Strength Of Asphalt Concrete Research Articles

CT imaging‐enhanced numerical simulation of microscopic structure and resilient safety of asphalt concrete

AbstractAsphalt concrete is a foundational material in water conservancy projects, serving a critical function in the construction of impermeable structures such as dams. The seismic response characteristics and resilient safety of concrete dams are heavily influenced by the arrangement and evolution of the microscopic structure of the dam material. In this study, a high‐precision computed tomography (CT) scanning technique, in conjunction with advanced numerical simulations, was employed to analyze the internal damage and crack extension mechanism of asphalt concrete. Microstructural images of the asphalt concrete specimen were accurately captured by CT scanning, followed by the construction of corresponding numerical models. Presented simulation results show that the displacement deformation of asphalt concrete reaches its maximum value in the top region of the model and subsequently decreases with depth. Material damage was first observed at the interface between aggregate and asphalt matrix, where microcracks emerge and extend to the entire asphalt matrix, resulting in a gradual deterioration of the model performance. The simulation results indicate that the overall strength of asphalt concrete is primarily influenced by the strength characteristics of its aggregates. The stress–strain curves obtained from the numerical simulations exhibit a hyperbolic relationship, which is in high agreement with the physical test results. This study not only enhances our comprehension of the mechanical behavior of concrete but also contributes to the analysis of seismic response and risk assessment in dam engineering through dynamic experimental testing and numerical simulation.

The Effect of the Microstructure and Viscosity of Modified Bitumen on the Strength of Asphalt Concrete.

The purpose of these studies was to establish the influence of the microstructural and rheological characteristics of modified bitumen compositions on the strength indicators of asphalt concrete. The effect of additives concentration on the rheological characteristics and microstructure of binary "bitumen-surfactant", "bitumen-AG-4I", and ternary "bitumen-AG-4I-AG-4I" systems has been studied. To assess the effect of bitumen dispersion on the physical and mechanical characteristics of modified asphalt concrete samples, the compressive strength value was determined. The following chemicals have been used as additives: the original product AS-1, industrial additive AMDOR-10, and used sealant AG-4I, a product based on polyisobutylene and petroleum oils. At an increased content of AG-4I (C ≥ 1.0 g/dm3) in ternary systems, the contribution of the emerging intermolecular polyisobutylene network to the development of structuring processes increases while the viscous effect of the surfactant AS-1 decreases. It has been established that the minimum size of bee-like bitumen structures (1.66 µm) is recorded with the joint presence of additives in the bitumen, AS-1 at a level of 1.0 g/dm3 and AG-4I at a level of 1.0 g/dm3. Under the same concentration regimes of the ternary bitumen composition, the maximum increase in compressive strength RD was achieved with the smallest size of bee-like structures of modified bitumen.

Tenability evaluation of road pavement with internal cracks

The article is a completed stage in the study of the multilayer road pavement with internal cracks tenability. The work tested the hypothesis adequacy about internal cracks’ effect on the pavement strength. The authors reviewed and analyzed the bench testing methods of road pavement. A program has been developed for testing two-layer asphalt concrete pavement samples in the presence and absence of an imitation crack in the lower pavement layer. Pavement test cylinders were made in the laboratory and tested for uniaxial compression and shear, and test beam for tension in bending, under various temperature conditions, simulating the operating pavement conditions on highways. In general, the test results confirm the proposed hypothesis adequacy and do not contradict the generally accepted asphalt concrete strength theory. Also, were executed mathematical modeling and stress-strain state evaluation of multilayer road pavement with internal cracks in the lower pavement layer. The mathematical model showed significant changes in the stress-strain state of samples with internal cracks, which correlates with the laboratory tests results. Based on the obtained results, a sample model reinforced with geosynthetic materials was developed and tested in the laboratory and mathematically. The fractured geogrid-reinforced sample showed higher tensile strength parameters in bending. In conclusion, recommendations are given to improve the crack resistance at the stage of repair work.

The Effect of Animal Bone Ash on the Mechanical Properties of Asphalt Concrete

For the sake of enhancing the mechanical properties and durability of asphalt concrete, many studies suggest adding different admixtures, such as waste materials in the form of filler. These admixtures have a significant influence on the performance of asphalt concrete by plying a roll in filling the voids between particles and sometimes as a cementitious material. This study aims to improve the strength of asphalt concrete by adding crushed animal bone to the mix after carbonization at a temperature of 800 Co. Seven different percentages (10, 20, 30, 40, 50, 60, and 100%) of animal bone ash as a replacement for the filler percentage were added to the optimum asphalt concrete mix. A number of tests were conducted on asphalt concrete specimens to measure Marshall stability (MS), Marshall flow value (MF), voids filled with asphalt percentages (VFA), air void percentages (VA), voids in mineral aggregate percentages (VMA), and maximum theoretical specific gravity (GMM). From the results, the maximum stability of 14.85 KN was reached when using animal bone ash of 20% as a partial replacement for the conventionally used filler (limestone). In general, there are some improvements in the physical properties of asphalt concrete with animal bone ash, which can be related to the increase in the bond between the particles of aggregates and the bitumen material. Doi: 10.28991/cej-2021-03091757 Full Text: PDF

Fatigue strength of asphalt concrete pavement on orthotropic steel deck considering temperature factor

Fatigue of any material is a process when micro-damage accumulates because of multiple load applications. The result is the appearance of defects after a while. Asphalt concrete pavement on orthotropic steel deck (OSD) of roadway bridges is prone to fatigue failure. There are several reasons for this. Firstly, there is a large number of vehicle impacts for pavement service life. Secondly, the pavement lies on the flexible load-bearing elements of the roadway deck. This leads to high stresses in the asphalt concrete. In general, stress limitation prevents fatigue defects. The value of this limit is set according to the results of fatigue calculation. This calculation is performed for main load-bearing elements but not for the pavement on the roadway. In this article the necessary of fatigue strength calculation of pavement on orthotropic steel deck is justified. Also, disadvantages of the existing fatigue calculation method of pavement on the ground are noted. This design method is not applied for fatigue strength calculation for OSD pavement because of these disadvantages. Available experimental results of fatigue strength of asphalt concrete are analyzed. As a result, the need to take into account the temperature factor is established. The hypothesis of linear summation of damages allows to take into account the change of fatigue strength of asphalt concrete at different temperatures. In the article the endurance of asphalt concrete as part of the typical pavement system on OSD is evaluated in accordance with the described approach. In addition, the tasks for the future are set. Solution of these tasks will allow to developing the method of pavement calculation on different bridges.

Effect of Pore Water Pressure on Response of Asphalt Concrete

Rapid traffic loading induces pore water pressure inside partially or fully saturated interconnected cracks and voids of asphalt concrete. The induced pore pressure contributes extra stresses within the pavement and accelerates crack evolution and propagation. Crack propagation facilitates diffusion of moisture through the solid phase and accelerates the degradation of the time-dependent stiffness and strength of asphalt concrete. Therefore, it is imperative to consider the coupled effects of pore water pressure, moisture diffusion, and mechanical loading on asphalt concrete pavement. The effect of pore water pressure was considered by using the effective stress concept inside deformable media. Biot’s approach was used and coupled to the nonlinear viscoelastic and viscodamage (moisture and mechanical) constitutive relationships for asphalt concrete. The models were implemented in PANDA, a finite element code developed at Texas A&M University. Capabilities of the proposed framework and constitutive relationships were demonstrated through the simulation of several realistic microstructural representations of asphalt concrete. The results of numerical simulations demonstrated how the effect of pore water pressure can intensify damage within asphalt concrete and reduce its strength. Therefore, this outcome emphasizes the importance of incorporating the effect of pore water pressure in investigating the response of asphalt concrete.

Reinforcement of Asphalt Concrete Mixture using Recycle Polyethylene Terephthalate Fibre

Objectives: To determine the reinforcing effect of a cheap Recycle Polyethylene Terephthalate (PET) fibre on asphalt concrete strength. The aim of this study was achieved by performing Resilient Modulus (MR) test in the laboratory on both unreinforced (i.e. neat asphalt mixture) and recycle PET fibre reinforced asphalt concrete mixtures. Methods: The percentage additions of recycle PET fibres are 0.3%, 0.5%, 0.7% and 1% of the total weight of the mixture. The result was analyzed by means of Response Surface Methodology (RSM) using Design Expert 7.0 software and validated using analysis of variance (ANOVA). Findings: The results indicated that recycle PET fibres have significantly increased the mixtures’ resilient modulus in lower temperature hence improved fatigue resistance, and moderately increased mixtures, resilient modulus at higher temperature hence improved rutting resistance. Novelty/Improvement: This research has introduced a sustainable means of producing Recycle fibres for the reinforcement of asphalt concrete mixtures. Recycle PET fibre have proved to be effective in strength improvement at 0.7% of total weight of asphalt concrete mixture.

Correlation between Asphalt Concrete Strength, Amount of Bitumen and Asphalt Mix Batching Modes

The article introduces the results of the experimental research of the effect of confinement and steel fiber reinforcement on the strength and strain of the compressed elements of high-modified as well as high-strength SFRC. Analytical expressions to describe the strength and strain of elements with confinement reinforcement under axial compression have been proposed. The results of the research of the effect of concrete age and temperatures elevated up to 150°C on the strength and strain of high-strength SFRC have been introduced.

Correlating the Dynamic Modulus and the Indirect Tensile Strength of Asphalt Concrete

This study has developed a relationship between the Dynamic Modulus (E*) and the Indirect Tensile Strength (ITS) of Hot-Mix Asphalt (HMA) using standard laboratory tests programs. Two types of SuperPave (SP) mixtures were considered namely, SP-III with 15% Reclaimed Asphalt Pavement (RAP) materials and SP-III with 35% RAP materials. Cylindrical samples of 100 mm diameter and 150 mm height were prepared. The samples were then tested for |E*| value at 210C at several loading frequencies following the AASHTO TP 62-07 test protocol. Next, the samples were cut into circular pieces of 38 to 50 mm thickness using laboratory saw. The samples are then tested for ITS value by applying a deformation rate of 50 mm per minute (AASHTO T 283 protocol). The ITS was calculated following the AASHTO T 283-07 test standard. The |E*| values (MPa) of SP-III with 15% RAP at 25, 10, 5.0, 1.0, 0.5, 0.1 Hz are measured to be 65, 59, 52, 34, 31, and 18 times of ITS (psi) respectively. The |E*| values (MPa) of SP-III with 35% RAP at 25, 10, 5.0, 1.0, 0.5, 0.1 Hz are measured to be 41, 38, 33, 24, 20, and 14 times of the ITS (psi) respectively. This study also draws a conclusion that increase in RAP has resulted in increased stiffness and strength.