Short-term Aging Research Articles

Neodymium Nitrate Improves the Germination of Aged Wheat Seeds by Increasing Soluble Substances and Activating Antioxidative and Metabolic Enzymes in Seeds

Seeds stored for a prolonged period are subject to aging and a reduction in germination potential (GP), which will negatively affect seed sales. Rare-earth elements have a synergistic effect on the improvement of seed GP. In this study, we examined the effects of neodymium on biochemical components, the antioxidant protective system, and metabolism-related enzymes during germination of naturally and artificially aged seeds of three wheat cultivars. Seed germination indices, biochemical substance contents, and enzyme activities decreased after seed aging. Soaking seeds in a neodymium nitrate solution revived aged wheat seeds at an optimal concentration of 20 µmol/L for 8 h. Soaking in a neodymium nitrate solution increased the GP4 (by 2.25–60.9%), germination index (by 1.69–29.2%), and vigor index (by 3.36–18.7%) of aged seeds. Compared with non-soaked seeds, soaking significantly changed the contents of biochemical substances, and the activities of antioxidant protective enzymes and metabolic enzymes in seedlings were increased. Soaking with neodymium may revive aged seeds by regulating the synthesis of soluble sugars, soluble proteins, chlorophyll, and carotenoids and decomposing malondialdehyde in the germinating seed. Root dehydrogenase and amylase showed different responses to the aging modes. The differential responses of root dehydrogenase and amylase may reflect differences in the resistance of enzymes to long-term mild seed aging and short-term severe environmental aging.

Golden-Free Robust Age Estimation to Triage Recycled ICs

Non-destructive golden-free detection of recycled/counterfeit integrated circuits (ICs) is the focus of this paper. This is achieved by estimating the functional/operational age of the IC. The age estimation method is based on exploiting short-term aging effects in advanced transistor technologies to induce bit errors at the IC’s output. Gate-level simulations are used to capture the impact of workload on short-term aging. In advanced technology nodes including bulk CMOS at 45 nm or below and FinFET, combining transistor aging with ultra-fast voltage scaling magnifies effects of aging-induced degradation at high voltage when voltage scales to a lower level, causing short-term aging-based timing violations. These timing violations create bit errors at IC outputs. We employ the bit error patterns to build a machine learning (ML) based non-linear regression model to estimate the IC’s age. Our study confirms that short-term aging-induced output bit error patterns can be used to estimate long-term age of an IC. If the IC’s age is beyond a pre-defined threshold, it can be marked as recycled. Although this paper considers FinFET technology, the method applies to bulk CMOS advanced nodes at 45nm or below. We model IC-to-IC variations taking into account voltage scaling. We demonstrate the approach on two cryptographic ICs and the method accurately estimates the long-term age of an IC, facilitating recycled IC detection.

Effect of short-term aging on rheological properties of bio-asphalt/SBS/PPA composite modified asphalt

Substituting petroleum asphalt with bio-asphalt produced by biological waste recycling can mitigate the dependence on non-renewable resource oil. This study aimed to investigate the effectiveness of bio-asphalt as a substitute for petroleum asphalt by analyzing its rheological properties. Therefore, in this study, modified asphalt was prepared using styrene-butadiene-styrene copolymer (SBS), polyphosphoric acid (PPA), and bio-asphalt (BA) as modifiers, and the short-term aging test of the modified asphalt was carried out. Then the rheological properties of the modified asphalt were analyzed through the Temperature Scanning (TS) test, the Multiple Stress Creep Recovery (MSCR) test, and the Bending Beam Rheometer (BBR) test; finally, the Fourier Transform infrared spectroscopy (FTIR) test, Fluorescence Microscopy (FM) test to study the modification mechanism and microscopic characteristics of asphalt. The results show that adding BA improved the low-temperature rheological properties of modified asphalt while reducing the high-temperature rheological properties of PPA modified asphalt. The BA, SBS, and PPA combination exhibited excellent performance in high and low-temperature conditions. The short-term aging process enhances the high-temperature rutting resistance of modified asphalt but adversely affects its low-temperature performance. Fluorescence microscopy tests have demonstrated that BA improves the compatibility of SBS and PPA in asphalt. Meanwhile, FTIR has revealed that BA and SBS are physically mixed, and BA and PPA undergo a chemical reaction. This study suggests that BA could be a viable and sustainable alternative to petroleum asphalt, with promising performance characteristics when combined with SBS and PPA modifiers.

Multiscale study on aging process and mechanism of high viscosity Asphalt: Macro-micro experiments and quantum chemical molecular simulation

Clarifying the aging mechanism of high viscosity asphalt (HVA) is the prerequisite for ensuring its durability, but there are relatively few studies on the aging mechanism of HVA under coupling effects. The quantum chemical simulation method can be applied to better reveal the mechanism of aging behavior from the molecule perspective compared with macro and micro tests. However, the quantum chemical method has not been applied in the HVA aging study. In this paper, the macro and micro tests were carried out to study the changes of macro properties, functional groups, molecular weight and microstructure of HVA after thermal oxygen aging. Quantum chemical simulation was conducted to analyze the reaction sites, steps and products of styrene–butadienestyrene (SBS) and asphalt components in HVA under the coupling effect of oxygen, water and ultraviolet. The results show that with the aging deepening, the penetration and ductility of HVA decrease, the softening point and complex modulus increase, the high-temperature performance increases and the low-temperature performance decreases. After short-term aging, the cross-linked structure destruction and the SBS degradation dominate, so the HVA viscosity decreases and the phase angle increases. After long-term aging, the polymerization of aromatics and saturates dominates, so the HVA viscosity increases and the phase angle increases. The most easily oxidized site in HVA is the carbon atom at the carbon–carbon bond in SBS molecule, followed by the carbon atom connected with the benzene ring in asphalt. SBS is easier to react with oxygen or water than asphalt, so SBS delays the aging of asphalt in HVA. Under different water content, the aging processes and products of SBS/asphalt components with oxygen/water are different, but the ultraviolet excitation does not change the reaction path. The HVA aging was enhanced with the water content increase or ultraviolet excitation by reducing the energy barrier in reaction.

Long-Term Performance Analysis of Epoxy Resin Ultra-Thin Wearing Course Overlay on Cement Concrete Pavement

The overall rigidity of the cement concrete pavement is high, but there are defects such as easy cracking and insufficient anti-slip performance. The epoxy resin ultra-thin wearing course overlay can effectively solve these issues. However, there is still a lack of knowledge about the long-term performance of epoxy resin ultra-thin wearing course overlay on cement concrete pavement. Therefore, this article analyzed the interlayer adhesion and durability of epoxy resin ultra-thin wearing course overlay through the Hamburg rutting test and a series of shear tests under damp heat, thermal oxygen aging, and ultraviolet (UV) aging conditions. Shear test results indicated that the shear performance of epoxy resin overlay grew with the increase in epoxy resin content and was severely affected by high temperature, and the optimal content was set as 3.4 kg/m2. The Hamburg rutting test results showed that the epoxy resin overlay exhibited satisfactory high-temperature performance and water resistance. For the damp heat effect, it was revealed that damp heat led to more significant shear strength loss compared with the overlay specimens without damp heat. The water immersion caused the shear strength decline due to the water damage to the overlay interface. As for the thermal oxygen aging effect, it was reflected that the short-term thermal oxygen aging had a minor impact on the shear performance of the epoxy resin overlay. However, with the increase in thermal oxygen aging duration, the shear strength of the epoxy resin overlay significantly decreased due to the aging of epoxy resin binders. Regarding the UV aging impact, it was also found that the shear performance of the epoxy resin overlay rapidly decreased as the UV aging duration grew whether at 20 °C or 60 °C. Moreover, UV aging led to a more significant impact on the shear performance of the epoxy resin overlay than thermal oxygen aging.

Tremella Polysaccharide Has Potential to Retard Wheat Starch Gel System Retrogradation and Mechanism Research.

This study investigated the effects of adding different concentrations of TP (tremella polysaccharide) on the water distribution, rheological, thermal, microstructure, and retrogradation properties of WS (wheat starch) gels. The results showed that the starch aging increased during storage, and the addition of TP reduced the rate of change of the elastic modulus of the starch gel and delayed the short-term aging of WS. In the same storage period, the hardness value of the gel decreased and the texture became softer with the increase in the mass fraction of TP. TP increased the T0 (starting temperature) of the system and decreased the enthalpy of retrogradation (ΔHr). No new groups were formed after the retrogradation of the compound system, the hydrogen bonding force increased with the increase in polysaccharide, and the relative crystallinity and the degree of ordering of the system decreased. The addition of TP increased the content of bound water and immobile water, decreased the content of free water, and increased the gel water-holding capacity, indicating that it could effectively inhibit the long-term retrogradation of WS. The findings provide new theoretical insights for the production of starch-based foods.

Study on aging mechanism of SBS/SBR compound-modified asphalt based on molecular dynamics

Abstract Component ratio change is considered to be the main reason leading to the deterioration of asphalt properties, but there are few studies on the aging mechanism from the perspective of modifier molecules. To reveal the aging mechanism of styrene–butadiene–styrene block copolymer (SBS)/styrene butadiene rubber (SBR) compound-modified asphalt, the micro mechanism in the aging process was studied by combining molecular dynamics (MD) and Fourier transform infrared spectroscopy (FTIR). First, MD was used to establish the micro models of SBS/SBR compound-modified asphalt at different aging stages (non-aging, short-term aging, and long-term aging) and to verify its rationality. Second, the micro characteristics of the SBS/SBR compound-modified asphalt micro model, such as solubility parameters, diffusion coefficient, interface interaction energy, and radial distribution function, were analyzed by calculation. Finally, the FTIR results proved the rationality of the simulation and explained the aging mechanism of SBS/SBR compound-modified asphalt. The results show that the cohesiveness density and solubility parameters of SBS/SBR compound-modified asphalt increase, the diffusion coefficient decreases, and the molecular interface stability increases during the aging process. And, the carbonyl index, sulfoxide index, and aromatic ring index increased in different degrees after aging. The study explains the aging mechanism of SBS/SBR compound-modified asphalt from the perspective of modifier molecules and provides a theoretical basis for the research of asphalt anti-aging.

Research on the Rheological Properties and Anti-Aging Mechanism of Paper-Black-Liquor-Modified Bitumen

The production process of the traditional paper making process produces a large amount of waste water, known as paper black liquor. It is needed to explore new ways of reusing this waste and replacing part of the base bitumen to reduce the consumption of non-renewable resources, such as petroleum, thus obtaining better environmental, economic, and social benefits. This paper analyses the feasibility of using paper black liquor, which contains a large amount of lignin, as a modifier for bitumen in the paper industry. Samples of modified bitumen were prepared with 15%, 30%, and 45% of the base bitumen replaced by paper black liquor, and a control group of base bitumen was prepared for testing. The samples were subjected to an 85 min short-term ageing test, FTIR scanning test, thermogravimetric test, frequency scanning test, MSCR test, and LAS test. The analysis of the FTIR and thermogravimetric tests showed that the paper black liquor was mainly composed of lignin and some cellulose, and contained a small amount of salts with Na ions; based on the results of the frequency scan, the compatibility analysis of the vGP curve showed that the modified bitumen was more compatible in the high-temperature range after short-term ageing, thus inferring that the water content of the concentrate had an influence on the compatibility, making it necessary to further investigate different optimum water contents to achieve the best performance and benefit. The incorporation of paper black liquor improved the rutting resistance and fatigue resistance of the modified bitumen, and also gave the paper-black-liquor-modified bitumen a better ageing resistance than the base bitumen. While demonstrating the feasibility of using paper black liquor as an bitumen modifier, this study also helps to provide a basis for theoretical applications of biomass materials in the field of road engineering.

Introduction of calcium lignosulfonate to delay aging in bituminous mixtures

This study examines the merits of using calcium lignosulfonate (CLS) to mitigate negative effect of aging on bituminous mixtures. To do so, we studied how fracture energy and fracture toughness of the bituminous mixtures containing CLS change when exposed to long-term aging. Aging is implicated in premature cracking including but not limited to top-down cracks and low-temperature cracks which negatively impact road roughness, and subsequently ride quality and driver safety. Considering that latter cracks are induced by tensile and shear forces, we used semi circular bending (SCB) test to quantify fracture energy and fracture toughness of mixtures containing 5–20% CLS under both mode I and II. Each mixture was exposed to short and long term aging and tested at temperature of +15 °C and −15 °C. The study results showed that introduction of CLS increased the fracture energy and fracture toughness of the mixtures under both modes I and II. The study outcomes provides insights for advancing socioeconomics of pavements by mitigating surface cracks which in turn enhances the driver safety, ride quality and maintenance cost of pavements.

Influence of SBS on the Aging Properties of High-Content Terminal Blend Rubber Modified Asphalt

The goal of this study was to investigate the effect of styrene-butadiene-styrene (SBS) polymer on the aging properties of high-content terminal blend rubber modified asphalt (HCTBMA). All asphalt was tested for chemo-rheological properties using an attenuated total reflection–Fourier transform infrared spectroscopy (ATR-FTIR) test, temperature sweep test, frequency sweep tests, and multiple stress creep recovery (MSCR) test. According to ATR-FTIR observations, SBS can retard the oxidation effect of HCTBMA during short-term aging, but its inhibitory effect is reduced during long-term aging. Furthermore, aging aggravates the degree of desulfurization of crumb rubber in HCTBMA as the SBS content increases. Compared with HCTBMA, neat asphalt has a lower elasticity at high temperatures and a higher elasticity at low temperatures. The addition of SBS to HCTBMA improves the elasticity of the material. The elasticity of HCTBMA decreases and then increases after aging, and SBS can reduce the aging degree of HCTBMA after aging. Moreover, based on Pearson correlation analysis, the correlation between the desulfurization of rubber and the degradation of polybutadiene in HCTBMA during aging is high.

Investigating the Addition of Organomontmorillonite Nanoclay and Its Effects on the Performance of Asphalt Binder

Asphalt binder aging is a complex phenomenon that plays an essential role in reducing flexible pavement serviceability. The aging resistance of asphalt binder can be enhanced through the binder modification. This research investigates the impact of aging on unmodified and organo-montmorillonite (OMMT) nanoclay modified asphalt binders. In this study, laboratory aging is carried out for asphalt binders modified with two types of OMMT nanoclays at different dosages (2% and 4% by weight of the binder). The asphalt binders are subjected to short-term and long-term aging using a rolling thin-film oven and pressure aging vessel equipment. Rheological properties of the aged and unaged binders are determined using a dynamic shear rheometer. In addition, storage stability, full performance grading, and rutting resistance of the binders are evaluated and compared. Aging indices were calculated to investigate the aging behavior of the unmodified and modified binders. The results showed that the montmorillonite nanoclay-modified asphalts had improved resistance to aging compared with the unmodified binder.

Early-life prophylactic antibiotic treatment disturbs the stability of the gut microbiota and increases susceptibility to H9N2 AIV in chicks

BackgroundAntibiotics are widely used for prophylactic therapy and for improving the growth performance of chicken. The problem of bacterial drug resistance caused by antibiotic abuse has previously attracted extensive attention; however, the influence of early-day use of prophylactic antibiotics on the gut microflora and on the disease resistance ability in chicks has not been explored. Here, we comprehensively evaluate the growth performance, gut microbial dynamics, level of antibiotic resistance genes (ARGs) in the gut microbial community, and resistance to H9N2 avian influenza virus (AIV) in chickens following long-term and short-term early-day prophylactic antibiotic treatment.ResultsUnexpectedly, long-term prophylactic enrofloxacin treatment slowed the growth rate of chickens, whereas short-term antibiotics treatments were found to increase the growth rate, but these changes were not statistically significant. Strikingly, expansions of Escherichia-Shigella populations were observed in early-life prophylactic antibiotics-treated groups of chickens, which is in contrast to the general perception that antibiotics should control their pathogenicity in chicks. The gut microbiota composition of chickens treated long term with antibiotics or received early-day antibiotics treatment tend to be more dramatically disturbed compared to the gut microbiome of chickens treated with antibiotics for a short term at a later date, especially after H9N2 AIV infection.ConclusionsOur data provide evidence that early-day and long-term antibiotic treatments have a more adverse effect on the intestinal microbiome of chickens, compared to short-term late age antibiotic treatment. Furthermore, our metagenomic data reveal that both long-term and short-term antibiotic treatment increase the relative abundance of ARGs. Our findings highlight the adverse effects of prophylactic antibiotic treatment and provide a theoretical basis for the cautious administration of antibiotics in food-producing animal management.Ao91n5eHkkQPyDkUXXsk_bVideo

Experimental Study on the Cracking Resistance of Asphalt Mixture with Different Degrees of Aging

The cracking resistance of asphalt mixture is a non-negligible issue. However, the cracking resistance evolution law, motivated by two factors (thermos-oxidative aging degree and test temperature), is not yet well understood. The aim of this investigation is to gain more insight into the effect of thermos-oxidative aging and test temperature on the cracking resistance of asphalt mixture. Asphalt mixture (AC-13) and stone mastic asphalt mixture (SMA-13) were selected and exposed to different thermo-oxidative aging degrees (unaging (UA); short-term thermo-oxidative aging (STOA); long-term thermo-oxidative aging for 2/5/8 days (LTOA2d/LTOA5d/LTOA8d)). A direct tension test at different test temperatures (10 °C, 20 °C, 30 °C, 40 °C) was adopted to obtain their stress–strain curves and evaluation indexes (tensile strength, ultimate strain, pre-peak strain energy density, and post-peak strain energy density). The comprehensive index-cracking resistance index (CRI) was established by the entropy weight method combined with the technique to order preference by similarity to ideal solution (TOPSIS) method and the corresponding aging coefficient was determined. The results showed that STOA can increase the aging coefficient of asphalt mixture, thereby boosting the cracking resistance. Additionally, the effect can be weakened by elevations in the test temperature. Meanwhile, LTOA can decrease the aging coefficient and thereby weaken the cracking resistance. This effect becomes more prominent with elevations in the test temperature. SMA-13 possesses a superior cracking resistance to AC-13, with a gap in CRI value of 3–69%, regardless of the aging degree and test temperature. A good relationship exists between the aging coefficient and the two factors (aging degree and test temperature).

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.

Research on strength formation mechanism and noise reduction characteristics of waste rubber powder micro-surfacing

The application and promotion of the traditional micro-surfacing is limited by the defects of high noise and poor wear resistance. In order to improve the adhesive strength and noise reduction properties of the micro-surfacing, an attempt was made to add waste rubber powder (WRP) in dry form to the micro-surfacing. Firstly, the mixtures were prepared by orthogonal tests taking into account the number of rubber powder grades, rubber powder dosages, asphalt-aggregate ratio and gradation. The microscopic strength formation mechanism at the micro-surfacing of the waste rubber powder was investigated by means of Scanning Electron Microscope (SEM). Secondly, the effect of waste rubber powder (WRP) on the modification of asphalt mastic was investigated with the Dynamic Shear Rheometer (DSR), both as unaged and after short-term ageing. Finally, the effect of waste rubber powder on the performance improvement and noise reduction characteristics of the micro-surfacing was analyzed through road performance tests, and to establish the correlation between microstructure and road performance. The results showed that 2% of 40-mesh rubber powder mixed with 8% asphalt-aggregate ratio of medium grade MS-3 micro-surfacing mixture, the densest structure of the slurry. Significantly improved high-temperature and ageing performance at the micro-surfacing reduced noise generation and suppressed noise transmission, but no significant improvement in water stability performance. The waste rubber powder enhances the strength of the micro-surfacing by interweaving with cement hydration products and asphalt mortar. It also optimizes the inter-aggregate embedding and void characteristics, and has an excellent noise reduction effect.

Research on high-temperature rheological performance of fiber reinforced high-viscosity asphalt mastics

High-temperature performance of high-viscosity asphalt mastic containing fiber additive were studied by means of rheological analysis. The effects of two types of asphalt, two types of fillers, and two types of fibers with three fiber contents on the high-temperature rheological properties of asphalt mastic were evaluated by temperature sweep test, multiple stress creep recovery test, and frequency sweep test using a dynamic shear rheometer. The master curve of fiber reinforced high-viscosity asphalt mastic and phase angle were constructed using 2S2P1D model. The results show that the nature of asphalt plays a leading role in improving the resistance to deformation of asphalt mastic at high temperature, compared with the type of mineral powder. For the short-term aging asphalt mastic, with temperature increasing, the unrecoverable creep compliance gradually increases and the differences between asphalt mastic with different fiber contents also become greater. The creep recovery rate of mastic with basalt fiber is much higher than that of polyester fiber under the same conditions. For long-term aging asphalt mastic, compared with increasing fiber content, the fiber type has more significant influence on the storage modulus. 2S2P1D model can well fit the master curve of the complex modulus of fiber reinforced high-viscosity asphalt mastic, but poorly fit with the phase angle. From master curves, it finds that the enhancement of the fiber to mastic is prominent in the low frequency which is corresponding to the extreme high-temperature condition.

Evaluation of Anti-Aging Effect in Biochar-Modified Bitumen

Increasing environmental awareness has led to a great research effort towards the formulation of increasingly sustainable pavements, mainly by developing bituminous mixtures incorporating waste materials. Furthermore, some waste materials have been proved to be useful for enhancing the performance of road bitumen and bituminous products, so their use is a potential solution for ensuring environmental, economic, and also technical benefits. Amongst the different wastes to be used for bitumen modification, a possible one is that obtained via the pyrolysis of biomass, named biochar. In the research reported here, a selected biochar was added to bitumen to verify the possibility of improving bitumen performance in terms of photo-oxidation resistance, which is a major problem in urban areas where black flexible pavements contribute to the urban heat island effect. Different biochar amounts were selected, and two different aging methods were performed: short-term aging and UVB aging resistance; they were monitored using rheological and spectroscopic analysis. The structural changes in bitumen in terms of carbonyl and hydroxyl accumulation were observed at various UV irradiation times. All the experimental data indicate that the use of biochar can have a positive effect on the UV resistance of bitumen, lowering its photo-oxidation tendency. This may lead to reductions in use of natural, non-renewable materials, since intervention maintenance may be scheduled at longer terms.

Laboratory Evaluation of the Effectiveness of Rejuvenation in Multiple Hot Recycling of Asphalt Mixtures

Abstract Because of the widespread use of reclaimed asphalt (RA) in new asphalt mixtures, multiple RA recycling is expected to become a common practice. Thus, the long-term properties of multiaged RA as well as the effectiveness of multiple-cycle rejuvenation of RA need to be properly investigated. Given this background, the present study was aimed at evaluating at laboratory scale the feasibility of multiple hot recycling of RA at both short-term aging (STA) and long-term aging (LTA) conditions. The effectiveness of rejuvenation of multiple recycled mixtures was also assessed. In particular, the effect on mixture performance of the rejuvenator addition at different recycling stages was evaluated both after mix rejuvenation and at the end of laboratory-simulated LTA. To these aims, the evolution of linear viscoelastic properties and tensile strength of a plant-produced asphalt mixture has been investigated over a series of short-term and long-term simulative aging cycles carried out with or without the addition of a rejuvenator product. The experimental findings mainly showed that recycling effect (i.e., stiffening and embrittlement) seems to stabilize over cycles with an effective rejuvenating contribution because of the recycling agent. Nevertheless, a specific design of the rejuvenator content considering the actual RA properties instead of requiring a fixed dosage based on RA binder content is only necessary because the recycling history undergone by RA (i.e., number of recycling cycles and use of rejuvenator over the different cycles) clearly affects the final properties of the recycled mixes.

Performance Evaluation of Long-Term Laboratory-Aged Asphalt Mixtures Containing Different Molecular Structures of SBS Copolymers

The current study emphasizes the impact of styrene-butadiene-styrene (SBS) molecular structures on the extent of performance deterioration in asphalt mixes after short-term and long-term laboratory aging. First, modified binders were prepared using linear (L-SBS), branched (B-SBS), high vinyl (HV-SBS), and di-block (DB-SB) SBS copolymers, and consequent asphalt mixes were fabricated using these modified binders. The influence of aging on the asphalt mixture performance has been evaluated through Cantabro mass loss, fracture properties, fatigue, and rut resistance behavior. Results showed that irrespective of the type of SBS polymer in the binder, the short-term aging (STA) of asphalt mixes had an insignificant effect on their performance properties. However, a substantial drop in all mix performances was observed after long-term aging (LTA) with L-SBS and B-SBS modified binders due to the degradation of the polymer chains. Mixes prepared with L-SBS and B-SBS copolymers depicted higher variation in the aging index after LTA than their counterparts and were also unable to protect the base binder from stiffening. In contrast, HV-SBS and DB-SB generate significantly lower temperature susceptibility in the asphalt mixture due to higher vinyl content (≥30%), i.e., location of the C=C group as the side chain in the butadiene segment. Fourier-transform infrared spectroscopy (FTIR) results reveal that the increase of carbonyl and sulphoxide compounds, and the lowering of polybutadiene compounds validate the adverse effect of LTA on L-SBS and B-SBS copolymers. On the contrary, such behavior was not reflected in HV-SBS and DB-SB copolymers. Thus, the current study presents the major limitation of using branched and linear SBS polymers having comparatively lower vinyl content, and recommends the mandatory use of high-vinyl SBS copolymers for ensuring enhanced long-term performance.

Microstructural evolution and mechanical properties of (FeCoNi)85·84Al7·07Ti7.09 high-entropy alloy by selective laser melting with aging treatment

Faced-centred cubic nanoparticles-strengthened FeCoNiAlTi system high-entropy alloy (HEA) has demonstrated unique mechanical performance advantages with recently developed HEA alloy compositions. One of the key factors determining the performance of an alloy is the efficient manipulation of precipitation. However, the traditional aging method used to achieve this can be problematic. It is time-consuming and difficult to accurately control the distribution of the precipitated phase, which restricts the development of new, high-performance structural materials. Consequently, researchers have been exploring alternative methods to more precisely and effectively manipulate precipitation in alloys. Here, we have utilized both high-efficiency additive manufacturing processes and a short-term aging process to produce (FeCoNi)85·84Al7·07Ti7.09 high-entropy alloys that exhibit outstanding mechanical properties with an ultimate tensile strength of 1625 MPa, yield strength of 1214 MPa and an elongation to failure of 11.6%. Our findings reveal the formation of L12 and L21 nanoparticles phases after aging treatment, and their contents gradually decrease with increasing aging treatment temperature. And, we introduce two strengthening mechanisms of dislocation strengthening and precipitation strengthening into the alloys, and realized the coexistence of high-density dislocations and precipitated phases, thereby exhibiting excellent comprehensive mechanical properties. This approach represents a promising new direction in the development of high-performance alloys, offering a more efficient and effective means of producing materials with improved properties.