Bending Research Articles

A novel approach to warm mix asphalt additive production from polypropylene waste plastic via pyrolysis

The utilization of waste plastics as an additive in warm mix asphalt (WMA), which is an environmentally friendly technology, by pyrolysis method is an emerging concept. In this study, WMA additive was synthesized from char (C) and wax (W) products obtained from the pyrolysis of polypropylene (PP) type waste plastics. Seven different pyrolysis modified bitumen were prepared as PP 6%C, PP 6%C-3%W, PP 6%C-6%W, PP 6%C-10%W, PP 3%C-6%W, PP 1%C-6%W and PP 6%W. Base bitumen and Sasobit® 3% (by weight of bitumen) modified bitumen were used as control groups. The rheological properties of the binders were investigated by Rolling Thin Film Oven, Pressure Aging Vessel, Rotational Viscometer, Dynamic Shear Rheometer and Bending Beam Rheometer tests, and the morphological properties were analyzed by Scanning Electron Microscope, Fourier Transformed Infrared Spectroscopy and Zeta Potential analysis. Asphalt mixture performance characteristics were evaluated by Marshall Design, Hamburg Wheel Tracking and Thermal Stress Restrained Specimen Tests. Binder test results demonstrated that with the addition of PP 6%C-6%W and Sasobit® 3%, the viscosity of bitumen decreased significantly and accordingly the plant temperature reduced by 14ºC and 9ºC. Besides, PP 6%C-6%W modified bitumen performed better than base bitumen at low, medium and high temperatures. Sasobit® 3% improved the high temperature performance of the bitumen. The additive-bitumen modification mechanism involved physical process. Furthermore, the additives were well distributed in bitumen and no agglomeration was observed. WMA-1 (PP 6%C-6%W) and WMA-2 (Sasobit® 3%) have 5% and 9% higher Marshall stability than hot mix asphalt (HMA), respectively. Moreover, the addition of PP 6%C-6%W and Sasobit® 3% increased the rutting resistance of the mixture by 9% and 21%, respectively. Moreover, PP 6%C-6%W improved the low temperature performance of the mixture by decreasing fracture temperature by 3ºC and increasing the fracture strength by 15%. All in all, PP pyrolysis products have strong indicators to become a WMA additive.

Optimization and characterization of composite modified asphalt with pyrolytic carbon black and chicken feather fiber

Abstract Asphalt is a vital construction material for roads, and its properties can be enhanced by modification. In this study, a composite modified asphalt was developed using pyrolytic carbon black (PCB) and chicken feather fiber (CFF). Box–Behnken design of response surface methodology was employed to optimize the preparation parameters, and the optimal parameters were determined to be a PCB dosage of 15% (weight ratio), a CFF dosage of 0.3% (weight ratio), and a chicken feather (CF) shear time of 8.2 min. A Dynamic Shear Rheometer (MCR302) was used to analyze the high-temperature rheological properties of the modified asphalt samples, and the results showed that the addition of PCB and CFF enhanced the high temperature performance and anti-aging performance of the asphalt. The rheological properties at high temperature increased progressively with the increase in CFF dosage. The Bending Beam Rheometer (BBR) test was conducted to evaluate the low-temperature rheological property of PCB/CFF composite modified asphalt, which was observed to decrease with the increase in CFF dosage. The microscopic properties and the chemical group of 15% PCB + 0.3% CFF with 8.2 min CF shear time composite modified asphalt (0.3%PC-MA) were analyzed using Fourier Transform Infrared spectrometer and Fluorescence Microscopy, and the results indicated that PCB and CFF were physically blended with asphalt without undergoing a chemical reaction, and they were well compatible with and evenly distributed in asphalt. Finally, the high- and low-temperature performances, as well as water stability, of the base asphalt (BA), 15% PCB dosage modified asphalt (P-MA), and 15% PCB dosage modified asphalt with x% CFF dosage with a shear time of 8.2 min (PC-MA) were compared. The addition of CFF significantly enhanced the high-temperature and low-temperature performances, as well as water stability of P-MA mixtures. The aim of this study is to provide a laboratory test basis for the application of PCB/CFF composite modified asphalt.

Investigation on the high-temperature stability and fatigue behavior of cold mixed epoxy asphalt mixture with different gradations

Cold mixed epoxy asphalt mixture (CMEAM) is widely applied on steel deck bridge pavements due to its excellent high temperature and fatigue resistance. However, previous studies investigated above two properties through destructive test or without considering water-damage factor, respectively, which is far away from real servicing condition. To distinguish above two properties of EA-05 and EA-10 (mixture with nominal maximum particle size of 4.75 mm and 9.5 mm), uniaxial static creep tests, dynamic modulus test and four-point bending beam fatigue test were applied in this paper. At the same time, to comprehensively acquire elastic, viscous-elastic and plastic performance of CMEAM, four kinds of constitutive models were also put forward. Results showed that seven-element viscous-elastic-plastic creep model has the highest correlation coefficients which proves there exists plastic deformation in CMEAM. Meanwhile, EA-10 is likely to present viscous-elastic deformation while EA-05 is more likely to show plastic deformation. Dynamic modulus among different gradation type mixture at 40 °C is not so apparent. But with the increase of frequency and testing temperature, this difference would be clear. The middle gradation of EA-10 has the most excellent high temperature stability under dynamic load. In terms of the resistance to fatigue damage of control or freeze-thaw treated samples, EA-05-U(the upper limit of EA-05 gradation type) always takes the first place and has the lowest sensitivity to the change of stress level and water damage.

Evaluating the Short-term Performance of Spray-on Rejuvenators using a Modified Bending Beam Rheometer Test Methodology

Spray-on rejuvenation is a preventive maintenance strategy that highway agencies use to prolong the service life of asphalt pavements. This process involves applying rejuvenators on the surface of asphalt pavement to reverse the stiffening caused by aging. However, with several rejuvenators available on the market, it can be challenging to select specific products without understanding their effects at the mixture level. In this study, 12 different spray-on rejuvenators were applied on two different test sections (each with multiple test cells) at the Minnesota Road Research Facility. To assess the short-term (1–2 months) performance of rejuvenators, bending beam rheometer (BBR) test beams were prepared from the surface of the field-extracted cores, and a creep stiffness test was performed. The creep stiffness was measured at three different temperatures to evaluate the effectiveness of rejuvenators at these temperatures. The BBR test was not used to assess the low-temperature cracking resistance; instead, it was simply used to measure the beams’ linear viscoelastic property (i.e., the creep stiffness). Results indicated that the effect of rejuvenation is more evident at higher temperatures (20°C in this case). Besides, specific unexpected effects of rejuvenator products were observed. One of the test sections included extensive microcracks visible on the surface (presumably because of construction-related issues). Some of the rejuvenators closed these microcracks, leading to a “bridging” effect and increasing the stiffness of the BBR beams. This study provides a reference for evaluating the effect of spray-on treatments at the asphalt mixture level, which can assist roadway agencies in decision-making.

Application of modified fracture criteria incorporating T-stress for various cracked specimens under mixed mode I-II loading

Accurate assessment of fracture behavior and life prediction of cracked materials based on the mixed mode fracture criteria is of utmost importance in fracture mechanics. In this study, the modified fracture criteria incorporating T-stress for mixed mode I-II cracks were comprehensively reviewed. Additionally, a comparative analysis was conducted between the experimental results obtained from five different cracked configurations and the theoretical predictions according to these modified criteria. Moreover, a brief discussion was held regarding the effect of T-stress on both crack initiation angle and fracture toughness, accompanied by providing some suggestions. The results revealed that the predictive accuracy of modified criteria exhibited noticeable variations across different cracked configurations due to the significant disparities in both the sign and magnitude of T-stress around the crack tip. However, it was observed that the predicted curves based on the modified fracture criteria for the semi-circular bend and edge-crack triangular specimens had remarkable similarities owing to their similar biaxial stress ratio B. When the mode II loading dominated, the generalized maximum tangential stress, generalized minimum strain energy density and generalized averaged strain energy density criteria were suitable for the semi-circular bend, edge-crack triangular, central crack rectangular and short bend beam specimens with positive T-stresses, whereas the maximum tangential strain, generalized maximum tangential stress and generalized maximum tangential strain energy density criteria could provide better theoretical predictions for central cracked Brazilian disk specimens having a negative T-stress.

A theoretical model for the prediction of fracture process zone in concrete under fatigue loading: Energy based approach

Characterizing the fracture behaviour of concrete and accurately predicting its service life under fatigue loading poses a significant challenge due to its heterogeneous nature and complex fracture mechanisms. The proposed study focuses on developing an energy based theoretical formulation for predicting the evolution of the fracture process zone throughout repetitive loading cycles. A stiffness degradation approach has been adopted for developing the formulations for the critical energy dissipation and fully developed fracture process zone. Subsequently, the proposed analytical expressions have been calibrated and validated by performing experiments under centre point bending and using available experimental results in the literature. Experiments have been conducted on a centre-point bend beam with varying aggregate size in conjunction with the digital image correlation (DIC) technique to estimate the fracture characteristics. The influence of specimen size and heterogeneity has been discussed in the context of predicting the fracture behaviour, critical dissipated energy, and process zone length of plain concrete beam specimens under fatigue loading. The results indicate that the process zone length and critical energy release rate increase with an increase in specimen size, while the same decreases with an increase in aggregate size.

Effect of alkali-treated bamboo fibers on the properties of asphalt mixture

ABSTRACT Bamboo fiber is a natural fiber that is ecologically beneficial and one of the best materials to replace lignin fiber for roads, which is still difficult to utilize properly in asphalt mixtures owing to its poor adherence, dispersion, and hydrophilicity. Previous research has discovered that alkali treatment, as an effective treatment approach, may effectively lower the hydrophilicity of plant fibers and improve their compatibility with the matrix. As a result, it is vital to investigate the effect of alkali treatment on bamboo fibers used in asphalt mixtures. The composition and microstructure of bamboo fibers treated with alkali were investigated using SEM and FTIR methods, while the adhesion between the bamboo fiber and asphalt before and after alkali treatment was tested using the fiber pull-out test. In addition, the dispersion rate of bamboo fibers in asphalt mixture was determined by developing a connection equation using the Schellenberg binder drainage test. The performance of bamboo fiber asphalt mixtures was then evaluated using rutting tests, beam bending tests, immersion Marshall tests, freeze-thaw splitting tests, and cyclic fatigue testing. The results showed that the alkali treatment successfully eliminated impurities in the outer layer of the bamboo fibers and reduced their hydrophilicity, which enhanced the asphalt-bamboo fiber interactions as well as the asphalt mixture’s water damage resistance, specifically manifested as the residual stability of ABM was enhanced by 7.8% and the splitting tensile strength of ABM was raised by 12.2%. Furthermore, the surface polarity of the bamboo fibers was reduced, which weakened the agglomeration phenomenon and increases the dispersion rate of bamboo fibers in the mixture by 9%, efficiently improving the low-temperature cracking resistance and fatigue performance of asphalt mixtures.

Performance evaluation of styreneic methyl copolymer regenerated SBS-modified asphalt and its mixture with high content RAP

The aging degree of reclaimed asphalt pavement (RAP) is complex and diverse, and the current utilization rate of RAP is far from meeting the needs of green cycle development. To explore the effect of Styreneic Methyl Copolymer (SMC) rejuvenator of aging asphalt and the performance of SMC regenerated asphalt mixture containing 50% and 60% RAP, this study used SMC rejuvenator to regenerate SBS-modified asphalt with different aging degrees. The high and low-temperature rheological properties of regenerated asphalt were evaluated by temperature sweep test, multi stress creep recovery test, and bending beam rheometer test. Then, the recommended content of the SMC rejuvenator was obtained by using Matlab to establish the corresponding model. Finally, the road performance of the regenerated mixture with high-content RAP was verified. The test results showed that the recommended content range of the SMC rejuvenator for the aging asphalt with PAV (Pressurized Aging Vessel) 0 h, PAV5h, PAV10h, PAV15h, PAV20h were 1.56∼2.31%, 3.03∼3.36%, 4.269∼4.48%, 5.23∼5.66%, 5.95∼6.91%, respectively. The road performance of the SMC regenerated asphalt mixture with 50% and 60% RAP content met the specification requirements. SMC rejuvenator had no significant negative impact on high-temperature performance, significantly improving low-temperature cracking resistance. SMC regenerator had a positive significance in improving regeneration efficiency.

Room-temperature strength of the interfacial bond between silica inclusions and iron

The strength of the interface between iron (Fe) and individual spherical silica (SiO2) inclusions of 5 ± 1 µm diameter is measured by means of in-situ micro-cantilever bending tests conducted under displacement control within a scanning electron microscope, using a wedge indenter tip. Attention is paid to ensure that reported data are not affected by either the electron beam during in-situ testing or by focused ion beam milling, used to produce the cantilevers. For the latter, a simple yet effective strategy, validated using finite element modeling, is devised to shift the peak interfacial stress towards the beam center, thereby relocating the fracture initiation position away from potential FIB-induced artefacts at the beam edge. All bend beams tested fractured along the Fe/SiO2 interface, with no visible evidence of silica microcracking or iron plastic deformation. The rapidly cooled iron matrix features a submicron ferrite grain size, causing its yield strength to exceed 1 GPa. Using classical Euler-Bernoulli beam theory, the estimated Fe/SiO2 interfacial tensile strength yields values ranging from 0.9 to 2.3 GPa, proving that SiO2 inclusions are strongly bonded to the Fe matrix at room-temperature. There is, thus, potential for engineering inclusion-containing Fe-based alloys that, under monotonic loading conditions, do not compromise the mechanical integrity of the ferrous matrix.

Cantilever beam bending as a potential method to determine the elasticity of cooked Udon noodles

AbstractElasticity is a critical measure of the eating quality of Udon noodles. To characterize the elasticity of Udon noodles, an instrumental method based on the cantilever beam bending test was established. Firstly, the optimum test parameters were determined. Then, texture profile analysis, compression, tension, and cantilever beam bending methods were used to measure the elasticity of 25 commercial Udon noodles with different shapes and sizes, and the correlations between elasticity obtained by the above instrumental methods and sensory evaluation were analyzed. Finally, how the shape and size of Udon noodles influenced their elasticity was discussed in detail. Within the deflection of 2.0 mm, the force increased approximately linearly with increasing deflection, and moderate loading speed (0.5–1.0 mm/s) should be used in the cantilever beam bending experiments to improve the accuracy of results. The bending stiffness obtained by the cantilever beam bending method exhibited a higher coefficient of variation and stronger correlation with the elasticity of sensory evaluation than other instrumental methods. Furthermore, the Udon noodle sample with a higher size, especially the thickness, had higher elasticity, and the Udon noodle sample with a rectangular cross‐section showed higher elasticity than that with a circular cross‐section. In conclusion, the bending stiffness determined by the cantilever beam bending method could be used to characterize the elasticity of cooked Udon noodles.

Influence of specimen geometry on the energy release rate in concrete

The energy release rate during the crack propagation in concrete was studied using three-point bending (TPB) beams with different geometries. Expressions for determining the energy release rate were established. A total of 44 beams, i.e., TPB specimens with the height of 150 mm and various spans and the same span of 800 m but different heights, named as Series-T and Series-TH, respectively, were tested. The obtained results reveal that (1) with the crack propagation, the energy release rate curves (GR-curves) monotonically increased and convergence to the fracture energy of each specimen, and the average values were 161.136 N/m and 112.343 N/m for Series-T and Series-TH. (2) For Series-T, with increasing the specimen span from 300 mm to 900 mm, the maximum fracture process zone (FPZ) length kept constant of 68.317 mm, and for Series-TH, the result increased by 187.6 % with increasing the specimen height from 100 mm to 300 mm. Moreover, the relative FPZ length was not affected by the spans and depths of the specimens. (3) The evolution of crack tip opening displacement was only affected by the specimen ligament length, i.e. for the same crack extension length, a larger value was noticed for longer ligament length. (4) The stability during crack propagation can be analyzed using GR-curves.

STATIC DEFORMATION ANALYSIS OF A MOBILE CUTTING MACHINE

A study of the special requirements and criteria to portable cutting machines was carried out. Based on the existing approaches to the deformation analysis of spindle units the calculation schemes and mathematical model for the static analysis of the problem were developed. The implemented approach makes use of the Timoshenko beam model. The resulting differential equation of the bent beam axis is solved by the method of initial parameters in the matrix form. The nonlinear equation system for the chosen calculation scheme is formed automatically and is solved iteratively. A special feature of the proposed approach is the nonlinear relation between the stiffness of the bearings and the forces acting upon them. As a model application example, the results of the static deformation analysis of portable boring machine XT7809-0524 are presented. An estimate of the bending stiffness and the corresponding distributions of bending deflections and rotations were obtained for several calculation schemes of the machine. The obtained solution quantities are presented in form of graphs along the spindle axis. It has been found, that the calculated equivalent stiffness of XT7809-0524 machine spindle shaft is lower than the normative value used in the industry. A strength assessment of the spindle shaft was also made and the distributions of internal forces and moments acting on shaft cross sections were obtained. It has been concluded, that under work loads the maximum stress in the shaft is acceptable to provide for the required factor of safety.

Nonlinear bending of unsymmetric double-layer lattice truss core sandwich beams

This paper studied the nonlinear bending of unsymmetric double-layer lattice truss core sandwich beams (LTCSBs). Five unsymmetric cases are considered by varying different materials and geometric thicknesses in two layers. To establish a theoretical model for the unsymmetric double-layer LTCSBs, Allen’s model and von Kármán nonlinear theory are employed. The present theoretical model is established by considering the midplane of the mid-sheet as the reference plane. Ritz method is applied to determine the deflection for the nonlinear bending, and verified by the finite element method (FEM). Finally, the effects of the loading direction, unsymmetric factors, and boundary conditions on the nonlinear bending behaviors of LTCSBs are studied. It is found that the nonlinear deflections of unsymmetric LTCSBs may exhibit softening-spring nonlinearity in one direction.

Specified criterion for delamination upon bending of a composite beam

The interlayer strength in polymer fiber composites is characterized mostly by the strength of the matrix, which is much lower than fiber strength. For this reason, the analysis of fracture occurred through delamination is extremely important for assessing the operability of composite structural elements. When designing critical structures, it is necessary to know the interlayer shear strength, for which the method of bending a short beam has been standardized. The shear stresses and the interlayer shear strength in bending theory are traditionally assumed to be independent of the length and width of the beam. However, a large number of experimental studies prove the opposite fact that the geometry of the specimen affects the value of critical stresses. The linear fracture criterion proposed by the authors allows explanation and quantitatively description of the interlayer shear strength dependence on the geometry of the specimen. The influence of the heterogeneity of interlayer shear stresses across the beam on the critical stresses is analyzed. A strict solution of the bending problem showed that taking into account the specified shear stress distribution gives an insignificant correction to the determined value of the interlayer strength, which makes it possible to use a simplest parabolic distribution in height. The results of the analysis are confirmed in three-point bending tests of short composite beams of different widths. The results of fatigue tests of short beams made of carbon fiber reinforced plastic are analyzed. The relationship between tensile fatigue curves of polymer fiber composites and the fatigue curves obtained in cyclic three-point bending test of short beams has been revealed using the proposed linear fracture criterion. The estimation of the strength scale effect on the basis of the energy criterion of delamination with and without taking into account the refined distribution of interlayer shear stresses is presented.

Fabrication and characterization of multiphase bituminous materials for cold region pavements

In this study, the low temperature creep properties of multiphase bituminous materials (binder, mastic, Fine Aggregate Matrix—FAM, and mixture) were experimentally evaluated, and the impact of size effect on FAM and mixture specimen was also assessed. First, the mix design of mastic and FAM was performed based on the reference mixture Asphalt Concrete (AC) 22 TS. The mathematical adaptation to the boundary sieve method was applied to calculate FAM gradation and binder content. Next, a preparation method was proposed to produce Fine Aggregate Matrix (FAM) in a laboratory environment, and scale-up slab samples were also fabricated for FAM and mixture specimens to evaluate the size effect phenomenon. Finally, three-point bending (3 PB) creep tests were conducted on the multiphase bituminous specimens with different dimensions at -6 °C, -12 °C, and -18 °C with a modified Bending Beam Rheometer (BBR) device and a dynamic loading machine, depending on the sample size. Results indicate that the creep stiffness of the FAM was close to mixtures and much higher than the one observed in binder and mastic. The proposed fabrication approach provides a satisfactory method for preparing a representative FAM phase in the mixture, while the air voids can be easily adjusted during the slab compaction procedure. This study supports the idea of using FAM to discriminate asphalt mixtures for cold regions. The correlation between up-scaled FAM and mixture specimens should be further investigated, including different mixture types and corresponding FAM.

Research on the performance and mechanism of asphalt modified by thermoplastic polyurethane with different chemical structures

Thermoplastic polyurethane (TPU) with different chemical structures is prepared by the prepolymer method and then mixed with base asphalt to obtain thermoplastic polyurethane modified asphalt (TPU-A). The structure of synthetic TPU was characterized by Fourier transform infrared spectroscopy (FTIR) and thermomechanical properties tests. The road performance of TPU-A is characterized by conventional performance tests, dynamic shear rheometer (DSR) and bending beam rheometer (BBR). The modification mechanism of TPU-A is studied by FTIR, fluorescence microscopy (FM) and electron microscopy (SEM). The results show that hard segment increases the polar groups of TPU and gives it higher thermal stability. The hard segment-rich TPU is disperse evenly as particles in the asphalt phase, which increases the thermal stability and shear deformation capacity of TPU-A. The amount of hard segment in TPU has a critical point (30 wt%) to improve the low and high temperature performance of TPU-A. The soft segment can be inflated by the asphalt to form a physical cross-linking network structure, which advances the low-temperature properties.

Physical, Rheological, and Anti-Ultraviolet Aging Performance of Layered Double Hydroxides + Styrene Block Copolymer-Modified Asphalt Binders

To determine the preparation parameters of layered double hydroxides (LDHs) + styrene butadiene styrene block copolymer (SBS)-modified asphalt binders (MABs) in engineering applications and identify the structure of LDHs used in asphalt modification, this paper investigated the physical, rheological, and UV aging resistance of LDHs + SBS MABs under various preparation parameters. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and an ultraviolet-visible spectrophotometer (UV-vis) were used to characterize the structure and UV resistance of LDHs and D-LDHs (dissolving from LDHs + SBS MABs). The mechanical properties of LDHs + SBS MABs were studied based on penetration, ductility, softening point, and rotational viscosity tests. The rheological performance and UV aging resistance of LDHs + SBS MABs were assessed using the bending beam rheometer (BBR) test, direct tensile test (DTT), dynamic shear rheometer (DSR) test, and FTIR. The results demonstrated that the crystal and chemical structures of LDHs remain unchanged before and after use in asphalt modification. The optimal preparation parameters of LDHs + SBS MABs were as follows: a preparation temperature of 170 °C, a shearing time of 60 min, and a shearing rate of 4000 r/min. The high-temperature performance of LDHs + SBS MABs improved significantly with LDHs added, and the low-temperature performance slightly decreased. The viscosity of LDHs + SBS MABs with 4 wt% LDHs at 135 °C was 1.920 Pa·s, which was 47.4% higher than that of SBS MABs. The DTT results indicated that SBS MABs have the highest fracture energy (FE) value of 4873 J/m2, showing the best low-temperature cracking resistance. In comparison, the FE values of MABs doped with 3 wt% and 4 wt% LDHs are 4518 J/m2 and 4248 J/m2, respectively, just 7.3% and 12.8% lower than that of ABs without LDHs. The complex modulus aging index (CMAI) of MABs doped with 4% LDHs is 14.3%, which is 15.9% lower than that of SBS MABs, indicating that the anti-ultraviolet aging performance of LDHs + SBS MABs has been improved. FTIR analysis demonstrated that the relative content of C=O (RCC) and S=O (RCS) of LDHs + SBS MABs decreased drastically compared with SBS MABs, indicating that the UV aging resistance of LDHs + SBS MABs was largely enhanced. Furthermore, the segregation test result of 3wt% LDHs + SBS-modified asphalt is 0.3 °C, showing the best compatibility with asphalt.

Influence of the Oriented Configuration of the BarChip Fibre Polypropylene to the Ductility Factor of the Reinforced Concrete Beam

Abstract
 Bending and shear strength of fiber reinforced polimer concrete beams was studied in this research project. The reinforced concrete beam behaves in brittle structure in the certain reinforcement configuration. BarChip fibre polypropylene as the material for enhancement of the ductility factor is applied to the concrete beam. Three types of BarChip fibre configuration were examined: randomly spreading, placing at the mid-span area, and concentration on the tension zone. The experimental program included five beam specimens. Two of the beams were control specimens in which one was reinforced with no fibre, while the other one did not have any Barchips polypropylene. Each one of the other three specimens was reinforced with one of the above mentioned fibers by 0,4% volumetric ratio. Investigating the following issues for medium-high concrete strength was the goal of this study. In order to determine whether adding 0.4% volumetric ratio of polypropylenes as additional bar reinforcement in beams would provide adequate strength and stiffness properties comparable to reinforcing steel used as minimum bar reinforcement, it was necessary to first assess the effectiveness of each type of oriented fiber configuration on the bending strength, then to look into each beam's bending strength, shear strength, toughness, crack patterns, and near ultimate load crack width. The findings demonstrated that the bending capacity of the beam specimens was raised by all three types of polypropylene configuration more than by the beam reinforced with the fewest amount of bar reinforcement. Additionally, some of the employed fibers may cause failures other than pure shear. It is reccomended to spread the polypropylene within the tension zone of the reinforced concrete beam on the bottom mid span.
 Keywords: Fibrous Concrete, Polypropylene, Ductility, Reinforced, Beam

Synergistic effect of surface modified nano-zinc oxide and organic vermiculite on long-term ultraviolet and thermal-oxidative aging resistance of different asphalt binders

Asphalt pavement will be subjected to the action of thermal, oxygen and ultraviolet during long-term service, which in turn causes the ultraviolet and thermal-oxidative aging of asphalt simultaneously. Based on the long-term aging mechanism, the double retarding effect of surface modified nano-zinc oxide (ZnO) and organic vermiculite (OEVMT) in different stages of long-term aging was utilized in the research. This work investigated the synergistic effect of ZnO and OEVMT on rheological properties and chemical structures of base asphalts (70# and SK-70) and polymer modified asphalts (SBS modified asphalt and SBR modified asphalt) after long-term ultraviolet and thermal-oxidative aging. Dynamic shear rheological (DSR), bending beam rheological (BBR) and Fourier infrared spectroscopy tests were utilized to study the DSR properties, BBR properties at low temperature and chemical structures, respectively. Meanwhile, the synergistic effect mechanism was analyzed. Results showed that the effect of 1 % ZnO to resist the long-term ultraviolet aging of 70# base asphalt approximates that of 3 % OEVMT, while the long-term thermal-oxidative anti-aging ability of 1 % OEVMT for 70# base asphalt is equivalent to that of 3 % ZnO. Besides, compared with 2 % ZnO or 2 % OEVMT, 1 % ZnO + 1 % OEVMT shows a better long-term ultraviolet and thermal-oxidative aging resistance for different asphalt binders, indicating its synergistic effect in strengthening the anti-aging performance of asphalt. Moreover, 1 % ZnO + 1 % OEVMT not only can effectively retard the oxidation rate of asphalt in the process of long-term aging, but also inhibit the degradation degree of modifiers in SBS modified asphalt. The research could propose a new design idea to effectively solve the long-term aging problem of asphalt.

Experimental Evaluation of the Properties of Asphalt Binders Modified with Calcium Sulfate Anhydrous Whiskers and Polyester Fibers

The use of waste calcium sulfate whiskers in pavement construction is cost-effective and beneficial to the environment. In this paper, modified asphalt binders are prepared by adding calcium sulfate anhydrous whiskers (ACSW, 9 wt.%,11 wt.%, and 13 wt.% by weight of asphalt binder) and polyester fibers (4 wt.%,6 wt.%, and 8 wt.% by weight of asphalt binder). The viscosity-temperature, rheological, and low-temperature properties of the modified asphalt binder were evaluated using the Brookfield rotational viscosity test, the dynamic shear rheometer (DSR) test, the bending beam rheometer (BBR) test, and the force ductility test. The results demonstrated that the addition of the ACSW and polyester fiber could improve the anti-deformation and low-temperature properties of the asphalt binders, but reduce their viscosity-temperature properties to some extent. The modified asphalt binder with 11 wt.% ACSW and 8% polyester fiber showed the best anti-deformation property, while the 11 wt.% ACSW and 6 wt.% polyester fiber modified asphalt binder had a better low-temperature performance. The force ductility test was more suitable than the BBR test to characterize the low-temperature properties of the modified asphalt binders. The Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM) tests were conducted to study the functional groups and micro-structure of the modified asphalt binders, and the results indicated that no new functional groups were generated and that the interaction between the ACSW, polyester fiber, and asphalt binder was a physical adsorption and interleaving process.