Permanent Deformation Research Articles

Modification of the Asphalt Binder with Nano-aluminum Oxide: An Alternative to Improve the Thermal Conductivity and the Rheological Properties of the Asphalt Matrix

Abstract This article presents the results of research that aimed to develop asphalt nanocomposites (conventional asphalt binder + nano-aluminum oxide [Al2O3]) with greater thermal conductivity and better rheological/mechanical properties, at high and intermediate temperatures, when compared to a reference matrix. The end goal was to be able to recommend a range of additional nanoparticle content to the conventional binder, establishing a direction for future investigations into the healing ability of asphalt mixtures with nano-Al2O3, both in the laboratory and in service. Conventional asphalt was modified with 1 %, 2 %, 3 %, 4 %, 5 %, and 6 % of nano-Al2O3 content in relation to the mass of the binder. Tests with a conductivity meter and a dynamic shear rheometer were performed on the developed nanocomposites. Rheological parameters related to susceptibility to permanent deformation and tolerance to fatigue damage were specially analyzed. As main findings, the addition of nanoparticles increased the thermal conductivity of the binder at the rate of 0.004 W/mK/%nano, improved the rheological parameters of asphalt at high temperatures (susceptibility to permanent deformation) for any incorporation content between 1–6 %, and impaired fatigue damage tolerance (at 20°C) with percentages greater than 3 %. The main conclusion of this research is that nano-Al2O3 can increase the thermal conduction capacity of the matrix and improve the rheological performance of the conventional binder, at high and intermediate temperatures, with certain percentages of incorporation (1–3 %). Finally, for future studies with asphalt mixtures, an additional range of nano-Al2O3 in the conventional binder from 1–3 % is recommended.

Strength, deformation, and environmental impact assessment of cement stabilized mine overburden soil

Mine haul roads are the unpaved roads that are constructed from the overburden materials obtained from the mining operations and are used for the movement of heavily loaded dumpers and trucks. The haul roads constructed from this overburden material shows continuous distress in the form of over ruts, potholes, and shear failures, creating major issues in the movement of dumpers. In the present research study, an experimental investigation was conducted based on mechanistic empirical design to evaluate the strength-deformation characteristics, durability, and environmental emissions of cement stabilized overburden soil of a local mine. The unconfined compression tests were conducted at cement dosages varying from 1 to 6% of dry soil mass and increase in the unconfined compressive strength were examined at different intervals of time until 28 days of the curing period. In the case of static triaxial tests, the enhancement in undrained shear strength and elastic modulus of stabilized specimens was determined in comparison to the untreated specimens, whereas in cyclic triaxial tests, the reduction in permanent deformations and increase in resilient modulus were evaluated under different confining pressures and cyclic deviatoric stresses. An empirical model has been proposed to predict the long-term rutting of overburden under repeated loading. The proposed model is based on the behaviour of various parameters, such as applied cyclic deviatoric stress, number of load repetitions, loading frequencies, and on the permanent deformation characteristic of mine overburden soil. In addition, durability and environmental sustainability aspects of the treatment has also been studied to determine the optimal dose of cement.

Improved deep neural network for predicting structural response of stiffened cylindrical shells to far-field underwater explosion

This paper is focused on the application of the machine learning for predicting structural response of ring stiffened cylindrical shells subjected to far-field underwater explosion. Three deep neural network (DNN) models are combined to predict the progressive plastic deformation behaviour of stiffened cylindrical shells subjected to the shock wave produced by a TNT charge. In the DNN regression models, the input variables include the charge mass, stand-off distance, detonation depth, cylindrical shell thickness, stiffener web and flange. These three DNN models composed of multi hidden layers are trained based on the data collection originated from a series of simulations performed by the ABAQUS finite element solver. Grid search is introduced to the hyperparameter tuning for deep learning, improving the prediction performance of machine learning methods. The DNN models are compared to the models trained using another three methods: multiple linear regression, decision tree and k-nearest neighbour. An improved Adam optimisation algorithm is used to increase the accuracy of prediction. The challenges encountered during the predictions are discussed to provide a more comprehensive insight into the advantage of the proposed DNN models. The DNN regression models can well predict the permanent plastic deformation and strain of stiffened cylindrical shells.

Modified Asphalt with Graphene-Enhanced Polymeric Compound: A Case Study

In recent years, the increased use of heavy commercial vehicles with higher axle weights has required the development of innovative technologies to improve the mechanical properties of asphalt concrete conglomerates, such as fatigue resistance and rutting. This study offers a comprehensive comparative analysis of different types of asphalt concrete tested in four trial sections (S1, S2, S3, S4) of the SP3 Ardeatina rural road in Rome, under actual traffic and operational conditions. More precisely, the pavement technologies applied include modified asphalt concrete with graphene and recycled hard plastics for S1, asphalt concrete modified with styrene–butadiene–styrene (SBS) for S2, asphalt concrete with a standard polymeric compound for S3, and traditional asphalt concrete for S4. The evaluation approach involved visual inspections in order to calculate the pavement condition index (PCI) and falling weight deflectometer (FWD) tests. In addition, back-calculation analyses were performed using ELMOD software to assess the mechanical properties. The laboratory tests revealed superior properties of M1 in terms of its resistance to permanent deformations (+13%, +15%, and +19.5% compared to M2, M3, and M4, respectively) and stiffness (10,758 MPa for M1 vs. 9259 MPa, 7643 MPa, and 7289 MPa for M2, M3, and M4, respectively). These findings were further corroborated by the PCI values (PCIS1 = 65; PCIS2 = 17; PCIS3 = 28; PCIS4 = 29) as well as the FWD test results after 5 years of investigation, which suggests greater durability and resistance than the other sections.

Performance evaluation of geosynthetic reinforced marginal material as base layer over weak subgrade

ABSTRACT The availability of quality materials for construction has been an issue in some regions. This scarcity obliged using marginal materials reinforced with geosynthetic materials as one of the quests for sustainability in the pavement industry. In this study, an attempt was made to stabilize the marginal materials by incorporating geosynthetics. The different geosynthetics used in the study are geogrid, geocell, double geogrid, and geocell + geogrid. A series of unreinforced (UR) and geosynthetic reinforced (GR) pavement prototypes were constructed in the laboratory with landslide debris as base material underlain by black cotton soil subgrade. Large-scale cyclic plate load (CPL) tests were performed on test prototypes constructed in the laboratory under cyclic loading following the trapezoidal loading pattern with 0.77 Hz frequency. The efficacy of geosynthetic reinforcement was quantified concerning permanent deformation (PD), resilient deformation (RD), Rut depth reduction (RDR), Traffic improvement ratio (TIR), and reduction in vertical stresses transmitted to the subgrade and reduction in base layer thickness. The test results indicate that the GR significantly reduced the rut depth and improved the traffic capacity. In addition, over all types of GRs, the combination of geogrid and geocell outperformed in terms of permanent deformation and rut depth reduction.

In vitro evaluation of shape-memory hydrogels for removable dental prostheses and optimization of phase-transition temperature for intraoral use

Removable dental prostheses require periodic relining with the loss of intaglio surface fit because of mucosal shape changes over time. Therefore, a new material with high adaptability to tissue changes over time would be beneficial. This study focused on a shape-memory gel (SMG) that softens when heated, retains its shape when cooled, and returns to its original shape when reheated. The purpose was to optimize SMG for intraoral use by controlling the ratio of 2 acrylate monomers and to evaluate the changes in the shape memory and physical properties of SMG with temperature and to evaluate biocompatibility. SMG specimens were synthesized using the following mixing ratios of 2 monomers, docosyl acrylate (DA) and stearyl acrylate (SA): 0:100, 25:75, 50:50, 75:25, and 100:0. SMG specimens were photopolymerized using a fluorescent light-polymerizing unit. To evaluate shape memory as a function of temperature, permanent deformation was measured based on the standardized compression set test for thermoplastic rubber. For evaluation of the physical properties and cytotoxicity, a 3-dimensionally printed denture base material was used as the control material. All assessments were compared between the groups by using 1-way analysis of variance followed by the Tukey-Kramer multiple comparison test (α=.05). SMGs with a higher amount of DA maintained their compressed shape at room and intraoral temperatures. However, the SMG matrices softened and recovered their original shapes above 60°C. SMGs showed Shore A hardness equivalent to that of the denture-base polymer material at intraoral temperatures because of the high phase-transition temperature. The low water solubility of SMGs supported the biocompatibility test results. SMG, in which the phase-transition temperature was controlled by mixing acrylate monomers with different melting points, exhibited shape memory in the intraoral environment. The results indicate the feasibility of applying SMG for the fabrication of removable dental prostheses because of its high adaptability to tissue changes over time and biocompatibility.

Influence of Petroleum-Based and Bio-Derived Recycling Agents on High-RAP Asphalt Mixtures Performance

Reclaimed asphalt pavement (RAP) has been utilized as a potential partial substitute for virgin asphalt binder in asphalt mixtures. However, a primary concern with increasing RAP content in asphalt mixtures is the cracking potential, attributed to the aged RAP asphalt binder (RAP-binder). To address this, the use of petroleum-based and bio-derived recycling agents (RAs) in enhancing the cracking resistance of high-RAP asphalt mixtures has been explored. The objective of this study is to ascertain the effectiveness of six RAs in mitigating cracking in high-RAP asphalt mixtures. The RAs considered include petroleum-crude-oil-derived aromatic oil, soy oil, and four types of tall-oil-derived phytosterol (industrial by-product, intermediate, purified, and fatty acid-based). The RAs’ dosages were optimized, based on RAP-binder and unmodified asphalt binder properties, to produce target PG 70-22 asphalt binder when incorporated in asphalt mixtures containing 30% RAP. To assess the engineering performance of these 30%-RAP asphalt mixtures for each RA, a conventional asphalt mixture incorporating styrene-butadiene-styrene (SBS)-modified PG 70-22 asphalt binder without RAP or RAs was benchmarked for comparison. Mechanical tests performed included Hamburg wheel-track testing (HWTT), intermediate-temperature fracture tests (semi-circular bend, Illinois flexibility index, and IDEAL cracking tolerance), and thermal stress-restrained specimen tensile strength test to evaluate permanent deformation, intermediate-temperature cracking resistance, and low-temperature cracking resistance, respectively. Results showed that petroleum-crude-oil-derived aromatic oil and tall-oil-derived fatty-acid-based oil RAs were able to rejuvenate RAP-binder as measured by the cracking tests performed. Further, the use of these RAs did not adversely impact the asphalt mixtures’ permanent deformation performance.

Morphological evolution and property changes of acrylate rubber/polyacetal thermoplastic vulcanizates during dynamic vulcanization process

AbstractA new type of thermoplastic vulcanizates (TPV) that is resistant to hot oil, high temperature, and aging was prepared using acrylate elastomer (ACM) and polyoxymethylene (POM) as raw materials. The phase transition process and micromorphology development of the blends with the change of dynamic vulcanization (DV) time, and to illustrate the effects of the phase transition and the degree of elastomer phase crosslinking on the macroscopic properties of TPV were investigated. It was shown that ACM crosslinking occurs continuously during 0–8 min of DV, whereas the phase inversion process occurs predominantly during 0–3 min. In contrast, the cross‐section of the blends after phase inversion is flat, The constant elongation stress under small deformation, hardness, and permanent deformation after break are reduced, and the elongation at break, nonrelaxable modulus, and aging resistance are improved. The increase in the degree of vulcanization of the ACM phase resulted in a significant increase in the modulus of the blends under large deformation, an increase in the nonrelaxable modulus and relaxable modulus, an increase in the aging resistance, and a decrease in the elongation at tear were observed.

Understanding the mechanical behavior of intrauterine devices during simulated removal

ObjectiveTo evaluate differences based on intrauterine device (IUD) frame geometry in force, and stress, and strain at the stem/arms junction during simulated IUD removal. Study designWe manufactured injection-molded frame models for three Nova-T IUDs (Mirena [model M]; Liletta [model L]; Kyleena [model K]) and a Tatum-T IUD (Paragard [model P]) at two-times scaling. We created a custom fixture to simulate the uterus and used a screw-driven machine to pull models at various displacement rates through the 10 cm fixture cavity to measure force and strain and calculate stress at the IUD stem/arms junction. We tested models at 30 mm/min and higher displacement rates for exploratory analyses. We used Mann-Whitney U test for statistical testing. ResultsWe completed testing at 30 mm/min using five of each Nova-T model and nine model P samples. Resistance against the cavity walls created significantly more force on model P (11.83, interquartile range [IQR] 11.61–12.31) than any Nova-T model samples (p < 0.001). The smaller model K created slightly more median stress (MPa) than the larger model M (0.36 [IQR 0.33–0.38] and 0.79 [IQR 0.76–0.80], respectively, p = 0.008); model P samples generated significantly more median stress than other models (1.70 [IQR 1.67–1.77], p < 0.001). Strain plots demonstrated permanent deformation for some samples during IUD removal simulation. We tested 20 samples at various higher displacement rates up to 2500 mm/min, with stress notably increasing for model P samples with increasing rates. No fractures occurred. ConclusionsForce and stress at the stem/arms junction are higher with Tatum-T-shaped compared to Nova-T-shaped IUD models under the same testing conditions, and a higher speed of extraction causes more stress. ImplicationsSharp corners create vulnerability under static and fatigue loading in structural components due to increased local stresses. Our findings suggest that IUDs with Tatum-T frames should be removed slowly to minimize the stress at the stem/arms junction. Future studies can provide more information if performed with commercially available products.

Uni- and tri-axial tests and property characterization for thermomechanical effect on hydrated lime modified asphalt concrete

Permanent deformation, fatigue and thermal cracking are the three typical distresses of flexible pavement. Using hydrated lime (HL) into the conventional limestone mineral additive has been widely practiced, including in Europe, to improve the mechanical properties of hot mix asphalt (HMA) concrete and as the result the durability of the constructed pavement. Large number of experimental studies have been reported to find the optimum addition of HL for the improvement on HMA concrete mechanical properties, moisture susceptibility and fatigue resistance. Pavement in service is under complex thermomechanical stress-strain conditions due to coupled atmospheric and surrounding environment temperature variation and the traffic loading. To predict and analyse the performance of pavement structures the data only from uniaxial compressive test for the resilient modulus and permanent deformation would be not enough. However, so far, the data of HL modified HMA concrete under complex loading conditions are still not well informatively complete. To contribute new knowledge, this paper reports an experimental study of both uni- and tri-axial tests for the asphalt concrete using HL into mineral additive for the mixes designed for the applications of wearing, levelling, and base layers, respectively. All the tests were conducted under three controlled temperatures and four stress deviations. The test results have showed that, for all three types of mixes, the permanent deformation of the HL mixes is less than the ones of no HL addition. The degree of the improvement on permanent deformation resistance using HL is much pronounced at high stress deviation states. The results have also showed that the resilient modulus strongly depends on the temperature and stress deviation while the mixes of HL addition demonstrate higher rigidity. At last, mathematical characterization models have been proposed for the measured material properties. A numerical simulation case study has been performed to test and demonstrate the application of the proposed unified property model.

The Effect of Axle Overloading and High Tire Pressure on Flexible Pavement Structure

Axle overloading and high tire pressures on the highways and motorways in Pakistan are one of the reasons that cause early pavement deterioration. There are numerous sections on the national highway on which trucks are reposted to be operating at 40-80 percent higher tire pressure than the legal limit, and the axle overloading is 30 percent greater than the legal axle load limit. This research aims at determining the effect of axle overloading and high tire pressure on the flexible pavement structure and derive the truck factors for trucks in order to quantify the damage to the pavement due to a single pass of 2-axle, 3-axle, 4-axle, 5-axle, and 6-axle truck using the results reported in the Pilot Axle Load Survey conducted by the National Transport Research Centre. In order to determine the effect of axle overloading and high tire pressure, a theoretical linear elastic mechanistic empirical analysis for different axle configurations was performed using KENLAYER and regression models were developed to find the Equivalent Axle Load Factor (EALFs) for the fatigue cracking, and permanent deformation. It was found that the EALFs were mostly controlled by permanent deformation distress criterion. The EALFs and the truck factors were highly influenced by the axle loads rather than the tire pressure. The 3-axle truck was found to be the most damaging truck followed by 6-axle truck, 5-axle truck, 2- axle truck, and 4-axle truck.

Enhancing Asphalt Performance and Its Long-Term Sustainability with Nano Calcium Carbonate and Nano Hydrated Lime

Nanomaterials enhance the performance of both asphalt binders and asphalt mixtures. They also improve asphalt durability, which reduces resource consumption and environmental impact in the long term associated with the production and transportation of asphalt materials. Thus, this paper studies the effectiveness of Nano Calcium Carbonate (Nano CaCO3) and Nano Hydrated Lime (NHL) as modifiers and examines their impact on ranges from 0% to 10% through comprehensive laboratory tests. Softening point, penetration, storage stability, viscosity, and mass loss due to short-term aging using the Rolling Thin Film Oven Test (RTFO) were performed on asphalt binders. Results indicated a significant improvement in binder stiffness, particularly at 4% Nano CaCO3 and 6% NHL content by weight. Dynamic Shear Rheometer (DSR) tests further revealed substantial improvements in rutting resistance, with NHL exhibiting superior high-temperature stability and a notable increase in the rutting factor. Marshall stability tests on asphalt concrete (AC) mixtures showed a 22.3% increase in stability with 6% NHL by weight, surpassing the 20.2% improvement observed with Nano CaCO3 and indicating enhanced load-bearing capacity. The resilient modulus of the mixtures consistently increased with the addition of NHL, suggesting improved durability in rutting. Moisture susceptibility tests revealed that NHL significantly enhances moisture resistance, exceeding the 80% TSR benchmark at just 2% content by weight and reaching an impressive 94.6% at 10% content by weight. In contrast, Nano CaCO3 demonstrated a more gradual improvement, achieving an 88.2% TSR at 10% content. Furthermore, permanent deformation analysis indicated a 68.64% improvement in rutting resistance with 10% NHL content by weight, exceeding Nano CaCO3’s improvement rate. Optimal fatigue resistance was achieved at 4% for Nano CaCO3 and 6% for NHL by weight, with respective CT index improvements of 30% and 35.4%, showing NHL’s consistent benefits across various nanomaterial contents. Overall, the study suggests that both Nano CaCO3 and NHL positively impact asphalt performance, with NHL offering more pronounced benefits across a range of properties. These findings provide valuable insights for pavement engineers and underscore NHL’s potential as an effective additive in asphalt mixture design. Real-world applications and validations are essential for a comprehensive understanding of these nanomaterials in practical pavement engineering scenarios.

Experimental Investigation of Polymer and Nanomaterial modified Asphalt Binder

Modifying the asphalt binder and mixture becomes one of the best ways to mitigate pavement distress and increase the service life of constructed road networks. This study aimed to evaluate the influence of modified asphalt binders with the best different percentages of polymer and nanoparticles. Typical asphalt binder (penetration, softening point, and viscosity) and frequency sweep tests were used to evaluate the physical and rheological properties of modified asphalt binders with 5% Acrylonitrile Styrene Acrylate (ASA), 5% aluminum oxide nanoparticles (Al2O3), and 5% calcium carbonate (CaCO3). The results showed that the physical properties of all modified blends improved compared to those of the base asphalt binder. The improvement in softening point was up to 19%, the penetration reduction was nearly 69%, and the sensitivity to elevated temperatures was reduced by up to 13%. Evaluation of the rheological properties showed that modified asphalt with 5% Al2O3 binder had the highest permanent deformation resistance, followed by 5% ASA. The 5% CaCO3 binder showed a small improvement compared to the other samples. The results showed that the 5% Al2O3 binder had the highest complex modulus and the lowest phase angle, which means that it has the best viscoelastic properties. Therefore, it can be recognized as the best asphalt binder among the modified binders in this study.

Evaluation of Rheological Properties of Polymer-Modified Asphalt Binders and Mastics with Organic Additive—Imidazoline

The article presents the results of testing the asphalt binder modified with SBS copolymer (5%) and its mixture with mineral fillers called asphalt mastics. The aim of the research and analysis was to check the possibility of using an organic additive in the form of imidazolines and to assess their impact on the viscoelastic properties of the obtained asphalt mastics. The main advantage of using imidazoline is the increased resistance of asphalt mixtures to low-temperature cracking at the top of the road route and reducing its maintenance costs. Based on the examination of the adhesion of the binder with the addition of various imidazolines to the aggregate, a selection was made from six analyzed subtypes. One of them was selected for further research. The tests were carried out in a dynamic shear rheometer in a wide temperature range from −36 °C to 82 °C, determining the most important parameters of the tested materials, i.e., dynamic shear modulus (|G*|), phase angle (δ) and the non-recoverable creep compliance (Jnr). The test results and their analysis confirmed the beneficial effect of imidazoline on the viscoelastic properties of mastics in the low-temperature range, even at the lowest content of 0.2%. Based on the results of the determination of Jnr and |G*|/sinδ in the range of high operating temperatures, no significant deterioration in permanent deformation parameters was observed. Moreover, the use of imidazoline reduces technological temperatures during the production of HMA used in the pavement and, therefore, reduces CO2 emissions into the atmosphere.

Evaluation of the Mechanical Performance of Warm Bio-Recycled Asphalt Mixtures

Currently, approximately 90% of road pavement mixtures are derived from fossil fuels, a major source of the greenhouse gases contributing to global warming. This fact, together with the scarcity of raw materials in pavement engineering, has prompted recent investigations into sustainable alternatives. Biobinders, serving as substitutes or modifiers for petroleum-based asphalt binders, have gained attention, alongside the integration of recycled materials in recycled asphalt (RA). This study addresses these concerns by combining three techniques: (1) substituting a bitumen-based binder with a biobinder; (2) incorporating a high RA percentage (&gt;30%); and (3) manufacturing the asphalt mixture at a reduced temperature (140 °C). These approaches result in the production and evaluation of warm bio-recycled asphalt mixtures. Materials were assessed at both the binder and mixture levels. The control binder, RA binder, and biobinder underwent conventional and rheological characterization. In terms of mixtures, warm bio-recycled asphalt mixtures employed a biobinder as the only virgin binder, with RA contents of 50% and 70%. Mechanical characterization focused on bearing capacity, cohesion, permanent deformations, and moisture damage. The warm bio-recycled asphalt mixtures exhibited adequate outcomes in bearing capacity through the stiffness modulus being 18,120 MPa and 15,683 MPa for bio-recycled asphalt with 50% RA and bio-recycled asphalt with 70% RA, respectively. Bio-recycled asphalt with 50% RA and bio-recycled asphalt with 70% RA showed low permanent deformation percentages, specifically 0.5% and 0.7%, respectively, in comparison to the reference recycled asphalt mixture with 1.5%, allaying concerns in practical applications due to the biobinder’s soft consistency. The bio-recycled asphalt mixture with 70% RA displayed good mechanical performance regarding the studied mechanical characterization, especially exhibiting the least susceptibility to water-induced damage with 97% of the retained indirect tensile strength ratio, addressing concerns related to moisture damage in warm asphalt mixtures with high RA content and biobinders. These findings offer valuable insights into the adoption of more sustainable practices in the asphalt pavement industry, reducing the concerns associated with warm bio-recycled asphalt mixtures.

Effects of moisture content and soil suction on the permanent deformation of tropical subgrade soils: experimental investigations and modelling

This study presents the effects of moisture variation and the influence of matric suction on the permanent deformation (PD) of three tropical soils with different geological-geotechnical characteristics used in road subgrades in southern Brazil. The experimental programme consisted in determining the soil-water characteristic curves and in dynamic triaxial tests to obtain the PD in different compaction and post-compaction moisture contents. The variation of compaction moisture content caused microstructural changes, influencing the plastic behaviour of soils: the higher the initial moisture content, the greater their accumulated permanent deformations. As expected, the post-compaction moisture variation (wetting process) tended to increase the plastic deformation of materials, evidencing the influence of the suction variation on the performance of the soils studied. In addition, matric suction proved to be the best variable to represent the effects of moisture variation on the plastic behaviour of soils subjected to cyclic loading. Thus, a PD prediction model for tropical soils with the inclusion of this parameter was proposed. The model proved to be highly predictive and may become an important tool to be incorporated into current mechanistic-empirical design methods.

Impact resistance of aramid honeycomb tandem sandwich composites reinforced with TiB2

A novel composite tandem sandwich structure made of aramid fabric and aramid honeycomb, impregnated in a matrix of epoxy resin combined with poly (vinyl butyral), PVB, is proposed. The composite was additionally reinforced with a small concentration of titanium diboride nanoparticles, TiB2, to study its effect on impact resistance. Sandwich composite samples were fabricated by impregnating the aramid fabrics and honeycomb in subsequent layers with the system epoxy/PVB/TiB2. Their mechanical behavior was examined through three-point bending test, Charpy impact test, and compressive test. The chemical reaction between PVB and epoxy resin, and chemical inertness between the nanoparticles and the other constituents were confirmed by FTIR analysis. The flexural strength and stiffness increased by 27.6% and 62.5%, respectively, in the presence of TiB2 reinforcement. Impact tests showed increase of 104% in impact toughness in the case of samples with TiB2. Nano TiB2 did not increase compressive strength of the proposed sandwich structure, but it improved its stiffness and reduced the permanent deformation. The achieved improvements in mechanical resistance make this new composite structure a promising candidate for automotive, airspace, naval, civil engineering, sports equipment industry, and for use in defense technologies.

Assessing pseudo-ductile behavior of woven thermoplastic composites under tension and bending

Most fiber-reinforced composites are inherently brittle and fail suddenly at low strains without yielding and energy-absorbing capability. Still, under some conditions, they can demonstrate ductile like response known as pseudo-ductility. To investigate such a response, experimental analysis of carbon- and glass-fabric reinforced thermoplastic polymer (C/GFRP) composites was performed in on- and off-axis orientations under service loading conditions of tension and bending. Tensile tests of off-axis specimens were conducted with a full-field strain-measurement digital image correlation (DIC) technique. Cyclic bending tests of on- and off-axis C/GFRP specimens were performed to assess their ductility and damage behavior. The tests revealed that on-axis CFRP laminates failed due to fracture of brittle carbon fibers under tension, monotonic and cyclic bending. The on-axis GFRP samples demonstrated a linear-elastic brittle response under tension but a visco-elasto-plastic nonlinear behavior under monotonic and cyclic bending with hysteresis and energy absorption. This nonlinearity could be due to stress stiffening of thin laminates under large-deflection bending and mesoscopic effects in the woven fabrics. The off-axis C/GFRP specimens exhibited ductile behavior akin to metals, enduring high strains with permanent deformation before ultimate failure, and absorbing substantial amounts of energy. The pseudo-ductile response of the off-axis specimens is attributed to plasticity due to matrix cracking, fiber-matrix debonding as well as fiber trellising, whereas in the on-axis GFRP specimens, it is primarily due to visco-elasto-plastic behavior of glass fibers and the TPU matrix. It is concluded that material's response can be tailored for stiffness, strength and ductility for specific applications.

Displacement analysis of the October 30, 2020 (M w = 6.9), Samos (Aegean Sea) earthquake

Abstract Destructive earthquakes with high deformations have occurred in the Aegean region since the historical period. The most destructive of these earthquakes in recent years is the October 30, 2020 (M w = 6.9) Samos (Aegean Sea) earthquake. This earthquake affected a wide area and caused numerous losses of lives and property especially in Izmir city. For examining the effects of the earthquake, Global Navigation Satellite System (GNSS) data before, during, and after the earthquake were processed, and coseismic and postseismic displacement evaluations were made. Interferometric Synthetic Aperture Radar (InSAR) ascending, descending interferograms, line of sight velocity, and displacement maps were obtained for the earthquake-affected area. The GNSS and InSAR data were evaluated together, and the areas with subsidence and uplift were determined in conjunction with the fault zone. In addition, the horizontal displacements were analyzed by using Coulomb failure criteria, and peak ground displacements were obtained from the strong motion stations located in the study region. As a result, from all the displacement analyses, it was determined that high-amplitude energy was released, at the regional scale from Ayvalık in the North to Datça in the South after the earthquake, and this earthquake generated permanent deformation in the affected region.

The Effect of a Liquified Wood Heavy Fraction on the Rheological Behaviour and Performance of Paving-Grade Bitumen

Biomass is one the most abundant renewable energy sources, and it can be processed through different thermochemical methods to obtain oils that can replace the petroleum bitumen used in road construction. For the construction industry to accept the bitumen replacement with bio-oil, it is necessary to know its properties and determine the applicability of conventional testing methods. This research utilized a liquified wood heavy fraction (bio-oil) obtained from waste wood through an innovative thermochemical liquefaction process. The aim was to investigate a kind of bio-bitumen produced by blending this bio-oil with paving-grade bitumen. The rheological behaviour in a wide temperature range, the performance relative to fatigue cracking and permanent deformation sensitivity, and the evolution with oxidative ageing were evaluated for the bio-bitumen and paving-grade bitumens. The bio-oil significantly affected the rheological behaviour of bitumen through an overall decrease in the phase angle and by failing the time–temperature superposition principle. The strong elastic response of the bio-bitumen improved resistance to fatigue and permanent deformation accumulation; however, resistance to oxidative ageing declined. Linear viscoelastic rheological indicators proposed in the literature to assess the material’s performance showed a similar trend of variation with oxidative ageing for bio-bitumen and paving-grade bitumen, though the indicators’ values could not be directly compared.