Asphalt Samples Research Articles

Enhancement of Anti-UV Aging Performance of Asphalt Modified by UV-531/Pigment Violet Composite Light Stabilizers

Ultraviolet (UV) radiation accelerates the aging of asphalt pavements and shortens the service life of the pavement. To effectively mitigate the impact of UV aging on asphalt performance, a novel composite anti-UV aging agent, 2-hydroxy-4-n-octyoxybenzophenone/pigment violet (UV-531/PV), was developed. After UV-accelerated aging, the modified asphalt samples were characterized by conventional performance tests, Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), and a dynamic shear rheometer (DSR). The results show that UV-531/PV-composite-modified asphalt maintains excellent conventional properties after UV aging. The FTIR testing showed that the changes in carbonyl index (Ic=o) and sulfoxide index (Is=o) of the composite-modified asphalt were significantly smaller than those of the matrix asphalt, indicating the less oxidation degree of the composite-modified asphalt. The GPC test results showed that the change in molecular weight of the composite-modified asphalt after UV aging was less than that of the matrix asphalt. DSR results showed that UV-531/PV-modified asphalt exhibited higher viscoelasticity and higher rutting resistance than unmodified asphalt. This study proposes a new method for preparing anti-UV aging asphalt, which can be used for micro-surfacing, fog sealing or ultra-thin overlay on road surfaces.

Optimised biopolymer-based capsules for enhancing the mechanical and self-healing properties of asphalt mixtures

The growing need to enhance our road infrastructure has driven the development of several innovative techniques in recent years. Among these advancements, encapsulated rejuvenator solutions for extrinsic self-healing asphalt have emerged as a significant topic of interest. This paper evaluates the effect of optimised capsules containing vegetal oil as a biorejuvenator on the physical, mechanical, and self-healing properties of dense asphalt mixtures. In this study, previously optimised polynuclear alginate-based capsules were synthesised using vibrating jet technology with 5% wt. calcium chloride and a biopolymer-to oil mass ratio 1:7. Optimised capsules were incorporated into the asphalt mixture at concentrations of 0.125% wt., 0.25% wt., and 0.5% wt. Their spatial distribution within the asphalt mixtures was evaluated using an alternative method to CT scans, which utilised machine learning-based image analysis of the core asphalt samples. The main findings of this research are as follows: (1) a uniform distribution of capsules was achieved throughout the asphalt mixture, although clustering was observed at higher concentrations. (2) The capsules successfully survived the asphalt manufacturing process, and mechanical tests highlighted the adhesive properties of the alginate encapsulation material. (3) Asphalt samples with 0.125% wt. capsules exhibited mechanical performance comparable to samples without capsules; however, this content did not significantly enhance their self-healing properties. In contrast, self-healing capabilities were significantly enhanced with a capsule content greater than or equal to 0.25% wt.; however, this enhancement slightly affected some physical–mechanical properties of the dense asphalt mixture.

Microwave healing properties and moisture sensitivity of asphalt mixture containing iron powder filler

Through experimental tests, this paper investigated the effectiveness of microwave healing on asphalt mixtures containing iron powder (IP) filler to improve durability and enhance mechanical properties. The moisture sensitivity of the asphalt mixes with varying iron powder filler contents was measured using the modified Lottman test. For evaluating the asphalt mixture healing ability, two complementary methods were used: the fatigue-based method, derived from the ability of microwave healing of asphalt mixture samples damaged up to 50% level of indirect tensile fatigue (ITF), and the fracture-based method, obtained from the strength recovery rate of broken semi-circular samples by applying consecutive breaking-healing cycles. The results showed that the greater the quantity of iron powder filler in the asphalt sample, the greater the sample’s indirect tensile strength and TSR ratio, indicating that IP had a positive effect on moisture sensitivity. The findings also indicated that utilizing iron powder as a filler positively strengthens the fatigue life, increases the toughness, and increases the microwave healing indices (both fatigue and failure approaches). Finally, according to the study results, substituting 70% iron powder as the filler is the most suitable option for improving the mechanical and self-healing characteristics of asphalt mixes.

Study on spinnability, thermal stability and microstructure of modified isotropic pitch by adding polyacrylonitrile melt blending

Asphalt samples modified by melting isotropic asphalt with polyacrylonitrile (PAN) are obtainable. Investigations were conducted on the spinnability, microstructure, and thermal stability of the modified asphalt. The results demonstrate that pan40w modified asphalt possesses the highest spinnability stability. Additionally, there is a reduction in viscosity within the smooth range, a slight increase in the flow point, and an enhancement in spinnability. Compared to other modified asphalt samples, PT403 containing 0.3 % PAN exhibited the highest comprehensive performance, characterized by a molecular weight of 400,000, enhanced spinnability, a larger and more uniform microcrystal size, and improved thermal stability. This study employs a distinctive modification scheme and provides a cogent explanation of the corresponding mechanisms, potentially contributing to the advancement of producing cost-effective pitch-based carbon fibers from petroleum by-products.

Introducing the rubber plate impact method: a versatile alternative to close proximity test for tire-pavement noise characterization on asphalt highways

Despite its widespread use, the close proximity (CPX) test for tire-pavement noise is limited to existing pavements, posing challenges for timely and effective corrections of noisy pavements. Additionally, the CPX test entails significant procurement and operation costs. Addressing these issues, this study introduces the rubber plate impact (RPI) method as a simple experimental technique for assessing tire-pavement noise in both laboratory and field settings. The RPI test utilizes the folding motion of the treaded rubber plate on the road surface to simulate air pumping and tread impact noise as two main contributors to tire-pavement noise. Indoor RPI tests on asphalt concrete samples of dense graded asphalt and porous asphalt mixes revealed dominant effects of air void content and associated surface texture on the level of noise. The RPI testing procedure was verified at 17 highway test sections, where both CPX and RPI tests were conducted for comparison. Multiple linear regressions between RPI and CPX data were analyzed to propose CPX prediction models at different speeds (80, 100, 120 km/h), and the performance of these prediction models was validated with independent noise datasets collected from four different highway routes. The findings suggest promising prospects for the RPI test as a cost-effective and versatile alternative to CPX for tire-pavement noise characterization on asphalt-surfaced roads, with implications for road materials design and noise mitigation strategies.

Nuclear Magnetic Resonance (NMR) Assessment of Bio and Crude Oil-Based Rejuvenation

Asphalt binders in pavements lose their stability through aging and eventually fail in the field. Using nuclear magnetic resonance (NMR) to monitor the primary longitudinal relaxation time of asphalt samples and the ratio of material that carries this primary relaxation time has been shown to indicate the impact of ultraviolet (UV) radiation on the aging of asphalt pavements. Longitudinal NMR relaxation was used to investigate two types of proposed asphalt rejuvenators, a bio-oil-based rejuvenator and a crude-oil-based rejuvenator. Two different binders with the performance grades (PG) 64-22 and 76-22 were considered for their interactions with the rejuvenators. After 72 h of exposure to intense UV radiation, specifically designed NMR relaxometry experiments were applied to compare the rejuvenation capabilities of the two rejuvenator samples. The crude oil-based rejuvenator was found to exhibit relaxation times similar to the binder samples while the bio-based material showed relaxation times that pointed to different nuclear hydrogen environments. Both rejuvenators reduced the primary relaxation time of the PG 76-22 binder, which indicates that their stiffness was reduced. Both types of rejuvenators also seemed to prevent the effects of UV aging. Two mechanisms of rejuvenation were identified by NMR relaxometry. The primary relaxation time can be used to indicate a change in stiffness while the primary ratio of the material is tied to oxidative aging. Oxidative aging creates distinct hydrogen environments due to asphaltene aggregation. The bio-based rejuvenator only reduced the binder’s stiffness, while the crude oil-based rejuvenator also reduced the aggregation of asphaltenes. Consequently, the bio-based rejuvenator could be classified as an asphalt softener, while the oil-based material acted like a true rejuvenator.

Using rheology to study the synergistic effect of anti-aging modifier and rejuvenator on aged asphalt binder

A composite anti-aging rejuvenator for road asphalt was studied and prepared. Asphalt samples with different aging degrees and modifier dosages were prepared by RTFOT(rolling thin film oven) and PAV(pressure aging vessle)， and the viscoelastic, high temperature, low temperature and fatigue properties of the modified asphalt were comprehensively characterised based on their rheological properties. The test results showed that the composite anti-aging rejuvenator improved the fatigue performance and low temperature performance of aging asphalt. Among them, the creep rate m value at −18°C was recovered to 99.2 % of the unaged level, and the G-R(Glover-Rowe) parameter was reduced to more than 90 %. After long term aging of the composite anti-aging reclaimed mixtures were still able to maintain the water stability and low temperature performance higher than the level required by the specification. The paper found the better effect of adding same ratio of rejuvenator and anti-aging agent to aging asphalt. The reason was that the same ratio of rejuvenator and anti-aging agent could have synergistic effect and enhance each other. This paper verified the road value of the composite anti-aging rejuvenator from asphalt and asphalt mixtures, which provides technical support and reference for the promotion of old pavement reclamation and long-life pavement.

Preparation and Properties of Waterborne Polyurethane and SBS Composite-Modified Emulsified Asphalt

To address the issue of insufficient durability of traditional modified emulsified asphalt in the application of cold mix and cold paving anti-skid wear layers, this study utilizes cationic waterborne polyurethane (PU+) for composite modification to enhance adhesion and performance across a range of temperatures. Initially, composite-modified emulsified asphalt samples were prepared with varying dosages of PU+ according to a gradient method. Routine performance tests were conducted on the evaporated residues for analysis. Advanced rheological tests, including temperature sweep (TS), frequency sweep (FS), linear amplitude sweep (LAS), and multi-stress creep recovery (MSCR) tests, were performed using a dynamic shear rheometer (DSR). Surface free energy (SFE) tests were conducted with a fully automated surface tension meter (STM). A comprehensive evaluation of the high-temperature rheological properties, fatigue properties, adhesion properties, and water damage resistance of the modified emulsified asphalt residues was carried out. Chemical changes before and after modification were characterized using Fourier transform infrared spectroscopy (FTIR), and the distribution of polymers in the evaporated residue was observed using fluorescence microscopy (FM). The results demonstrated that cationic waterborne polyurethane significantly enhanced the fatigue and adhesion properties of SBS-modified emulsified asphalt, but it also weakened the water damage resistance of asphalt. MSCR tests revealed that the addition of cationic waterborne polyurethane might reduce the elastic recovery performance of modified asphalt, thereby weakening its resistance to rutting. Among the samples, the modified asphalt with a PU+ content of 6% exhibited good high-temperature shear resistance and elastic recovery performance, demonstrating the best anti-rutting performance.

Asphalt-Binder Mixtures Evaluated by T1 NMR Relaxometry

Asphalt pavements make up a majority of the essential transportation systems in the US. Asphalt mixtures age and degrade over time, reducing the pavement performance. Pavement performance critically depends on the aging of asphalt binder. The aging of asphalt binder during construction is traditionally modeled by rolling thin film oven (RTFO) testing, while aging during service life is modeled by pressure aging vessel (PAV) testing. Comparing these models to the aging of binders in actual pavements is limited because, to be used for current testing, binders must be separated from the pavement’s aggregate by solvent extraction. Solvent extraction will, at least in part, compromise the structural integrity of asphalt binder samples. Spin-lattice NMR relaxometry has been shown to nondestructively evaluate asphalt properties in situ through the analysis of hydrogen environments. The molecular mobility of hydrogen environments and with it the stiffness of asphalt binder samples can be determined by characteristic T1 relaxation times, indicating the complexity of asphalt-binder aging. In this study, two laboratory-generated asphalt mixtures, a failed field sample, and several laboratory-aged binder samples are compared by NMR relaxometry. NMR relaxometry was found to be able to differentiate between asphalt samples based on their binder percentage. According to the relaxometry findings, the RTFO binder aging compared favorably to the 6% laboratory-mixed sample. The PAV aging, however, did not compare well to the relaxometry results found for the field-aged sample. The amount of aggregate was found to have an influence on the relaxation times of the binder in the mixed samples and an inverse proportionality of the binder content to the primary NMR relaxation time was detected. It is concluded that molecular water present in the pores of the aggregate material gives rise to such a relationship. The findings of this study lay the foundation for nondestructive asphalt performance evaluation by NMR relaxometry.

Electromagnetic tomography measuring bench for estimating the density of materials

In the laboratory, the density of pavement cores (cylindrical samples of hot mix asphalt (HMA) material taken from roads) is assessed using an electromagnetic (EM) bench consisting of two ultra-wideband (UWB) Vivaldi antennas and a vector network analyser (VNA). The main objective is to replace the nuclear gauge system currently used in the laboratory as the standard method for this purpose. Firstly, specific antipodal Vivaldi antennas have been adapted from the literature. Their dimensions are 7 × 7 cm with a bandwidth [1.5–15 GHz]. Secondly, a tomographic approach is compared with an analytical solution and a Finite-Difference Time Domain (FDTD) simulation, based on a time-domain estimation of the dielectric under test (DUT) with a single transmitter/receiver configuration. A laboratory validation is presented and the adapted antennas as well as the time domain approach show acceptable results for assessing the dielectric constant on known materials. Finally, to show that the proposed EM bench is a promising non-ionizing solution, the density or equivalent compactness of HMA cylindrical samples is estimated and compared with nuclear gauge results.

Thermal Behaviour of Cool-Pavement Materials Development using Palm Oil Shell Aggregate

Cool-pavement technology has emerged as a potential solution to environmental issues posed by the urban heat island phenomenon, with surface temperature acting as a vital parameter in the evaluation of its thermal performance. This study focuses on the thermal performance results of modified asphalt concrete mix, wherein palm oil shell (POS) serves as a replacement for fine aggregate. Modified asphalt samples prepared using the Marshall Mix Design, with varying degrees of fine aggregate substitution (0%, 10%, 20%, 30%, 40%, and 50%), underwent a 24-hour continuous surface temperature measurement over a span of 20 days, under real-world tropical climate conditions. The findings demonstrated that sample P5, comprising 50% fine aggregate substitution, exhibited the highest reduction in surface temperature when compared to control sample P0, registering a significant decrease of up to 3.29°C during the period of peak solar intensity. ANOVA test-based statistical analyses confirmed significantly lower temperatures for all test samples, barring sample P1 (10% aggregate replacement), relative to the control sample. The results highlight the efficacy of POS as a fine aggregate substitute in asphalt concrete, significantly lowering asphalt pavement surface temperature, thereby endorsing the potential use of POS-modified asphalt in cool-pavement applications.

Effects of cutting temperature on the genes and fatigue properties of asphalt during its refining process

Asphalt binders performance is affected by refining process and crude oil. In this work, we investigated the effect of cutting temperature on the genes and fatigue properties of asphalt during asphalt refining. Five cutting temperatures (420 °C to 440 °C, interval of 5 °C) were set during the asphalt preparation, expanded the asphalt samples through ageing method. Fourier Transform Infrared (FTIR), Gel Permeation Chromatography (GPC), Nuclear Magnetic resonance Spectrum (1HNMR), Elemental analyzer, and improved Brown-Ladner method were used to characterize the asphalt genes. The fatigue performance of asphalt through Linear Amplitude Sweep (LAS) combined with the Simplified Viscoelastic Continuum Damage (S-VECD). Finally, the Pearson correlation method was used to analyze the correlation between genes and fatigue parameters of binders. The results showed that the cutting temperature and aging process changed the genes distribution of binders and these influence the fatigue properties of binders. In addition, the fatigue life of asphalt decreased at high strain levels and increased at low strain levels as the cutting temperature and the degree of ageing increased. The Pearson correlation results indicated a significant correlation between the genes and fatigue parameters of asphalt, however, the key genes affecting low-strain (2.5% and 5 %) and high-strain (10% and 20%) level fatigue in asphalt are significantly different. The outcomes of the paper provide insights about the influence of cutting temperature on the variation of asphalt genes and fatigue parameters, to allow more informed to promote of asphalt preparation.

Analysis of viscoelastic behaviour in asphalt pavement through four-point beam bending tests

This study, conducted in accordance with ASTM T321-14 standards, offers crucial insights into the behaviour of asphalt materials subjected to cyclic loading. For proper maintenance and pavement design, it is essential to understand the material response under different loading conditions. This study focuses on the four-point beam bending test to investigate the viscoelastic behaviour of asphalt pavement. The four-point beam bending test is a useful method for determining the material's ability to withstand cyclic loading and deformation, which the material experiences during field traffic conditions. The experimental setup involves subjecting asphalt samples to cyclic loading using a four-point bending apparatus. The imposed load causes the specimen to experience bending strains, representing the actual loading conditions that pavements endure. The data gathered during testing include stress, strain, and deformation properties under various loading conditions. The stress-strain response demonstrates the material's resilience to fatigue, with a gradual decrease in stiffness beyond 10,300 cycles. Fatigue failure criteria include a 50% reduction in initial stiffness for strain-controlled fatigue tests and cracking in stress-controlled tests. The dynamic modulus in a compressive-type, repeated load test follows a three-phase pattern, highlighting the impact of temperature and binder characterization methods on sample performance. The results provide information about the material's resilience to rutting and fatigue cracking, the most significant distresses indicated in asphalt pavements. The findings from this study contribute to an in-depth understanding of the viscoelastic behaviour of asphalt pavement and can aid in the development of improved design guidelines and maintenance strategies characterizing the material response to cyclic loading. Engineers and researchers can make better decisions on the durability and performance of asphalt pavements, resulting in more cost-effective and sustainable road infrastructure.

Effect of Salt Solution Environment on the Aging of Styrene-Butadiene-Styrene (SBS)-Modified Asphalt.

The aim of this paper is to investigate the aging mechanism of asphalt in the sea salt erosion environment from a rheological point of view. In order to simulate the real pavement aging process in the sea salt erosion environment, base asphalt and Styrene-Butadiene-Styrene (SBS)-modified asphalt were selected for salt environment aging tests. The asphalt samples were aged via a thin film oven test (TFOT) and a pressure aging vessel (PAV) test. Then, thermo-oxidizing conditions were created after the samples were immersed in salt solution, mixed with four different concentrations of sodium chloride (NaCl) and sodium sulphate (Na2SO4), to investigate the aging state of asphalt. Temperature scan (TS), frequency scan (FS), and multiple stress creep and recovery (MSCR) tests performed using a Dynamic Shear Rheometer (DSR) were used to investigate the effects on the rheological properties of aged asphalt in a salt environment. The results showed that both base asphalt and SBS-modified asphalt were aged to different degrees under mixed salt solutions. The two asphalt samples aged in a salt environment showed increased hardness. SBS-modified asphalt exhibited higher aging resistance compared with base asphalt in the sea salt environment. However, due to the degradation of the SBS modifier and the aging of base asphalt, the properties of the SBS-modified asphalt showed more obvious complexity with changes in salt solution concentrations.

The effect of runoff acidity on fatigue cracking of hot mix asphalt using thermodynamic concepts

This study examined the fatigue performance of hot mix asphalt (HMA) under the influence of runoffs entering the pavement with different acidity degrees. Based on the fatigue test results, changing the runoff acidity and increasing the temperature decreased the number of cycles leading to HMA fracture (fatigue life) and accelerated the damage. The results of the surface free energy (SFE) method were aligned with the fatigue test results, indicating that changing the runoff acidity increased the bitumen-water adhesion SFE, aggregate-water adhesion SFE, and bitumen-aggregate debonding SFE. These changes diminished the fatigue cracking resistance of HMA. According to the Pull-Off test results, altering the runoff acidity and increasing the temperature reduced the adhesion and cohesion strength. According to the two principal factors in fatigue cracking (fracture adhesion and cohesion), the reduced fatigue life of the samples due to variations in the runoff acidity and temperature increase was acceptable according to the SFE and Pull-Off test results. The independent samples t test revealed that changing the runoff acidity led to a significant decline in the asphalt samples' performance parameters compared to neutral conditions.

Assessing the Performance of Recycled Asphalt Mixtures Using Rejuvenators

After serving their intended purpose, traditional asphalt pavements are destroyed and dumped across the neighboring fields in Pakistan, affecting the natural environment. Only 15% of the old asphalt material has been recycled on the Motorway (M-2) near Shekhupura. Thus, the current study was intended to increase the amount of recycled asphalt, utilizing waste engine oil (WEO), waste cooking oil (WCO), and waste brown grease (WBG) as rejuvenators. Therefore, the asphalt mixture containing 50% recycled materials, rejuvenated with 5%, 10%, 15%, 20%, and 25% WEO, WCO, and WBG, respectively, were investigated. The asphalt samples for Marshall Stability, indirect tensile strength, and rut resistance were prepared and tested as per ASTM D1559, ASTM D979, and ASTMD8360, respectively. The results showed that WEO, WCO, and WBG of 15% and 20%, respectively, are best for equating the properties of recycled binder to those of neat binder, except for ductility characteristics. The results also demonstrated that, in comparison to the traditional asphalt mixture, asphalt mixes with 50% recycled materials performed significantly better in terms of Marshall stability at 15% utilization of WEO, WCO, and WBG, respectively. Additionally, it is established that recycled asphalt mixture, at WEO of 15%, displayed equivalent rut resistance to virgin asphalt mixture. The results of this study will help recycle old asphalt materials for practical engineering purposes, lowering the dependence on natural resources and benefiting the environment.

Predicting the rutting behaviour of asphalt concrete in the modified wheel tracking test using DEM and a cohesive viscoelastic–elastoplastic-damage contact model

This study used an advanced modelling approach capable of capturing the complex behaviour of asphalt concrete to model the modified wheel tracking test using a recent advanced experimental test set-up in accordance with ASTM D8292-20. The modelling approach uses the discrete element method (DEM) to naturally produce the heterogeneous internal structure and governs the behaviour of asphalt concrete at the grain level by an interparticle contact model. The contact model used is capable of characterising the rate and time dependency, viscoelastic-damage, and plastic-damage behaviour of asphalt concrete utilising the coupling of an elastoplastic-damage law with a viscoelastic-damage law. Unlike the conventional wheel tracking tests run in a fixed boundary condition (fully confined), the modified wheel tracking test considers the effect of boundary conditions on the rutting behaviour of asphalt mixes. Through comparisons and verifications with laboratory data of the rutting test at different boundary conditions (fully confined and unconfined), the modelling approach shows its capability of capturing the rutting behaviour of asphalt concrete in the modified wheel tracking test. Micromechanics analysis shows that the third (tertiary) stage of rutting behaviour is due to the weakening of the internal structure of the asphalt samples with contact bond breaks over time, which is found in the unconfined test. Meanwhile, the tertiary stage hardly occurs in the fully confined test once densification leads to contact of the aggregate–aggregate skeleton, forming a rigid structure to resist the load with lateral support from the fixed boundary condition. Finally, a parametric study was also conducted to provide further insight into the current testing set-up, including the effect of the sample size and boundary condition on the rutting behaviour of asphalt concrete.

Emission reduction effect of eco-friendly asphalt modified with isocyanate-nanoclay composites

The environmental and health issues associated with the generation of fumes during hot mix asphalt used in road construction necessitate the exploration of cleaner production methods. This study investigated the viability of utilizing isocyanate-nanoclay composites as modifiers for eco-friendly modified asphalt. The composite modified asphalt samples were prepared by adding isocyanate (isophorone diisocyanate, IPDI) and nanoclay (organic montmorillonite, OMMT or attapulgite, ATT) to the base asphalt at varying contents. A device for generating and collecting asphalt fumes was developed. The impact of modifier dosage on fume emission reduction was assessed quantitatively and qualitatively using ultraviolet–visible spectrophotometry and gas chromatography-mass spectrometry, yielding the optimal ratio of composite modifiers. The fume emission reduction mechanism of the modifiers was elucidated by analyzing changes in distribution, functional group composition and micromolecular spacing of asphalt using fluorescence microscopy, fourier-transform infrared reflection, and X-ray diffraction. Results revealed that the intercalation effect between nanoclay and asphalt, combined with chemical reactions between isocyanates and functional groups of nanoclay/asphalt components, effectively impeded the escape of fume molecules. Modified asphalt with 3% ATT+3% IPDI achieved an impressive fume emission reduction rate of 44.67% and enhanced basic performance of base asphalt. The findings contribute to the development of cleaner production methods for hot mix asphalt, thus paving the way for sustainable and safer construction practices in the future.

Ultrasound-assisted preparation of crumb rubber modified asphalt: Characterization and molecular dynamics simulation

The traditional method of crumb rubber modified asphalt (CRMA) preparation can improve the stability but is not conducive to cleaner production. From the perspective of process optimization, ultrasound is introduced into the crumb rubber modified asphalt preparation process, and the high temperature, high pressure and high energy accompanied by the cavitation effect are used to generate free radical triggering chemical effects at the two-phase interface between crumb rubber and asphalt. In this paper, the influence of ultrasound on the compatibility and stability of crumb rubber modified asphalt system was evaluated by combining experiment and molecular dynamics simulation. An experimental platform for ultrasound-assisted preparation of crumb rubber modified asphalt was established. The effects of ultrasonic on the physical properties of asphalt and crumb rubber modified asphalt were studied through Brookfield viscosity test, thin film oven aging test and Fourier infrared spectroscopy. The base, aged, and ultrasonically treated asphalt samples were simulated using molecular dynamics, and various parameters such as Cohesive Energy Density (CED), Mean Square Displacement (MSD), and Free Volume Fraction (FFV) of asphalt and its components were calculated and analyzed. The results showed that under the ultrasonic-assisted preparation, the agglomeration phenomenon of rubber particles is weakened, the particle size is reduced, the penetration degree is reduced, and the compatibility between rubber and asphalt is improved. Under the action of ultrasonic, the MSD and diffusion coefficient of crumb rubber modified asphalt are much higher than other kinds of asphalt, the dipole moment is increased, and the molecular motion range is wider. This indicates that the diffusion ability of crumb rubber modified asphalt is significantly enhanced under the external force of ultrasonic simulation. The molecular bonds of crumb rubber modified asphalt changes greatly, the energy decreases obviously, and the system stability increases. In conclusion, ultrasonic action on crumb rubber modified asphalt preparation is a green and effective way to improve system stability and compatibility.

EVALUATION OF LOCUST BEAN POD ASH AS MINERAL FILLER IN HOT MIX ASPHALT

An increase in the consumption of agricultural products generates large quantities of waste daily. The husks of the locust bean seeds when removed from the plant are littered in the environment which negatively affects the environment. In this research, locust bean pod ash (LBPA) was used as a mineral filler in hot mix asphalt. Physical and chemical tests were done on the aggregate, bitumen and LBPA, showing adequacy for use in asphalt concrete production. All tests were conducted in accordance with relevant standards. LBPA was admixed with granite dust from 0–50% (at intervals of 10%) with varying bitumen content from 4–7% (at 0.5% intervals). For this experiment, the Marshall mix design method was used. The Marshall stability of samples containing LBPA improved by 19%, from 8.16kN to 9.67kN. Similarly, Marshall flow decreased by 19% from 3.4 mm to 2.75 mm. The density-void analysis of the asphalt samples also revealed an improvement. The microstructural examination revealed an enhanced structural arrangement due to the flocculation of the LBPA particles. Overall, the hot mix asphalt samples meet the Federal Ministry of Works and Housing specifications for flexible pavement-wearing courses. It was determined by the study that adding 40% LBPA with 60% granite dust at 5% bitumen content would improve the performance of hot mix asphalt.