Indirect Tensile Stiffness Modulus Research Articles

Influence of Bio-Additives on Recycled Asphalt Pavements.

The construction and maintenance of asphalt pavements is a resource-consuming sector, where the continuous rehabilitation of the superficial layers demands large volumes of non-renewable resources. The present work focuses on the design and characterization of asphalt mixtures for the binder layer of an asphalt pavement containing 50% reclaimed asphalt (RAP), in which seven different bio-based additives, identified as R1A, R1C, R2A, R2B, R2C, R3A, and R3B, were added to improve the workability, strength, and stiffness properties. The experimental program envisioned the hot mixing of aggregates and RAP with either a 50/70 or a 70/100 bitumen and, in turn, each of the seven bio-additives. The asphalt mixtures underwent the characterization of their densification properties; air voids; indirect tensile strength (ITS); indirect tensile stiffness modulus at 10, 20, 40, and 60 °C; and rutting resistance at 60 °C. The results highlighted that the performance in terms of workability and ITS of the resulting mixtures depends on the type of bio-additive and largely on the fresh bitumen type, while the stiffness at high temperature is not significantly affected by the presence of the bio-additives.

Investigating the Influence of Mineral Fillers at Australian Asphalt Mixtures

Abstract It is commonly known that mineral fillers significantly affect the asphalt mixture's performance. Superior flexible pavement performance can be ensured by gaining a deeper understanding of the function of filler. This research investigates the influence of three different fillers: granite dust, cement, and hydrated lime, at Australian asphalt mixtures. The testing program includes Marshall testing, moisture damage resistance, indirect tensile strength (ITS), and indirect tensile stiffness modulus (ITSM) tests of asphalt mixtures. Analysis of variance (ANOVA) was used to statistically assess the results obtained, besides damage analysis. The results indicate that using natural granite dust yields the highest resistance to moisture, while cement produces the highest stability, ITS, and ITSM. Unexpectedly, using hydrated lime filler decreases the stability/stiffness and moisture resistance of asphalt mixtures. ANOVA tests indicate that the type of filler affects ITS, TSR, and ITSM results (i.e., the p-value <0.05). The damage analysis shows that the design life of the asphalt mixture made with cement filler is higher than that of mixtures made with natural granite dust and hydrated lime fillers respectively. The findings indicate the important role of nontraditional fillers at the performance of Australian asphalt mixtures.

Effect of wet-dry history on performances of dense asphalt mixture: Experimental investigation and predicting model

Asphalt pavement experiences various wet-dry histories in the service stage. However, the influence of wet-dry history on asphalt mixture is unknown. Therefore, to clarify the performance degradation mechanism and predict the performance of asphalt mixture under the action of wet-dry history, the creep-recovery test, indirect tensile stiffness modulus test and indirect tensile strength test were conducted at different temperatures. The finite element method was adopted to analyze the moisture diffusing profile inside the specimen after wet-dry cycles. A moisture damage model considering the soaking time and repeated characteristics was developed to predict the damaged properties. Results show that wet-dry cycles cause a slight mass loss of asphalt mixture. Wet-dry cycling action leads to the increment in high-temperature deformation, and reductions in stiffness modulus and tensile strength. The increase of high-temperature deformation is primarily caused by viscoplastic component. Even if the soaking time is short, high moisture damage occurs while the wet-dry cycle is sufficient. Numerical simulations show that the moisture concentration profiles inside asphalt mixture vary under different wet-dry histories, leading to variations in the damage zone. The degree of damage is also closely related to the acting time of moisture. The critical immersion time of the dense asphalt mixture (about 43 hours) was determined in this study. When the immersion period is shorter than the critical immersion time, the strength loss is greater than the modulus. On the contrary, the degree of modulus damage is higher than that of strength. Considering the actual rainfall climate in China, the strength damage of the on-site asphalt mixture in the field predominates. The proposed model could reflect the weakening trends of modulus and strength. It has good universal applicability in predicting the damaged Marshall stability, modulus, and strength at different temperatures.

Performance evaluation of stone mastic asphalt reinforced with shredded waste E-cigarette butts

The recycling of waste materials in asphalt pavements is pivotal for advancing the road industry, offering numerous environmental, economic, and societal benefits. This study explores the recycling potential of waste electronic cigarette butts (E-CBs) within stone mastic asphalt (SMA) mixtures, serving as a substitute for cellulose fibres and enhancing mechanical performance. Considering the critical role of fibre size in asphalt mixtures, two different E-CB shredding sizes (10 and 15 mm) were selected for examination. Additionally, the influence of the plastic component within E-CBs was investigated. The stabilizing effects of using the shredded E-CBs were evaluated via drain-down tests, followed by a series of standard laboratory tests aimed at assessing physical and mechanical properties. Results demonstrate acceptable drain-down properties, volumetric properties, and moisture susceptibility for the use of all four shredded E-CBs. Among the four mixtures incorporating the waste fibres, the utilization of 15 mm shredded E-CBs without plastic constituents yielded the highest values for indirect tensile strength (ITS) and indirect tensile stiffness modulus (ITSM), coupled with excellent water susceptibility and rutting performance. It can be considered a promising alternative to the traditional cellulose fibre. Larger shredded E-CBs exhibited potential for improving mechanical properties, encompassing cohesion, stiffness modulus, and rutting resistance. Although plastic inclusion can enhance rutting resistance, the higher thermal susceptibility associated with plastic warrants careful consideration. Future research may focus on investigating the fatigue and low-temperature cracking properties, as well as the reinforcing mechanisms of shredded E-CBs in asphalt mixtures using micro-characterization techniques.

Effect of RAP fractionation and dosage on design and mechanical behaviour of cold asphalt mixes

This study examines the effect of reclaimed asphalt pavement (RAP) material dosage and incorporation method on the mechanical characteristics of Cold Asphalt Mix (CAM). The RAP materials were fractionated into fine and coarse in addition to the unfractionated method. Four levels of RAP dosage (25, 50, 75, and 100%) were considered for each category. The mix design parameters, such as total fluid and emulsion content, were evaluated using the Indirect Tensile Strength (ITS) test. Overall, 455 specimens were prepared for mix design. The Optimum Emulsion Content (OEC) is the design emulsion content determined at peak value of ITS test. ITS, Indirect Tensile Stiffness Modulus (ITSM), and moisture susceptibility tests were conducted. Incorporating RAP in CAM increased the average tensile strength predominantly by 34% in coarse mixes, 28% in unfractionated, and < 10% in fine mixes. The average ITSM of the mixture increased by 30%, 60%, and 80% for fine, coarse, and unfractionated RAP. Further, emulsion demand was reduced by 53%, 43%, and 79% for fine, coarse, and unfractionated RAP, which showed that the RAP incorporation method profoundly influenced OEC. However, regardless of fractionation, CAM mixes showed lower cracking resistance and higher moisture susceptibility with increased RAP dosage. Two different conditioning protocols were used to capture the variation in moisture susceptibility for all 13 mix combinations. Coarse and unfractionated RAP mixes significantly differed in ITS, moisture susceptibility, cracking tolerance index, and ITSM. VIseKriterijumska Optimizacija I Kompromisno Resenje (VIKOR) approach was selected to rank the outperforming combination. The overall ranking of RAP incorporation showed that the coarse RAP mixes outperformed fine and unfractionated RAP mix characteristics. The study recommends restricting RAP usage by up to 75% to ensure the required performance of CAM mixtures.

A novel foaming additive derived from waste polyethylene terephthalate (PET) for low-carbon warm mix asphalt

Plastic pollution is growing relentlessly due to the careless disposal of waste plastic products. This study focuses on converting waste plastic bottles into a foaming additive for the production of eco-friendly warm mix asphalt (WMA) for paving purposes. The additive, namely PET-TETA, was synthesized from waste polyethylene terephthalate (PET) via an aminolysis process. Its chemical and physical properties were characterized by the scanning electron microscope (SEM), X-ray diffractometer (XRD), and thermogravimetry-differential thermal analyzer (TG-DTA) tests. The WMA mixtures were prepared using PET-TETA and a commercial foaming additive, and their properties were studied and compared to a conventional hot mix asphalt mixture. The performances of the asphalt mixtures were characterized through the indirect tensile stiffness modulus, moisture susceptibility, and immersion Hamburg wheel-tracking tests. The findings revealed that PET-TETA was a semicrystalline material containing approximately 26 % hydration water, which could be released gradually during the preparation of asphalt pavements. The performance of the WMA mixture utilizing PET-TETA was comparable to the other two asphalt mixtures, and it exhibited higher strengths and better resistance to stripping. Therefore, it is promising to apply PET-TETA as a sustainable and effective WMA additive for paving purposes, providing a solution to the issue of waste plastic disposal.

Exploring waste marble dust as an additive in cementitious grouts for semi-flexible pavement applications: Analysis and optimization using RSM

This research aims to explore the potential utilization of waste marble dust (MD) within cementitious grouts for applications in semi-flexible pavements, a hybrid pavement type combining the benefits of both flexible and rigid pavements. MD was used to replace cement (ranging from 0 to 25%), combined with w/c ratios of 0.35 to 0.50, in the formulation of cementitious grouts. The assessment of grout characteristics encompassed evaluations of flowability and compressive strength (7d and 28d curing). Moreover, the microstructural characteristics of cement grouts incorporating MD were scrutinized through Scanning electron microscope-SEM and Energy dispersive X-Ray spectroscopy-EDS analyses. Additionally, response surface methodology (RSM) was used for experimental design, analysis, and the optimization of the factors (MD and w/c ratio). The significance of the model was examined through various statistical indicators. The optimal composition of cementitious grouts was determined using optimization technique within the RSM framework. Furthermore, optimal grout combinations were employed in fabricating semi-flexible mixtures and evaluated for Marshall stability, moisture susceptibility, indirect tensile stiffness modulus, dynamic modulus, compressive strength, and resistance to fuel spillage. The results indicated that an optimal combination of 15% waste marble dust and a 0.40 w/c ratio was identified through optimization techniques within the RSM methodology. Furthermore, Analysis of variance formula-ANOVA outcomes exhibiting a higher R² value (>0.80) and higher adequate precision (>4.0) underscore the significance of the proposed models, revealing a robust correlation between experimental and predicted data. The semi-flexible mixtures also showcase superior performance in terms of Marshall stability, stiffness, dynamic modulus, moisture resistance, and resistance to fuel spillage. Moreover, the integration of waste marble dust in cementitious grouts for constructing semi-flexible pavements not only addresses disposal concerns but also contributes to environmental sustainability.

Repurposing agricultural waste: The effectiveness of peanut husk ash in improving asphalt mixture properties

Using agricultural waste in asphalt pavements presents a promising solution for addressing environmental concerns related to waste disposal and resource conservation while enhancing pavement performance. This study aimed to scrutinize the impact of incorporating peanut husk ash (PA) as a modifier for asphalt binder on hot mix asphalt (HMA) characteristics. The base asphalt binder, which had a penetration grade of 60/80, was initially mixed with PA at various concentrations through the utilization of a high-shear mixing apparatus. The resultant modified asphalt binder was then utilized to prepare asphalt mixtures. Various performance evaluations were performed, comprising Marshall, indirect tensile fatigue (ITF), repeated load axial (RLA), and indirect tensile stiffness modulus (ITSM) tests. The incorporation of PA improved the adhesion force between the aggregates and asphalt, resulting in enhanced resistance to applied loads, reversibility, and stiffness modulus. The use of PA also increased the resistance of the mixtures to rutting and reduced their thermal susceptibility. Additionally, adding PA to asphalt mixtures in concentrations up to 8% has the effect of increasing their resistance to fatigue and avoided the occurrence of vertical cracks resulting from horizontal tensile stresses. This study concluded that a substantial enhancement in the mechanical behavior of HMA may be achieved through the incorporation of PA, as compared to a conventional mixture.

Laboratory evaluation of oak ash waste for use in hot mix asphalt modification

In this study, the effect of Oak Ash (OA), a biomass waste, on the mechanical properties of hot mix asphalt (HMA) was investigated and its usability in road engineering was evaluated. For this purpose, firstly, various physical and chemical properties of B70/100 penetration class pure asphalt, OA and crushed limestone aggregate were determined. Then, the optimum asphalt content (OAC) of the mixture was determined according to the Marshall mix design method using aggregate and pure asphalt. Based on this determined content, pure and OA added (1%, 2%, 4% and 6% by weight of asphalt) modified hot mix specimens were prepared. Pure and OA added modified mixture specimens were subjected to Marshall stability, indirect tensile strength (ITS), moisture damage, indirect tensile stiffness modulus (ITSM), static-dynamic creep and calorie tests. According to the results obtained, it has been determined that the OA additive has an improving effect on all mechanical properties of the mixtures, especially on the permanent deformation resistance at high temperatures. It is considered that the use of this additive at a rate of 2% in the hot mixture can increase the resistance of the pavement against deterioration and reduce the maintenance and repair costs of the road.

The Effect of Wetfix and Nanohydrated Lime Additives on Bitumen Aging and the Cohesion and Adhesion Failure Mechanisms of Hot Asphalt Mixtures

Aging due to sunlight and the passage of time is an effective element in the occurrence of moisture damage in hot asphalt mixtures. Still, the effects of this parameter are scarcely considered in the experiments examining the moisture damage potential. Accordingly, this study investigated the effect of aging on the performance of hot asphalt mixtures and examined the improvement of moisture damage performance by using antistripping additives via mechanism and functional tests. Two types of aggregates (limestone and granite) with different degrees of moisture sensitivity, two types of bitumen (PG64-16 and PG58-22) with different performances, and two additives (Wetfix liquid additive and nanohydrated lime) as bitumen modifiers were used. Bitumen samples and asphalt mixtures were subjected to short- and long-term aging. The pull-off test was performed to explore the aging effect on different failure mechanisms (cohesion and adhesion), and the indirect tensile stiffness modulus (ITSM) test was conducted to study the asphalt mixture’s performance against moisture damage. The results specify that aging, in terms of hot asphalt mixture hardening in dry and wet conditions, decreased the MSR (resilient modulus wet to resilient modulus dry ratio), and this decline was greater in long-term aging. The pull-off test results exhibited that aging, especially in the long term, decreased the asphalt mixture’s adhesive strength in dry and wet conditions; this decline in adhesion was greater in the wet than in the dry state, and this difference decreased the wet-to-dry adhesion strength ratio (the pull-off ratio). The additives relatively improved the yield modulus of the asphalt mixture, but their effect was greater in the wet state. A comparison of the pull-off test results in cohesion and adhesion failure demonstrated that Wetfix was more effective in improving bitumen–aggregate adhesion, whereas nanohydrated lime was more effective in enhancing bitumen adhesion. The resilient modulus (Mr) ratio in wet-to-dry conditions indicated that nanohydrated lime had better effects on the overall performance of the aged asphalt mixture against moisture damage. To investigate the effect of additives on the performance of asphalt mixtures, a t-test was performed in all modes of control, short-term aging, and long-term aging. The findings showed the effect of Wetfix and nanohydrated lime on increasing the modulus of elasticity of the samples.

Stiffness of cold-recycled mixtures under variable deformation conditions in the IT-CY test

Stiffness modulus belongs to the most important properties describing the cold-recycled mixtures (CRM) in terms of their usability in road pavement structures. Previous research proved that this property is strongly dependent on the scheme and conditions of the test (temperature and time of loading) and the time that has passed since the compaction of the specimen or pavement layer. It is a result of the influence of two different types of bonds – hydraulic bonds from cement and bituminous bonds from bituminous emulsion or foamed bitumen. Research presented in this paper showed that the target horizontal deformation values selected during the stiffness modulus test have a strong impact on the obtained results as well. In this paper the popular Indirect Tensile Stiffness Modulus (ITSM) test on cylindrical specimen (IT-CY scheme) was used to show the dependence of the stiffness modulus values on the selected target horizontal deformation level. Research was conducted on four different CRM mixtures and three reference materials. The research proved that even for a narrow deformation range the CRMs do not present linear viscoelastic behavior and display very high effort of material even for typical test conditions. In consequence, they are very prone to failure. Research also proved that CRM mixtures present different rheological behavior than cement concrete or asphalt concrete, and more attention should be given to establishing proper test conditions. Based on the research, it was determined that the recommended target horizontal deformation in IT-CY test of CRM should be reduced to 3 µm.

Mechanical Properties of Open-Graded Asphalt Friction Course Mixtures with Basic Oxygen Furnace Steel Slag as Coarse Aggregates

Open-graded asphalt friction course (OGAFC) is an asphalt course constructed over a dense-graded and impermeable surface to allow quick drainage of surface water runoff and enable reduction of hydroplaning and splash and spray. OGAFC mixtures demand high-quality aggregates to perform the intended functions while transferring traffic loads to the underlying layer. Steel slag is a byproduct generated during steel production, and large quantities are unutilized in steel-producing countries, including India. This study evaluated the mechanical performance properties of OGAFC mixtures using basic oxygen furnace (BOF) steel slag as replacement for coarse aggregates at percentages of 0%, 25%, 50%, 75%, and 100%. OGAFC mixtures with two types of modified asphalt binders and five percentage replacements of coarse natural aggregates with BOF steel slag were fabricated. The mechanical performance of the OGAFC mixtures was evaluated in terms of rutting resistance (dynamic creep test and Hamburg wheel tracking device test), cracking potential (indirect tensile strength, cracking tolerance index, and semicircular bending test), fatigue life (indirect tensile fatigue test), and modulus properties (indirect tensile stiffness modulus and resilient modulus). The test results indicated that the use of BOF steel slag not only improved the performance of OGAFC mixtures in terms of rutting resistance, cracking potential, and modulus properties, but also increased the fatigue life of the OGAFC mixes. OGAFC mixes up to 100% BOF steel slag content exhibited superior performance compared with the mixtures with natural aggregates.

Waste Silt as Filler in Hot Mix Asphalt: A Laboratory Characterization

Several studies aimed to improve both the performance and environmental impact of asphalt pavements using waste and recycled materials as fillers. This study focused on the effect of untreated and thermally treated silt as a filler in hot mix asphalt (HMA). The silt used in the study was a byproduct from a local aggregate production plant in Bologna, Italy. Mineral and chemical analyses revealed that the waste silt required thermal treatment at 750 °C for 2 h. The study compared the use of calcined silt, untreated silt, and a common limestone filler in the production of asphalt mastics and HMA specimens. The rheological properties of the mastics were analyzed using frequency sweep and multiple stress creep recovery tests. The physical and mechanical characteristics of the HMAs were evaluated through the air voids content, Marshall stability and indirect tensile strength tests. Additionally, the water susceptibility and thermal sensitivity of the HMAs were evaluated through the indirect tensile strength ratio and indirect tensile stiffness modulus at different testing temperatures. The results showed that the addition of calcined silt had no significant effect on the rheological properties of the mastic or the optimal binder content. However, the samples produced with thermally treated silt showed the highest stiffness and resistance to rutting compared with the other samples. On the other hand, the addition of untreated silt slightly decreased the stiffness value of the samples. In conclusion, the use of waste silt as a filler has potential as a sustainable and eco-friendly solution for HMAs.

Laboratory Study of the Effects of the Mixer Type and Mixing Time on the Volumetric Properties and Performance of a HMA with 30 Percent Reclaimed Asphalt Pavement.

This study examined the effects of the laboratory mixer type and mixing time on a hot-mix asphalt (HMA) using three different types of mixers and four different mixing times. The asphalt mix used is a semi-open graded mix (ESG-10) with 30% reclaimed asphalt pavement (RAP), and a range of tests were conducted including bitumen extraction by ignition, particle size distribution, maximum specific gravity (Gmm), a SUPERPAVE gyratory compactor (SGC), bulk specific gravity (Gmb), indirect tensile stiffness modulus (ITSM), and indirect tensile strength (IDT). The statistical analysis of variance (ANOVA) was also applied to quantify the effect of mixer type and mixing time. The results indicated that both mixing type and time had a significant effect on the properties of the HMA (volumetric properties and compactability) and that the type of mixer used also affected the performance of the HMA (stiffness and cracking resistance), with some mixers producing asphalt mixes with better properties than others. The study ultimately demonstrated that it is possible to produce a mix that exhibits good performance and meets or does not meet the compactability specifications depending on the mixer type used.

Application of paper sludge ash and incinerated sewage ash in emulsified asphalt cold mixtures

Certain disadvantages could have appeared while using hot mix asphalt (HMA), such as the release of unhealthy gases into the environment (environmental issues), difficulty in sustaining the temperature over long distances (logistical issues), and consuming a sufficient amount of energy while preparing and laying down (practical and economic issues). To overcome the aforementioned issues, this study aimed to develop rapid-curing emulsified asphalt cold mixes (EACM) comprising a cementitious filler made from industrial by-product materials. Paper sludge ash (PSA) is used as an active filler for application in the EACM rather than conventional mineral filler. Additionally, to maximize the effect of PSA’s hydraulic activity, incinerated sewage ash (ISA) is utilized as an activator at a concentration of 0%–4% by mass of the aggregates. The results demonstrate that the use of waste PSA significantly improves the indirect tensile stiffness modulus (ITSM) by around 10 times more after 2 days than the traditional emulsified asphalt cold mixes. In addition, the improvement in ITSM was around 30% and 65% for 6%PSA+1%ISA and 6%PSA+4%ISA mixes, respectively. Furthermore, the rutting for the 6%PSA+1%ISA and 6%PSA+4%ISA mixes decreased to around 19% and 11% in comparison to the traditional 131-pen HMA. The formation of hydration products and rapid demulsification of asphalt emulsion, which results in binding within the mixtures, are responsible for the increased ITSM and rutting resistance. As a result, environmental issues are minimized, and energy preservation may be maintained.

The development of an eco-friendly cold mix asphalt using wastewater sludge ash

The aim of this research was to develop a sustainable and ecologically sound, non-traditional cold mix asphalt (CMA) that can be used in the construction industry. This new type of CMA incorporates wastewater sludge fly ash (UFA) and bottom ash (UBA) as a replacement filler for ordinary Portland cement and limestone. Silica fume (SF) was also used as an additional filler. The mechanical and durability characteristics of the new CMAs were examined in terms of indirect tensile stiffness modulus (ITSM), and rutting, fatigue, water and fuel resistance. The results showed that CMA with 2.1% OPC +3.9% UFA at 3 days of age, had ITSM values 11 times that of traditional CMA, while CMA with 2.1% OPC+ 3.3% UFA +0.6% UBA, had ITSM values 5 times that of traditional CMA at 28 days of age. SF activated hydration for both mixes, significantly increasing ITSM. These results indicate that CMA has a comparable mechanical performance to standard Hot Mix Asphalt (HMA) mixtures for use as surface pavement layers. This study offers a novel CMA with improved mechanical performance. It is economically effective and ecologically beneficial, compared to HMA, due to its ability to accommodate wastewater sludge ashes that are often disposed of in landfill sites.

Stiffness and Creep Properties of HRS-BC Powered by Palm Shell Gasification in Dryer Unit

Roads are infrastructure that is very important in supporting people’s daily lives. With the high growth rate of traffic, the traffic load will cause damage to the road pavement in the form of deformation (rutting) and fatigue. The performance of an HRS-BC asphalt mixture was investigated to determine the asphalt’s resistance to damage. HRS-BC asphalt mixture specimens were produced by a palm shell AMP and by a diesel AMP. The performance of the HRS-BC asphalt mixture was tested in the laboratory with indirect tensile stiffness modulus (ITSM) and dynamic creep test. The results showed that the HRS-BC asphalt mixture sample produced by the palm shell AMP had better stiffness than the HRS-BC asphalt mixture produced by the diesel AMP. Both the samples of the HRS-BC asphalt mixture produced by the palm shell AMP and by the diesel AMP were not deformed when given a standard load of 100 kPa and 3,600 load repetitions.

Estudo da adesividade e do comportamento mecânico em misturas asfálticas com adição de cal hidratada e rejeito de mármore

Esta pesquisa teve por objetivo analisar os efeitos da cal hidratada e do rejeito de mármore nas propriedades mecânicas e adesividade das misturas asfálticas. Foi realizada a substituição de 1,5% no peso total do corpo de prova por cal e rejeito de mármore, comparando-os com uma mistura convencional. Foram executados os ensaios de resistência à tração por compressão diametral, módulo de resiliência, estabilidade e fluência, cântabro e dano por umidade. Os corpos de prova utilizados foram moldados conforme metodologia Marshall e distribuição granulométrica pertencente ao centro da faixa C do Departamento Nacional de Infraestrutura de Transportes. Os resultados mostraram que a utilização da cal e do rejeito de mármore melhoram consideravelmente a suscetibilidade ao dano e as propriedades mecânicas da mistura. Dessa forma, este trabalho corrobora com os efeitos benéficos da adição da cal em misturas asfáltica já descritos na bibliografia e identificou o potencial de uso do rejeito de mármore.

Comparison of accelerated laboratory curing and maturation under uncontrolled conditions of gravel emulsions using a nonlinear weighted least-squares predictive model

ABSTRACT Cold-asphalt mixtures (CAMs) are evolved materials whose mechanical strength increases with their maturation. The relationship between CAM field maturation and laboratory-accelerated cure procedures is not well understood. Furthermore, there is controversy on the recommended methodology for laboratory-accelerated cure. So, in this work, the accelerated curing protocol for a CAM-type gravel emulsion was examined, and its uncontrolled maturation and performance were contrasted. For this, the mixture was subjected to either accelerated curing (from 0 to 7 days in a 50 °C oven) or natural curing (from 0 days to 6 months at 20 3 °C in the laboratory and at an unfixed temperature outside the laboratory). We analysed, as functions of time, the moisture, indirect tensile stiffness modulus (ITSM), and moisture damage resistance. A curing protocol of 2 days at 50 °C yielded ITSM values closer to those obtained under uncontrolled conditions. Nevertheless, total maturation of the mixture was achieved after 3.5 days of curing. The nonlinear weighted least-squares method yielded an expression that better predicted the performance of the gravel emulsion for the first six months of life. The model parameters were easily fitted using ITSM measurements derived from samples cured for 2 days in a 50 °C oven.

Performance assessment of asphalt mixtures produced with a bio-binder containing 30% of lignin

Lignin is one of major by-product from wood and paper industry. As natural biopolymer, it could be a valid alternative as bitumen replacement and/or modifier to enhance the relevant performance of asphalt mixtures, promoting concurrently environmental benefits. In this context, the study focused on the effects of two different binders containing 30% of lignin (by weight) on the mechanical properties of bio-asphalt mixtures. Specifically, two different lignins were blended with two plain bitumens having different consistencies so obtaining two bio-binders with a similar consistency to that of a reference plain bitumen. The two bio-binders and the reference bitumen were used to produce in the laboratory three dense graded asphalt mixtures for binder courses according to the Italian Technical Specifications. The binder-aggregate adhesion, Indirect Tensile Strength, Stiffness Modulus, thermal susceptibility, fatigue resistance, and low-temperature cracking of mixtures were analysed in both unaged and long-term aged conditions. Overall, this investigation demonstrates that bio-mixtures containing lignin offer comparable results to the reference asphalt mixture. Moreover, the bio-asphalt mixtures exhibit a lower thermal susceptibility, as well as lower aging susceptibility. The findings of this research highly encourage the use of lignin as partial replacement of bitumen in asphalt pavements.