Bitumen Content Research Articles

Experimental investigations on carbon black in bituminous concrete mixes for road works

This critique reports the laboratory investigations performed to evaluate the possibility of using carbon black as a modifier on VG 30 grade bitumen and bituminous concrete mixes to obtain improved mix characteristics. The influence of carbon black on physical, rheological, rutting and fatigue parameters, Marshall and workability properties at various dosages was investigated. To investigate the physical characteristics of modified bitumen, tests such as penetration, softening point, viscosity, separation, and elastic recovery were carried out. Rheological test was conducted to characterize the carbon black modified bitumen, using Dynamic Shear Rheometer (DSR) as per ASTMD7175-08 (2004) in terms of phase angle and complex modulus, hence rutting and fatigue parameters were determined.The mid-point gradation at 30% combined index was used to make the grade-I bituminous concrete mixes in accordance to MoRTH guidelines. The specimens underwent the Marshall Stability test in accordance to ASTM D 1559. The prepared specimens were subjected to conventional Marshall Stability test. Workability of bituminous mix was assessed in terms of torque value, which was in turn related to viscosity of bitumen and aggregate shape factors.Test results showed that carbon black is a potential material that can be used as a modifier in improving the bitumen properties. The test results of DSR showed that carbon black enhanced rutting and fatigue resistance of the bituminous mixes at wide range of temperatures compared to plain bitumen. The Marshall Stability test has resulted in better properties for bituminous mixes at optimum bitumen content using carbon black. Thus, the study offers encouraging findings that support the exploit of carbon black as modifier in bitumen. The study can prove to be a step closer towards global bitumen sustainability as well as achieve improved mix properties resulting in enhanced performance.

EFFECTS OF WASTE CROSSED-LINKED POLYETHYLENE ELECTRICAL WASTE COATING ON THE PROPERTIES OF BITUMEN

The high cost of construction materials and increased axle loads has motivated researchers to seek alternative cost-effective materials for road construction. Studies on the use of waste thermoplastic polyethylene material to improve bitumen properties have been investigated. However, few studies on the use of thermoset polyethylene (cross-linked polyethylene) to modify bitumen have been carried out. This research investigated the use of waste cross-linked polyethylene (XLPE) cable coating on bitumen properties. An FTIR analysis carried out on waste XLPE cable coating revealed that it is predominantly composed of XLPE material. A comparative study carried out on the bitumen properties revealed that the modifier had a decreasing effect on its penetration and ductility but, had an increasing effect on softening point and specific gravity; Hence, a considerable improvement in the temperature susceptibility and stability of the bitumen. The short-term ageing analysis carried out revealed that the modified bitumen can withstand short-term ageing requirements at 2% and 4% by weight of pure bitumen. FTIR analysis carried out on the pure and modified bitumen revealed that changes observed in bitumen properties with increasing modifier content were a result of physical changes and not chemical changes. A one-way ANOVA carried out on the properties of various bitumen content revealed that the modifier had a significant effect on the properties of pure bitumen with increasing bitumen content. The regression models developed properly described the relationship between the modifier content and the bitumen properties as they expressed very good R2 values.

Partial Replacement of RCA and LDPE in Bituminous Pavement

Bituminous concrete mix is a composite material which is widely used for the construction of flexible pavements, surfacing of roads and airports, various parking lots etc. It generally consists of bitumen which works as a binder material, coarse aggregates, fine aggregates and filler materials which are generally mixed together in right proportion and laid down in layers followed by the compaction. In this present age of modernization and urbanization, construction is non stoppable and the construction by demolishing of old building has arisen a serious problem of treatment of demolished waste. Similarly, the use of plastic in our day-to-day life and its improper disposal is also creating serious environment pollution. So, there is big challenge in managing the demolished waste as well as the waste plastics. In this project i.e. partial replacement of RCA and LDPE in Bituminous concrete mix we have tried to replace the RCA (25%) in Natural Aggregates and LDPE (2%, 4%, 6% and 8% respectively) in bitumen content for the improvement of the pavement characteristics satisfying both the strength criteria and the economic aspects giving emphasize to less environment degradation and sustainability.

ЗАЛЕЖНІСТЬ ОБ’ЄМНИХ ВЛАСТИВОСТЕЙ АСФАЛЬТОБЕТОНУ ВІД НАЙБІЛЬШОГО НОМІНАЛЬНОГО РОЗМІРУ ЗЕРЕН ЗАПОВНЮВАЧА ТА МЕТОДУ УЩІЛЬНЕННЯ

Introduction. One of the aspects of Ukraine's European integration is the introduction of European approaches to the design of asphalt mixtures. In Ukraine, as in other European countries, when designing the asphalt mixtures, asphalt concrete samples are made by compaction in the laboratory; however, different compaction methods are used for this purpose. Statement of the problem. In Ukraine, the method of compaction of asphalt mixtures in the laboratory at a pressure of (30.0 ± 0.3) MPa is used if the crushed stone content in the mixture is higher than or equal to 35%, or at a pressure of (40.0 ± 0.4) MPa if the crushed stone content in the mixture is up to 35%. In the countries of the European Union, the Marshall impact compaction method of 100 strokes (50 strokes on each side) is mainly used for this purpose. Therefore, it is advisable to determine the effect of the method of compaction of asphalt mixtures on the volumetric properties of asphalt concrete, depending on the largest nominal grain size of the aggregate and the compaction method. Objective. To determine the dependence of the volumetric properties of asphalt concrete on the largest nominal grain size of the aggregate and the compaction method. Materials and methods. Analysis of literature sources and laboratory research. Results. With an increase in the bitumen content, there is a decrease in the maximum density of the asphalt mixture and an increase in the bulk density of asphalt concrete. The increase in the bulk density of asphalt concrete is associated with both improved compaction of the asphalt mixture as a result of an increase in the bitumen content and more filling of air pores, as evidenced by the values of the pore content in the mineral aggregate. The only exception is the AC 16 asphalt mixture, for which the values of the pore content in the mineral aggregate remain unchanged, i.e. in this case, the increase in bulk density is due exclusively to the filling of pores in the mineral aggregate. The largest nominal size of the aggregate in the asphalt mixture affects the total pore content of the mineral aggregate. This suggests that the increase in the required bitumen content in the asphalt mixture with a decrease in the largest nominal size of the aggregate is largely due to the need to fill more pores, rather than to an increase in the total specific surface area of the aggregate.

ДОСЛІДЖЕННЯ ВПЛИВУ НАПОВНЮВАЧІВ РІЗНОГО ПОХОДЖЕННЯ НА ВЛАСТИВОСТІ АСФАЛЬТОБЕТОНІВ

Introduction. The properties of a bituminous material are determined by the peculiarities of the bonds that arise between individual mineral grains and depend on the properties of bitumen, the thickness of the bitumen layer covering the mineral grains, as well as on the processes of interaction between mineral materials and bitumen on their common interface. To ensure a strong and stable bond between the grains, bitumen should evenly cover the surface of the mineral materials with a thin layer. To increase the strength of the pavement constructed from bituminous material, it is necessary that the maximum amount of bitumen is adsorbed by the mineral material, and the content of free bitumen is reduced to a minimum value. Problem Ыtatement. Depending on the nature of the mineral material and the chemical composition of the bitumen, the properties of its thin layers change in different ways. The strength of bitumen in a thin layer on an active mineral surface increases with decreasing thickness, while on an inactive surface the strength of bitumen changes little with decreasing layer thickness. Objective. The present study was devoted to determining the effect of aggregates of different origins on the volumetric properties of asphalt concrete and the mechanical properties of asphalt concrete, as well as on their weather resistance. Materials and methods. Mineral filler from limestone, granite, quartzite, and fly ash was used for the study. Results. The results of the research showed that the type of aggregate has virtually no effect on changes in the volumetric and mechanical properties of asphalt concrete. However, at the same time, asphalt concrete with different aggregates differs significantly in water and frost resistance.

ОГЛЯД МЕТОДІВ ПІДБИРАННЯ СКЛАДУ АСФАЛЬТОБЕТОННИХ СУМІШЕЙ

Introduction. Asphalt mixtures are the most widely used road construction material for the arrangement of the top layers of road pavement. Asphalt mixtures are also used to arrange airfield runways, bridges deck surfacing, streets, pedestrian and cycle paths, etc. There is a large number of asphalt mixtures types that differ by grading, the largest nominal aggregate size, crushed stone content, crushed and uncrushed sand content, quality of components, and viscosity of the bitumen binder. Problem statement. The national method for asphalt mixture design is very similar to the Marshall method and the Superpave method in terms of determining the optimal bitumen binder content by the bulk properties of asphalt concrete. The only difference is that, according to the Marshall and Superpave methods, the optimal bitumen content is the one with an air pore content of 4.0 %. However, in accordance with the national method, the design air pore content varies depending on the type of asphalt mixture. A significant innovation of the Superpave method is the determination of asphalt performance indicators, such as rutting resistance, crack resistance, and resistance of the material to fatigue cracking. Apparently, these methods should also be implemented in Ukraine over time. Purpose. Analysis of the methods for asphalt mixtures design. Materials and methods. Analysis of literature sources on various methods of asphalt mixtures design. Results. The analysis of literary sources on different methods of asphalt mixtures design was carried out. Conclusions. The use of different methods of asphalt mixtures compaction can lead to the production of asphalt concrete with different volumetric properties, which will affect both the optimal bitumen content and the performance of asphalt concrete, thus further research should be aimed at defining the effect of the compaction method on the volumetric properties of asphalt concrete and their relationship with the production compaction of asphalt mixtures.

Alternative bio-based emulsifiers for road materials

Three bio-based compounds have been investigated as emulsifiers and stabilisers for bitumen emulsion preparation. The emulsifiers used are biopolymer, native nanoparticles and nanoparticles modified to be more hydrophobic. The comparison was made with a usual cationic surfactant for bitumen emulsion, used to manufacture the emulsion. Bitumen-in-water emulsions with a bitumen content of 60% were further obtained with biopolymers and nanoparticles. These emulsions were characterised and compared to a classical bitumen emulsion with amine-type surfactant. Cold mix asphalt specimens were successfully manufactured, moulded and used to evaluate the water recovery and stripping resistance. Different behaviours have been observed and interpreted. They are strongly linked to the emulsion formulation.

Nanocellulose-stabilized bitumen emulsions as a base for preparation of nanocomposite asphalt binders

Pickering bitumen emulsions stabilized by 1 % aqueous dispersion of microfibrillated cellulose (MFC) were used to obtain micro- and nanocomposite asphalt binders. Initial bitumen emulsions are characterized by a yield stress for a bitumen content of up to 40 %, while higher bitumen amounts result in phase inversion with the formation of highly viscous inverse emulsions. Drying of emulsions leads to the production of nanocomposite bitumen binders containing from 0.6 % to 8.3 % of MFC. In this case, the MFC content of 1.5 % or more formed a microfibrillar network in the bitumen, which gives it gel-like properties and the yield stress, increasing its cohesive strength and resistance to rutting. The effect of addition of 5 % sodium dodecyl sulfate (SDS) on the properties of the bitumen emulsions and the resulting binders is considered. SDS increases the emulsifying ability of MFC, making it possible to obtain 70 % direct bitumen emulsions and reducing their effective viscosity together with the yield stress. However, the presence of SDS in the dried binders increases the aggregation of MFC, reducing the stiffness of the resulting microcomposite binders, their yield stress, and rutting resistance.

Determination of Marshall parameters of bituminous mix by using non-destructive testing method

Non-destructive test (NDT) is a fast, easy, cost-effective in-situ method of inspecting, testing, evaluating the different materials, component assemblies, etc. Ultrasonic Pulse Velocity (UPV) test is one of the best NDT methods frequently used for cement concrete for evaluating various parameters e.g., strength, life, crack depth, corrosion, etc. Conventional destructive test (e.g., Marshall Test) is performed to determine the optimum bitumen content (OBC) and various Marshall parameters of bituminous concrete. Destructive tests are laborious, time-consuming, costly, moreover; it is impossible to find the in-situ characteristics of pavement by destructive test. In recent times, the UPV test has been emerging for bituminous concrete work. However, much reliability of non-destructive test on bituminous mix has not been developed. In this study, the Proceq UPV apparatus has been used to determine the dynamic modulus by a non-destructive test. To implement such study different proportions of virgin aggregate and of RAP material such as 0:100, 10:90, 20:80, 30:70, 40:60 and 50:50 % was utilized to fabricate the bituminous concrete (BC). Correlations between dynamic modulus and stability, flow value, density, OBC (Optimum bitumen content) have been developed. These correlations can predict Marshall strength and parameters of conventional and non-conventional bituminous mix using the UPV apparatus. The results suggested that the 40:60% RAP-modified BC mix has executed superior results than the other mixes.

Study on low noise pavements using waste plastics

The quality of life along heavily travelled roads is impacted by traffic noise. According to research on pavement noise, it is possible to plan and construct pavement surfaces that will result in quieter roads. Environmental contamination is a pressing problem today, and incorrect plastic waste disposal is a major contributor to it. Utilizing waste plastic has shown that it not only solves disposal issues, but also improves the qualities of bituminous mixtures. We propose use of PET waste plastic to build low-noise pavements in order to address the problems of waste plastic and traffic noise. By using a smooth surface texture and a tiny maximum size aggregate, a low-noise road surface can be constructed while also taking cost, durability, and safety into account. Current work includes testing of materials like aggregate, polymer modified bitumen and analysing them according to specifications and performing the mix tests with and without waste plastic in the mix. Optimum polymer modified bitumen content for Open Graded Friction Course (OGFC) and Stone Matrix Asphalt (SMA) mixes were found to be 5.5% and 6.0% respectively. Cantabro test results indicated very nominal wear and tear. Addition of waste plastic of 5% by weight of bitumen along with cellulose fibres in OGFC course yielded a considerable increase in sound absorption i.e 3.5 dB when compared to bituminous concrete course. Addition of waste plastic of 20% by weight of bitumen along with cellulose fibres in SMA course resulted a considerable increase in sound absorption i.e 6 dB when compared to BC course.

Effect of Adding LDPE Bags on Rutting and Stripping Behaviour of Asphalt Mix

Disposal or incineration of waste low-density polyethylene (LDPE) bags is a major problem, as it causes pollution. The pavement over time gets deteriorated by vehicular traffic, which mostly results in rutting and other distresses. This research is based on the performance evaluation of hot mix asphalt (HMA) modified with LDPE. Aggregates National Highway Authority Pakistan (NHA) gradation B, bitumen grade 60/70 and waste LDPE bags from the dump yards of Islamabad (Pakistan) were used in this study. Penetration, ductility and softening-point tests were conducted with bitumen modified with different contents of waste LDPE bag flakes; i.e., 0%, 2%, 4%, 6% and 8% to figure out the optimum modifier content (OMC). Marshall testing was performed for the determination of optimum bitumen content (OBC). Using OBC and incorporating LDPE contents as a replacement for OBC, HMA samples were tested for performance evaluation, including rutting resistance and moisture susceptibility and compared with the performance of unmodified HMA. It was observed that 4% of LDPE as a replacement for OBC in the HMA can be used as OMC and yielded better performance results than unmodified asphalt mix. Rutting resistance was improved by 20.86% and tensile strength ratio (TSR) for moisture susceptibility evaluation was above the specified limit of 80%. KEYWORDS: Waste LDPE bags, Low-cost bitumen modifier, Performance evaluation, Performance improvement, Cost comparison, Sustainable environment.

Performance of Plastic Waste and Waste Engine Oil as Partial Replacements of Bituminous Asphalt Concrete in Flexible Pavement

Plastic waste is an emerging issue posing serious pollution problems to the environment. Waste Engine Oil has also become an environmental nuisance causing water pollution and soil degradation. New effective waste management options need to be considered, especially on recycling concepts. In addition to the emerging environmental issues, the sources of bitumen for road construction are continuously being depleted hence the need for innovative ways of sustaining road construction through the use of plastic waste and waste engine oil. This research project reviewed available literature on the concept of using waste plastic and waste engine oil as partial replacements of bitumen in road construction together while also carrying out the Marshall Stability test in both neat and bituminous mixes modified with plastic waste and waste engine oil. The optimum bitumen content was determined as 6% from the neat samples. Samples of the modified mix were then prepared with the percentage plastic content varying as 10%, 20%, 30%, and 40% of the mass of bitumen. The optimum plastic content was determined at 18% with a stability value of 8580N (an increase from 8337.4N for the neat samples). Samples with both plastic waste and waste engine oil replacements were prepared with 18% plastic waste being replaced with 10%, 20%, 30%, and 40% waste engine oil. The optimum replacement was determined at 19% giving the highest stability of 8820N (an increase of 2.8% from the plastic-only modified mix and an increase of 5.8% from the neat sample). With the utilisation of polymer-modified bituminous mix in highway construction, the pollution and disposal problems of waste plastic may be partly reduced. The use of innovative technology will not only strengthen road construction but also increase road life as well as will help to improve the environment

Solvent Extraction for Separation of Indonesian Oil Sands.

Based on the examination of the basic properties, the solvent extraction process (SEP) was applied with high efficiency in the extraction of bitumen from Indonesian oil sands. To separate the oil sands, different organic solvents were first screened, and the extraction effects were analyzed to select a suitable solvent. Then, the effects of operating conditions on the extraction rate of bitumen were investigated. Finally, the compositions and structures of the bitumen obtained under suitable conditions were analyzed. The results showed that the Indonesian oil sands were oil-wet oil sands with a bitumen content of 24.93%, containing a large number of asphaltenes and resins with high polarity and complex structures. The separation performance was affected by different organic solvents and operating conditions. It was shown that the closer the structure and polarity of the selected solvent is to the solute, the better the extraction effect. The extraction rate of bitumen reached 18.55% when toluene was used as the extraction solvent under the operating conditions of V (solvent):m (oil sands) 3:1, temperature 40 °C, stirring velocity 300 r/min, time 30 min. The method could also be applied to the separation of other oil-wet oil sands. The compositions and structures of bitumen can guide the separation and comprehensive use of industrial oil sands.

Effect of recycled crushed bricks as additive in pavement material

Recycling waste materials has gained its own demand and popularity especially in solving disposal problems, hence creating opportunity for researcher to study the advantage of using recycling materials in their products. This paper studied on the impact of indirect tensile strength(ITS) tests on the characterization of bituminous mixes. It focuses on the Marshall Mix design process to determine the optimum binder content in asphalt mixtures of Hot Mix Asphalt (HMA) with recycled crushed bricks (RCB). Samples were prepared with grading the natural aggregates and RCB according to the AC14 grading limit. At 160°C, the samples were blended with 4-6% bitumen content of grade 60/70 until uniformly mixed. Next, another 18 samples were prepared in accordance with Marshall optimization to analyse the performance of sample by conducting both dry and wet ITS test. 20% and 30% of RCB were added to replace fine aggregates of 1.18 mm to pan sieve. The result shows that the dry method gives a better result of ITS with 20% to 30% of replacement of fine aggregates with RCB. The average maximum load that can be load to the sample was 13.185 kN of load for dry sample whereas the wet sample with 11.23 kN of load.

Performance Evaluation of Hot Mix Asphalt (HMA) Containing Polyethylene Terephthalate (PET) Using Wet and Dry Mixing Techniques

This study evaluates the performance of Polyethylene Terephthalate (PET)-modified hot mix asphalt. Aggregate, bitumen of grade 60/70 and crushed plastic bottle waste were utilized in this study. Polymer Modified Bitumen (PMB) was prepared using a high shear laboratory type mixer rotating at a speed of 1100 rpm with varying PET content of 2%, 4%, 6%, 8% and 10%, respectively. Overall, the results of preliminary tests suggested that bitumen hardened with the addition of PET. Following optimum bitumen content determination, various modified and controlled HMA samples were prepared as per wet and dry mixing techniques. This research presents an innovative technique to compare the performance of HMA prepared via dry and wet mixing techniques. Performance evaluation tests, which include the Moisture Susceptibility Test (ALDOT-361-88), Indirect Tensile Fatigue Test (ITFT-EN12697-24) and Marshall Stability and Flow Tests (AASHTO T245-90), were conducted on controlled and modified HMA samples. The dry mixing technique yielded better results in terms of resistance against fatigue cracking, stability and flow; however, the wet mixing technique yielded better results in terms of resistance against moisture damage. The addition of PET at more than 4% resulted in a decreased trend for fatigue, stability and flow due to the stiffer nature of PET. However, for the moisture susceptibility test optimum PET content was noted to be 6%. Polyethylene Terephthalate-modified HMA is found to be the economical solution for high volume road construction and maintenance, besides having other significant advantages such as increased sustainability and waste reduction.

Comparative Evaluation of the Engineering Properties of Asphaltic Concrete from Selected Asphalt Plants in Southwestern Nigeria for Road Construction

In this study, the engineering properties of asphaltic concrete from selected asphalt plants in Southwestern Nigeria for road construction were sampled for three months, analysed and compared with regulatory body specifications. The penetration test, Ductility test, Marshall Stability and flow tests results indicated good conformity to the regulatory specificationby all the plants with JBN exhibiting highest range value while LSPWC has the least. Also, asphalt samples from all the plants passed the Ring ball and softening point test with Julius Berger Nigeria having highest value between 53.5-53.7 while SEQUOIA has the least with 50-50.2 when compared to standard value 47-56. For bitumen content tests with 5-8% Specification, ESPRO failed with 3.9-4.8, LSPWC show inconsistence result of 3.9-5.6, SEQUOIA had the highest between 6.4-7.0, while CCECC and JBN conform to specification. The density-void ratio and particle size specification were met by only JBN with major deviation recorded from LSPWC. The result indicated JBN is the only company that satisfy all the engineering properties specification while others exhibit inconsistency in aggregates proportion thereby making the asphalt concrete a possible cause for pavement failure in Southwest Nigeria.

DEVELOPMENT OF MELTED EXPANDED POLYSTYRENE AS ΒITUMEN MODIFIER FOR PAVEMENT CONSTRUCTION

This study was designed to investigate the Performance of melted Expanded Polystrene (EPS) wastes on the quality of bitumen used in asphaltic concrete. The EPS materials were ground and then melted (200-400 oC) to form a slurry. Specific gravity of the EPS and chemical composition were determined by AAS analyses. The melted EPS was used as a modifier in mix proportions of 0, 2.5, 5, 7.5 and 10% by weight of bitumen. The 5% unmodified bitumen content obtained from the Marshall mix design was used to prepare asphalt concrete samples with 0 to 10% contents of melted EPS. The products were tested for Marshall stability, specific gravity, penetration, softening point, ductility, loss on heating, viscosity, flash and fire points and the melting point tests using standard methods. The ground EPS was uniform and well-graded (4.750-0.010 mm) with a specific gravity of 0.012, having a styrene structure with methanol on the ring. The specimen prepared with the specified mix proportion of EPS produced results that ranged between 5598.71-16937.70 N for Marshal stability; 2.02-3.54 for specific gravity; 129-152 mm for penetration; 42.80-47.50 oC for softening point; 75.00-32.90 cm for ductility; 0-3.48% for loss on heating; 208-2204 sec.STV for viscosity; 243.3-269.0 oC for flash point; 196.1-211.0 oC for melting point. The results also showed that with correlation coefficients ranging from r = 0.658-0.999, there is a strong positive correlation between the improvement exhibited in the specimen tested properties and melted EPS used in bitumen. At the 5% bitumen with 5% EPS by weight of asphalt concrete, the results of stability, flow and optimum bitumen content satisfied the British Standard Specification framework for polymer-modified bitumen and it is therefore suitable for flexible pavement construction.

Experimental Analysis of Hot-Mix Asphalt (HMA) Mixtures with Reclaimed Asphalt Pavement (RAP) in Railway Sub-Ballast.

Environmental safeguards promote innovative construction technologies for sustainable pavements. On these premises, this study investigated four hot mix asphalt (HMA) mixtures-i.e., A, B, C, and D-for the railway sub-ballast layer with 0%, 10%, 20%, and 30% reclaimed asphalt pavement (RAP) by total aggregate mass and a rejuvenator additive, varying the bitumen content between 3.5% and 5.0%. Both Marshall and gyratory compactor design methods have been performed, matching the stability, indirect tensile strength, and volumetric properties of each mixture. Dynamic stiffness and fatigue resistance tests provided mechanical performances. Laboratory results highlighted that the RAP and the rejuvenator additive increase the mechanical properties of the mixtures. In addition, the comparative analysis of production costs revealed up to 20% savings as the RAP content increased, and the life cycle impact analysis (LCIA) proved a reduction of the environmental impacts (up to 2% for resource use-fossils, up to 7% for climate change, and up to 13% for water use). The experimental results confirm that HMA containing RAP has mechanical performances higher than the reference mixture with only virgin raw materials. These findings could contribute to waste management and reduce the environmental and economic costs, since the use of RAP in the sub-ballast is not, so far, provided in the Italian specifications for railway construction.

Optimization and Performance Evaluation of Steel Slag Asphalt Mixture Modified with Fibers under Freeze–Thaw Cycles

Recycling waste steel slag for asphalt pavement construction can reduce energy consumption and preserve nonrenewable natural resources. However, the moisture susceptibility of steel slag asphalt mixture (SSAM) in severe freeze–thaw regions should be taken into consideration. In light of this, three types of fibers (basalt fiber, polyester fiber, and lignin fiber) and rubber powder were blended into the SSAMs, and their freeze–thaw damage characteristics were investigated. First, the optimum bitumen and fiber content of SSAMs were determined based on Marshall design using response surface methodology. Then, the air voids of SSAMs were identified through X-ray computed tomography (CT) technology, while the effects of the fiber and freeze–thaw cycles on the moisture stability of SSAMs were investigated. Moreover, the enhancement effects of the fibers were analyzed using scanning electron microscopy (SEM). The results show the optimum fiber content of different fiber-reinforced SSAMs are 0.35%, 0.29%, and 0.23%, respectively, and the optimum bitumen content is 6.7% for all cases. The effect of freezing–thawing leads to an increase of the air voids in the middle part of the specimen, whereas the incorporation of fibers weakens the adverse action of freezing–thawing and effectively improves the moisture stability of the SSAMs. Furthermore, the network structure formed by basalt fibers in asphalt mastic significantly improves the integrity of the SSAM. Additionally, basalt fiber reinforced SSAM shows the best resistance to moisture damage.

Performance Analysis of Bio-Based Asphalt Mixtures Containing Lignin

Given the need to promote the circular economy and sustainability, one of the main current trends in road materials construction is to employ industrial residues and by-products deriving from renewable sources as extender, replacement or modifier of bitumen, obtaining the so-called “bio-binders”. As regards, lignin can represent a potentially attractive solution, because it is the most abundant natural biopolymer, available in large quantity and characterized by certain chemical similarity with bitumen. In this context, this study focuses on the evaluation of two dense-grade asphalt mixtures for binder layer made with bio-binders containing two different lignins, as partial replacement of bitumen. A preliminary phase allowed to optimize lignin content (30% by bio-binder weight) based on empirical test (i.e. dynamic viscosity, penetration and softening point tests) with the aim of maximizing the bitumen replacement and at the same time obtaining two bio-binders having a consistency similar to a reference plain bitumen. In the second phase, two bio-based mixtures were produced by using the before-optimized bio-binders in different attempt contents. After mixing, specimens were produced by means of a gyratory compactor at set gyrations. Then, the two lignin-based asphalt mixtures were compared with the reference mixture in terms of workability, Indirect Tensile Strength (ITS) and water sensitivity. Despite the bio-based mixtures revealed a slightly penalized workability, overall results showed that they are characterized by fully comparable performances to the reference one, allowing a reduction of the effective bitumen content.