumens) and fibres (natural/synthetic) employed. The preliminary results demonstrated that the presence of recycled aggregates did not negatively affect the workability and the mechanical performances of the two sustainable mixtures in terms of stiffness, tensile resistance, rutting and moisture susceptibility. Of these, the TAO mix with neat bitumen and synthetic fibres showed enhanced mechanical performance highlighting the structural effects of the used fibres.

The various acknowledged benefits given by the use of fibre for construction materials made this component essential for specific applications, including asphalt pavements. Fibres in asphalt mixtures usually play two important roles: acting as an asphalt stabilizer to decrease the drain-down effect; and as a reinforcing additive to enhance the mechanical performance of asphalt mixtures. To better understand their use, this paper aims to review the various uses of different types of fibres in asphalt pavements. The main variables that influence the effectiveness of fibres and the reinforcing mechanism of using fibres are discussed. Furthermore, a state-of-the-art of the combined use of fibres and other additives, such as crumb rubber, polymer modifiers, and nano-size modifiers, is presented. Results from relevant studies confirmed the effectiveness of using fibres in asphalt pavements and the significance of optimizing the mixing method, size and dosage of fibres to achieve more suitable performance. Additionally, the latest research findings and experimental applications are discussed, with a specific focus on waste and recycled materials. Exploring feasible recycled alternatives to natural and traditional fibres, optimizing the use of fibres from wastes, and combining the use of fibres with other sustainable technologies, could maximize the environmental benefits of using fibres in asphalt pavements.

The widespread use of natural aggregates is one of the main causes of the depletion of natural resources, as aggregates are constituents of several construction materials. Alternatively, it is, today, proven to be feasible to use mining tailings, either natural or recycled materials, to produce artificial aggregates through specific processes. A possible way to produce artificial aggregate is through the alkali activation of the powdered material in a process called geopolymerization. This study proposes to use a basalt powder and two different metakaolins as precursors for the production of an alkali-activated artificial aggregate, with a specific shape and size achieved by using 3D-printed molds. The experimental aggregates were evaluated using traditional tests for natural aggregates, such as resistance to compression, specific density and resistance to abrasion and fragmentation. Furthermore, the material was chemically analyzed in order to evaluate the geopolymerization process promoted by the two adopted metakaolins. The physical tests showed that artificial aggregates do not perform well in terms of resistance to wear and fragmentation, which can be improved. However, they revealed promising results in terms of skid, polishing and micro-texture.

Most of the waste materials recycled for the production of new construction materials are by-products of various manufacturing processes, such as the aggregate washing process. Recycling such materials is of paramount importance since it could reduce the adverse environmental impacts resulting from landfilling. Various studies have attempted to recycle different types of waste materials and by-products into concrete paving blocks. However, the availability of literature on concrete paving blocks containing waste silt is quite scarce. Thus, the current paper focuses on mix design optimization and production of concrete paving blocks containing high amounts of waste silt resulting from the aggregate production process. Using the mixture Design of Experiments (DOE), 12 sets of concrete paving blocks with different aggregate blends were produced to optimize the mix design. Once the final mix design was achieved, the physical and mechanical properties of the concrete paving blocks were investigated following the EN 1338 standard. Shape and dimension measurements and various tests, including water absorption, tensile splitting strength, abrasion resistance, and slip/skid resistance were conducted on the experimental concrete paving samples. Overall, the produced concrete paving blocks showed promising properties for future applications in pedestrian walking paths.

Reclaimed Asphalt Pavement (RAP) material mainly consists of removed asphalt concretes from existing infrastructures and, to a minor extent, of wasted or rejected mixes during the production processes. Being composed of two valuable non-renewable resources, i.e., aggregates and bituminous binder, its conscious use can ensure the sustainability of asphalt pavement construction. Thanks to the use of RAP material in new asphalt products, the USA saved 4.1 million tons of virgin binder and 78 million tons of virgin aggregates in 2018. Therefore, the use of RAP for the production of new asphalt formulations at the top of the recycling hierarchy is preferable instead of being down-cycled in low-value applications. The RAP material represents one of the most re-used construction products worldwide; in 2018, approximately 88% wt. and 72% wt. of RAP were used in USA and Europe, respectively, as aggregates for Hot, Warm and Cold Asphalt Mixtures and for unbound layers. Several studies have revealed positive responses of the recycled asphalt mixtures with high or very high content of RAP. However, the common practices of many countries still limit the RAP content to a 15–20% wt., on average, in the recycled asphalt mixes. The amount of RAP in asphalt concretes can be significantly increased by applying good management practices of the RAP, either processed or not, as well as novel production technologies and advanced mix design approaches. This manuscript aims to summarize the state-of-the-art of use of RAP aggregates in new asphalt mixtures. The economic and environmental benefits are also discussed.

This study aims to investigate the feasibility of including silt, a by-product of limestone aggregate production, as a filler in geopolymer cement. Two separate phases were planned: The first phase aimed to determine the optimum calcination conditions of the waste silt obtained from Società Azionaria Prodotti Asfaltico Bituminosi Affini (S.A.P.A.B.A. s.r.l.). A Design of Experiment (DOE) was produced, and raw silt was calcined accordingly. Geopolymer cement mixtures were made with sodium or potassium alkali solutions and were tested for compressive strength and leaching. Higher calcination temperatures showed better compressive strength, regardless of liquid type. By considering the compressive strength, leaching, and X-ray diffraction (XRD) analysis, the optimum calcination temperature and time was selected as 750 °C for 2 h. The second phase focused on determining the optimum amount of silt (%) that could be used in a geopolymer cement mixture. The results suggested that the addition of about 55% of silt (total solid weight) as filler can improve the compressive strength of geopolymers made with Na or K liquid activators. Based on the leaching test, the cumulative concentrations of the released trace elements from the geopolymer specimens into the leachant were lower than the thresholds for European standards.

Carbon footprint reduction of paving materials could be explored through recycling mining by-products into different applications, which will preserve natural resources and decrease environmental issues. One possible approach is to reuse quarry dust and mining ore waste as precursors in geopolymer applications. geopolymers are mineral polymers rich in aluminosilicates with an amorphous to a semi-crystalline three-dimensional structure. The current review aims to summarize the studies conducted during the past decade on geopolymers containing quarry dust and mine tailings. The first section discusses various precursors used for geopolymer cement production such as metakaolin, ground granulated blast furnace slag (GGBFS), fly ash, and quarry/mining ore wastes including silt, tungsten, vanadium, copper, gold, zinc, marble, iron, basalt, and lithium. Different calcination treatments and curing conditions have been summarized. In some cases, the precursors are required to be calcined to increase their reactivity. Both ambient temperature and elevated temperature curing conditions have been summarized. Less attention has been paid to room temperature curing, which is necessary for field and industrial implementations. Engineering properties such as compressive strength, density, durability and acid resistance, water absorption and abrasion of geopolymers containing mining waste were reviewed. One of the main barriers preventing the widespread use of waste powders, in addition to economic aspects, in geopolymers could be due to their unstable chemical structure. This was shown through extensive leachate of Na+ or K+ cations in geopolymer structures. The review of over 100 articles indicated the need for further research on different aspects of quarry waste geopolymer productions before its full industrial implementation.

Aiming to study the rheo-mechanical effects of fine crumb rubber into gap graded stone mastic asphalt (SMA) mixtures, a multi-scale experimental approach was adopted. Therefore, in the perspective of the reuse of end of life tires&rsquo, in asphalt layers, the adopted new dry-hybrid technology effects have been investigated from the mastic, mortar and mixture points of view. The new rubberized asphalt production technology allows the use of rubber powder as filler, the rubber amount optimization being validated through multi-scale performance tests. Mastics and mortars&rsquo, complex modulus measured with dynamic shear and torsional tests were related to the mixture stiffness modulus recorded in direct tension-compression mode. The rheological properties of mastic are strictly influenced by the rubber presence, and consequently the asphalt mixtures stiffness and thermo-sensitivity are connected to the mastic and mortar rheo-mechanical behavior. Results are consistent through the adopted approach and reveal that with the new dry-hybrid technology, overcoming the wet and dry limits, it seems to be possible obtaining more durable and eco-friendly bituminous pavement layers.

Mineral fillers have a key role in controlling the mechanical characteristics of asphalt concretes (AC). The cohesion properties of bituminous mastics depend upon the fillers used, and, therefore, so do the effective strength of asphalt concretes and the durability of the pavement layers. Recent research has studied the using of waste bleaching clays from the food industry as a substitute of common limestone filler traditionally used in the production of ACs for binder layers. In this paper, a waste bleaching clay is proposed as alternative filler for the production of a porous asphalt (PA) mixture. The waste filler (Ud) comes from two consecutive stages in the industrial process for decolouring vegetable oils and producing biogas from bleaching clays. The aim of this research was to assess the performance of the PA, in terms of physical and mechanical characteristics, when compared to traditional PA. Thus, two porous asphalt mixtures with the same dosages of binder and aggregates gradation were studied in the laboratory: one with traditional limestone filler and one with waste bleaching clay. Tests results are promising in terms of increasing of Indirect Tensile Strength, stiffness, and resistance to permanent deformations.

This paper presents the results of a laboratory research on asphalt concretes made with synthetic expanded aggregates produced from waste materials. In the last years, the use of wastes for the production of new construction materials is constantly increasing. In the present research, through the alkali-activation process, two different wastes are used for the production of synthetic lightweight aggregates: a digested spent bentonite clay and a basalt powder. Both experimental aggregates have been fully characterized in compliance with the reference standards for lightweight aggregates. Taking as a reference some Italian specifications for special wearing course asphalt concretes, the physical and mechanical properties of two different experimental asphalt mixtures have been evaluated. For this purpose, a mixture prepared with traditional expanded clay aggregates was used as reference material. The presented preliminary results indicate that the use of alkali-activated lightweight aggregate in total substitution of the expanded clay does not negatively affect the performances of the asphalt mixture. Moreover, the alkali-activation of these waste materials seems to be a suitable and sustainable solution for the production of lightweight aggregates for this and other purposes.

Besides the many advantages of porous asphalt (PA), the permanent deformation resistance, fatigue strength, stripping and moisture susceptibility are not as good as for dense graded mixtures. In this research, the effectiveness of adding crumb rubber (CR) by dry method to PA mixtures was assessed. Rubberized porous asphalt (RPA) mixtures manufactured incorporating CR into SBS modified asphalt concrete were produced and compared with a control mixture by means of Indirect Tensile Strength (ITS), Indirect Tensile Stiffness Modulus (ITSM), moisture susceptibility, permeability, Cantabro, rolling bottle, draindown and creep tests. Results proved that although the application of CR reduces the vertical permeability and permanent deformation resistance, it improves the bitumen/aggregate affinity and it controls the draindown rate without adding fibres. On the other hand, the use of CR decreased the ITSM value at low temperature, which represents a lower susceptibility to thermal cracking. Other complementary test results in this research support the effectiveness of RPA mixtures.

Every year, up to 3 billion tons of non-renewable natural aggregates are demanded by the construction sector and approximately 623 million tons of waste (mining and quarrying) was produced in 2018. Global efforts have been made to reduce the number of virgin aggregates used for construction and infrastructure sectors. According to the revised waste framework directive in Europe, recycling at least 70% of construction and demolition waste materials by 2020 was obligatory for all member states. Nonetheless, quarries must work at full capacity to keep up with the demands, which has made quarry/mining waste management an important aspect during the past decades. Amongst the various recycling methods, quarry waste can be included in cement mortar mixtures. Thus, the current research focuses on producing cement mortars by partially substituting natural sand with the waste silt obtained from the limestone aggregate production in S.A.P.A.B.A. s.r.l. (Italy). A Design of Experiments (DOE) method is proposed to define the optimum mix design, aiming to include waste silt in cement mortar mixtures without affecting the final performance. Three cement mortar beams were produced and tested for each of the 49 randomized mixtures defined by the DOE method. The obtained results validate the design approach and suggest the possibility of substituting up to 20% of natural sand with waste silt in cement mortar mixtures.

Alternative materials to replace cement in pavements have recently been widely studied with the purpose of decreasing the environmental impacts that the construction industry generates. In this context, the implementation of sustainable urban drainage systems has grown, especially with porous pavements, with the intention to reduce water and environmental impacts. In the present investigation, the addition of alternative materials to minimize the use of cement in porous concrete pavements is evaluated. Starting from a partial substitution of Portland cement with metakaolin, experimental geopolymer concretes were produced with metakaolin and waste basalt powder according to several dosages. Two sets of mixtures were analyzed to evaluate the Porous Concrete Design (PCD) methodology for porous concrete mixtures with alternative materials. A deep analysis was proposed for the evaluation of the mechanical and volumetric properties of the mixtures. Results demonstrated that replacing 5% of cement with metakaolin can increase both permeability and indirect tensile strength. Geopolymer mixtures can achieve permeability significantly higher than the traditional porous concrete, but this decreases their indirect tensile strength. However, considering the promising results, an adjustment in the mix design of the geopolymer mixtures could increase their mechanical properties without negatively affecting the porosity, making these materials a suitable alternative to traditional porous cement concrete, and a solution to be used in urban pavements.

Today the use of recycled and second-hand materials can be considered as a suitable solution for the construction or the rehabilitation of road pavements. The increasing interest in this process lead to the study and the evaluation of different waste materials, not directly connected to the construction field, among these Crumb Rubber from end-of-life tires. To date, this recycled material has been added into bituminous mixes for road pavements according to several technologies, for the production of different mixtures. In the present paper, the crumb rubber was used for the production of Stone Mastic Asphalt (SMA) according to a new dry-hybrid technology. A full laboratory investigation and a trial field study are here presented. A complete physical and mechanical characterization was carried out to define a specific mix design. Once defined these properties, a full-scale test section was constructed: specific in situ tests and collection of samples were planned. In both the laboratory and trial field phases, tests results were always compared to those obtained with a traditional SMA mixture. In an environmental prospective, fumes and emissions during laying were also analyzed. The goal of this research project was to analyze and evaluate the different physical, mechanical and functional characteristics induced by the use of Crumb Rubber for the production of SMA mixtures according to the proposed new dry-hybrid technology. As overall result, the presence of Crumb Rubber does not seem to negatively affect the volumetric properties of the mixture. SMA1.20 shows mechanical properties comparable to the reference mixture and higher if compared to SMA0.75. As for the acoustic properties, both the rubberized surfaces reduce the emission of noise if compared to the traditional SMA layer. The monitoring of pollutants during paving operations confirms the effective environmental benefits deriving from the use of the new dry-hybrid technology here proposed.

There is growing interest in construction field issues related to environmental protection, energy saving and raw materials. Therefore, the interest in recycling waste materials to produce new construction ones is constantly increasing. This study proposes a new methodology to produce lightweight aggregates (LWAs) by alkali-activation of two different waste powders: a digested spent bentonite clay and a basalt powder. Metakaolin, as secondary precursor, was added to the mixtures according to mix-design proportions, to improve the mechanical properties of the final materials, while a specific activators mix of Sodium Silicate and Sodium Hydroxide enabled the alkali-activation. The expansion process, on the other hand, was obtained using Peroxide within the liquid mix. The experimental LWAs were analyzed and tested in compliance with the EN 13055-1 standard. A more in-depth analysis on LWAs&rsquo, air voids content and porosity was also carried out by the means of Mercury Intrusion Porosimetry and Nuclear Magnetic Resonance. The results were compared with those obtained from commercial Lightweight Expanded Clay Aggregate, which represents one of the most common LWAs in the construction field. According to the presented preliminary results, the use of alkali-activated waste powders seems to be a suitable solution for the production of eco-friendly LWAs by allowing the recycling of waste materials and energy saving for their production.

Undoubtedly, the most commonly used method for road maintenance includes the use of winter service vehicles to clear thoroughfares of snow and the spraying of chemicals to prevent ice formation on the road surface. The application of these traditional methods on road and airport pavements possesses numerous environmental, organizational, and technical challenges. To overcome these critical issues, new nontraditional technologies that act within the pavement, thereby increasing its temperature, have been developed. In relation to the heat source used, these are classified into chemical and physical methods. The purpose of this research is to study the temperature variation under the thermal transient process produced by the action of the physically heating device installed in the road pavement. The heating device is a ribbon, made of amorphous material, which is able to produce heat to warm up the pavement and its surface. Based on its principle of operation, it is classified among the nontraditional physical methods for the treatment of snow and ice. In this work, the performance of the heating ribbons on an experimental site at the G. Marconi International Airport in Bologna (Italy) is presented.

Today, it is a well known fact that mineral fillers have a key role in controlling the mechanical characteristics of hot mix asphalts. The cohesion properties of bituminous mastics depend upon the fillers used, and, therefore, so do the effective strength of asphalt concrete and the durability of the pavement layer. In this study, waste bleaching clays from the food industry are proposed as an alternative to common limestone mineral filler for the production of Hot Mix Asphalts (HMA). The bleaching clays used here come from two consecutive stages in the industrial process for decolouring vegetable oils and producing biogas from waste clay, where the former is richer in residual organic fats (20–25% in weight against less than 1%). The aim of this research was to assess the performance of a common binder course asphalt mixture, in terms of physical and mechanical characteristics, when waste bleaching clays are used as an alternative. For this purpose, data obtained from a control hot mix asphalt produced with traditional limestone filler were compared to those recorded for bituminous samples containing waste bleaching clay from either the first or the second stage above, in place of the limestone filler. Results show a significant difference between the effects produced by the bleaching clays from the two stages on the performance of the asphalt concrete, where the second stage shows more positive effects both on indirect tensile strength and stiffness and on the bituminous mixture’s resistance to permanent deformations.

Today recycling is one of the most innovative and interesting techniques for the rehabilitation of destressed road pavements. In recent years the increased interest in this process, has led to the development of various alternative methods for the recovery and the reuse of road bituminous materials. Cold recycling is, among the recycling techniques, certainly the most studied and developed: it allows the recovering of bituminous material from an existing pavement without the addition of heat, whilst ensuring the creation of high quality bound base layers. A wide range of materials have been tested together with Reclaimed Asphalt Pavement (RAP) and, consequently, there is a large number of variables that can be considered in the mix-design process of new eco-friendly Cold Recycled Mixes. In particular, the present research involves the use of Crumb Rubber within a mixture containing 100% Reclaimed Asphalt Pavement, cold recycled with bitumen emulsion and cement. Two different Crumb Rubbers were adopted: one from the ambient production method, and one produced with the cryogenic process. The goal of this research project was to analyze and evaluate the different physical and mechanical characteristics induced by the shared use of two different types of Crumb Rubber in the Cold Recycled Mixes.

Asphalt concrete (AC) recycling is probably the most cost-effective technique for the rehabilitation of stressed road pavements and for the construction of new ones. The increased interest in this technology comes from the need of reducing the costs connected to the production processes and to the use of virgin raw materials. In fact, the benefits connected to the use of Reclaimed Asphalt Pavement (RAP) are related to the possibility of substituting the natural aggregates and the virgin binder of an AC mixture, without negatively affecting its mechanical properties. When this process is made at ambient temperature (Cold Recycled Mixes – CRM), more advantages are brought about with, above all, the reduction in energy consumption and emissions during in plant production and laying, in addition to the actual possibility of achieving durable pavement layers. A CRM totally made of RAP is proposed in this research, the main goal of which was to evaluate the different physical and mechanical characteristics derived by the large use of recycled materials. According to the final mix-design, CRM does not show significant differences in terms of physical properties, when compared to a Hot Mix Asphalt (HMA) for base layers. Moreover, even if the experimental mixture shows lower mechanical values, these are acceptable and higher than the limits imposed by the most common Italian technical specifications for Cold Mix Asphalts containing up to 30% RAP.

Asphalt concrete mixtures are composed of two main components: aggregates and binder. The fraction of aggregates passing through the 63μm sieve is traditionally considered as filler. During years, several researches have shown the importance and the influence of filler in controlling the physical and mechanical properties of Hot Mix Asphalts (HMAs). The main objective of this research is to investigate and to assess the effects given by the use of Mining Waste Powder (MWP) within HMAs in total substitution of traditional limestone filler. The MWP used in this study is a residual of the tungsten extraction process in Panasqueira (Portugal) mine. The evaluation of properties conferred by the presence of the MWP filler within asphalt mixtures is based on a physical and mechanical laboratory characterization. For this purpose, tests have been performed both on bituminous mastics and on HMAs. Results indicate that the use of MWP in total substitution of limestone filler does not negatively affect the performances of HMAs and their bituminous mastics.

The infrastructure system has experienced an unprecedented development in the last fifty years. Most of the road pavements have been used for over twenty years and today require increasing maintenance to keep acceptable their levels of performance. In addition, the use of virgin and raw materials has been strongly restricted by raising price and eco-friendly policies. As a result, researchers and companies have focused their attention on recycling techniques with waste and second-hand materials that could lead to the construction and restoration of civil infrastructures without negatively affecting their mechanical properties. The study presented in this paper pursues this trend of research, by the evaluation of the performance of two different 100% Recycled Cement Bound Mixture (RCBM) for base layers. Data were always compared to those obtained for a traditional Cement Bound Mixtures (CBM) entirely made of virgin aggregates. The experimental programme was divided into two different and consecutive phases: a laboratory study and a trial field phase. In the first, the aim was the mix design and the physical and mechanical characterization of three mixtures. In the second phase, a full-scale trial field was realized: in situ tests and sampling were planned in four dates, corresponding to 0, 60, 180 and 365 days of trafficking. Based on results, the replacement of virgin aggregates with waste materials in CBMs, according to these specific mix designs seems to be a practicable solution for the construction of base layers with suitable performance.

Based on the initial results obtained in the research program REMINE (H2020 RISE-Marie Curie Action) in progress, authors discuss the potential use of Panasqueira mine waste aggregates and fillers in the production of construction materials for transportation infrastructures. An estimate of the economic and social impact that this form of recycling could have on the local communities and on the perspective of other mining activities in Portugal and Europe is given. The main goals of the project are to explore materials design methods of alkali-activated composites from mining/quarrying wastes based on the demanding requirement of rheology to fit for various processing techniques and applications. The development of artificial aggregates through alkali-activation of mining waste presents itself as a viable technical solution to compete with other commonly adopted materials and may lead to the manufacturing of less porous and harder aggregates for the production of most of the road paving materials.

The use of waste materials in road construction is becoming widely spread due to economic and environmental needs. Construction and demolition waste materials and mining residues have been studied for a long time. However, the use of fine materials, mainly from mine tailing and mining residue, is still complex, as they can be used as inert materials into the mix or can become a reactive agent in geopolymer mixes. In the present paper, an experimental application of basalt powder is proposed in the geopolymerisation reaction to produce artificial aggregates. In order to understand the input and output variables’ interactions used in the mix design, a statistical method called Design of Experiments was applied. With this design approach, it was possible to optimize the mix design of the experimental geopolymer mortars. The study evaluated several mixes with respect to their workability, compressive strength, and success rate of aggregates production. Finally, a model for predicting compressive strength is proposed and evaluated.

There has been a significant increase in the demand for using recycled materials in construction because of the lack and limitation of available natural resources. A number of industrial and domestic waste products are being used in the replacement of traditional materials for road construction, and many studies have been carried out in recent years on the use of different recycled materials in substitution of conventional fillers in Asphalt Concretes (AC). The aim of this laboratory research is to analyze the physical characteristics of three different recycled fillers and compare them with those of a traditional limestone filler. The alternative fillers presented in this paper are: a waste bleaching clay that comes from two consecutive stages in the industrial process for decolouring vegetable oils and producing biogas (Ud filler), a dried mud waste from a tungsten mine (MW filler) and a recycled glass powder (Gl filler). Results show significant differences between the fillers, and, in particular, Rigden Voids (RV) seem to have the largest potential influence on the rheology of ACs.