Aging Resistance Research Articles

Innovative Materials Based on Epoxy Resin for Use as Seat Elements in Bulk Transport.

The subject of this research is the development of epoxy composites with a defined service life for the purpose of seat elements in rail vehicles, which will be more environmentally friendly. The produced materials based on epoxy resin filled with PLA or PLA and quercetin were subjected to solar aging tests for 800 h to investigate the impact of the additives used on the aging behavior of the epoxy matrix. Firstly, the TGA analysis showed that the use of the proposed additives allowed for the maintenance of the thermal stability of the epoxy resin. Moreover, based on an optical microscopy test, it was noticed that the introduction of PLA and PLA with quercetin did not contribute to an increase in matrix defects. The one-directional tensile tests carried out before and after solar aging showed that the presence of polylactide in epoxy composites causes a slight growth of the stiffness and strength. Based on contact angle and color change measurements, it was found that quercetin was oxidized, thus ensuring protection for the epoxy matrix. This phenomenon was confirmed by FTIR study, where the carbonyl index (CI) value for the R-PLA-Q composite was lower than for the reference sample. The obtained composite structures may be a good alternative to traditionally used systems as seat elements in rail vehicles, which are not only characterized by high aging resistance but are also more eco-friendly.

Design and experimental study of electron beam treatment for composite insulator sheds

Composite insulators, widely used in high-voltage transmission lines, feature silicone rubber sheds that age in complex natural environments. Applying electron beam irradiation to the silicone rubber can enhance their ageing resistance and hydrophobic properties. To advance the study of sheet silicone rubber to the entire insulator, this study proposes a method utilising a 5 MeV Dynamitron accelerator for treating a irregularly structured insulator. The insulator is irradiated in a state of tilted placement and rotation about its axis to achieve a uniform and consistent dose across the sheds. The irradiation process of the insulator with electron beams is simulated using Geant4, considering both instantaneous and cumulative states separately. The deflected particles from scattering and reflection of high-energy electrons interacting with insulator components have a significant impact on the dose distribution in each shed. Moreover, an optimal tilt of 20° ensures similar irradiation doses and high uniformity across all sheds. An experimental platform is developed for rotational irradiation of the insulator to ensure stable operation. Preliminary experimental results confirm that the doses across all sheds are uniform and consistent.

Simultaneously achieving excellent heat aging resistance and grip performance in carbon black/glass flake/EPDM rubber composite for overhead line spacers

The preparation of wire clamp rubber with semiconductivity, low compression set (C-Set), high mechanical strength, heat aging resistance, and high grip strength is vital for overhead line spacers. This study delves into the formulation design of high-performance ethylene-propylene-diene monomer (EPDM) composite materials for wire clamp rubber. The effects of the vulcanization system, carbon black type, and loading on the essential material properties of EPDM rubber were investigated. The results showed that a hybrid vulcanization system containing peroxide and sulfur simultaneously endowed EPDM rubber with high elasticity and tear strength. N330 carbon black-filled EPDM rubber had the advantages of semiconductivity and high tensile strength, and N774 carbon black-filled EPDM rubber exhibited low C-Set and high heat aging resistance. When EPDM rubber was reinforced with the mixture of 50 phr N330 and 20 phr N774 carbon black, the rubber synchronously exhibited semiconductivity (2.64×106 Ω·cm), high tensile strength (20.2 MPa), low C-Set (32.5%, 150°C×3d), and high heat aging resistance (maintaining 98% of its initial tensile strength after aging at 150°C for 3d). In addition, introducing a 10-phr glass flake into EPDM wire clamp rubber improved the grip force by 83%. The improvement mechanism may be attributed to the increased compression stress of wire clamp rubber on cable and the restricted slippage of rubber molecular chains.

Radiation and Radical Grafting Compatibilization of Polymers for Improved Bituminous Binders-A Review.

This review scrutinizes current research on new methods for enhancing bituminous binder performance through radiation and radical grafting of polymer modifiers of bitumen. It investigates innovative methods, including using waste polymers as modifiers and applying radiation for polymer grafting, to overcome challenges like high costs, low aging resistance, and storage stability issues, of which separation of phases polymer/bitumen is the most significant obstacle. These advanced modification techniques promise sustainability through the decrease of the carbon footprint of transportation systems by improving the properties and durability of binders. Additionally, this review discusses the parameters and mechanistic aspects from a scientific perspective, shedding light on the underlying processes that contribute to the improved performance of modified bituminous binders.

MFAP4-Deficiency Aggravates Age-Induced Changes in Resistance Artery Structure, While Ameliorating Hypertension.

Abnormalities of resistance arteries may play essential roles in the pathophysiology of aging and hypertension. Deficiency of the vascular extracellular matrix protein MFAP4 (microfibrillar-associated protein 4) has previously been observed as protective against aberrant arterial remodeling. We hypothesized that MFAP4-deficiency would reduce age- and hypertension-dependent arterial changes in extracellular matrix composition and stiffening. Mesenteric arteries were isolated from old (20-23 months) littermate Mfap4+/+ and Mfap4-/- mice, and 2-photon excitation microscopy imaging was used to quantify elastin and collagen volumes and dimensions in the vascular wall. Ten-week-old littermate Mfap4+/+ and Mfap4-/- mice were subjected to 20 days of continuous Ang II (angiotensin II) infusion and hypertension was monitored using invasive blood pressure measurements. Arterial stiffness, responses to vascular constrictors, and myogenic tone were monitored using wire- or pressure-myography. Collagen contents were assessed by Western blotting. MFAP4-deficiency significantly increased collagen volume and elastin fragmentation in aged mesenteric arteries without affecting arterial stiffness. MFAP4-deficient mice exhibited reduced diastolic pressure in Ang II-induced hypertension. There was no significant effect of MFAP4-deficiency on mesenteric artery structural remodeling or myogenic tone, although collagen content in mesenteric arteries was tendentially increased in hypertensive Mfap4+/+ mice relative to Mfap4-/- mice. Increased efficacy of vasoconstrictors (phenylephrine, thromboxane) and reduced stiffness were observed in Ang II-treated Mfap4-/- mouse mesenteric arteries in ex vivo myography recordings. MFAP4-deficiency reduces the elastin/collagen ratio in the aging resistance artery without affecting arterial stiffness. In contrast, MFAP4-deficiency reduces the stiffness of resistance arteries and ameliorates Ang II-induced hypertension.

Grafting of voltage stabilizer onto EPDM surface and its inhibition effect on the breakdown of EPDM/XLPE interface

Surface discharge on the EPDM/XLPE interface is threatening the safe operation of power cable system and limiting the further improvement of its voltage level. To improve the electrical strength of EPDM/XLPE interface, the surface of EPDM was modified by grafting of voltage stabilizer 4-allyloxy-2-hydroxybenzophenone (AOHBP) based on liquid-phase impregnation and subsequent free radical grafting reaction thermally initiated by DCP. EPDM samples were modified by mixed reagents of DCP and AOHBP with different mass ratios of 1:2, 1:3 and 1:4, respectively. The SEM observation and XRD analysis results indicate that the crystals of AOHBP with a uniform distribution are covered on the surface of EPDM during the sample preparation process and then dissolved after extraction by acetone. The FTIR and ATR results show that the AOHBP molecules are successfully grafted onto the surface of EPDM samples, but there remain a lot of ungrafted reagent molecules on the surface of EPDM before solvent extraction. The grafting rate of AOHBP increases with the proportion of DCP in the mixed reagents. As for the unextracted modified EPDM samples, both the AC and DC breakdown voltage of the EPDM/XLPE interface are increased compared with pure EPDM, and further increased after the ungrafted molecules are extracted because the effect of voltage stabilizer on scavenging high-energy electrons is more efficiently utilized at a smoother interface. The interface breakdown voltage of the sample modified with 1:2 mass ratio of DCP/AOHBP mixed solution is the highest because of its highest grafting rate of voltage stabilizer. This work has proposed a new technical path to improve the electrical aging resistance of polymer insulating surface.

The beneficial effect of lauric acid addition in nucleation stage on the soot catalytic combustion performance of cerium-manganese catalyst

For cerium-manganese catalyst system, increasing the threshold of the amount of Mnx+ entering into the CeO2 lattice can generate more oxygen vacancies and adsorb more active oxygen species, thus promoting its soot catalytic combustion. However, this is difficult to achieve under the premise of fixed cerium-manganese ratio of the catalyst. Fortunately, the results of this study show that the addition of lauric acid at the nucleation stage of the cerium-manganese catalyst can effectively improve its activity and high temperature aging resistance. Combined with a series of characterization results, the addition of lauric acid can increase the threshold of Mnx+ content in CeO2 lattice, improve the structural performance of the catalyst, increase the specific surface area and pore volume of the catalyst, inhibit the secondary aggregation of catalyst particles, increase the content of surface Ce3+, increase the low temperature reduction performance and the content of surface chemical desorbed oxygen of the catalyst. In addition, it can also prevent the phase separation of cerium-manganese solid solution, the growth of grains, the increase of reduction peak temperature and the decrease of H2 consumption during high temperature aging. Moreover, the addition of lauric acid also greatly improves the release performance of active oxygen in cerium-manganese catalyst. Therefore, this study plays a positive role in promoting the commercial application of highly active cerium-manganese catalyst.

The influence of zinc oxide-silicate composites on the aging resistance of asphalt

Asphalt binder is susceptible to aging from heat, air and sunlight exposure during service, leading to pavement distresses. This study aimed to improve the aging resistance of asphalt using zinc oxide-silicate (ZOS) composites. ZOS containing 2–8 wt% ZnO were synthesized via a one-step sol-gel method and incorporated into an unmodified 70/100 penetration grade asphalt binder. The rheological properties and aging characteristics were evaluated before and after rolling thin film oven and pressure aging vessel protocols. Dynamic shear rheometry showed increased complex modulus and decreased phase angle for ZOS-modified binders, indicating improved rutting resistance. Aging indices revealed the 6% ZOS composite had the least susceptibility to oxidative aging. FTIR analysis confirmed the formation of carbonyl and sulfoxide functional groups during aging, which were mitigated by ZOS addition. Scanning electron microscopy visualized nano-scaled ZnO particles dispersed within the silica matrix and asphalt binder. The ZOS composites delayed the aging rate through physicochemical interactions between ZnO and the asphalt medium. An optimum ZOS dosage of 4–6% was found to enhance the anti-aging properties. The renewable silica-supported ZnO composites show potential as cost-effective modifiers for improving asphalt durability.

Investigation of rheological properties and modification mechanism of SBS-modified asphalt with different warm mix additives

ABSTRACT The application of warm mix asphalt (WMA) technology in polymer-modified asphalt becomes increasingly widespread, but it lacks thorough investigation on the interaction mechanism between warm mix additives and polymers. Accordingly, two new warm mix additives, an organic viscosity-reducing modifier (A) and a surfactant-based modifier (C), were selected to prepare the warm mix SBS-modified asphalt. The basic properties, viscosity-temperature characteristics, ageing resistance and rheological properties of modified asphalt were tested. At last, the modification mechanism was elucidated through a series of microscopic tests. The results indicated that A could more effectively enhance the construction workability of SBS-modified asphalt, while C had little effect on its basic properties. Both new modifiers, especially A, reduced the high-temperature property of asphalt, with partial recovery after short-term ageing. The microstructure test results indicated that the two modifiers were physically modified with SBS-modified asphalt. Both additives improved the dispersion uniformity of SBS particles in asphalt, and the microscopic morphology parameters obtained from quantitative analysis reflect the macroscopic properties of asphalt. Moreover, the light components and rubber powder of A improved the flexibility of asphalt, and C enhanced its low-temperature performance, which demonstrated that these two modifiers were more suitable for asphalt pavements in cold regions.

Effect of aging on micromechanical behavior of asphalt surfaces using an atomic force microscope

The micro-mechanical properties of asphalt surfaces are significantly impacted by short-term aging during construction and long-term aging in service. This, in turn, affects macroscopic characteristics such as asphalt-aggregate adhesion and water stability of asphalt mixtures. The study investigated different aging processes had different impacts on the micromechanical properties of the asphalt on the surface. The short-term aging process had the most significant effects, while the subsequent long-term aging had similar but less important effects. The adhesion, surface energy, and Young's modulus of five different types of asphalt using atomic force microscopy (AFM) in their original state, after short-term aging through the Rolling Thin Film Oven Test (RTFOT), and after long-term aging through the RTFOT+Pressure Aging Vessel (PAV). The results showed that ZH and SK asphalts had a distinct "bee structure", and aging had varying effects on adhesion, surface energy, and Young's modulus in different areas (peak, valley, and other region). Before and after asphalt aging, the adhesion and surface energy approximately followed the order other region > peak > valley, while Young's modulus approximately followed the peak>valley> other region. This indicates that the bumpy "bee structure" does not always correspond to higher modulus or lower adhesion. It was also found that ZH asphalt and SK asphalt with a "bee structure" exhibited better aging resistance compared to KL asphalt without a "bee structure". The study also revealed that aging led to decreased adhesion and surface energy, while increasing Young's modulus. This finding indicates that as asphalt ages, adhesion decreases and asphalt elasticity increases. Additionally, it was observed that the modified asphalt showed less change in adhesion, surface energy, and Young's modulus after aging compared to the matrix asphalt, indicating that SBS modifiers contribute to improving the aging resistance of asphalt. These results will provide a good reference for understanding the microscopic changes in asphalt aging properties.

Remediation of Cd(II), Zn(II) and Pb(II) in contaminated soil by KMnO4 modified biochar: Stabilization efficiency and effects of freeze–thaw ageing

Biochar has been widely used in soil remediation because of its porosity and impressive efficiency. Many studies have demonstrated the good affinity of biochar for heavy metals (HMs), but efficient modification methods to increase the stability of multiple HMs are lacking. Moreover, few studies focus on biochar’s potential ability to ageing resistance and changes in its physicochemical properties during freeze–thaw (F/T) cycles. Here, KMnO4-modification biochar (MBC) was prepared and the immobilization and anti-freeze performance of MBC on Cd, Zn and Pb in soil were investigated. The addition of 10 % MBC decreased concentrations of toxicity characteristic leaching procedure (TCLP) by 66.80 %, 25.39 % and 99.68 % for Cd, Zn and Pb, respectively, after 28 days, accompanied by a significant decrease in the phytoavailability and bioaccessibility of HMs in soil. Soil fertility was also improved by MBC application. Furthermore, frequent F/T cycles obviously induced the fragmentation of soil particles and enhanced the activity of HMs. Conversely, MBC particles became finer, accompanied by further oxidation and higher alkalinity but degraded pore structures during F/T cycles. The oxidation of lignocellulose and changes in C-O stretching were greatest among all functional groups in biochar. Therefore, MBC could suppress the migration of HMs through precipitation, cohesion of soil particles, and stronger complexation by oxygen-containing functional groups. Moreover, fractions of HMs were also transferred from exchangeable to potentially labile or nonlabile species. Overall, MBC displayed advantages in the stabilization of HMs and showed higher resistance to F/T cycles and promise for long-term remediation of HM-contaminated soils in cold regions.

Study on thermal cycling ageing resistance of performances of polypropylene/elastomer/boron nitride nanocomposites for high voltage direct current cable insulation

AbstractThe influences of thermal cycling ageing on structures and insulation performances of polypropylene (PP)/elastomer/boron nitride (BN) nanocomposites are investigated. The Melt blending method was used to prepare the nanocomposites, in which propylene‐based elastomer (PBE) or ethylene‐octene copolymer elastomer (EOC) was contained for comparison. Then, the samples were treated using a thermal cycling process with a temperature range from −30 to 150°C, and the number of thermal cycles was set from 0 to 15. Scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry and X‐ray diffraction measurements were taken to facilitate the comprehension of structural changes. Additionally, measurements were taken to assess the trap distribution and direct current (DC) breakdown strength of the samples. The obtained results revealed that following thermal cycling ageing, the morphology and crystallinity of PP/PBE/BN remained almost unchanged. In contrast, PP/EOC/BN exhibited substantial microstructural damage accompanied by a significant reduction in crystallinity. As the number of thermal cycles increased, the trap level and DC breakdown strength of PP/PBE/BN were maintained at high levels, while those of PP/EOC/BN initially remained stable but then experienced a sharp decline. It is suggested that the addition of BN nanoparticles enhances the thermal cycling ageing resistance of the PP/PBE blend, whereas it weakens this resistance of the PP/EOC blend.

Preparation and Study of EPDM Composites with High Volume Resistance Retention Rate

LDPE/ EPDM composites were prepared by mechanical blending method. The effects of two compatibilizers MA/Zn and CPE on the vulcanization properties, mechanical properties, aging resistance and electrical properties of the composites were studied. The results showed that the addition of two kinds of compatibility significantly improved the compatibility of LDPE and EPDM. Compared with CPE, the addition of MA/Zn can improve the properties of the composites better. The mechanical and electrical properties of the composite were improved by the addition of MA/Zn compatibilizer. The volume resistivity of sample L3M2 is the highest at room temperature and 125 ℃, which are 19.8×1013Ω·m and 16.8×1012Ω·m, respectively. Compared with L3, the increase was 26.1% and 25.8%, respectively. The tensile strength is 14.1MPa, which is 90.5% higher than L3.

Multiscale optimization on polymer-based rejuvenators for the efficient recycling of aged high-viscosity modified asphalt: Molecular dynamics simulation and experimental analysis

With the depletion of fossil fuels, the advancement of efficient pavement recycling technology has garnered widespread attention, which contributes to the promotion of sustainable economic and environmental development. The polymers in polymer-based composite rejuvenators (PBCRs) are the key to restoring the performance of aged high-viscosity modified asphalt (HVMA). To optimize the polymers in PBCRs, this study investigates the rejuvenation effect and interface diffusion mechanism of various PBCRs using molecular dynamics simulation and experimental analysis. First, four PBCRs with different polymer components were designed, and their impact on the performance of weather-aged HVMA were examined using the rheological test, low-temperature force ductility test, crack resistance test, and aging resistance test. Subsequently, the rejuvenation effects of four PBCRs were ranked using the comprehensive performance radar chart. Finally, molecular models and layer models of weather-aged HVMA and four PBCRs were constructed, and the diffusion fusion process and interaction mechanism were analyzed using the molecular dynamics simulation. The findings indicate that PBCRs can rebuild the polymer network structure, partially restore the rheology, elastic recovery, and low-temperature ductility of aged HVMA. Additionally, PBCRs significantly reduce the crack potential of aged HVMA and ensure satisfactory aging resistance. Molecular dynamics simulation shows that due to the differences in their molecular structures, the diffusion ability of PBCRs is ranked as follows: crumb rubber rejuvenator (CR + R) > SBR rejuvenator (SBR + R) > SBS rejuvenator (SBS + R) > HVM rejuvenator (HVM + R). In summary, SBS + R proves most effective in regulating asphalt components and rebuilding the polymer network structure, but its interfacial diffusion ability is inferior to CR + R and SBR + R. CR + R has the highest diffusion coefficient, but its rejuvenation effect is not ideal. HVM + R is slightly less effective at rejuvenation than SBS + R, but has the worst diffusion capacity. The rejuvenation effect and diffusion ability of SBR + R are both not ideal. This study has significant implications for optimizing the polymers in PBCRs and promoting the efficient rejuvenation and eco-friendly sustainable development of HVMA.

Boosting mechanical and aging resistance performances of filled-rubber with MgO and ZnO co-cure activators in diverse vulcanization systems

Over the decades, ZnO has been the primary cure activator in the sulfur vulcanization of rubber, but due to its environmental impact on aquatic ecosystems, its use in rubber formulation must be reconsidered. This study explores the effects of MgO, known for its low toxicity, as a cure activator, either alone or in combination with ZnO, in carbon black-filled various vulcanization systems such as efficient, semi-efficient, and conventional vulcanization (EV, SEV, and CV). Curing, mechanical, and aging resistance properties were thoroughly examined. Curing studies indicate that incorporating MgO into binary cure activator systems significantly accelerates vulcanization. In the SEV vulcanization system, ZnO/MgO binary cure activators, with a 1:2 ratio totaling 3 phr (per hundred grams of rubber), exhibit a comparable tensile modulus at 100% elongation, along with higher tensile strength, elongation at break, and improved aging resistance compared to conventional ZnO as a sole cure activator. Notably, in ZnO-free compounds, MgO as a single cure activator demonstrates superior tensile strength, elongation at break, and excellent aging resistance. In conclusion, this study suggests that the usage of ZnO can be optimized in rubber vulcanization by considering the desired mechanical properties along with improved aging resistance performances.

Functionalized lignin nanoparticles assembled with MXene reinforced polypropylene with favorable UV-aging resistance, electromagnetic shielding effects and superior fire-safety

Deterioration in mechanical performances and aging resistance due to the introduction of flame retardants is a major obstacle for bio-based fire-safety polypropylene (PP). Herein, we reported a kind of functionalized lignin nanoparticles assembled with MXene (MX@LNP), and applied it to construct the flame-retardant PP composites (PP-MA) with superior fire safety, excellent mechanical performance, electromagnetic shielding effects and aging resistance. Specifically, the PP-MA doped with only 18 wt% flame-retardant additives (PP-MA18) achieved the UL-94 V-0 rating. In comparison to pure PP, PP-MA18 presented a greatly decreased peak of heat release rate (pHRR), total heat rate (THR), and peak smoke production rate (pSPR) by 79.7 %, 69.0 % and 75.8 %, respectively, and satisfactory decrease in total flammable and toxic volatiles evolved. The formed fine solid microstructure of carbon residuals effectively promoted the compactness of char layers. More importantly, the nano-effect and the strong interface interaction between the complexed MX@LNP and PP enhanced the tensile strength (45.78 MPa) and elongation at break (725.95 %) of PP-MA. Additionally, the significant ultraviolet absorption and electromagnetic wave dissipation performance of MXene and lignin enabled excellent aging resistance and electromagnetic shielding effects of PP-MA compared with PP. This achieved MX@LNP afforded a novel approach for developing flame retardant materials with excellent application performance.

Improving UV aging resistance by loading PDA on the surface of PBO fibers via Fe (III) coordination

Poly(p-phenylene-2,6-benzobisoxazole) (PBO) fiber is currently one of the best-performing organic fibers; however, its low UV aging resistance limits its use. To improve the UV aging performance of PBO fibers, a novel PBO-Fe-PDA fiber was created by depositing a biomimetic structure of polydopamine (PDA) on the surface of PBO fibers with the transition metal ion Fe3+ as the active center. The surface morphology and elemental composition of PBO-Fe-PDA fibers were investigated. It was revealed that Fe3+ formed a coordination bond structure with the oxazole ring, and PDA was successfully loaded onto the surface of PBO-Fe fibers. After UV aging, the crystallinity and crystallographic orientation of PBO fibers significantly decrease, microcrystals inside the fibers slip, and the size of microvoids in the fibers rises. As a result, the strength of PBO fibers was significantly decreased after UV aging. The anti-UV aging capacity of PBO-Fe-PDA fibers, on the other hand, has been enhanced, as evidenced by a slight drop in crystallinity and crystallographic orientation and a significant decrease in the size growth of internal microvoids in the fibers after UV aging. The tensile strength retention of PBO-Fe-PDA fibers after UV aging increased by 93.13% when compared to PBO fibers without altering the fibers’ initial strength. The testing results show that this surface modification method is simple to employ and extends the service life of PBO fibers significantly.

Biomimetic mineralization of silicon dioxide onto carbon fiber for elevated interfacial properties and hydrothermal aging resistance of carbon fiber/epoxy composites

AbstractA carbon fiber‐tannic acid‐silicon dioxide (CF‐TA‐SiO2) reinforcement with a “diatom frustule‐like” structure was built via biomimetic mineralization to boost the performance of carbon fiber/epoxy resin (CF/EP) composites. As a bio‐based polyphenolic compound, TA was used to modulate the mineralization of SiO2, and the easy agglomeration of SiO2 was effectively avoided. The interfacial adhesion of the CF/EP composites was considerably heightened by improving the roughness and wettability of CF as well as by increasing the interfacial interactions between CF and the EP. Compared with the pristine composites, the flexural strength, interlaminar shear strength and interfacial shear strength of the CF‐TA‐SiO2/EP composites increased by 41.2%, 56.6%, and 50.4%, respectively. Moreover, the introduction of Si‐O‐Si and C‐O‐Si bonds at the interface led to a remarkable improvement in the hydrothermal aging resistance. This research provides a novel interfacial design for advanced composites with excellent interfacial properties, which broadens the application of these composites in hygrothermal environments.Highlights A “diatom frustules‐like” structure was successfully constructed on the CF surface. This biomimetic mineralization was simple and environmentally friendly. This method solved the problem of easy agglomeration of SiO2. The interfacial properties of composites were obviously improved. The hydrothermal aging resistance of composites was enhanced.

Natural ageing of one-component polyurethane bonded preservative treated wood evaluated using fracture energy tests

At present, increasing emphasis is being placed on the use of sustainable materials such as wood for construction. In exterior environments, preservative treatments are regularly required to achieve adequate durability. In laminated timber elements that use such preservative treatments, limited technical information exists on the ageing resistance of one-component polyurethane (1C-PUR) adhesives. A natural ageing study which involved full exposure for twelve months was undertaken to assess the durability of two different 1C-PUR adhesives for the bonding of untreated, chromated copper arsenate (CCA) and micronized copper azole (MCA) preservative treated wood. Resorcinol formaldehyde (RF) bonded specimens and solid wood specimens were used as a control. Reduced delamination resistance was experienced by both 1C-PUR adhesives in comparison to RF bonded specimens. Readings were higher for all adhesives when bonding CCA preservative treated wood. Latewood delamination was noticeability highest because of its higher density and the increased swelling that it experiences. The MCA bonded specimens experienced minor delamination. Mode I fracture testing demonstrated that because of the ductile nature of the 1C-PUR adhesives, higher energy release rates could be achieved with aged bonded specimens in comparison to unaged solid wood specimens. Mean wood failure percentage readings exceeded 90% for all intervals of ageing. Scanning electron microscopy revealed greater effective penetrations in the earlywood in comparison to the latewood. The 1C-PUR with lower viscosity achieved higher effective penetration and improved delamination resistance. Because of differences between the two 1C-PUR adhesives, no clear evidence existed to state the preservatives reduced the effective penetration.

Study on the change rule of low-temperature properties of asphalt binder with aging time

ABSTRACT Low-temperature cracking is common distress in asphalt pavements. Understanding the change rule of its low-temperature properties is helpful in investigating the optimal maintenance timing of asphalt pavement. In this paper, the change rule of low-temperature properties of asphalt binders with aging time is investigated by various indexes. Four asphalt binders and four anti-aging modified asphalt binders were subjected to the rolling thin film oven (RTFO) test and pressure aging vessel (PAV) test. Dynamic Shear Rheometer (DSR) with the 4 mm parallel plates was used to determine the low-temperature properties of asphalt binders. The results show that aging and low temperature have a negative impact on the low-temperature properties of asphalt binders. The anti-aging agent improves the low-temperature properties and aging resistance of asphalt binders. Compared with other indexes, the critical cracking temperature Tc and the critical temperature difference ΔTc are more suitable for analysing the effect of aging on the low-temperature properties of asphalt binders. Also, the ΔTc shows the three-stage decreasing rule of ‘fast-slow-fast’, with the inflection points. It meant that the low-temperature properties of asphalt binders had been altered at the inflection points, which provided a favourable reference to research on the optimal maintenance timing of asphalt pavement.