An integrated approach to measure and model fatigue damage and healing in asphalt composites

textThis study presents a test and analysis method to determine both damage and healing characteristics of asphalt composites using the same test specimen. The test involves applying multiple stretches of load cycles, each separated by a period of zero load introduced at several different levels of reduced stiffness. The analytical procedure involves (1) using modified correspondence principles to transform the time-dependent physical quantities (stress, strain and energy density) into time-independent pseudo-elastic quantities, and then (2) using viscoelastic continuum damage mechanics to quantify damage and healing properties of the material based on the transformed quantities. The results obtained using two different asphalt mortars subjected to uniaxial and shear load cycles confirmed the findings from the previous researchers that the characteristic pseudo stiffness versus damage relationship for a given material is independent of testing conditions. More importantly, this study demonstrated that the aforementioned relationship was also independent of the rest periods introduced intermittently during the cyclic tests. Results also show that healing defined in terms of the change in the internal state variable for damage represents the true healing potential of a material. Furthermore, healing properties obtained using the proposed test method (a) agreed with the properties obtained using a more rigorous protocol with multiple test specimens, and (b) were independent of the loading conditions used to induce fatigue damage. These observations strongly suggest that the proposed method can be used to predict damage and healing properties for any arbitrary loading condition from properties determined using the proposed protocol.Civil, Architectural, and Environmental Engineerin

COMPUTATIONAL AND EXPERIMENTAL CHARACTERIZATION OF BITUMINOUS COMPOSITES BASED ON EXPERIMENTALLY DETERMINED PROPERTIES OF CONSTITUENTS

The stiffness of asphalt concrete mixtures is characterized in terms of the dynamic modulus for designing the thickness of flexible pavements. The dynamic modulus value of asphalt concrete is either determined experimentally or predicted by using empirical, semi-empirical, analytical or computational micromechanics models. This study proposes to use a computational micromechanics model to predict the dynamic modulus of asphalt concrete mixtures based on the experimentally determined properties of the constituents in the heterogeneous microstructure. The model defines asphalt concrete mixtures as the composites of two different homogeneous isotropic components – the viscoelastic fine aggregate matrix phase and the elastic aggregate phase. Mechanical properties are determined by oscillatory torsional shear tests of cylindrical bars of fine aggregate matrix mixtures, and quasi-static nanoindentation tests of aggregates. A protocol is developed to mix-design and fabricate the Superpave gyratory compacted fine aggregate matrix mixture as a replicate of fine aggregate matrix phase of asphalt concrete mixtures in terms of binder content, air void content and specific gravity. The cyclic uniaxial compressive tests are computationally simulated based on the finite element method (FEM). The model uses the material properties of the two-dimensional microstructure that are obtained from digitally processed images of asphalt concrete mixtures. The results are compared with the experimentally determined dynamic modulus tests of the same cylindrical samples of asphalt concrete mixtures. FEM simulations of the dynamic modulus of rectangular microstructure agreed with the laboratory tests of cylindrical samples

Field Efficacy of Different Insecticides Against Fall Armyworm (Spodoptera frugiperda J.E. Smith) in Spring Maize (Zea mays L.)

An experiment was conducted from February to June 2022 to determine the effectiveness of different insecticides in controlling fall armyworm (Spodoptera frugiperda: FA) under field conditions. The experiment followed a randomized complete block design (RCBD) with 5 treatments and 4 replications. Insecticides were applied three times at 7-day intervals. The treatments included: T1 - untreated or control (water spray), T2 - Cypermethrin 5% + Chlorpyriphos 50% EC, T3 - Chlorantraniliprole 18.5% SC, T4 - Emamectin Benzoate 5% SG, and T5 - Spinetoram 11.7% SC. Data were collected for the number of live larvae, damage to the top four leaves and whorls, and yield attributes. The results showed that the lowest FA infestation was observed in the plots treated with Chlorantraniliprole 18.5% SC, while the highest infestation was observed in the control group. The highest yield (7.52 t/ha) was obtained from the Emamectin Benzoate treatment, while the lowest yield (5.74 t/ha) was recorded in the control group. Among the different control measures, spraying Chlorantraniliprole 18.5% SC at 7-day intervals was found to be the most effective method to control FA in spring maize variety TX-369, achieving 100% efficacy. These results provide valuable guidance to growers in selecting effective insecticides for FA control. This study addresses the challenge of FA management in maize crops while aligning with multiple Sustainable Development Goals (SDGs)

Nanoindentation Test Integrated with Numerical Simulation to Characterize Mechanical Properties of Rock Materials

It is important to determine the mechanical properties of rock materials accurately from the viewpoint of the design, analysis, and modeling of various transportation infrastructure systems. Conventional methods have some drawbacks, including relatively inaccurate measurements, cumbersome testing-analysis processes, and high variability in measurements. A nanoindentation test integrated with a numerical modeling technique has been validated in other fields as an efficient and accurate tool for the characterization of the key mechanical properties of various irregularly shaped materials, such as the rock materials in this study. This paper presents an integrated experimental-numerical effort based on the nanoindentation measurement and finite-element modeling of a representative rock material, limestone. The experimental efforts, including specimen fabrication and laboratory tests, are presented, and the corresponding analyses of test results combined with the finite-element technique and linear interpolation to evaluate the property measurements are discussed. The elastic properties estimated from the nanoindentation test are similar to the simulation results, demonstrating the validity of the test method and modeling approach. The success of the proposed approach should facilitate the better design of mixtures and structures based on the more accurate characterization of the core material properties

Material-Specific Effects of Hydrated Lime on the Properties and Performance Behavior of Asphalt Mixtures and Asphaltic Pavements

This study evaluates hydrated lime-treated hot-mix asphalt (HMA) mixtures through various labor-atory tests, including the dynamic modulus test and performance tests to characterize permanent deformation and fatigue damage resistance both in displacement-controlled and force-controlled modes. Two different asphalt mixtures—the asphalt concrete mixture and the fine aggregate asphalt matrix mixture—which differ only in the amount of additional hydrated lime (0.5–3.0%), are tested. Test results demonstrate material-specific damage characteristics of hydrated lime and the existence of a more appropriate amount of hydrated lime to be added to the HMA mixtures than the current typical application rate such as the addition of 1.0% lime to dry or premoistened aggregates. In ad-dition, the newly released Mechanistic-Empirical Pavement Design Guide (MEPDG) is used for pre-dicting pavement performance related to hydrated lime content. The MEPDG analysis results show that damage prediction models implemented in the current MEPDG are limited to accurately pre-dicting material-specific damage characteristics. Mechanistic models that consider material-specific crack phenomenon and fracture behavior should be pursued